Dr Barney Wainwright

Bike positional configuration changes strongly affect cycling performance. While consensus has emerged on saddle height optimisation, there is none for the relationship between other bike positional variables and cycling performance. Accordingly, this systematic review examines the effect of all major positional variables on performance in cycling, assessing differences between cycling disciplines and sex where possible. The systematic review, conducted per PRISMA guidelines, searched databases including Embase, Web of Science, Medline, and CINAHL, screening 16,578 studies. Of these, 47 were fully analysed. Study quality assessment using the NIH tool revealed none rated “good”, 5 “fair” and 33 “poor”. The analysis involved 724 participants (90 female, 454 male, 180 sex unstated). Studies focused on trunk angle/upper body position, handlebar height, Q factor, foot position, saddle fore-aft/height, seat tube angle and crank length. Participant cycling disciplines were often unspecified and few papers address women cyclists specifically. Key findings were associated with changing saddle height, trunk angle and saddle fore-aft. For trunk angle, accounting for the biomechanical and physiological effects as well as aerodynamic changes is important. Saddle fore-aft affects the hip angle and trunk angle. There are no clear recommendations for crank length, handlebar height, Q factor or cleat position.

Key areas of sports science research investigate the functional role of muscle activations within human movement. Even within relatively constrained movements like cycling, significant variability is observed in muscle activation strategies. Particular attention has been given to particular muscles, despite Soleus and Tibialis anterior muscles presenting a potentially functionally relevant split between monomodal and bimodal activation strategies. The current study (N = 54) investigated the prevalence and functional implications of these different strategies and identified, in addition to monomodal [Soleus: N = 24, Tibialis anterior: N = 7] and bimodal [Soleus: N = 12, Tibialis anterior: N = 31] strategies, a third group switching between strategies [Soleus: N = 16, Tibialis anterior: N = 13]. The combined Soleus group showed significantly higher Index of Force Effectiveness, lower negative work and lower radial forces than the bimodal group. Furthermore, bimodal Soleus strategies produced a period of significantly greater plantar flexion during the upstroke. No differences were found between the Tibialis anterior groups. These data show an identifiable group of cyclists utilising a combination of monomodal and bimodal strategies potentially benefiting mechanical effectiveness. Awareness of such functional implications can aid researchers and practitioners when interpreting cycling biomechanics data or intervention responses. Further research should investigate the factors that mediate transitions between activation strategies within the combined groups.

INTRODUCTION: Kinematic analysis in cycling via videography is becoming increasingly popular. Accuracy of commercial systems is improving rapidly and a shift is seen from 2D to multi-camera systems. Research shows a potential increase in validity and accuracy from 2D to 3D data (Fonda et al. 2014). Factors still affecting data accuracy in 3D systems are camera quality, calibration settings, marker sets and marker placement. The quality of camera systems is continuously increasing whilst marker placement is a trainable skill. However, uncertainty exists on how the 3-point angle method typically used in such systems differs from joint angles obtained through more valid modelling methods. Such information is crucial to understand how accurate these commercial setups can become when camera quality and operator training are optimised. METHODS: Data from 25 males were collected using a Qualisys (Sweden) system. Two marker sets were used: a 3-point angle (Trochan- ter Major, Lateral Femoral Epicondyle, Lateral Malleolus) and a modelling based set with extra markers on the Medial Femoral Epicon- dyle, Medial Malleolus and four tracking markers on the thigh and shank. Three 60s trials were captured at 250Hz for each participant and the following variables were calculated: peak knee flexion (PF), peak knee extension (PE) and mean knee angle (KA). Agreement between the two sets was tested through 95% Limits of Agreement (LoA), 95% Coefficient of Variation (CV) and Intraclass Correlation Coefficient (ICC). RESULTS: Regarding PE, LoA, CV and ICC were 9.6°±3.9, 4.7% and 0.92 respectively. For PF, LoA were 0.8°±5.5, CV=2.6% and ICC=0.71. In terms of KA, LoA were 5.3°±4.2, whereas CV and ICC were 3.6% and 0.82 respectively. CONCLUSION: The largest difference between sets is seen in PE, though the large systematic error could be easily corrected for. Random errors are highest for PF whilst ICCs may not provide a clear picture of the absolute error. Random errors of 4-6° need to be considered when measuring knee angles through a 3-point angle. However, modelling derived angles are also prone to some error, mainly due to marker placement, skin artefacts and individual anatomical differences, albeit to a smaller extend than in 3-point angles. Literature suggests cyclists should aim for knee angles of 25° to 35° at PE (Peveler et al. 2011). The size of random errors found in this study ques- tions the applicability of simplified marker sets when measuring knee angle in cycling. System developers are advised to critically look at marker sets used with their systems in order to provide a more accurate alternative and apply correction factors when appropriate. REFERENCES: Fonda B, Sarabon N, François-Xavier L. (2014). J Sports Sci, 32(10), 940-946. Peveler WW, Green JM. (2011). JSCR, 25(3), 629-633.

Introduction Within the scientific literature there is little evidence available to provide practitioners with information on strength and power profiles of cyclists, resulting in a limited understanding of neuromuscular factors related to cycling performance. Information on the legs’ elastic energy utilisation, force-velocity and length-tension curves can inform training programs and aid in talent identification. Other sports where such information is more widely available have already successfully implemented this within preparation programmes (e.g. McBride et al., 1999). Methods A total of 44 cyclists were recruited for this project, of which 15 classified in a Novice category by having no racing experience at all (age 35.5 ± 11.4 yrs; height 177.4 ± 6.5 cm; mass 77.4 ± 9.3 kg; FTP 3.28 ± 0.47 W/kg), 14 in the Road racing category as they competed for at least the past year at British Cycling Category 2 level or higher and no experience in Time-Trial (TT) races (age 35.9 ± 12.7 yrs; height 179.1 ± 6.5 cm; mass 76.6 ± 9.0 kg; FTP 3.88 ± 0.49 W/kg), and 15 in the TT category as they considered TT racing as their main competitive aim, rode in dedicated TT positions and had recently produced a 10 or 25 mile personal best of <23 or <58 minutes respectively (age 38.0 ± 9.6 yrs; height 184.0 ± 3.9 cm; mass 80.1 ±6.2 kg; FTP 3.74 ± 0.46 W/kg). Muscle function was tested through a range of tests. Jump height achieved during a squat jump (SJ) and a countermovement jump (CMJ) was used to define the balance between muscular power and elastic capacities of the legs (Kubo et al., 2000). A 20-Kg loaded jump squat (LJS) was used alongside the CMJ to provide data on the force-velocity relationship (F-V) in a multi-joint movement by calculating the theoretical peak force (Fpeak), theoretical peak velocity (Vpeak) and theoretical peak power (Ppeak) values (Cuk et al., 2014). Force plates (Kistler, Switzerland) recorded data during the jumps at 2000Hz. Furthermore, single joint isokinetic dynamometry (Biodex, USA) of the hip and knee was conducted for a range of angular velocities (30 to 270 °/s) to capture an accurate strength profile of the relevant muscle groups. Torque-Velocity profile was quantified by determining the relative reduction in torque with increasing velocity, length-tension relationships were evaluated using the angle of peak torque at 30 °/s and relative strength was quantified as a hip/knee torque ratio. Results The cyclists tested showed an average jump height of 29 ± 6 cm, 25 ± 5 cm and 20 ± 5 cm for the CMJ, SJ and LJS respectively, there were no significant differences between the groups (p = 0.939). The ratio of SJ over CMJ height averaged on 0.87 ± 0.11 with competitive cyclists scoring slightly but not significantly lower (0.84 ± 0.09) than the novice cyclists (0.89 ± 0.12; p = 0.329). Calculating Fpeak, Vpeak and Ppeak from the two-load method (CMJ and LJS), produced averages of 1903 ± 472 N, 5.74 ± 4.38 m/s and 2620 ± 1581 W respectively with no significant differences between the groups (p = 0.666, p = 0.520 & p = 0.396 respectively). Dynamometry data revealed a greater hip joint torque over knee torque in flexion and extension (hip/knee ratio > 1) for all groups. This dominance was significantly less prominent in the TT group for flexion conditions (1.35 ± 0.18) compared to Road (1.56 ± 0.22; p = 0.031) and Novice (1.53 ± 0.19; p = 0.004) groups. Joint flexion torques showed non-significant trends; they were slightly higher in the knee and lower for the hip (1.43 & 2.08 Nm/kg respectively) in TT athletes compared to Road (1.35 & 2.14 Nm/kg) and Novices (1.36 & 2.22 Nm/kg) (p = 0.429 & 0.189). No differences were found for the angle at which peak torque occurred. The velocity effect on torque production was comparable between the groups. It decreased from its peak at 30 °/s, to 82 ± 11 % of that when tested at 270 °/s for knee flexion and to 61 ± 9 % for knee extension. Hip torque reduced to 66 ± 10 % and 79 ± 10 % for flexion and extension respectively, when tested at 210 °/s compared to 30 °/s condition. Discussion The CMJ data show that cyclists – both novice and competitive – perform poorly on vertical jumping (29 ± 6 cm) compared to strength trained (48.2 ± 2.8 cm) and even untrained individuals (33.7 ± 2.3 cm) (McBride et al., 1999). This is in line with previous research on endurance type athletes showing long-distance runners to perform inferiorly on jump tasks compared to an untrained population (27.8 ± 4.3 cm vs 37.3 ± 3.1 cm; Kubo et al., 2000). In contrast to the findings by Kubo et al. (2000), the tested competitive cyclists showed lower SJ/CMJ ratios compared to the untrained controls indicating a relatively large utilisation of elastic energy storage compared to muscular power in jump performance. Based on the dynamometry testing, it seems most plausible to suggest that the reduced hip flexion capacity in TT riders results from these muscles being disused during cycling due to the extreme hip flexion angles common in their riding positions. It could be suggested that an attempt is made to compensate for this loss in hip flexion capacity through increased knee flexors’ strength. An increased knee flexor torque in TT riders could also indicate a mechanically more effective pedalling technique on the bike, as previous literature has linked hamstring activity with increases in Index of Force Effectiveness on the bike (Bini et al., 2013). Greater separation between tested groups might have been masked due to variation in preferred bike setup within the groups, TT riders also training in road setups and novice cyclists having undergone minor adaptations through recreational cycling activities. Based on these results, it seems appropriate to advise strength training to be tailored to the type of competition a cyclist is aiming to perform on. TT riders should focus on knee flexor strength, while road cyclists could benefit from a more balanced approach between hip and knee strength. Currently ongoing research is investigating how these strength characteristics relate to determinants of cycling performance in order to further help optimising training protocols and talent identification strategies. References Bini RR, Hume P, Croft J, Kilding A. (2013) J Sci Cycl, 2(1), 11-24. Kubo K, Kanehisa H, Kawakami Y, Fukunaga T. (2000). EJAP, 81(3), 181-187. McBride JM, Triplett-McBride T, Davie H, Newton RU. (1999). J Biom, 32(10), 1021-1026. Cuk I, Markovic M, Nedeljkovic A, Ugarkovic D, Kukolj M, Jaric S. (2014). EJAP, 114(8), 1703-1714.

INTRODUCTION: Kinematic analysis in cycling via videography is becoming increasingly popular. Accuracy of commercial systems is improving rapidly and a shift is seen from 2D to multi-camera systems. Research shows a potential increase in validity and accuracy from 2D to 3D data (Fonda et al. 2014). Factors still affecting data accuracy in 3D systems are camera quality, calibration settings, marker sets and marker placement. The quality of camera systems is continuously increasing whilst marker placement is a trainable skill. However, uncertainty exists on how the 3-point angle method typically used in such systems differs from joint angles obtained through more valid modelling methods. Such information is crucial to understand how accurate these commercial setups can become when camera quality and operator training are optimised. METHODS: Data from 25 males were collected using a Qualisys (Sweden) system. Two marker sets were used: a 3-point angle (Trochan- ter Major, Lateral Femoral Epicondyle, Lateral Malleolus) and a modelling based set with extra markers on the Medial Femoral Epicon- dyle, Medial Malleolus and four tracking markers on the thigh and shank. Three 60s trials were captured at 250Hz for each participant and the following variables were calculated: peak knee flexion (PF), peak knee extension (PE) and mean knee angle (KA). Agreement between the two sets was tested through 95% Limits of Agreement (LoA), 95% Coefficient of Variation (CV) and Intraclass Correlation Coefficient (ICC). RESULTS: Regarding PE, LoA, CV and ICC were 9.6°±3.9, 4.7% and 0.92 respectively. For PF, LoA were 0.8°±5.5, CV=2.6% and ICC=0.71. In terms of KA, LoA were 5.3°±4.2, whereas CV and ICC were 3.6% and 0.82 respectively. CONCLUSION: The largest difference between sets is seen in PE, though the large systematic error could be easily corrected for. Random errors are highest for PF whilst ICCs may not provide a clear picture of the absolute error. Random errors of 4-6° need to be considered when measuring knee angles through a 3-point angle. However, modelling derived angles are also prone to some error, mainly due to marker placement, skin artefacts and individual anatomical differences, albeit to a smaller extend than in 3-point angles. Literature suggests cyclists should aim for knee angles of 25° to 35° at PE (Peveler et al. 2011). The size of random errors found in this study ques- tions the applicability of simplified marker sets when measuring knee angle in cycling. System developers are advised to critically look at marker sets used with their systems in order to provide a more accurate alternative and apply correction factors when appropriate. REFERENCES: Fonda B, Sarabon N, François-Xavier L. (2014). J Sports Sci, 32(10), 940-946. Peveler WW, Green JM. (2011). JSCR, 25(3), 629-633.

A new volume in the Handbook of Sports Medicine and Science series from the International Olympic Committee, this volume Canoeing provides an accessible and comprehensive summary of the topic.

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.

Little is known about the biomechanics of sprint canoeing, especially for women’s canoeing, and a quantitative kinematic description of the motion would help coaches to develop valid technique coaching models. Five highly-trained female canoeists were filmed at 150 Hz while undertaking a 50 s maximal effort on a canoe ergometer, whose trolley motions were taken to represent those of the boat. Selected boat, body and paddle kinematics were evaluated at three key stroke cycle events (Contact, Paddle Vertical, and End of Drive) and their patterns monitored across the stroke cycle. While no clear trends between the kinematics and power output emerged, a range of strategies were identified and the data represent an initial step in the construction of detailed technique models that can be used to evaluate and monitor individual athletes.

It is anticipated that women’s Canoe Sprint will be included in the Olympic programme in Tokyo in 2020. Although the discipline has been a part of the Men’s programme since 1948, little biomechanics-based research has taken place and coaches have limited scientific information to guide their technique analysis or coaching interventions. Therefore the purpose of this study was to quantitatively report kinematics of women’s sprint canoeing technique at different intensities to establish key aspects of the movement patterns that were similar across the group, and also those that differed between participants. Five highly-trained competitive female canoeists (age 21.6 ± 2.5 years; C1 200m personal best, 56 ± 6 s) (mean ± SD), who comprised two right-sided and three left-sided paddlers, participated in the institutional ethics approved study. Participants completed three randomised 30 s efforts at 60, 80 and 100% of the power output of a 50 s simulated 200m race effort on a canoeing-specific ergometer (WEBA sport, Austria). 3D kinematic data were collected using a methodology previously reported (Wainwright et al., 2016, Proceedings of ISBS Conference) using individualised inertia models (Yeadon, 1990, Journal of Biomechanics, 23, 67-74) within an inverse kinematics model in Visual3D. While many of the kinematics presented similar trends the movements of the pelvis relative to the boat, and trunk relative to the pelvis, demonstrated the largest variations within and between participants across the intensities. Pelvis and trunk flexion and extension were found to be coupled, as were pelvis and trunk internal and external rotation. During the drive phase the pelvis tilt decreased as the trunk increased flexion, while the pelvis and trunk rotated towards the stroke side. Pelvis rotation started after the trunk and was of a shorter duration. Differences were observed in the magnitudes of pelvis and trunk rotation and flexion, and timings of the segmental movements within and between participants across the intensities. Therefore each participant displayed subtle and consistent changes in their individualised movement patterns in response to the task demands. This study generated an appropriate methodology that successfully quantified the kinematics of the Canoe Sprint movement, and has demonstrated that a range of individualised strategies can be employed in response to changes in the task. Further research is required to understand the relationships between subtle within and between participant differences in pelvis-trunk co-ordination, on-water boat velocity and performance in order to provide coaches with an improved ability to enhance on-water performance.

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.

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.

The purpose of the study was to assess the validity and inter-bike reliability of 10 Wattbike cycle ergometers, and to assess the test–retest reliability of one Wattbike. Power outputs from 100 to 1000 W were applied using a motorised calibration rig (LODE) at cadences of 70, 90, 110 and 130 rev · min−1, which created nineteen different intensities for comparison. Significant relationships (P < 0.01, r2 = 0.99) were found between each of the Wattbikes and the LODE. Each Wattbike was found to be valid and reliable and had good inter-bike agreement. Within-bike mean differences ranged from 0.0 W to 8.1 W at 300 W and 3.3 W to 19.3 W at 600 W. When taking into account the manufacturers stated measurement error for the LODE (2%), the mean differences were less than 2%. Comparisons between Wattbikes at each of the nineteen intensities gave differences from 0.6 to 25.5 W at intensities of 152 W and 983 W, respectively. There was no significant difference (P > 0.05) between the measures of power recorded in the test–retest condition. The data suggest that the Wattbike is an accurate and reliable tool for training and performance assessments, with data between Wattbikes being able to be used interchangeably.

A sprint kayaking specific deterministic model was used to identify key performance related technique factors using data from 12 international-level kayakers. There was large variability in the strength of the between-factor relationships across the group. The pull phase was split into 3 components with the 1st phase contributing the most to increases in boat velocity and the 3rd phase causing a decrease in velocity. The propulsive impulse had the largest influence on velocity, but the magnitude of the impact was moderated by blade slip. Large propulsive impulses in the 3rd phase of the pull were associated with larger decreases in velocity. The results show that the model can be used to identify key technique factors on an individual level, although the use of the model should be confirmed on additional kayakers before being used in an applied setting by practitioners.

The symposium will provide an overview of how a multi-disciplinary research team engaged in supporting the British Canoeing Women’s Sprint Canoe Coach around the technical aspects of the Sprint Canoe stroke. Within the 60 minute session, the presenters will discuss how a coach’s technical model for a skill can be captured, and used, to better inform quantitative analysis of athlete technique which in turn can be used to check and challenge the technical understanding of the coach. The development of a reciprocal relationship can provide coaches with meaningful, purposeful feedback on their own technical understanding and on their athlete’s level of technical skill development while producing impactful research driven by real world coaching issues. Reflections will be provided within the symposium around developing a relationship with the coach to better understand their technical knowledge needs, tailoring the feedback of technical information to the coach to reflect their learning preferences and how that knowledge can be used to inform their practice. The symposium will conclude with a proposed framework for researchers to use when working with coaches to better bridge the gap between researchers and practitioners to produce meaningful, informed research that has real world coaching impact and application.

Purpose: Establish the short-term reliability and acute responsiveness of biomarkers of physiological stress to exercise in the heat. As such, informing their prospective application in research and field settings. Method: Fourteen male endurance trained cyclists/triathletes completed two heat stress tests (HST), separated by 5-7 days. HST’s involved 45-minutes fixed-intensity cycling (2.5W.kg-1) under hot-humid conditions (32oC and 70% relative humidity). Venous blood was drawn pre- and immediately post-HST for the concentration of normetanephrine (NMET), metanephrine (MET), kidney-injurymolecule1(KIM-1),neutrophilgelatinase-associatedlipocalin(NGAL),serumosmolality (Sosmo) and copeptin. Results: No biomarker displayed systematic trial order bias (p ≤ 0.05). The majority of biomarkers had acceptable within-participant variation (CV range: 0.9-14.3%). Copeptin had the lowest short-term variation at rest (CV = 0.9%) and post-HST (CV = 1.2%). However, greater variation was evident in biomarkers MET and KIM-1 at rest (CV = 28.6 & 43.2%) and post-HST (CV = 29.9 & 29.6%), respectively. NMET exhibited very large increases (trial 1 = Δ1048 ± 461; trial 2 = Δ 1067±408)inresponsetoexertionalheatstress(p<0.0001,d=2.8;p<0.0001,d=3.8).Incontrast, KIM-1 demonstrated trivial changes (trial 1 = Δ -3 ± 21; trial 2 = Δ 2 ± 17) in response to exercise in theheat (p=0.53,d=0.1;p=0.60,d=0.1).Conclusion:Eachbiomarker,exceptMETandKIM-1had acceptable reliability at rest and following exercise. In addition, biomarkers NMET, copeptin and NGAL demonstrated large increases in response to exercise in the heat. Thus, these markers can provide accurate and sensitive measurement for wide-spread application in laboratory and field research.

Abstract

Introduction Heat adaptation is protective against heat illness however its role in heat syncope, due to reflex mechanisms, has not been conclusively established. The aim of this study was to evaluate if heat acclimation (HA) was protective against heat syncope and to ascertain underlying physiological mechanisms. Method 20 (15 males, 5 females) endurance trained cyclists were randomised to either 8 days of mixed active and passive HA (HEAT) or temperate exercise (CONTROL). Prior to, and following, the interventions participants underwent a head up tilt (HUT) with graded lower body negative pressure (LBNP) continued until presyncope with measurement of cardiovascular parameters. Heat stress testing was performed to determine physiological and perceptual measures of HA. Results There was a significant increase in orthostatic tolerance (OT), as measured by HUT/LBNP, in the HEAT group (pre-intervention; 28 ± 9 mins, post-intervention; 40 ± 7 mins) compared to CONTROL (pre-intervention; 30 ± 8 mins, post-intervention; 33 ± 5 mins) (p = 0.0116). Heat acclimation resulted in a significantly reduced peak and mean rectal and skin temperature (p < 0.0141), peak heat rate (p < 0.0033), thermal comfort (p < 0.0411) and rating of perceived exertion (p < 0.0251). There was a significantly increased plasma volume (PV) in the HEAT group in comparison to CONTROL (p = 0.0293). Discussion Heat adaptation causes improvements in OT and is likely to be beneficial in patients with heat exacerbated reflex syncope. Heat acclimation mediated PV expansion is the likely predominant physiological mechanism underlying improved OT.

A mixed‐method heat acclimation (HA) protocol may optimise performance by supporting the training taper while promoting thermal adaptation; however, the impact on cardiovascular and fluid‐regulatory adjustments to protect health is unknown. Therefore, we examined the effects of a mixed‐method heat protocol on physiological responses, including cardiovascular and fluid‐regulatory strain with exercise‐heat stress, and self‐paced performance in the heat. Twenty (15 males, five females) triathletes were randomised to 8 days of HA (HOT), or exercise in thermoneutral conditions (TEMP). A heat stress test (HST) comprising 45 min of cycling in a climatic chamber (32°C, 70% relative humidity) was performed on days 1, 5 (HOT only) and 8. Before and after the intervention, a cycling time trial was conducted in the same climatic conditions (days 0 and 10). Venous blood samples were analysed at rest and post‐HST (days 1 and 8 only) for the catecholamine product normetanephrine and the vasopressin surrogate copeptin. Following 7 days of HA (days 1 vs. 8) resting rectal temperature was significantly lower in the HOT compared to the TEMP group (−0.32 ± 0.36°C, P = 0.002). Normetanephrine was 24.3% lower after 7 days of HA (P = 0.012), and copeptin was 53.4% lower at the post‐HST time point (HOT vs. TEMP, P = 0.012). However, HA had no effect (0.3%, P = 0.984) on self‐paced performance in the heat. Mixed‐method HA elicited a progressive reduction in cardiovascular strain and a net reduction in fluid‐regulatory strain without improving self‐paced performance in the heat.

We investigated the effect of an acute creatine loading (25 g per day for 4 days) and longer-term creatine supplementation (5 g of creatine or 5 g of placebo per day for 2 months) on the performance of 22 elite swimmers during maximal interval sessions. After the acute creatine loading, the mean of the average interval swim times for all swimmers (n = 22) improved (44.3 +/- 16.5 s before vs 43.7 +/- 16.3 s after supplementation; P ≪ 0.01). Three of the 22 swimmers did not respond positively to supplementation. After 2 months of longer term creatine supplementation or placebo,neither group showed a significant change in swimming performance (38.7 +/-13.5 s before vs 38.7 +/- 14.1 s after for the creatine group; 48.7 +/- 18.0 s before vs 48.7 +/- 18.1 s after for the placebo group). We conclude that, in elite swimmers, 4 days of acute creatine loading improves swimming performance significantly when assessed by maximal interval sessions. However, longer-term supplementation for 2 months (5 g of creatine per day) did not benefit significantly the creatine group compared with the placebo group.

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.

Introduction: This thesis addresses a critical gap in track cycling research, presenting the first academic study focused on identifying performance factors in the elite men’s Omnium Points Race, a field where, until now, coaches have largely relied on experiential insights, or extrapolated data from other cycling disciplines. Grounded in the author’s dual role as a coach and analyst with national cycling teams from Japan and the USA, the thesis is shaped by three primary aims: (1) to investigate elite coaches' perceptions regarding key performance factors in the Points Race, and the role of data in competitive decision making and outcomes; (2) to analyse physical, tactical, and strategic performance factors in the Points Race; and (3) to develop an actionable framework to support coaches and analysts in integrating insights from data to enhance training, competition strategies, and overall performance.Methodology: A multi-method approach was employed, including semi-structured interviews with elite coaches and video-based performance analysis of seven world-class Points Races from the 2019/20 season. These data informed the development of the Racecraft Framework – a systems informed conceptual model that reflects the complexity of Omnium racing, mapping how multiple interdependent factors underpin race outcomes.Results: In Chapter 5, coaches of elite male Omnium cyclists revealed that performance is conceptualised as a multifaceted combination of physical attributes (e.g., power and aerobic capacity), tactical intelligence, strategic awareness, and psychological resilience. Chapter 6 reveals that repeatable access to high speed, rather than peak speed alone, is more indicative of performance, aligning with a view of racing as a dynamic system of shifting demands. Chapter 7 highlights that there was a variation in the speed of points scoring sprint ranks throughout the subsectionTenLaps leading into each intermediate sprint highlighting a variety of tactics used. Positional analysis showed the top-ranked cyclists achieving advanced positions earlier in the subsection to make the most of point scoring opportunities. Analysis of successful lap gains reveal that they often occur as part of broader strategic plays that include intermediate point accumulation, with most lap gains made by small groups, and most frequently take between 9.5-10.5, or 15.5-16.5 laps to complete. Chapter 8 then explores the strategies among cyclists, emphasising the systems thinking needed to manage energy, positioning, and point scoring over time. High-ranking cyclists score consistently across intermediate sprints and secure positions by capitalising on speed variations throughout the race, often establishing an unassailable lead before the final sprint.Practical Applications: The Racecraft Framework, developed iteratively through a review of and reflection on existing literature, interviews with coaches, video analysis, and the authors own experiences of working as a track cycling coach and performance analyst at the highest level, provides a conceptual model for coaches and analysts to evaluate the physical, tactical, and strategic complexity of Points Race performance. Its real-world utility was demonstrated in athlete preparation for the Tokyo Olympics. A final reflections chapter draws together methodological, applied, and personal insights, reinforcing the thesis’s value as both an academic and practical contribution to enhancing track cycling performance.

The Tokyo 2020 Olympic Games were due to be the hottest on record, with hot (>30 °C) and high-humidity environmental conditions (70-90% relative humidity). Olympic Distance Triathlon comprises a 1.5 km swim, a 40 km bike ride, and a 10 km run performed successively. Prolonged exercise in the heat produces greater physiological and perceptual strain compared to exercising in temperate environmental conditions at the same intensity. Athletes competing in middle- and long-distance events are at a higher risk of reductions in exercise performance and incidence of heat illness compared to short distance events in the heat. Heat acclimation (HA) is the most effective countermeasure to protect athlete health and improve performance. Research on applied and effective HA strategies which confer the necessary heat adaptation responses while still conforming to the ecological training needs of highly trained athletes is limited. The first study (Chapter 4) of this thesis established the reliability of novel blood biomarkers and classical physiological and perceptual markers of heat stress during a new cycling heat stress test (HST) which fixes the intensity relative to body mass. The test offers a reliable assessment tool to evaluate the effectiveness of HA protocols employed. Chapter 5 evaluated whether 5-days isothermic HA was an effective preparation strategy for the Tokyo 2020 Olympic Games in endurance trained athletes. Reduced cardiovascular and perceptual strain, plasma volume expansion and an increase in sweat loss were evident. However, there was no change in body temperature or surrogate biomarkers of physiological stress. Chapter 6 investigated the effectiveness of a novel and ecologically valid 8-day HA strategy which combined modes of HA; isothermic HA and post-temperate exercise hot water immersion (HWI). There was reduced thermal, cardiovascular, and perceptual strain after 4-days HA, with no further improvement at day 8 of HA. Diminished sympathetic activity and fluid-regulatory stress were evident after 8-days HA. However, no change in performance was demonstrated during a 20-km cycling time trial in the heat. This thesis provides practitioners and coaches within British Triathlon Federation a reliable assessment tool of heat dissipation capacity in Tokyo specific environmental conditions. 5-days isothermic HA induced partial HA, affording athletes a time-efficient approach for rapid adaptation. However, a combined HA protocol of isothermic HA and HWI over 4 and 8-days induces superior thermoregulatory, perceptual, and biochemical adaptations. Hence, is the recommended approach for elite triathletes prior to competition at the Tokyo 2020 Games.

This project aimed to investigate the effect of a 6-week repeated sprint in hypoxia (RSH) intervention in normobaric hypoxia (NH) on middle-distance performance and performance parameters in middle-distance athletes, and to establish the potential underpinning adaptation to performance enhancement through the use of near-infrared spectroscopy (NIRS). The novelty of this thesis was its aim of producing a protocol which was specific to middle-distance runners, produced with the help of Leeds Beckett Coaches, to replicate a typical track interval session to allow real-world application. 5 trained middle-distance athletes completed a 6-week (12 session) repeated sprint training intervention in hypoxia (3000m in week 1-3; 3750m in week 4-6) or normoxia (sea-level; 0m) (RSN), both completed in a NH chamber to blind the participants. Weekly sessions were comprised of a low-intensity session (6 sets; 6 reps at 90% of 800m pace) and a high intensity session (5 sets: 4 reps at 120% of 800m pace), with intervals of 15-seconds interspersed by 30-seconds passive recovery. Performance outcomes were measured using an 800m time-trial, submaximal and time to exhaustion test (TTE). With underpinning adaptations measured using carbon monoxide (CO) rebreathing to determine haemoglobin mass (Hbmass) and changes in muscle oxygenation measured using NIRS. No overall improvement was found in 800m time-trial performance following RSN (pre: 148.6 ± 16.84 vs. post: 148.6 ± 13.40 seconds), however, participant 6 of the hypoxia group (HYP) showed the greatest overall improvement of 6 seconds. Whereas, following RSN there was an overall reduction in 800m time-trial performance (+1.3 seconds). Aerobic capacity (V̇O2max) and V̇O2 onset kinetics were reduced following RSH and RSN, while mean reaction time (MRT) was improved in HYP (—21.24 seconds; d=2.6, p=0.08). Muscle oxygen saturation (SmO2) was improved following RSH in participant 6 (-2.01 ± 5.25 vs. 6.99 ± 1.35 %). Total haemoglobin (tHb) was increased (19.07 ± 2.67 μM) following the intervention in participant 2 (NOR), and participant 3 increased slightly (1.94 ± 9.88 μM), however, there was no overall trend found for the hypoxic group. Although the findings of this study were inconsistent and showed no overall change, individual improvements suggest that with a greater sample size and greater control on external training to reduce confounding factors, RSH could be a beneficial intervention for improving middle-distance performance through improvements in peripheral adaptations to muscle oxygenation.

• There is a growing need to develop measures for assessing performance and health status under heat stress, as heat-related health risks increase with global warming. • The ACSM recommends that a tailored heat tolerance assessment (HTA), based upon participants’ fitness levels, should be applied for individual’s affected by heat related illness. • Aerobically-trained athletes show features of heat adaptation at baseline and, in our experience, a standardised HTA to provide robust heat stress and challenge fitter individuals is lacking. • We designed a progressive HTA to be performed in uncompensable conditions, in order to minimise differences attributable to variation in body size and increase comparability.

Background and Objectives: Neurobiomarkers measured in peripheral blood can supplement management strategies following traumatic brain injury (TBI). Dual-assay of glial fibrillary acid protein (GFAP) and ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1) is FDA-approved to inform a decision threshold approach (GFAP >30 μg.L-1 and/or UCHL1 >360 μg.L-1) for post-TBI neuroimaging. As physical activity and thermal strain often accompany TBI-prone activities, we investigated whether each molecule’s quantification - and, by extension, clinical decisions - could be influenced by exercise-heat stress. Methods: In healthy volunteers monitored continuously for body core temperature (Tc), we used the i-STAT Alinity to assess plasma GFAP and UCHL1 responses to exercise in the laboratory (four female, eighteen male trained participants, cycling for 45 min in 32 °C) and field (three female and 22 male recreational marathon runners, finishing time 231± 34 min, peak ambient temperature 11 °C). Results: Respective ΔTc overall were 1.42 ± 0.37 °C and 1.87 [1.53, 2.31] °C. With laboratory exercise, GFAP and UCHL1 did not exceed the manufacturer’s decision threshold. Across the marathon, GFAP was stable, whereas UCH-L1 more than doubled (200 [200, 200] vs 462 [310, 782] μg.L-1, P<0.0001), breaching the decision threshold for neuroimaging in 18/25 runners. Discussion: Confounding from more severe exercise-heat stress should be considered when interpreting near-care assay of UCHL1 for TBI management.

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.

Heat adaption through acclimatisation or acclimation improves cardiovascular stability by maintaining cardiac output due to compensatory increases in stroke volume. The main aim of this study was to assess whether 2D transthoracic echocardiography (TTE) could be used to confirm differences in resting echocardiographic parameters, before and after active heat acclimation (HA). Thirteen male endurance trained cyclists underwent a resting blinded TTE before and after randomisation to either 5 consecutive daily exertional heat exposures of controlled hyperthermia at 32◦C with 70% relative humidity (RH) (HOT) or 5-days of exercise in temperate (21◦C with 36% RH) environmental conditions (TEMP). Measures of HA included heart rate, gastrointestinal temperature, skin temperature, sweat loss, total non-urinary fluid loss (TNUFL), plasma volume and participant’s ratings of perceived exertion (RPE). Following HA, the HOT group demonstrated increased sweat loss (p = 0.01) and TNUFL (p = 0.01) in comparison to the TEMP group with a significantly decreased RPE (p = 0.01). On TTE, post exposure, there was a significant comparative increase in the HOT group in left ventricular end diastolic volume (p = 0.029), SV (p = 0.009), left atrial volume (p = 0.005), inferior vena cava diameter (p = 0.041), and a significant difference in mean peak diastolic mitral annular velocity (e’) (p = 0.044).Cardiovascular adaptations to HA appear to be predominantly mediated by improvements in increased preload and ventricular compliance. TTE is a useful tool to demonstrate and quantify cardiac HA.

The purpose of this study was to assess the reliability of blood biomarkers that can signify exercise-induced heat stress in hot conditions. Fourteen males completed two heat stress tests separated by 5-7 days. Venous blood was drawn pre- and post- heat stress for the concentration of normetanephrine, metanephrine, serum osmolality, copeptin, kidney-injury molecule 1 and neutrophil gelatinase-associated lipocalin. No biomarker, except copeptin, displayed systematic trial order bias (p ≥ 0.05). Normetanephrine, copeptin and neutrophil gelatinase-associated lipocalin presented acceptable reliability (CV range: 0.9-14.3%), while greater variability was present in metanephrine, osmolality and kidney-injury molecule 1 (CV range: 28.6-43.2%). Normetanephrine exhibited the largest increase (p <0.001) in response to heat stress (trial 1 = 1048 ± 461 pmol. L-1; trial 2 = 1067 ± 408 pmol. L-1), whilst kidney-injury molecule 1 presented trivial changes (trial 1 = -4 ± 20 ng. L-1; trial 2 = 2 ± 16 ng. L-1, p >0.05). Normetanephrine, copeptin and neutrophil gelatinase-associated lipocalin demonstrated good reliability and sensitivity to an acute bout of heat stress. These biomarkers may be suitable for application in laboratory and field research to understand the efficacy of interventions that can attenuate the risk of thermal injury whilst exercising in the heat.

ORAL PRESENTATION Purpose: To evaluate and compare the acute group and individual endogenous hormone responses to three resistance exercise workouts and two load carriage workouts. Understanding hormone responses specific to military settings may enhance training optimisation in the future. Methods: Eighteen resistance exercise-trained male civilians (age: 19 to 38 y, mean 24.9 y) completed five experimental workouts and a control condition in a randomised order; three resistance exercise workouts (cluster, hypertrophy, endurance), two load carriage (90-min constant pace [CO-LC] or 6 × 8-min intervals [IT-LC], both carrying a rucksack with 25% body mass) workouts, and a control condition (60-minutes of rest). Venous blood was drawn before, immediately post workout, and 30-min and 24-h post workout. Testosterone (T), free testosterone (fT), growth hormone (GH), dehydroepiandrosterone sulphate (DHEAS), androstenedione (ANST), and insulin-like growth factor 1 (IGF-1) concentrations were subsequently analysed via liquid chromatography-mass spectrometry. Group responses were evaluated using two-way ANOVA’s with Tukey’s post-hoc analysis. The standardised standard deviations of the pre-post change scores (SDIR) were calculated to identify the presence of individual responses (Hopkins, 2015). Results: Group responses were observed despite large individual variations. T concentrations increased in response to hypertrophy (p < 0.001) and CO-LC (p = 0.02) workouts; fT concentrations increased in response to CO-LC (p < 0.001) and decreased following the hypertrophy (p = 0.035) workout; ANST concentrations increased in response to CO-LC (p = 0.007); GH increased following hypertrophy (p = 0.004), endurance (p = 0.04), IT-LC (p < 0.001), and CO-LC (p < 0.001) workouts; IGF-1 increased in response to the endurance (p = 0.018) workout. The SDIR effect size thresholds of extremely large (T, GH, DHEAS) and very large (T, GH, DHEAS, ANST, IGF-1) were achieved, representing an individualised pattern of hormone production in response to the different resistance exercise and load carriage workouts. Conclusions: The presence of within-workout variations in the hormonal responses to all workout types suggests that the mean group responses may not reflect the response experienced by all participants, and that the hormonal anabolic response differs between individuals. The group responses and within-workout variation suggest that a wide panel of endogenous hormones should be measured to provide clarity on the anabolic response to different types of training stimuli at the individual level. Military Impact: The anabolic response to training type differs between individuals. This research provides support to further investigate whether training interventions based upon an individualised anabolic hormone response to acute exercise lead to improved physical outcomes. Funding for this research was provided by Dstl MOD. References: Hopkins W. J Appl Physiol, 118:1444–1446,2015; doi:10.1152/japplphysiol.00098.2015

Introduction Heat adaptation is protective against heat illness; however, its role in heat syncope, due to reflex mechanisms, has not been conclusively established. The aim of this study was to evaluate if heat acclimation (HA) was protective against heat syncope and to ascertain underlying physiological mechanisms. Methods Twenty (15 males, 5 females) endurance-trained athletes were randomized to either 8 d of mixed active and passive HA (HEAT) or climatically temperate exercise (CONTROL). Before, and after, the interventions participants underwent a head up tilt (HUT) with graded lower body negative pressure (LBNP), in a thermal chamber (32.0 ± 0.3°C), continued until presyncope with measurement of cardiovascular parameters. Heat stress tests (HST) were performed to determine physiological and perceptual measures of HA. Results There was a significant increase in orthostatic tolerance (OT), as measured by HUT/LBNP, in the HEAT group (preintervention; 28 ± 9 min, postintervention; 40 ± 7 min) compared with CONTROL (preintervention; 30 ± 8 mins, postintervention; 33 ± 5 min) (P = 0.01). Heat acclimation resulted in a significantly reduced peak and mean rectal and skin temperature (P < 0.01), peak heat rate (P < 0.003), thermal comfort (P < 0.04), and rating of perceived exertion (P < 0.02) during HST. There was a significantly increased plasma volume (PV) in the HEAT group in comparison to CONTROL (P = 0.03). Conclusions Heat acclimation causes improvements in OT and is likely to be beneficial in patients with heat exacerbated reflex syncope. Heat acclimation–mediated PV expansion is a potential physiological mechanism underlying improved OT.

This study aimed to establish whether a series of 3 apneas before a 400-m freestyle time-trial affected swimming performance when compared with and combined with a warm-up. Nine (6 males and 3 females) regional to national standard swimmers completed four 400-m freestyle time-trials in 4 randomized conditions: without warm-up or apneas (CON), warm-up only (WU), apneas only (AP), and warm-up and apneas (WUAP). Time-trial performance was significantly improved after WUAP (275.79 ± 12.88 seconds) compared with CON (278.66 ± 13.31 seconds, p = 0.035) and AP (278.64 ± 4.10 seconds, p = 0.015). However, there were no significant differences between the WU (276.01 ± 13.52 seconds, p > 0.05) and other interventions. Spleen volume compared with baseline was significantly reduced after the apneas by a maximum of ∼45% in the WUAP and by ∼20% in WU. This study showed that the combination of a warm-up with apneas could significantly improve 400-m freestyle swim performance compared with a control and apnea intervention. Further investigation into whether long-term apnea training can enhance this response is justified.