Dr Lysander Pollitt

BACKGROUND: Squatting is a core exercise for many purposes. However, there is still controversy surrounding the practice of targeting specific muscle groups when performing the back squat with different stance widths or foot positions. Therefore, this study aimed to assess lower limb muscle activation during different form of back squat when adopting three different foot angles. METHODS: Eight male active participants (age: 24.0±0.8 years, height: 1.80±0.63 m and mass: 85.8±8.7kg) performed maximal isometric squat, back squat with an overalod of 80% of 1 repetition maximum, and countermovement jump (CMJ) when adopting three foot rotation angles: parallel (0°), +10° outward (external rotation), and +20° outward (external rotation). We calculated the root mean square of the electromyographic signals recorded from eight participant’s dominant leg muscles. RESULTS: During the descending phase of the back squat, the 20° external foot rotation elicited greater activation of the biceps femoris (+35%; P=0.027) and gastrocnemius medialis (+70%; P=0.040) compared to parallel foot. There were no significant differences among the other muscles and exercise conditions. CONCLUSIONS: The +20° foot position increased BF and GasM muscle activity only during the downward phase of the back squat. Strength coaches should consider the present findings when selecting specific resistance exercises aiming to improve athletes’ strength and physical fitness.

DROP JUMPING ONTO UNSTABLE SURFACES DOES NOT IMPAIR SUBSEQUENT STABLE JUMPING PERFORMANCE Pollitt, L., Bissas, A. School of Sport, Leeds Metropolitan University, UK Introduction Although interest has grown over recent years in training using unstable surfaces, its acute and chronic performance effects are still not fully understood. Furthermore, this has excluded consideration of dynamic exercise where instability during landing may cause a heightened neuromuscular response to negotiate increased stability demands. An increased neural drive may then be directed towards the agonistic muscles when stability demands are reduced. This study was therefore designed to compare the effects of drop-jumps (DJ) onto unstable and stable surfaces on subsequent stable countermovement jump (CMJ) performance. Methods In a random crossover design 14 males (21.09 ± 2.4yrs) completed 3 experimental conditions, with each condition consisting of an activation exercise (3 sets of 5 DJ from 0.4m) onto either unstable (BOSU, mini-trampoline (MT)) or stable (ground) surfaces, and a control condition. The experimental conditions represented a typical post-activation potentiation (PAP) protocol for an acute study (Saez Saez de Villareal et al., 2007). Testing consisted of 3 maximal CMJ on a force plate (1000Hz) before and after (t=5, t=9min) each protocol and the best jump at each point was analysed. Four practice sessions were also conducted beforehand, with absolute and relative reliability statistics establishing the level of reproducibility for CMJ and DJ performance so the magnitude of any pre-post differences could be appreciated. Data were analysed using Repeated Measures ANOVA. Results No differences were observed between conditions with respect to any kinetic, temporal or performance variables. With regards to the time factor each condition, including the control, followed a similar trend. No pre-post significant differences were observed for temporal variables (e.g. eccentric phase), while the reductions observed for key kinetic variables (e.g. peak power, take-off velocity) and specifically jump height [control (-5.5%), BOSU (-5.3%), MT (-2.6%), ground (-5.4%)] were within the reproducibility random error limits. Discussion The results across conditions with respect to time do not indicate that PAP was present, as no significant changes were observed during post-testing. This may arise from failure to employ the optimal protocol to evoke PAP, for which there is no uncontroversial standard. Nevertheless, these findings suggest that acute DJ sessions onto unstable surfaces yield similar effects to commonly performed DJ onto stable surfaces. Dynamic training onto unstable surfaces may therefore be beneficial during all stages of structured training, including rehabilitation, by reducing impact forces upon landing while maintaining performance and possibly conditioning the neural circuit.

This report provides detailed phasic and temporal analysis of each transition zone during the men's 4x100 m relay final and semi-finals. Additionally, this report also indicates 100 m split times as well as individual leg times. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

Biomechanical Report for the IAAF World Championships 2017: 4x100 m Men's ABSTRACT This report provides detailed phasic and temporal analysis of each transition zone during the men's 4x100 m relay final and semi-finals. Additionally, this report also indicates 100 m split times as well as individual leg times. The full report is available from the IAAF website: https://www.iaaf.org/about-iaaf/documents/research

THE INFLUENCE OF FAMILIARISATION ON VARIATION IN PERFORMANCE DURING DROP JUMPING Pollitt L, Bissas A School of Sport, Leeds Metropolitan University, UK Introduction Jumping tasks are often used to assess the level of development of the lower extremities, and the reliability of the countermovement jump (CMJ) in this regard has been extensively established (Moir et al., 2004). The reliability of the more complex drop-jump (DJ) is however less established as the goal of minimising ground contact time (GCT) while maximising subsequent jump height, especially at greater drop heights, requires a high degree of athletic competence in the test subjects. Therefore, without extensive familiarisation of less-trained subjects with the DJ, the influence of performance variability likely results in low credibility of test results used to evaluate the effectiveness of training interventions. Methods 44 males undertook a 2-week progressive DJ familiarisation, in preparation for a 6-week training study, onto surfaces with varying levels of stability. Within 6 sessions, participants completed a total of 120 DJ (0.5-1m), and also a further 48 jumps (CMJ, DJ0.2, 0.6 and 1m) to replicate the testing component, onto a force platform (1000Hz). At the initial stage, the best CMJ were determined from jump height (JH), and DJ from GCT and reactive strength index (RSI), calculated from the resultant JH/GCT. The within-subject variability for a large number of mechanical and performance variables was assessed by a range of relative and absolute reliability statistics including limits of agreement (LOA) and coefficient of variation (CV%). Results Variability (CV%) across CMJ performance (3.1-4.7%) was much lower than for all DJ variables (7.5-16.2%), however a trend of a reduction in variation was observed across each variable over the 6 sessions. The greatest reduction in variation was observed during DJ from 1m for RSI from 16.2-11.6% (LOA: -19.1 & 54.4 to -8.2 & 34). Similar changes in variation also occurred at DJ0.6m for both: CGT 12.3-8.4% (LOA: -0.027 & 0.140 to -0.018 & 0.085) and RSI 13.4-9.1% (LOA: -10.3 & 45 to -7 & 35.8). The mean improvement in GCT at DJ0.6m was 311ms - 262ms (15.7%). Discussion These findings highlight the importance of familiarisation to establish variability and systematic errors within tasks requiring a greater degree of competence. As indicated, CMJ variability was relatively small and stable however the measures of absolute and relative reliability for DJ variables showed that the combined error reached high levels. Therefore, due to the greater variation in DJ performance variables across increasing drop heights, test results should be interpreted with caution especially if used to assess training adaptations.

LONG TERM EFFECTS OF LANDING SURFACE STABILITY ON DROP JUMP PERFORMANCE Pollitt L, Bissas A Leeds Beckett University, UK Introduction Although the direct effect of unstable surfaces on explosive performance may be a reduction in power output due to impaired agonist functioning, the long term effects of unstable training (UST) on stable ground performance have not been investigated. With training, the sensorimotor system may modulate the detrimental compensatory responses on performance by reducing the sensitivity required on a stable surface, thereby allowing greater agonist force production due to reduced shear forces. This study examined the long-term effects of dynamic UST on subsequent stable ground drop jump (DJ) performance. Methods 44 males undertook a 6-week progressive DJ intervention training, randomly assigned to one of 5 groups based on landing surface stability: mini-trampoline (MT), BOSU, MIX (BOSU & stable), stable, or control. In total, participants completed 1080 DJs. Each session involved 4*5 DJ from 3 drop heights which progressed from 0.2-0.4m (weeks 1&2) to 0.8-1m (weeks 5&6). Testing consisted of 3 maximal DJ at 0.2, 0.6 and 1m onto a Kistler force platform (1000Hz) before and after the training intervention. Instruction was to minimise ground contact time (GCT) while maximising subsequent jump height (JH). Results DJ1.0m: Statistical analysis showed that all groups improved their GCT (p<0.01). For RSI, all training groups significantly improved their performance (MT: 37%, BOSU: 28%, Stable: 25%, MIX: 18%, p<0.01) except for control (-7%). For JH, the performance for all training groups remained unaltered while the control experienced a significant drop in their pre-training values (-18%, p<0.05). DJ0.6m: Significant improvements over time (p<0.01) were found for all groups for GCT and RSI whereas for JH, the post-pre changes for stable (17%) and control (-9.4%) differed significantly (p<0.01) while the other groups remained unchanged. DJ0.2m: Significant improvements over time in GCT were recorded (p<0.01 – 0.05) with BOSU (-75ms) and controls (-80ms) exhibiting the greatest changes while the same trend was noted for RSI. In terms of JH, the post-pre changes for stable (+2.8cm) and control (-4.1cm) differed significantly (p<0.01) with the other groups unchanged. Discussion On the debate about UST, no significant differences in performance measures were observed between stable and unstable (BOSU, MT or MIX) groups. These findings of similar improvements suggest that exposure to UST may be as effective as stable training, which may be of particular interest to athletes in-season when reduced impact loads are necessary. Furthermore, although all groups recorded improvements in GCT across jump heights, JH was impaired in the controls at each height. Therefore, improvements in GCT alone may not represent the whole spectrum of performance adaptations when analysing DJ performance.

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

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

SURFACE INSTABILITY DOES NOT ADVERSELY AFFECT DROP JUMPING PERFORMANCE: A MULTI-VARIABLE BIOMECHANICAL INVESTIGATION Pollitt L, Hanley B, Bissas A Leeds Beckett University, UK Introduction Currently, despite the widespread practical use of surface instability training, little is known about its long-term effects, or about the effect it has on stable surface performance once its demands have been removed. The purpose of this study was to conduct a multi-variable biomechanical evaluation of the effects of adaptation to progressive drop jump (DJ) training conducted with varying levels of landing surface stability. Methodology 42 physically active males were exposed to 8 weeks of DJ training using increasing drop heights (i.e., 0.2m to 1.0m) onto Mini-Trampoline, BOSU, Stable, or Mix (BOSU & Stable) landing surfaces. A Control group was also included. Pre and post-testing (DJ1.0m, DJ0.6m, DJ0.2m and CMJ) was conducted on a stable surface where kinetic, kinematic, and EMG data were collected. Additional to independent analyses of these systems, muscle moment-power, work-energy and mechanical stiffness data were also constructed to provide an insight into the internal mechanisms of training adaptions. The multi-variable approach yielded a vast array of related variables. For example, dissection of the force-time curve into 66 variables and EMG analysis of specific 50ms windows including identification of the short, medium and long latency reflex responses. Results The most important finding was that exposure to landing surface instability did not adversely affect muscle activation, mechanical work and stiffness or energy contributions across joints. Only select changes in neural and mechanical variables reached statistical significance. Improvements in reactive strength index for the surface instability groups at DJ1.0m (18-37%), DJ0.6m (14-28%), DJ0.2m (16-43%), were similar to the Stable group (25, 31 & 21%). Significant improvements in comparison to the Control group (p<0.05) were found for the BOSU and Stable groups at each drop height. Discussion The absence of any adverse effects in neuromuscular or mechanical variables following surface instability training provides a new insight into the ability of the human body to adapt performance while learning new movement patterns. Essentially, the inclusion of instability with DJ training is as effective as stable landing surface conditions. The findings also suggest that when adaptations are made to the imposed demands, the adverse effects associated with surface instability have been overstated and that the principle of training specificity is not violated. Furthermore, incorporating surface instability may be beneficial to the principle of variability and as an independent consideration within an athletic training cycle, where it could reduce loading demands or be used in combination with skill acquisition, while maintaining levels of performance enhancement similar to those provided by stable conditions.

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 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

Introduction: Information on the acute metabolic responses to resistance exercise (RE) may provide valuable information regarding peripheral fatigue factors. However, most studies have examined a relatively narrow range of metabolic responses to different RE workouts. In addition, much of the research has not accounted for plasma volume (PV) changes. This study compared a wider profile of metabolic responses following strength (STR) and hypertrophy-type (HYP) back squat workouts, when corrected for PV changes. Methods: Following one repetition maximum (1RM) testing, seven trained males (23.6±2.7 years) completed a STR workout (4x6 repetitions, 85% 1RM, 5 min rest intervals), a HYP workout (4x10 repetitions, 70% 1RM, 1.5 min rest intervals) and a control condition (CON) in a randomised cross-over design separated by at least 48 hours. Capillary blood samples were taken pre- (-20min,-10min,-0min) and post-exercise (+0min,+10min,+60min) in order to measure concentration of blood lactate (BL), electrolytes, haemoglobin (Hb) and haematocrit (Hct). The samples were analysed using a blood gas CO-Oximeter and electrolyte analyser (GEM Premier 4000). Following calculation of PV changes from Hb and Hct, variables were corrected using the method of Kraemer & Brown (1986). A two-factor within subjects ANOVA was employed for statistical analysis. Results: Average PV changes were -8.05 ± (11.45%), -8.02 ± (6.54%) and -3.32 ± (6.97%) for the STR, HYP and CON conditions respectively. Repeated contrast tests revealed a significantly (p<0.05) greater increase (at +0min) in BL concentration following the HYP condition (0.83 ± 0.13 mmol/L-1 to 9.67 ± 2.45 mmol/L-1) than the STR (1.07 ± 0.38 mmol/L-1 to 6.66 ± 2.31 mmol/L-1) or CON (0.97 ± 0.48 mmol/L-1 to 1.15 ± 0.55 mmol/L-1) conditions, this was also evident at +10min. In addition, the HYP workout resulted in significantly greater (p<0.05) reductions in chloride, sodium and potassium than the CON condition whilst the STR workout also resulted in significantly greater reductions in chloride, sodium and calcium than the CON condition. Discussion: PV changes were similar to those reported previously following RE (Wallace et al., 1990). In addition, the HYP workout had a notable impact on metabolite accumulation as evidenced by significant changes in the concentration of BL and a number of electrolytes. Greater metabolic stress has been previously reported following HYP than STR workouts (McCaulley et al., 2009). However, the data highlight the need to consider a wider profile of metabolic variables when examining the acute responses to HYP workouts.

Introduction: Hypertrophy-type (HYP) resistance exercise (RE) is typically designed to elicit changes in fibre size whereas strength-type (STR) RE is usually employed to improve strength via mainly neural adaptations. Although previous studies have investigated the acute responses to different RE workouts (McCaulley et al., 2009), the mechanisms responsible for different long-term adaptations are still widely debated. Thus, this study examined the acute neuromuscular responses to STR and HYP workouts which utilised the back squat exercise. Methods: Seven trained males (23.6 ± 2.7 years) completed a STR workout (4x6 repetitions at 85%1RM, 5 min rest intervals), a HYP workout (4x10 repetitions at 70%1RM, 90s rest intervals) and a control condition (CON) in a randomised cross-over design separated by at least 48 hours. Subjects performed 3×4s maximal isometric back squats (100o knee flexion), by using a modified squat rack attached to a Kistler force platform (1000 Hz), immediately pre- and post- each workout. Several kinetic performance variables were determined and investigated statistically by using a two-factor within subjects ANOVA. Results: Repeated contrast tests showed a greater reduction in Peak Isometric Force following the HYP (-18.06%) than CON condition (-1.21%) (p=0.017). Also the HYP workout resulted in greater reductions in the rate of force development (RFD) during the initial 0.05s (-21%, p=0.023) and 0.1s (-29%, p=0.047) of the force-time curve as well as greater increases in the time required to produce 500N (92%, p=0.018) when compared with the CON condition. The STR workout was characterised by a greater reduction in RFD during the initial 0.2s of the force-time curve (-0.19%, p=0.034) as well as greater increases in the time required to produce 250N (28%, p=0.025) when compared to the CON condition. No significant differences were observed between the STR and HYP conditions for any variable. Discussion: Both workouts resulted in acute neuromuscular fatigue possibly via different pathways. The acute reductions in RFD following the STR workout may have resulted from central fatigue whereas the reductions in RFD and PF following the HYP workout may be indicative of central and peripheral fatigue (Hakkinen et al., 1994; McCaulley et al., 2009). Although STR and HYP workouts are typically prescribed in order to emphasise different long-term adaptations, marked differences in the acute neuromuscular responses were not observed. Such findings may question the prescription of future similar workouts when aiming to elicit distinctly different neuromuscular stimuli.

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.

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

The aims of this study were: (1) to quantify interlimb asymmetries in EPL soccer players in the context of kicking limb preference and (2) to establish the relationship between interlimb asymmetries and measures of physical performance. Twenty-two players (age: 21.8 ± 4.4 years) from an EPL club performed a running gait assessment (20 km/h) and unilateral countermovement jumps, a CoD assessment (modified 505 test), and an isokinetic knee extension/flexion protocol using each leg. Asymmetries were quantified using the percentage difference method and Pearson’s correlations were used to quantify the association between variables. Players displayed the greatest level of asymmetry in isokinetic strength measures (5.9-12.7%) and lower levels of asymmetry in gait (1.6-7.7%), jump (0.9-7.0%) and CoD (1.9-3.5%) assessments. The influence of the preferred kicking limb was most evident in the isokinetic assessment with the players showing dominance in the preferred limb for knee flexor strength and in the non-preferred limb for knee extensor strength. These manifested in the asymmetry values calculated for the hamstring:quadricep (H:Q) ratios at 60°/s (8.80 ± 7.82%) and 240°/s (11.22 ± 7.04%) and in the functional H:Q ratio (12.67 ± 8.25%). The asymmetry values for peak extensor moment at 240°/s showed a significant correlation (ρ = ─0.55, p = 0.034) with 10 m time in the CoD assessment. These findings provide benchmark asymmetry data for soccer practitioners and reveal that kicking limb preferences may bring about interlimb differences in the H:Q ratio which raises important considerations in the design of testing batteries and injury reduction interventions.