Abstract
Aim: Hamstring muscle injury is the main injury related to sports requiring sprint acceleration. In addition, hamstring muscles have been reported to play a role in horizontal force production during sprint acceleration performance. The aim of the present study was to analyze (i) the determinants of horizontal force production and (ii) the role of hip extensors, and hamstring muscles in particular, for horizontal force production during repeated sprint-induced fatigue conditions.Method: In this experimental laboratory setting study including 14 sprint-trained male athletes, we analyzed (i) the changes in sprint mechanics, peak torque of the knee and hip extensors and flexors, muscle activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus, and sagittal plane lower limb motion, before and after twelve 6-s sprints separated by 44 s rest on an instrumented motorized treadmill, and (ii) the determinants of horizontal force production (FH) during the sprint acceleration in a fatigue state (after 12 sprints).Results: The repeated-sprint protocol induced a decrease in maximal power output (Pmax) [-17.5 ± 8.9%; effect size (ES): 1.57, large] and in the contact-averaged horizontal force component (FH) (-8.6 ± 8.4%; ES: 0.86, moderate) but not meaningful changes in the contact-averaged resultant (total) force (FTot) (-3.4 ± 2.9%; ES: 0.55, small) and vertical force component (FV) (-3.1 ± 3.2%; ES: 0.49, small). A decrease was found in concentric peak torque of the knee flexors and extensors and in gluteus and vastus lateralis muscle activity during entire swing and end-of-swing phase. An increase was found in contact time and swing time, while step frequency and knee speed before ground contact decreased. Muscular determinants associated with FH and its decrease after the repeated-sprint protocol were concentric peak torque of the hip extensors (p = 0.033) and a decrease in gluteus maximus activity at the end-of-swing (p = 0.007), respectively.Conclusion: Sprint-induced fatigue lead to changes in horizontal force production muscular determinants: hamstring muscle seems not to have the same role than in non-fatigue condition. Horizontal force production seems to be more dependent on the hip extensors and gluteus maximus function. Given the fatigue-induced decrease in hamstring muscle strength, we can hypothesize that muscle compensatory and kinematic strategies reported in a fatigued state could be an adaptation to allow/maintain performance and a protective adaptation to limit hamstring muscles constraints.
Highlights
IntroductionHamstring muscle injury (HMI) is, despite improvements in knowledge and prevention strategies, the main injury related to sport requiring sprint acceleration, such as football (Woods et al, 2004; Ekstrand et al, 2011, 2016), rugby (Brooks et al, 2006), and athletics (Opar et al, 2014; Edouard et al, 2016)
The main findings of the present study were that (i) the repeated sprints (RS) protocol induced a clear decrease in sprint acceleration performance (Pmax) and in horizontal force production (FH), which can be considered markers of neuromuscular fatigue, (ii) higher horizontal ground force production (FH) in a fatigue state was mainly associated with a higher concentric peak torque (PT) of the hip extensors, (iii) the lower decrease in horizontal force production after fatigue was mainly associated with a lower decrease in gluteus maximus activity at the endof-swing, and (iv) hamstring muscle torque during knee flexion was not associated with horizontal force production in a fatigue state, contrary to what was observed in the non-fatigue condition (Morin et al, 2015)
This study allows better understanding of the determinants of sprint acceleration performance and horizontal force production in fatigue conditions and the role of the hamstring muscles in such conditions, which presents relevant perspectives in practice given the interest of repeated sprint ability in team sports and the importance of Hamstring muscle injury (HMI) in sports including sprinting and multiple acceleration
Summary
Hamstring muscle injury (HMI) is, despite improvements in knowledge and prevention strategies, the main injury related to sport requiring sprint acceleration, such as football (Woods et al, 2004; Ekstrand et al, 2011, 2016), rugby (Brooks et al, 2006), and athletics (Opar et al, 2014; Edouard et al, 2016). HMI leads to considerable consequences for athletes, such as time-loss from sport and high risk of recurrence (Woods et al, 2004; Ekstrand et al, 2011, 2016; Malliaropoulos et al, 2011; Edouard et al, 2016). This makes HMI a challenge for all stakeholders around the athletes to better understand and prevent them. We suggest that better understanding sprint performance and mechanics is a key parameter to improve HMI prevention
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