INTRODUCTION: Soccer is a high-intensity intermittent team sport, during which neuromuscular factors are heavily taxed to perform quick accelerations, decelerations, and changes of direction (COD) [1]. Inter-limb strength asymmetries have been reported to negatively affect physical performance including COD tasks across various team sports [2], however little is known about their impact on muscle fatigability during soccer specific exercises such as repeated CODs. Therefore, this study examined the effect of peripheral muscle strength asymmetries across a repeated COD task on muscle fatigability in adult professional soccer players. METHODS: A total of 249 male professional soccer players (age: 25±5 yrs; stature: 182±6 cm; body mass: 78±7 kg) participated in this study. Each player performed a repeated COD test at least once (range: 1-23; total number of individual test sessions: 1.009). The repeated COD test encompassed four levels of intermittent runs with multiple CODs performed at increasing standardized intensities over an 8-m course. After each level, right and left knee extensors were electrically stimulated in resting isometric conditions to evoke a peak twitch (PT) response (an indicator of peripheral muscle strength). The main outcomes were PT torque after the first (PT1) and fourth (PT4) levels as well as the highest absolute value (PTmax) for both sides. Players were then allocated to specific groups according to their inter-limb asymmetry in PT1, PT4 and PTmax (LOW: =10%, MID: 10-20%, HIGH: >20%) and according to the difference in asymmetry between PTmax and PT4 (DeltaPT4-PTmax). Muscle fatigability (PTdec) was calculated as the mean percentage decline from PTmax to PT4. RESULTS: Mixed models were used to determine differences in PTdec between asymmetry groups. No significant differences in PTdec were observed between groups for PT1 and PTmax asymmetries (p=0.402 and p=0.102, respectively). On the other hand, PTdec was moderately affected by asymmetries observed at PT4 (p<0.001; LOW, 17.8%, range: 3.4%-49.5%; MID, 19.1%, range: 3.5%-58.7%; HIGH, 25.7% range: 5.3%-79.6%). In the same way, asymmetries based on DeltaPT4-PTmax largely influenced PTdec (p<0.001; LOW, 16.2%, range: 3.4%-39.6%; MID, 22.4%, range: 7.2%-52.5%; HIGH, 35.5%, range: 12.0%-79.6%). CONCLUSION: The current findings suggest that larger peripheral muscle strength asymmetries under fatigue (i.e. at PT4) and larger changes in asymmetries during the COD test (DeltaPT4-PTmax) were associated to higher levels of muscle fatigability during repeated CODs in professional soccer players. This study provides novel insights about how peripheral muscle strength asymmetries may impact a soccer-specific task in the presence of muscle fatigability. The present results also highlight the need to evaluate inter-limb strength asymmetries under fatigue and possibly to reduce their extent with the ultimate goal to enhance physical performance.
© Copyright 2022 27th Annual Congress of the European College of Sport Science (ECSS), Sevilla, 30. Aug - 2. Sep 2022. Published by Faculty of Sport Science - Universidad Pablo de Olavide. All rights reserved.