Abstract
In elite North American soccer, the challenges of preparing for a rigorous competition are compounded by multiple, challenging environmental and logistical issues throughout the season. The purpose of this five-study thesis was to explore the relationships between extensive travel and changes in temperature and altitude with physical performance and match outcomes in an applied “real-world” context.Study 1 (Chapter 3), a systematic review of the literature, revealed a lack of data on elite team sport athletes competing in heat or at altitude. The few studies that were included in the review reported heterogeneous effect sizes. At altitude, total distance was reduced (effect sizes ranging from -0.96 to -0.13) and high-speed running distance ranged from a moderate reduction to a trivial increase (-0.69 to 0.12). The effects of performing in heat (temperatures greater than 20°C) were inconsistent across the studies (total distance -1.35 to 0.13, high-speed running distance -4.71 to 1.30, and number of high-speed runs -0.92 to 0.26). The literature dearths and inconsistencies indicated a need for further research in elite / professional team sport athletes.
Study 2 (Chapter 4), a retrospective, quasi-experimental design, was used to evaluate current data practices within a Major League Soccer (MLS) team with a focus on the association between external load on a given training or game day and the next day subjective, athlete-reported outcome measures (AROMs). Initially, the construct validity and internal consistency of current AROM data was explored through Cronbach’s alpha and principal component analysis (PCA). The PCA revealed three main components with soreness, mood and nutrition loading highest on each component respectively. The PCA revealed the components with the highest effects on AROMs were soreness, mood, and nutrition loading, respectively. There were large negative correlations (r = -0.43 to -0.55) between soreness and measures of external load during the in-season phase, aiding in the understanding of the stressors that players perceived across the season. As such, athlete reported soreness may be a useful item to report when investigating the response to training and match load in challenging environments.
Study 3 used a natural cross-over design to explore changes in external, and perceived internal load with acute stays at different altitude zones (Chapter 5; sea level; 0-1000m, low altitude; 1000-2000m, and moderate altitude; >2000m). No significant changes in external match load were observed between see level and low altitude; -299 95% confidence intervals, -897 to 298; or moderate; -509, -1216 to 198).
Study 3 (Chapter 5) used a natural cross-over design to explore changes in internal (perceived) exertion and external training and match load with acute stays at different altitude zones (sea level 0-1,000m, low altitude 1,000-2,000m, and moderate altitude > 2,000m). Mean differences (MD) and 95% confidence levels (CI) were used to study changes. No significant changes in external match load were observed between sea level and low altitude (MD -299, CI -897 to 298), sea level and moderate altitude (MD 508, CI -126 to 198), nor low and moderate altitude (MD -210, CI -986 to 564]). Similarly, there were no significant differences in cardiorespiratory ratings of perceived exertion (session RPE breathlessness [sRPE-B) or neuromuscular exertion (sRPE-L). However, the difference between perceptual responses (sRPE-B - sRPE-L) significantly changed at low (-11.0, -14.90 to -7.01 AU) and moderate altitude (-8.66, 95% CI = -13.60 to -3.76 AU), representing a significant shift from neuromuscular to cardiorespiratory response. Similarly, there were no significant differences in session ratings of perceived exertion for cardiorespiratory breathlessness (sRPE-B) or neuromuscular exertion for the legs (sRPE-L). However, the difference in arbitrary units (AUs) between perceptual responses (sRPE-B minus sRPE-L) significantly changed at low altitude (MD -11.0, CI -14.90 to -7.01 AU) and moderate altitude (MD -8.66, CI -13.60 to -3.76 AU), representing a notable shift from neuromuscular to cardiorespiratory response.
Study 4 (Chapter 6) explored the association between changes in heat and physical performance using a single club retrospective observational design. We observed trivial to small correlations between temperature indices, kick of temperature (kick-off temperature, average weekly temperature, kick-off heat index) and match total and high-speed running distance (r = -0.05 to - 0.17). Study 4 (Chapter 6) explored the association between changes in heat and physical performance using a single MLS club retrospective observational design. The results indicated trivial to small correlations between temperature indices (kickoff temperature, average weekly temperature, kickoff heat index) and match total and high-speed running distance (r = -0.05 to -0.17).
Given the noted limitations of single-team studies, a league wide approach was taken to explore travel and both match and physical performances encompassing 148 matches [team-based data] and 1252 player-matches from 297 players; age 22.7 ± SD 4.5 (Chapter 7). Accumulated travel travel metrics were positively associated with team (travel distance [r = 0.20; 95% confidence intervals 0.03 to 0.25], travel time [r = 0.20; 0.06 to 0.37] and time away [r = 0.20; 0.06 to 0.37]) and individual player (travel distance, [r = 0.14; 0.08 to 0.19], travel time [r = 0.17 to 0.23] and time away [r = 0.13; 0.07 to 0.18]) high intensity running. Study 5 (Chapter 7) involved a league-wide approach to explore travel and both match and physical performances. The team-based data encompassed 148 matches and 1,252 player-matches from 297 players: age 22.7 ± SD 4.5). Using 95% confidence intervals, accumulated travel metrics were positively correlated with high-intensity running for both the team (travel distance [r = 0.20, CI 0.03 to 0.25], travel time [r = 0.20, CI 0.06 to 0.37], and time away [r = 0.20, CI 0.06 to 0.37]) and the individual player (travel distance [r = 0.14, CI 0.08 to 0.19], travel time [r = 0.17, CI 0.12 to 0.23], and time away [r = 0.13, CI 0.07 to 0.18]). Accumulative time away was negatively associated with team points (r = -0.14; -0.28 to -0.001) and positively associated with goals conceded (r = 0.14; 0.01 to 0.27), no clear association between acute travel metrics and match outcomes or physical performance were observed. Accumulative time away was negatively correlated with team points (r = -0.14, CI -0.28 to -0.001) and positively correlated with goals conceded (r = 0.14, CI 0.01 to 0.27); however, there were no clear correlations between acute travel metrics and match outcomes or physical performance.
In summary, environmental challenges were associated with physical and / or match performance but these associations were generally trivial or small. However, in elite sport small effects may still be important, I also observed individual variability in regression slopes and further research exploring individual variation in response to environmental stressors is warranted. In the synthesis of the studies (Chapter 8), environmental challenges were associated with physical and / or match performance and individual variability was observed in regression slopes. Though correlations were generally trivial or small, even small effects may be important for elite athletes. Therefore, further research that is focused on individual variations in response to environmental stressors is warranted.
| Date of Award | 21 Jun 2024 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Matthew Wright (Supervisor), Jonathan Taylor (Supervisor) & Matthew Portas (Supervisor) |