Dr Josh Walker

The aim of this study was to explore the sprint mechanical and kinematic characteristics of sub-elite and recreational male sprinters during the acceleration phase of a linear sprint running section. Eighteen sprinters (nine sub-elite, nine recreational) performed two all-out 30-m sprints. Three high speed panning cameras were used to record the entire sprint distance continuously. The sprint velocity-time data of each camera were determined by temporal analysis of the video recording. These values were used to determine the variables of the horizontal F-v profile (theoretical maximal values of horizontal force [F0], velocity [v0], power [Pmax], the maximal ratio of horizontal to resultant force [RFmax], the decline in the ratio of horizontal force production as the running speed increases [DRF]) and key kinematic characteristics. Significant differences were observed between the groups for v0 (0.79 ± 0.24 m∙s-1, p = 0.005), Pmax (3 ± 1.17 W∙kg-1, p = 0.020) and RFmax (3.1 ± 1.2 %, p = 0.021). No statistical differences were found for F0 (0.55 ± 0.46 N∙kg-1, p = 0.25) and DRF (0.2 ± 0.5 %∙s∙m, p = 0.67). The mean running velocity and mean step rate were higher, whereas mean ground contact time was shorter in sub-elite sprinters. There were no differences in mean step length and mean flight time. The subelite sprinters in our study demonstrated the capacity to generate higher amounts of horizontal forces at higher running speeds, apply horizontal force to the ground more efficiently and achieve higher step rates during sprint acceleration than recreational sprinters.

The Reactive Strength Index-Modified (RSlmod) is a reliable method of measuring the explosiveness of an athlete during a range of plyometric exercises. The purpose of the current study was to measure the between-limb differences in RSlmod across three different plyometric tasks. Eleven recreationally active participants performed countermovement jumps, stop jumps and single-leg jumps. The study found no significant differences in RSlmod between dominant and non-dominant limbs across all three tasks (p>0.05), but did find RSImod to be higher in the stop jump than a countermovement jump and single leg stop jump for both dominant and nondominant limbs. These findings show RSlmod may not be an indicator of limb asymmetry, but may be useful for the coach when looking to develop explosive performance in an athlete or performer.

INTRODUCTION: Static ultrasound (US) imaging is a popular tool when monitoring muscle architectural changes. A common limitation of static imaging is restricted field-of-view (FOV), which can be counteracted by methods which increase both image acquisition and analysis time (e.g., panoramic imaging). With a shift towards automated analysis using computer vision (e.g., deep learning), there is a need to identify the most optimal way of training algorithms to optimise fascicle length (FL) estimations from single static US images. METHODS: B-mode US images of gastrocnemius medialis were obtained using a 50 mm linear array probe (Acuson P300, Siemens AG, Germany) from the muscle belly, with the probe aligned with the direction of muscle fibres. Twenty-five (from a subset of 301) images were analysed with ImageJ 1.52i (National Institute of Health, USA) to provide FL estimations using five methods: manual linear extrapolation (MLE), the methods of Kawakami (KAWA) et al. [1], Blazevich (BLAZ) et al. [2], and Finni (FIN) et al. [3], and a new approach which uses muscle thickness in the proximal region of the image divided by the sine of the pennation angle obtained from the distal region of the image (the “proximal-distal method” [PD]). RESULTS: Mean ± Standard Deviation FL values for each method for the subset were: 64.61 ± 8.86 mm (MLE), 59.18 ± 9.81 mm (KAWA), 72.51 ± 14.44 mm (BLAZ), 69.46 ± 15.23 mm (FIN), and 65.20 ± 9.22 mm (PD). When comparing MLE with each of the other methods the PD returned a Bias ± Random Error of −0.59 ± 8.44 mm (ICC 3,1: 0.89), followed by KAWA with 5.43 ± 6.44 mm (ICC: 0.81), FIN with −4.85 ± 15.17 mm (ICC: 0.76), and BLAZ with −7.91 ± 15.03 (ICC: 0.66). CONCLUSION: The use of two-dimensional US with restricted FOV for FL measurements still poses challenges with accuracy and reliability. The origin of the imprecision arises from the fact that there is not always a true value within the examined image to obtain. Even when a full fascicle is visible, its curvature alongside possible image distortion can affect the measurement. All aforementioned techniques are based on sound logic and geometric principles. Yet, they may provide for the same fascicle differences exceeding at times 20 mm whereas for a series of measurements their level of agreement may range from almost identical to highly dissimilar. The PD method showed overall strongest agreement and lowest systematic bias versus MLE which included several full fascicles in view. There could be a range of technical and anatomical of reasons for this, for example we scanned the gastrocnemius medialis whereas past studies established their estimation techniques on different muscles. As we are moving into the markerless era, more robust and streamlined ways of training tracking algorithms are needed. REFERENCES: [1] Kawakami, Y. et al. (1995). Eur. J. Appl. Physiol.;72:37-43. [2] Blazevich, AJ. et al. (2006). J. Anat.;209:289-310. [3] Finni, T. et al. (2001). Eur. J. Sport Sci.;1:1-13.

This project aimed to explore the structural and functional properties of the triceps surae muscle-tendon complex in cyclists, triathletes, and untrained individuals. The interaction between contractile and series-elastic elements of the gastrocnemius medialis muscle-tendon unit was explored at various cycling intensities alongside kinetic and kinematic measurements of cycling performance. An understanding of the relationship between pedalling mechanical effectiveness and metabolic efficiency was also explored, as well as the impact of morphological and mechanical properties of the triceps surae on key cycling performance indicators. These measurements were compared, for the first time, between cyclists and triathletes to develop an appreciation for the chronic adaptations to different types of mechanical loading through endurance exercise. Various muscle-tendon unit differences were observed between the groups, with triathletes displaying an increased Achilles tendon thickness (p ≤ 0.048) and higher ankle joint passive stiffness (p ≤ 0.048). Cyclists tended to show poorer dorsiflexor strength compared to untrained controls (p ≤ 0.028), although triathletes did not show the same weakness. During cycling, mechanical effectiveness increased across all groups as cycling intensity increased (p < 0.001). There was also a significant shift in the ankle joint to a more dorsiflexed position (p < 0.001), which in turn led to a greater gastrocnemius medialis muscle-tendon unit range of motion (p < 0.001). However, there was no change in fascicle mechanical behaviour across the different intensities, characterised by similar fascicle range (p = 0.991) and fascicle shortening velocities (p = 0.919). The amplitude of muscle activity also increased in all muscles measured (p < 0.001). There were no between-group differences in any biomechanical, neuromechanical, or physiological parameter of cycling at any measured power output. There were very strong associations discovered between mechanical effectiveness and gross efficiency (mean r = −0.91, p < 0.001), although there were no strong associations for any kinematic, neural, or mechanical variable measured. Overall, this project showed that despite observing some structural muscle-tendon unit differences between triathletes and cyclists, there are no mechanical behavioural differences during cycling, suggesting that the adaptations that might be specific to triathlon performance do not have a beneficial or detrimental effect on cycling performance. It also showed for the first time that there are strong associations between mechanical effectiveness and metabolic efficiency, although no specific neuromechanical characteristic in the triceps surae strongly affects this relationship.

Sagittal and frontal plane knee kinematics have been linked to anterior cruciate ligament injury risk during several jumping and landing tasks. The purpose of this study was to compare the knee joint kinematics of the dominant and non-dominant leg during two types of stop jump. Eleven recreationally active participants performed a stop jump from an anteroposterior approach and from a mediolateral approach. The study found significant differences in knee flexion for both limbs, and significant between-limb differences in knee flexion for the mediolateral approach and knee varus/valgus for the anteroposterior approach (p<0.05). These findings indicate that both types of stop jump may pose a risk of injury, but particularly during the anteroposterior approach for both limbs, and the mediolateral approach for the non-dominant limb only.

This report provides a comprehensive analysis of the block start and initial acceleration phase, including spatiotemporal and kinematic analysis of the first four ground contacts. An overall time to the first hurdle, and subsequent hurdle split times, are also provided. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

Cyclists are known to change their cycling position to reduce aerodynamic drag. Research has shown that this compromises their physical capacity to perform, but there is considerable inter-individual variability present. Proposed training specificity effects by cycling position do not explain all of the observations in the literature, so a search for other influencing parameters is warranted and might help practitioners to further optimise cycling position. This study captured full-body kinematics and 2D crank forces in 19 Time-Trial (TT) and 36 Road trained cyclists. Data in preferred and standardised cycling positions were systematically evaluated and showed that, amongst other kinematic differences, TT cyclists prefer a more forwardly positioned hip joint over Road cyclists. Despite their different setup, no effects in mechanical effectiveness were seen between the groups when tested in their preferred position. Across the standardised positions, the full cohort showed lower mechanical effectiveness when lowering trunk angle. However, significant group by position interactions showed this effect to be less extreme for the TT group. Kinematic data revealed that an increased pelvic tilt resulted in increased hip flexion and induced a more dorsiflexed ankle angle. In addition, linear hip position acutely responded to positional changes by moving forwards when the trunk angle was lowered. A more forwards hip position is thus associated with maintaining a better mechanical effectiveness in aerodynamic cycling positions. This suggests that there is potential to mitigate the effect of negative crank forces in aerodynamic positions by acutely adjusting the saddle placement to facilitate linear hip movement.

Previous high jump studies have yielded important information regarding successful performance. However, analyses in competitive scenarios have often disregarded athletes' unsuccessful attempts. This study aimed to investigate the biomechanical differences between successful and unsuccessful jumps during competition. High-speed video footage (200 Hz) was obtained from 11 athletes during the 2018 men's World Athletics Indoor Championship Final. From each athlete, one successful (SU) and one unsuccessful (UN) jump at the same bar height were included in the analysis, leaving seven athletes in total. Following whole-body 3D manual digitization, several temporal and kinematic variables were calculated for the run-up, take-off, and flight phases of each jump. During SU jumps, athletes raised the CM to a greater extent (p < 0.01) from take-off. Touchdown in SU jumps was characterized by a faster anteroposterior velocity (p < 0.05), lower backward lean (p < 0.05) and changes in joint angles for the stance and trail limbs (p < 0.05). Athletes also shortened the final contact time during SU jumps (p < 0.01) after producing a longer flight time in the final step of the run-up (p < 0.05). Elite level high jumpers undertake a series of adjustments to successfully clear the bar after UN jumps. These adjustments reinforce the importance of the run-up in setting the foundations for take-off and bar clearance. Furthermore, the findings demonstrate the need for coaches to be mindful of the adjustments required in stance and trail limbs when looking to optimize feedback to athletes during training and competition.

This report provides a comprehensive analysis of the block start and initial acceleration phase, including spatiotemporal and kinematic analysis of the first four ground contacts. An overall time to 10 metres is also provided. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides a comprehensive analysis of the block start and initial acceleration phase, including spatiotemporal and kinematic analysis of the first four ground contacts. An overall time to 10 metres is also provided. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

Objectives: Achilles tendon rupture leads to functional impairments and these may be underpinned by morphological changes in the muscle-tendon unit. Functional performance of the injured limb will be impaired regardless of time since surgery and these impairments occur alongside changes in muscle-tendon morphology. Methods: Following operative treatment of Achilles tendon rupture and short term immobilisation, 12 patients completed a battery of tests during a single visit to the laboratory (performed an average of 4.4 ± 2.6 years post-surgery). Patients completed the Achilles’ tendon rupture score (ATRS), tests of ankle and hip range of motion (ROM) and ultrasound measurements of muscle-tendon architecture. Data on isokinetic (30 o/s, 60 o/s) plantar flexion strength, jumping performance and walking-running were also collected on the same visit. Percentage deficits were expressed relative to the non-injured limb and determined for statistical significance (p < 0.05). Relationships between outcomes measures and time since surgery were tested using Pearson’s correlation coefficients (p < 0.05). Results: The repaired limb showed a shorter muscle fascicle length (12.1-19.6%), increased fascicle pennation (18.0±22.14%) and reduced muscle thickness (9.1-20.1%) in the gastrocnemius and/or soleus along with greater tendon cross-sectional area (46.7±34.47%). Functionally, the repaired limb displayed lower countermovement jump height (-12.6±15.68%) and longer drop jump contact times (5.5±5.7%). Also, the repaired limb showed reduced hip internal-external ROM (6.3±8.2%) but no differences existed between limbs for plantar flexion ROM and strength or gait characteristics. Good ATRS outcomes were reported (mean: 87.9±16.2, range: 43-100) which related to time since surgery (r=0.79) but individual ATRS items did not correlate with corresponding objective measures. Conclusion: Plantar flexor atrophy following surgically treated Achilles tendon rupture is partially compensated for by remodelling of the fascicles however, impairments may still persist many years into the postoperative period although these may be more pronounced in high-velocity activities.

This report provides a comprehensive analysis of the block start and initial acceleration phase, including spatiotemporal and kinematic analysis of the first four ground contacts. An overall time to the first hurdle, and subsequent hurdle split times, are also provided. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

Preferred walking speed (PWS) is lower when wearing a controlled ankle motion (CAM) boot, which can potentially make comparisons between footwear conditions difficult. Standardising walking speed accounts for this but lacks the ecological validity of PWS. The aim of this study was to compare acute biomechanical responses to CAM boot wear when walking is freely chosen and when it is controlled. Twelve healthy participants walked on an instrumented treadmill at their PWS and at three standardised speeds: 3, 4, and 5 km/h. They did so in three footwear conditions: (1) with a Rebound® Air Walker CAM boot on the right leg, (2) with a Rebound® Air Walker on the right leg and an Evenup Shoelift™ on the left, and (3) in normal footwear. Comparisons between footwear conditions were largely similar in the ipsilateral limb at PWS and at the standardised speeds, which included a decrease in total mechanical work and ankle joint work during CAM boot wear (p < 0.001). At the standardised speeds, total mechanical work and hip joint work were lower during CAM boot wear than wearing normal shoes and the Evenup Shoelift™ (p ≤ 0.014), although there were no differences between footwear conditions at PWS (p ≥ 0.095). As such, acute responses to CAM boot wear are different when speed is standardised compared to when speed is freely chosen, meaning conclusions cannot necessarily be transferred between approaches. Based on these differences observed between walking speeds, it would be prudent for future studies to try to maintain ecological validity by using PWS.

Research investigating ankle function during walking in a controlled ankle motion (CAM) boot has either placed markers on the outside of the boot or made major alterations to the structure of the CAM boot to uncover key landmarks. The aim of this study was to quantify joint kinematics and kinetics using “in-boot” skin markers whilst making only minimal structural alterations. Seventeen healthy participants walked at their preferred walking speed in two conditions: (1) in standard athletic trainers (ASICS patriot 8, ASICS Oceania Pty Ltd, USA), and (2) using a hard-cased CAM boot (Rebound® Air Walker, Össur, Iceland) fitted on the right foot. Kinematic measurements revealed that CAM boots restrict sagittal plane ankle range of motion to less than 5°, and to ∼3° in the frontal plane, which is a reduction of 85% and 73% compared to standard footwear, respectively (p < 0.001). This ankle restriction resulted in a reduction of ankle joint total limb work contribution from 38 ± 5% in normal footwear to 13 ± 4% in the CAM boot (p < 0.001). This study suggests that CAM boots do restrict the ankle joint’s ability to effectively perform work during walking, which leads to compensatory mechanisms at the ipsilateral and contralateral hip and knee joints. Our findings align with previous research that employed “on-boot” kinematic measurements, so we conclude that in-boot approaches do not offer any benefit to the researcher and instead, on-boot measurements are suitable.

Introduction Controlled ankle motion (CAM) boots are a below-knee orthotic device prescribed for the management of foot and ankle injuries to reduce ankle range of motion (RoM) and offload the foot and ankle whilst allowing continued ambulation during recovery. There is a lack of clarity within the current literature surrounding the biomechanical understanding and effectiveness of CAM boots. Aims To summarise the biomechanical effects of CAM boot wear as an orthotic for restricting ankle RoM and offloading the foot. Methods A systematic literature review was conducted in accordance with the PRISMA 2020 guidelines. All papers were independently screened by two authors for inclusion. Methodological quality was appraised using Joanna Briggs Critical Appraisal checklists. A narrative synthesis of all eligible papers was produced. Results Thirteen studies involving 197 participants (113 male and 84 female) were included. All studies were quasi-randomised and employed a within-study design, of which 12 studies included a control group and a range of CAM boots were investigated. CAM boots can be seen to restrict ankle RoM, however, neighboring joints such as the knee and hip do have kinetic and kinematic compensatory alterations. Plantar pressure of the forefoot is effectively redistributed to the hindfoot by CAM boots. Conclusion The compensatory mechanisms at the hip and knee joint during CAM boot wear could explain the secondary site pain often reported in patients, specifically at the ipsilateral knee and contralateral hip. Although CAM boots can be used to restrict ankle motion, this review has highlighted a lack of in-boot kinematic analyses during CAM boot use, where tracking markers are placed on the anatomical structure rather than on the boot, or through video fluoroscopy, urging the need for a more robust methodological approach to achieve this. There is a need for studies to assess the biomechanical alterations caused by CAM boots in populations living with foot and ankle pathologies. Future research, adopting a longitudinal study design, is required to fully understand the effectiveness of CAM boots for rehabilitation.

Isokinetic strength assessments are common outcome measures following operatively treated Achilles tendon (AT) ruptures. However, there is a lack of clarity on whether commonly reported outcome measures (such as peak joint moment) are sufficient to describe the extent of long-term functional deficits following AT rupture and repair. The present study conducted a comprehensive isokinetic evaluation of the Triceps surae complex in 12 participants who previously underwent AT rupture and repair. Testing occurred 4.4 (±2.6) years following surgery, and consisted of maximal isokinetic strength assessments of the plantarflexors at two angular velocities (30 and 60 °∙s-1) with the knee in flexed and straight positions. Differences between injured and non-injured limbs were tested through discrete and statistical parametric mapping analysis. Average joint moment showed significant main effects between injured and non-injured limbs, but common isokinetic parameters such as peak moment and angle of peak moment did not. The normalised moment curves showed a significant main effect of limb, angular velocity and knee joint position on joint moment throughout different portions of the range of motion. Temporal analysis revealed a significantly greater ability of the non-injured limb to sustain plantarflexor moments across a range of testing conditions. Participants who had undergone operative treatment of AT ruptures did not display inter-limb differences in discrete isokinetic strength outcomes that are often used in the literature. Instead, temporal analyses were required to highlight the reduced capacity of the injured limb to generate end-range joint moments and to sustain higher levels of joint moment for longer periods.

Hinged controlled ankle motion boots are used to incrementally increase ankle joint range of movement during rehabilitation following Achilles’ tendon rupture. This increased movement should induce mechanical stress on the tendon via cycles of stretching and shortening. However, research has yet to determine how this permitted range of movement influences tendon length change. Eight healthy individuals (age: 23 ± 2 y; stature = 1.70 ± 0.09 m; body mass = 67.7 ± 13.7 kg) walked at a self-selected speed on an instrumented, motorised treadmill in a hinged controlled ankle motion boot with three pre-established ankle ranges of movement: 0, 15, and 30°, which were all compared with walking in normal footwear. Kinematic and kinetic measurements were obtained using motion capture and the treadmill. Triceps surae mechanical characteristics, including Achilles’ tendon stretch, were obtained with B-mode ultrasonography. Achilles’ tendon stretch significantly (p < 0.001) increased as boot range of movement increased and was strongly correlated with measured ankle joint range of movement when the boot was set to a 15 or 30° range of movement (r ≥ 0.84, p ≤ 0.009). Increasing controlled ankle motion boot range of movement also increased ankle joint mechanical work done and total mechanical work done by the boot-wearing limb, which led to an increase in self-selected walking speed (all p < 0.001). These findings provide preliminary evidence that hinged controlled ankle motion boots have the capacity to provide a controlled mechanical stimulus to the Achilles’ tendon when range of movement is increased. This has possible clinical application for the early management of Achilles’ tendon rupture, potentially improving healing and functional outcomes if it can be translated into a patient population.

Background Controlled ankle motion (CAM) boots are often prescribed during the rehabilitation of lower limb injuries and pathologies to reduce foot and ankle movement and loading whilst allowing the patient to maintain normal daily function. Research question The aim of this study was to quantify the compensatory biomechanical mechanisms undergone by the ipsilateral hip and knee joints during walking. In addition, the compensatory mechanisms displayed by the contralateral limb were also considered. Methods Twelve healthy participants walked on an instrumented treadmill at their preferred walking speed. They underwent kinematic and kinetic analysis during four footwear conditions: normal shoes (NORM), a Malleo Immobil Air Walker on the right leg (OTTO), a Rebound® Air Walker on the right leg with (EVEN) and without (OSS) an Evenup Shoelift™ on the contralateral leg. Results CAM boot wear increased the relative joint contribution to total mechanical work from the ipsilateral hip and knee joints (p < 0.05), which was characterised by increased hip and knee abduction during the swing phase of the gait cycle. EVEN increased the absolute work done and relative contribution of the contralateral limb. CAM boot wear reduced walking speed (p < 0.05), which was partially compensated for during EVEN. Significance The increased hip abduction in the ipsilateral leg was likely caused by the increase in effective leg length and limb mass, which could lead to secondary site complications following prolonged CAM boot wear. Although prescribing an even-up walker partially mitigates these compensatory mechanisms, adverse effects to contralateral limb kinematics and kinetics (e.g., elevated knee joint work) should be considered.

This report provides a detailed analysis of the men's final, including key parameters during each phase of the movement up to release. The motion path and velocity of the discus has been shown for each athlete's best attempt. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

Most measurements of isokinetic hamstring:quadriceps (H:Q) strength ratios are conducted using concurrent repetitions, whereby active knee extension is immediately followed by active knee flexion. To reduce the influence of the stretch-shortening cycle and limit axis misalignment, isolated repetitions have been recommended, whereby extension and flexion are completed separately. To inform screening protocols, this study examined the effect of concurrent and isolated trials on discrete and angle-specific H:Q ratios. Fifteen males (age: 27 ± 4 years; height: 184 ± 9 cm; body mass: 80 ± 9 kg) performed isokinetic tests of the knee flexors and extensors (60 °/s) using concurrent and isolated trials while sagittal kinematics were captured (100 Hz). Statistical parametric mapping enabled the effects of protocol type (concurrent vs. isolated) and axis misalignment (uncorrected vs. corrected) to be compared. Uncorrected data resulted in an underestimation of discrete conventional (−10.17%, p < 0.001) and functional (−9.21%, p < 0.05) ratios with differences being observed for all angle-specific ratios (p < 0.001). The use of concurrent repetitions resulted in a significant overestimation of the conventional H:Q ratio (+7.41%, p < 0.05) with the differences being most prevalent at more extended (24 - 45° knee flexion, p < 0.05) knee joint positions. Dynamometer users should be aware that concurrent repetitions increase the likelihood of “false negative” injury risk categorisation. Nevertheless, the common practice of using uncorrected data from concurrent repetitions does not lead to significant differences in discrete or angle-specific H:Q ratios when compared with corrected data obtained from isolated repetitions.

Training for both sporting and military performance is common practice within army trainee populations, although it is currently unknown what effect this combination of training methods may have on the physical attributes required for overall physical preparedness. This study examined the effects of sport-specific training on general fitness in a professional military population. Four hundred and twenty-three Greek male army cadets completed a 12-week training regimen involving standard physical training (callisthenics, strength and endurance running exercises) and either general military training (GMT) or sport military training (SMT). A series of physical tests took place before and after the training period: a mile run, pull-ups, 50 m swim and an obstacle course run. Both the GMT and SMT groups showed significant (p < 0.001) improvements in all physical tests. However, the SMT group produced significantly greater improvements in all four tests (pull-ups [p < 0.001], 50 m swim [p < 0.05], obstacle course [p < 0.01] and mile run [p < 0.01]) compared to the GMT group. Furthermore, different types of SMT (e.g. rock climbing and track sprinting) achieved greater improvements (p < 0.001–0.01) in certain physical tests when compared to other forms of SMT (e.g. Pankration, Fencing). These results indicate that cadets undertaking concurrent participation in general and sport military training are overall better prepared for physical performance than their counterparts who undertake only general military training. Military conditioning per sonnel should be aware of the positive interplay between general and sports specific training in forming a preparation strategy designed for physical performance.

This report provides a detailed analysis of the women's final, including key parameters during each phase of the movement up to release. The motion path and velocity of the discus has been shown for each athlete's best attempt. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

INTRODUCTION: Recent research suggests that return-to-play protocols may benefit from the inclusion of angle-specific hamstring:quadriceps (H:Q) ratios to accurately understand muscle balance through the ROM (Lunn et al. 2023). In undertaking angle-specific analyses, most isokinetic knee extension-flexion protocols are conducted using concurrent repetitions (CON) whereby active knee extension is immediately followed by active knee flexion. To reduce the influence of the stretch-shortening cycle and limit axis misalignment, isolated repetitions (ISO) have been recommended (Alt et al. 2014) whereby extension and flexion are completed separately. To inform athlete screening protocols, this study examined the effect of CON and ISO protocols on discrete and angle-specific hamstring:quadriceps ratios. METHODS: Fifteen healthy males (age: 27 ± 4 years; height: 184 ± 9 cm; body mass: 80 ± 9 kg) performed isokinetic tests of the knee flexors and extensors (60 deg/s) using CON and ISO repetitions while sagittal-plane kinematics were captured (100 Hz) to quantify axis misalignment. Statistical parametric mapping then enabled the effects of protocol type (CON vs. ISO) and axis misalignment (uncorrected vs. corrected data) to be compared. RESULTS: The use of uncorrected data resulted in an underestimation of discrete conventional (−10.2%, p < 0.001) and functional (−9.2%, p < 0.05) H:Q ratios with these differences being observed for all angle-specific ratios (p < 0.001). The use of concurrent repetitions resulted in a significant overestimation of the H:Q ratio (+7.4%, p < 0.05) with the differences being most prevalent at extended knee joint positions. Despite the main effect(s) of protocol type and axis misalignment, no significant interactions were observed. CONCLUSION: Practitioners should be mindful that the use of concurrent repetitions will result in a significantly higher conventional H:Q ratio which will particularly influence angle-specific ratios in more extended knee joint positions. This may increase the likelihood of “false negative” injury risk categorisation during “time-efficient” protocols involving concurrent repetitions. Whilst the use of corrected knee moment data is preferable, practitioners should be mindful that the use of isolated repetitions and corrected joint moment data does not lead to significant differences in discrete or angle-specific H:Q ratios when compared with uncorrected data obtained from concurrent repetitions.

The sprint hurdle events require athletes to cross ten hurdles between the start and finish line. The height of the hurdles, and the distances between them, differ for men and women, possibly resulting in technical differences. The aim of this study was to provide a kinematic comparison of in-competition hurdle technique for world-class men and women hurdlers. Video data were collected for the 16 finalists in the 100 m and 110 m hurdles events at the 2017 IAAF World Championships using four high-speed cameras (150 Hz), focusing on the sixth hurdle for the men and fifth for the women. Center of mass (CM) position, joint angles, step lengths and clearance times were compared between sexes at key events before, during and after hurdle clearance. The hurdle height was ~7% higher for men when calculated as a proportion of stature (p < 0.001). This discrepancy in relative hurdle height provided women with a kinematic and mechanical advantage over men as they took off farther from the hurdle (relative to hurdle height) (p < 0.001), leading to a lower and more efficient flight parabola. Women were also able to maintain longer relative step lengths after hurdle clearance and showed minimal vertical oscillation of the CM in the stance phases before and after the hurdle compared with men. The lower relative hurdle heights in the women's event provide a less demanding task, and thus these findings present preliminary evidence to those coaches who advocate revising the women's hurdle heights in competition.

Introduction: Measurements of passive stiffness (PS) are often used to quantify the passive resistance of a muscle-tendon unit (MTU) to stretching, which is interesting in populations who undergo chronic loading and/or excessive stretching through exercise (Moltubakk et al., 2018). This metric may also be used to monitor the ‘neuromuscular condition’ of a participant taking part in experiments involving multiple visits. However, the repeatability of PS measurements has yet to be established. Methods: Twenty-nine participants (10 cyclists, nine triathletes and 10 controls) carried out an ankle PS test on three separate occasions. Testing was carried out on an isokinetic dynamometer (Biodex, USA) throughout each participant’s individually determined range of motion (ROM). Passive joint moments at a common angle (5° dorsiflexed) and at individual peak dorsiflexion were measured during slow (10°/s), passive rotation. PS was calculated as the leading edge of a 4th-order polynomial of the moment-angle curve (Moltubakk et al., 2018) at the same locations as passive moment. For a subset of data (n=11), the right gastrocnemius medialis was imaged using a 60 mm linear array ultrasound probe (Telemed, Lithuania) to measure fascicle length change during passive dorsiflexion. This was used to deconstruct the changes in MTU length (Fukunaga et al., 2001; Hawkins & Hull, 1990). Results: Although ankle ROM showed moderate agreement between the three sessions, passive joint moment showed lower repeatability, both at the common ankle angle and individual peak dorsiflexion. PS at the same locations showed similar repeatability, although these values were more repeatable in the triathletes who showed higher absolute PS values. For the subset of MTU data, both fascicle range and series-elastic element range show poor repeatability between sessions. However, changes in series-elastic element range were associated with a change in passive moment at peak dorsiflexion and ankle ROM (r-values: 0.568 – 0.876). Conclusion: The use of a standardised PS test does not show good repeatability across the whole population. Some between-group variation was observed, suggesting this methodology is more repeatable for certain athlete populations. Based on the MTU data, changes in ankle ROM, and thus changes in some PS parameters, are associated with changes in series-elastic element range, but not the contractile element. It remains to be determined whether between-session variation in PS parameters is caused by physiological changes to the MTU or whether the methodology itself is reliable. Investigating group-based and individual differences here could provide further evidence.

Racewalking is an unconventional form of competitive gait that elicits a unique loading profile on lower limb muscles and tendons. This study mapped the structural and mechanical properties of lower limbs in competitive racewalkers and made associations with World Athletics competition performance points. Fourteen international racewalkers (seven men, seven women) were recruited for this study. Static ultrasonography was used to quantify muscle and tendon morphological characteristics. An isokinetic dynamometer was used to measure passive musculotendinous stiffness of the triceps surae, isometric (seven knee/ankle angle combinations) and isokinetic (four angular velocities) strength parameters in the plantarflexors and dorsiflexors, and isokinetic knee flexion and extension strength at five angular velocities. Correlations were found between performance and fascicle length of gastrocnemius medialis (r = –0.569, p = 0.034), dorsiflexor strength at 120°/s (r = 0.649, p = 0.016) and knee flexor strength at 30°/s (r = 0.632, p = 0.020). No associations were found for isometric plantarflexion or passive stiffness properties. Overall, the study showed various morphological and mechanical properties are associated with performance in competitive racewalkers. These associations seem to be related to the specific and unique biomechanical characteristics of racewalking.

This report provides a detailed analysis of the women's final, including key parameters during each phase of the movement up to release. Spatiotemporal variables and motion path of each athlete has been shown. Additionally, an in-depth analysis of javelin release has been presented for each athlete's best attempt. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

INTRODUCTION: Muscle-tendon interaction during movement can be categorised into energy conservation or power amplification/attenuation strategies (1), and the mechanical and morphological properties of male athletes’ tendons adapt to these loading demands (2). Although previous research observed no differences in tendon properties between female endurance runners and inactive controls (3, 4), little is known about these properties in females undergoing habitual power amplification-type loading, such as that experienced by team sport athletes. Therefore, this study investigated Achilles’ tendon (AT) properties in trained female endurance runners and netballers. METHODS: An observational investigation of 7 national level female netballers (16.2 ± 4.5 years netball training experience) and 7 female runners (8.3 ± 2.9 years training) was conducted. AT thickness was assessed at rest using B-mode ultrasound. The AT moment arm was calculated using the tendon excursion method. Participants performed graded isometric ankle plantar flexion contractions on a Cybex dynamometer until a voluntary maximum was reached, whilst dynamic ultrasound recorded displacement of the gastrocnemius medialis myotendinous junction. From each contraction plantar flexion moment, AT force, elongation, and strain were calculated. AT stiffness was defined as the slope of the AT force-elongation relationship (from 20-100% of maximum force). Mean differences (MD) with 95% confidence intervals (CI), Student’s t-tests, and Hedge’s g effect sizes (ES) were used to assess differences in AT properties between groups. RESULTS: Netballers displayed a significantly greater maximal plantar flexion moment (MD 58.1 N.m-1, CI 35.5-80.7 N.m-1, ES 2.81, p<0.001), AT force (MD 822.4 N, CI 294.4-1350.5 N, ES 1.70, p=0.008), AT elongation (MD 5.70 mm, CI 0.40-11.07 mm, ES 1.17, p=0.044), and AT thickness (MD 0.69 mm, CI 0.08-1.30 mm, ES 1.24, p=0.031). No significant differences were found in maximal strain, stiffness, length, or moment arm. CONCLUSION: The greater AT thickness of the netball group suggests that the power amplification-type loading demands inherent to netball training (i.e., jumping, landing) have a hypertrophic effect on the tendon. Additionally, the greater maximal plantar flexion moment, and hence AT force experienced by the netballers may also contribute to this hypertrophic stimulus. This adaptation may be protective in nature, as increased thickness (and presumably cross-sectional area) would reduce peak operating stress and enhance the safety factor of the tendon. Despite differences in AT thickness, no differences in strain or stiffness were found, corroborating earlier findings of uncoupled mechanical and morphological properties (2). These results provide evidence that the AT can adapt to high intensity loading in females. 1. Roberts and Azizi, J Exp Bio, 2011 2. Wiesinger et al., PLOS One, 2016 3. Magnusson et al., Int J Exp Path, 2007 4. Westh et al., Scand J Med Sci Sport 2008

Introduction: Chronic exposure to strenuous mechanical loading has been shown to alter muscle neuromechanical behaviour during locomotion (Bissas et al., 2020) and mechanical profiles such as joint moment-angle relationships (Herzog et al., 1991). These adaptations might be movement-specific, although there is a lack of empirical evidence showing whether changes to muscle-tendon mechanical profiles translate to improved neuromechanical performance during movement. Therefore, the purpose of the study was to compare muscle-tendon profiles in trained cyclists, triathletes, and untrained controls, and to quantify neuromechanical characteristics during steady state cycling. Methods: Twenty-nine participants (10 cyclists, nine triathletes and, 10 controls) cycled at four intensities (150, 200, 250, and 300 W). Measurements of pedal forces (Radlabor, Germany), joint kinematics (Qualisys, Sweden), muscle activity (Delsys, USA), and fascicle mechanical behaviour of the gastrocnemius medialis (Telemed, Lithuania) were measured during the final minute of each 5-min trial. In addition, muscle-tendon morphological and mechanical properties were measured in the form of B-mode ultrasound (Siemens, Germany) to obtain muscle and tendon thickness, fascicle length, and pennation angle, as well as isometric/isokinetic dynamometry (Biodex, USA) to obtain passive ankle stiffness, moment-angle, and moment-velocity profiles. Results: Increases in pedal kinetics, ankle dorsiflexion angle, and normalised muscle activity were observed with an increase in exercise intensity (all p < 0.001). However, there were generally no differences in fascicle mechanical function (fascicle range, shortening velocity, pennation angle change), although some changes in muscle gearing were observed. There were also no differences between groups at any exercise intensity. There were typically no differences in isometric/isokinetic strength between groups. However, triathletes had a higher Achilles tendon thickness across multiple sites and a higher passive stiffness than the other groups (p ≤ 0.048). Conclusion: The triceps surae behave like a strut during cycling, transferring forces from proximal joints to the pedal. We showed that this behaviour is consistent across exercise intensities and between trained and untrained populations, concluding that the requirements and subsequent performance of the ankle plantarflexors at these intensities are unaffected by chronic exposure to loading. The tendon morphological and mechanical adaptations seen in triathletes appear to be specific to, or at least caused by, running but these do not lead to any neuromechanical differences during cycling. References: Bissas, A., Havenetidis, K., Walker, J., Hanley, B., Nicholson, G., Metaxas, T., Christoulas, K., Cronin, N. J. (2020). Scand J Med Sci Sports, 30, 1151-1162. Herzog, W., Guimaraes, A., Anton, M., Carter-Erdman, K. (1991). Med Sci Sports Exerc, 23, 1289-1296.

Introduction Conventional and functional knee strength ratios, defined using peak joint moment of the flexors and extensors, are used in practice to estimate injury risk (Baroni et al., 2020). Despite literature commonly reporting these values there remains uncertainty regarding their functional value (Kellis et al., 2022). It has been suggested that using a time-series metric from angle-specific joint moments might be more successful at identifying injury risk (Read et al., 2022). Therefore, the aim of this study was to compare discrete strength ratios commonly used in practice with angle-specific ratios to determine differences between the two measures. Method Twenty-eight footballers were recruited from the same English Premier League club (age: 22±4 y; stature: 1.81±0.07 m; body mass: 75.2±6.8 kg). Isokinetic testing was conducted for the knee flexors and extensors in a concentric motion at two angular velocities (60°/s and 240°/s) and in an eccentric motion (for the knee flexors only) at one angular velocity (30°/s) using an isokinetic dynamometer (Biodex Medical Systems). Conventional, discrete H:Q ratio’s (cHQR-D) were calculated as the ratio between peak joint moment in the flexors and extensors at 60°/s. Functional, discrete H:Q ratio’s (fHQR-D) were calculated as the peak joint moment in the flexors during the eccentric condition (30o/s) and the extensors at 240°/s. Angle-specific ratios (cHQR-AS and fHQR-AS) were computed as the ratio between flexor and extensor joint moments for all angles where both muscle groups were in the isokinetic range. Mean absolute residuals were then computed to compare between discrete and angle specific ratios. Results Peak joint moment for flexors and extensors at 60°/s was 129.4±21.6 and 240.9±35.6 Nm, respectively (cHQR-D = 0.54±0.07). Eccentric peak joint moment for the flexors was 165.9±34.6 Nm, and concentric peak moment for the extensors at 240°/s was 145.3±18.4 Nm (fHQR-D = 1.15±0.21). Throughout the isokinetic range, average cHQR-AS ranged from 0.41-0.98 with a mean absolute residual of 0.11±0.11 versus cHQR-D. In comparison, the average fHQR-AS ranged from 0.98-1.33 with a larger mean absolute residual of 0.26±0.14 versus fHQR-D. Conclusion Neither conventional nor functional discrete ratios were fully representative of angle-specific ratios throughout the isokinetic range. However, the average residual for the conventional ratio was lower than the functional ratio, despite a greater range of values for cHQR-AS. Suggesting that discrete conventional ratios are more representative of angle-specific ratios over a greater range of joint angles, compared to discrete functional ratios. Furthermore, discrete functional ratios are not representative of angle specific functional ratios, which could mask athletes who may have fHQR deficits and may be at risk of injury. References Baroni, BM et al. (2020). J Strength Cond Res, 34, 281-293. Kellis, E et al. (2022). J Sport Health Sci. Read, PJ et al. (2022). J Sports Sci, 1-7.

This report provides a detailed analysis of the men's final, including key parameters during each phase of the movement up to release. Spatiotemporal variables and motion path of each athlete has been shown. Additionally, an in-depth analysis of javelin release has been presented for each athlete's best attempt. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides a comprehensive split time analysis between each hurdle, as well as key kinematic parameters for the clearance of hurdle six, including take-off and touchdown postural characteristics. Temporal analysis of the step leading up to the finish line are also provided for the final. Hurdle split times are also provided for the semi-finals. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides split time analysis and key kinematic parameters for the women's 100 m finalists. Kinematic data are provided for steps during high velocity running and in the final metres of the race. Split time analysis is also provided for all three semi-finals. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides split time analysis and key kinematic parameters for the men's 100 m finalists. Kinematic data are provided for steps during high velocity running and in the final metres of the race. Split time analysis is also provided for all three semi-finals. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides a comprehensive split time analysis between each hurdle, as well as key kinematic parameters for the clearance of hurdle five, including take-off and touchdown postural characteristics. Temporal analysis of the step leading up to the finish line are also provided for the final. Hurdle split times are also provided for the semi-finals. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

There has been increasing interest in new measurement systems that provide instantaneous spatiotemporal data whilst being less expensive and more accessible to practitioners. The aim of this study was to examine the agreement between the OptoJump Next system (OJ), videography and force platform methods for measuring spatiotemporal variables during the acceleration phase of sprinting. Ninety-nine university students completed two maximal 20 metre sprints in which spatiotemporal parameters (contact time [CT], flight time [FT], step length [SL] and step rate) were simultaneously obtained using the OJ system (1000 Hz), videography (200 Hz), and force platforms (1000 Hz). The OJ and video systems showed high agreement for the measurement of step length (bias: 0.003-0.007 m, random error [RE]: 0.057-0.071 m). For temporal parameters, OJ tended to overestimate CT compared to the force platforms (bias: 0.012-0.014 s, RE: 0.009-0.021 s) and also underestimated FT (bias: 0.012-0.013 s, RE: 0.011-0.012 s). Despite the lower sampling rate, videography showed a closer agreement with the force platform for both CT (bias: 0.005-0.010 s, RE: 0.009-0.021 s) and FT (bias: 0.005-0.007 s, RE: 0.008-0.010 s). Although OptoJump next provides instantaneous spatiotemporal parameters, coaches may wish to adjust for the systematic overestimation of CT (0.013 s) and underestimation of FT (0.012 s) in order to obtain sprint spatiotemporal data that aligns to force platforms.

The Achilles tendon is the most frequently ruptured tendon in the body with an annual incidence of 21 ruptures per 100,000 individuals per year (Lantto et al., 2015). Achilles tendon rupture is highest in middle-aged people (40-50 years) and males are more frequently affected the females (Lawrence et al., 2017). In the last decade, there has been an increasing amount of literature investigating non-operative management of Achilles tendon tears (Hutchinson et al., 2015). There is an ongoing debate regarding the optimum management method for Achilles tendon ruprtures, however, much of the research focuses on complications following treatment such as tendon re-rupture. Very little information exists regarding the functional outcomes of treatment which is needed to manage patient expectations regarding return to activity and long-lasting functional impairments (Khan et al., 2005). Very recent research has examined the longer term functional outcomes of Achilles tendon ruptures using more sophisticated measures (e.g. strength assessments), however this research has focused on the outcomes of non-operative management (Lawrence et al., 2017). As a result, this study aims to examine the neuromuscular and functional outcomes of operatively managed ruptures using sophisticated measures such as ultrasound and gait analysis.

Muscle-tendon unit (MTU) assessments can be categorised into local (e.g. tendon strain) or global (e.g. jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global MTU assessments during two testing sessions separated over 24-72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096-0.936). Good to excellent reliability was found for all global measures (ICC: 0.788-0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635-0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635-0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6-35.9%), global measures (CV: 1.6-12.9%) were more reproducible than local measures (CV: 3.6-64.5%). However, local metrics directly measure specific properties of the MTU, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU assessments within female athletes, which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

This study tested the performance of OpenPose on footage collected by two cameras at 200 Hz from a real-life competitive setting by comparing it with manually analyzed data in SIMI motion. The same take-off recording from the men's Long Jump finals at the 2017 World Athletics Championships was used for both approaches (markerless and manual) to reconstruct the 3D coordinates from each of the camera's 2D coordinates. Joint angle and Centre of Mass (COM) variables during the final step and take-off phase of the jump were determined. Coefficients of Multiple Determinations (CMD) for joint angle waveforms showed large variation between athletes with the knee angle values typically being higher (take-off leg: 0.727 ± 0.242; swing leg: 0.729 ± 0.190) than those for hip (take-off leg: 0.388 ± 0.193; swing leg: 0.370 ± 0.227) and ankle angle (take-off leg: 0.247 ± 0.172; swing leg: 0.155 ± 0.228). COM data also showed considerable variation between athletes and parameters, with position (0.600 ± 0.322) and projection angle (0.658 ± 0.273) waveforms generally showing better agreement than COM velocity (0.217 ± 0.241). Agreement for discrete data was generally poor with high random error for joint kinematics and COM parameters at take-off and an average ICC across variables of 0.17. The poor agreement statistics and a range of unrealistic values returned by the pose estimation underline that OpenPose is not suitable for in-competition performance analysis in events such as the long jump, something that manual analysis still achieves with high levels of accuracy and reliability.

This study compared angle-specific hamstring:quadricep (H:Q) ratios with their discrete counterparts during strength testing in pro fessional male footballers. Twenty-eight professional English Premier League footballers were recruited for this study (age: 22 6 4 years; stature: 1.81 6 0.07 m; body mass: 75.2 6 6.8 kg). Isokinetic testing of the knee flexors and extensors was conducted concentrically at 2 angular velocities (60˚ and 240˚·s21 ) and eccentrically (for the knee flexors only) at 30˚·s21 . Conventional H:Q ratio was calculated as the ratio between peak joint moment in the flexors and extensors at 60˚·s21 . Functional H:Q ratio was calculated as the peak joint moment in the flexors during the eccentric condition and the extensors at 240˚·s21 . Discrete conventional and functional H:Q ratios were 0.56 6 0.06% and 1.28 6 0.22%, respectively. The residual differences between discrete values and angle-specific residual values were 13.60 6 6.56% when normalized to the magnitude of the discrete value. For the functional ratios, the normalized residual was 21.72 6 5.61%. Therefore, neither discrete ratio was representative of angle-specific ratios, although the conventional ratio had lower error overall. Therefore, practitioners should consider H:Q ratio throughout the full isokinetic range of motion, not just the discrete ratio calculated from peak joint moments, when designing and implementing training programs or monitoring injury risk, recovery from injury, and readiness to return to play

This study aimed to compare joint kinematics and center of mass parameters throughout hurdle clearance between world-class men and women sprint hurdlers, who were competing in a World Championships final. This was the first study to present time-series kinematic data around hurdle clearance, and given the technical ability of the athletes analyzed, it can be used as a template when analyzing the technique of other athletes in similar competitions and training. Video data were collected of the 16 finalists at the 2017 IAAF World Championships using four high-speed cameras (150 Hz). Video files were continuously digitized manually from touchdown before hurdle clearance to toe-off after landing around the sixth hurdle for men and the fifth hurdle for women, and sex-based comparisons were made at key discrete time points using independent t-tests, and throughout the entire hurdle phase using statistical parametric mapping. When calculated relative to hurdle height, the women's center of mass height was significantly greater than the men's throughout the full analyzed sequence (p < 0.001). Men also displayed more hip flexion in the lead leg at take-off before hurdle clearance (p = 0.029) as well as a more extended knee joint at intervals during flight and upon landing (p ≤ 0.037). Women completed the hurdle phase in a significantly shorter time than men (~11% difference, p < 0.001). Finally, women seemed to be more efficient by maintaining and even exceeding their entry velocity for the first 40% of the hurdle phase. These results show a lower technical demand for the women to successfully negotiate hurdle clearance, thus providing further evidence to support the argument that the women's hurdle height is too low for their performance capabilities and should be raised in senior competition.

This report provides detailed split time analysis of the women's 400 m final and semi-finals. Additionally, this reports shows key spatiotemporal and kinematic step parameters of each finalist a specific stage of the race. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides detailed split time analysis of the men's 400 m final and semi-finals. Additionally, this reports shows key spatiotemporal and kinematic step parameters of each finalist a specific stage of the race. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides detailed split time analysis of the women's 200 m final and semi-finals. Additionally, this reports shows key spatiotemporal and kinematic step parameters of each finalist a specific stage of the race. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

This report provides detailed split time analysis of the men's 200 m final and semi-finals. Additionally, this reports shows key spatiotemporal and kinematic step parameters of each finalist a specific stage of the race. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

We mapped structural and functional characteristics of muscle‐tendon units in a population exposed to very long‐term routine overloading. Twenty‐eight military academy cadets (age = 21.00 ± 1.1 years; height = 176.1 ± 4.8 cm; mass = 73.8 ± 7.0 kg) exposed for over 24 months to repetitive overloading were profiled via ultrasonography with a senior subgroup of them (n = 11; age = 21.4 ± 1.0 years; height = 176.5 ± 4.8 cm; mass = 71.4 ± 6.6 kg) also tested while walking and marching on a treadmill. A group of eleven ethnicity‐ and age‐matched civilians (age = 21.6 ± 0.7 years; height = 176.8 ± 4.3 cm; mass = 74.6 ± 5.6 kg) was also profiled and tested. Cadets and civilians exhibited similar morphology (muscle and tendon thickness and cross‐sectional area, pennation angle, fascicle length) in 26 out of 29 sites including the Achilles tendon. However, patellar tendon thickness along the entire tendon was greater (P < .05) by a mean of 16% for the senior cadets compared with civilians. Dynamically, cadets showed significantly smaller ranges of fascicle length change and lower shortening velocity in medial gastrocnemius during walking (44.0% and 47.6%, P < .05‐.01) and marching (27.5% and 34.3%, P < .05‐.01) than civilians. Furthermore, cadets showed lower normalized soleus electrical activity during walking (22.7%, P < .05) and marching (27.0%, P < .05). Therefore, 24‐36 months of continuous overloading, primarily occurring under aerobic conditions, leads to more efficient neural and mechanical behavior in the triceps surae complex, without any major macroscopic alterations in key anatomical structures.

The effect of the inclusion of a high hurdle 13.72 m after the start line on elite sprint start and initial acceleration technique has yet to be investigated or understood. This highly novel study addresses that lack of information in an exceptional manner, through detailed biomechanical analysis of the world's best sprint and hurdle athletes, with data collected in situ at the 2018 IAAF World Indoor Championships, held in Birmingham, UK. High speed videos (150 Hz) were compared for eight sprinters and seven hurdlers for the start and initial acceleration phase of the finals of the men's 60 m and 60 m hurdles. Temporal and kinematic data were supplemented by vector coding analysis to investigate mechanisms by which these world-class athletes translate their centres of mass (CM) up to the fourth touchdown post-block exit. The sprinters and hurdlers coordinated their lower limb and trunk movement in a similar manner throughout the start and initial acceleration phases, which contributes new conceptual understanding of the mechanisms that underpin start and initial acceleration performance. Differences between groups were initiated from block set-up, with the hurdlers utilising a larger block spacing, but with the front block nearer to the start line than sprinters. Even after accounting for stature, the biggest differences in the raising of the CM occurred during the block phase, with hurdlers greater than sprinters (difference in vertical CM displacement scaled to stature = −0.037, very large effect size). Subsequent flight phases showed the biggest differences in the translation of the CM, in part due to longer flight times in the hurdlers, whilst the techniques of the two groups generally converged during the ground contact phases of initial acceleration. In highlighting that similar techniques are used by world-class sprinters and hurdlers, despite differing task constraints, this study has provided invaluable insights for scientists, coaches, and athletes, that will inform further developments in understanding and practice across both sprints and hurdles.

Measurements of muscle-tendon unit passive mechanical properties are often used to illustrate acute and chronic responses to a training stimulus. The purpose of this study was to quantify the inter-session repeatability of triceps surae passive stiffness measurements in athletic and non-athletic populations, with the view to discussing its usefulness both as a muscle-tendon profiling tool and a control measure for studies with multiple data collection sessions. The study also aimed to observe the effects of quiet standing on passive stiffness parameters. Twenty-nine men (10 cyclists, nine triathletes, 10 controls) visited the laboratory on three separate occasions, where passive stiffness tests were carried out using an isokinetic dynamometer and B-mode ultrasound. Participants were fully rested on two of the sessions and subjected to 20 min of quiet standing in the other. The passive stiffness assessment generally showed only moderate inter-session repeatability but was still able to detect inter-group differences, with triathletes showing higher passive stiffness than cyclists (p < 0.05). Furthermore, quiet standing impacted passive stiffness by causing a reduction in ankle joint range of motion, although mechanical resistance to stretch in the muscle-tendon unit at a given joint angle was relatively unaffected. These findings show that passive stiffness assessment is appropriate for detecting inter-group differences in the triceps surae and even the effects of a low-intensity task such as quiet standing, despite showing some inter-session variation. However, the inter-session variation suggests that passive stiffness testing might not be suitable as a control measure when testing participants on multiple sessions.

Muscle-tendon unit (MTU) assessments can be categorised into local (e.g., tendon strain) or global (e.g., jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global MTU assessments during two testing sessions separated over 24–72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096–0.936). Good to excellent reliability was found for all global measures (ICC: 0.788–0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635–0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635–0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6–35.9%), global measures (CV: 1.6–12.9%) were more reproducible than local measures (CV: 3.6–64.5%). However, local metrics directly measure specific properties of the MTU, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU assessments within female athletes which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

We do not yet understand the concurrent validity of markerless motion capture (MMC) to measure kinematic differences between multiple gait speeds. This study determined the capacity of Theia3D (Theia Markerless Inc.) MMC to detect sagittal-plane kinematic responses to different gait speeds during walking (3 and 5 km/h) and running (10 and 12 km/h). Fourteen participants ambulated on a motorised treadmill, while markerbased motion capture, through optoelectronic cameras (Oqus 7+, Qualisys AB), and MMC, through videos (Miqus, Qualisys AB) were synchronously collected. Sagittal plane changes in pelvis, hip, knee, and ankle kinematics were compared. Mostly excellent waveform similarity was found for joint kinematic changes (coefficient of multiple determination [CMD] ≥ 0.87), but pelvic tilt was less similar (CMD ≤ 0.48). Agreement between outcome measures (joint minima and maxima, range of motion) was mostly good-to-excellent (intraclass correlation coefficient [ICC] = 0.475-0.950) with standard error of measurement values of less than 1°. Pelvis kinematics showed lower agreement between systems (ICC = 0.032-0.776). In this study, Theia3D detected changes in hip, knee, and ankle sagittal-plane joint kinematics between speeds with a similar accuracy to the marker-based approach. Therefore, Theia3D is appropriate for use if interested in lower-limb sagittal joint kinematics, but not pelvic tilt.

Abstract

Measurements of muscle-tendon unit (MTU) function can be categorised into local (e.g. tendon strain) or global (e.g. jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU function assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global assessments of MTU function during two testing sessions separated over 24-72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096-0.936). Good to excellent reliability was found for all global measures (ICC: 0.788-0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635-0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635-0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6-35.9%), global measures (CV: 1.6-12.9%) were more reproducible than local measures (CV: 3.6-64.5%). However, local metrics directly measure specific aspects of MTU function, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU function within female athletes, which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

Bissas, A, Paradisis, GP, Nicholson, G, Walker, J, Hanley, B, Havenetidis, K, and Cooke, CB. Development and maintenance of sprint training adaptations: an uphill-downhill study. J Strength Cond Res XX(X): 000-000, 2020-We examined the development of performance adaptations resulting from an uphill-downhill training program and monitored the decline of adaptations during detraining. Twenty-eight men were randomly assigned to 1 of 2 sprint training groups who trained 3 times per week for 6 weeks and a control group (C). The uphill-downhill group (U+D) trained on an 80-m platform with 3° slopes, whereas the horizontal (H) group trained on flat track. Subjects were tested for maximal running speed (MRS), associated kinematics, and leg strength before and after training, with U+D subjects also tested after weeks 2 and 4 of training, and after a 3-week detraining period. The U+D group increased their MRS by 3.7% (from 8.75 ± 0.72 to 9.07 ± 0.64 m·s, p < 0.05), their stride rate by 3.1% (from 4.21 ± 0.21 to 4.34 ± 0.18 Hz, p < 0.05), and their knee extensors' maximum isometric force by 21% (from 2,242 ± 489 to 2,712 ± 498 N, p < 0.05) after training. The time course of changes showed declines for weeks 1-4 (1.4-5.1%), but an ascending trend of improvement compensated all losses by the end of week 6 (p < 0.05). During detraining, no decreases occurred. No changes were observed for the H and C groups. The minimum period to produce positive effects was 6 weeks, with a very good standard of performance maintained 3 weeks after training. U+D training will prove useful for all athletes requiring fast adaptations, and it can fit into training mesocycles because of its low time demands.

Abstract

The aim was to investigate the kinematic factors associated with successful performance in the initial acceleration phase of a sprint in the best male athletes in the World at the 2018 World Indoor Athletics Championships. High speed video (150 Hz) was captured for eight sprinters in the men's 60 m final. Spatio-temporal and joint kinematic variables were calculated from the set position to the end of the first ground contact post-block exit (GC1). Normalised average horizontal external power (NAHEP) defined performance and was the dependent variable for a series of regression analyses. Clear relationships were found between GC1 NAHEP and 10-m time, 60-m time, change in velocity, acceleration and contact time in the first ground contact (r = –0.74, –0.64, 0.96, 0.91 and –0.56, respectively). Stepwise multiple linear regression of joint kinematic variables in the first ground contact revealed that trunk angle at take-off and thigh separation angle at take-off explained nearly 90% of variation in GC1 NAHEP (R

2

We evaluated sprint mechanical asymmetry in world-class competitors and evaluate whether interlimb sex-based differences in sprinting mechanics exist. The eight finalists in the men’s and women’s 100 m events at the 2017 IAAF World Championships were studied. Five high-speed cameras (150 Hz) were used to capture two consecutive steps of the whole body between 47.0 m and 55.5 m from the start, while four additional cameras (250 Hz) focussed on the lower extremities. A total of 33 spatio-temporal, touchdown and toe-off joint angles, and horizontal and vertical foot velocity parameters were extracted through three-dimensional analysis. Group mean asymmetry scores were assessed using the symmetry angle (SA) where scores of 0% and 100% represent perfect symmetry and perfect asymmetry, respectively. Although considered generally low (SA < 3% for 22 out of 33 parameters), the magnitude of mechanical asymmetry varied widely between sprinters of the same sex. However, there was no mean SA scores difference between men and women for any stride mechanical parameters (all P≥0.064). Asymmetry scores were inconsistent between parameters and phases (touchdown vs toe-off instants), and sprinting mechanics were generally not related to asymmetry magnitudes. In summary, low to moderate asymmetry is a natural phenomenon in elite sprinting. Asymmetry was inconsistent between parameters and competitors during near maximum-velocity running, yet mean values for a given parameter generally did not differ between sexes. Sprinters’ performances were not related to their SA scores.

INTRODUCTION: Markerless motion capture (MMC) is increasing in popularity among biomechanists because of the reduced data collection time and removal of subjects needing to wear tight, minimalist clothing [1]. However, gait analysis often requires subjects to walk or run at multiple speeds, such as in an incremental exercise test. The sensitivity of MMC to detect kinematic changes across speeds has yet to be thoroughly explored, so the aim of this study was to compare kinematic responses to changes in gait speed when measured with a widely used marker-based system versus a MMC system. METHOD: Fifteen healthy, adult participants walked on an instrumented treadmill (1,000 Hz; Gaitway3D; h/p/cosmos) at 3 and 5 km/h and ran at 10, 11, and 12 km/h. A 14-camera optoelectronic motion capture system (Oqus 7+, Qualisys) was used to collect marker data, where markers were placed according to Cappozzo et al. [2]. Markerless video data were collected synchronously with 12 high-speed video cameras (Miqus, Qualisys). Both systems were sampling at 100 Hz. Markerless data were exported to Theia3D for processing, before being exported to Visual3D for modelling alongside marker data. Gait events were determined using the kinetic data, which was the same for both motion capture systems. Kinematic data were exported to MATLAB to calculate changes in sagittal angular data between gait speeds. RESULTS: For walking (changes between 3-5 km/h), MMC demonstrated the capacity to measure similar changes in joint range of motion (ROM), peak flexion, and peak extension for hip, knee, and ankle joints (ICC[3,1] ≥ 0.892) when compared to marker-based data, and there were no significant differences between the change in joint kinematics between systems (p > 0.05). MMC also displayed moderate-to-excellent agreement for knee and ankle joint kinematics during running (changes between 10-11 and 11-12 km/h), including ROM and peak flexion/extension (ICC ≥ 0.626). However, the hip joint was less consistent, with poor-to-moderate agreement generally being found, especially in peak hip extension (ICC = 0.198 when comparing differences between 11-12 km/h). There were no significant differences between systems during running (p < 0.05). CONCLUSION: MMC was able to measure small changes in joint angles during walking at similar magnitudes to traditional marker-based motion capture, which is promising for clinical biomechanists and gait analysis clinics. However, MMC importantly performs less well when trying to measure joint angle changes during different running speeds, with varying results between lower limb joints. Researchers and practitioners should be cautious when interpreting sagittal-plane kinematic changes during running when employing MMC as the chosen method of motion capture. REFERENCES: [1] Kanko, RM et al. (2021) J Biomech;127:110665 [2] Cappozzo, A et al. (1995) Clin Biomech;10:171-8