PINNIGER, G. J., J. R. STEELE, and H. GROELLER. Does fatigue induced by repeated dynamic efforts affect hamstring muscle function? Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 647–653, 2000.
Purpose: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running.
Methods: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects’ sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded.
Results: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects’ running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride.
Conclusions: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.
Whether it occurs during activities of daily living, recreation, or work, muscle fatigue is a major limiting factor to sustained physical effort. Muscle fatigue has also been implicated as a predisposing factor in sporting injuries (6), in particular, hamstring muscle strains (19,23). Hamstring muscle strains are incurred frequently by athletes competing in explosive activities such as sprinting and jumping events (18,25). This injury is also common in team sports involving maximal or near maximal sprints that are repeated over an extended period. For example, hamstring muscle strains are the most common injury sustained by Australian Rules Football (ARF) players, accounting for 13% of all injuries and 16% of total time missed due to injury (15). Seward and Patrick (16) noted that hamstring muscle strains tended to occur in the first 10 min of the first and second quarters and toward the end of the third and fourth quarters of ARF matches. On the basis of these findings, the authors suggested that inadequate warm-up and player fatigue were factors associated with hamstring muscle strains (16).
As a predisposing factor in hamstring injuries and a limitation to sustained physical effort, extensive research has focused on muscle fatigue. There has also been an emerging interest in recent years into the effects of fatigue on the performance of explosive activities such as sprinting (11–14,17,20). This research has shown fatigue induced alterations to the biomechanics of sprint running, including decreased hip flexion and thigh angular velocity and increased knee extension during the swing phase of the stride cycle (17,20). The magnitude of myoelectric activity in select lower limb muscles has also been shown to increase during fatigued sprint running (11,13,14). Furthermore, long-duration fatiguing tasks have been shown to increase the duration of myoelectric activity of the involved muscles (9).
However, most of this research has utilized single maximal efforts to induce fatigue. No research was located which investigated alterations in sprinting biomechanics caused by fatigue induced by repeated dynamic sprint efforts, efforts which are more typical of most team sports compared with single effort sprints. Therefore, the purpose of the present study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. It was hypothesized that after hamstring fatigue, subjects would display a reduced efficiency of the hamstring muscles, reflected by changes in leg and thigh motion, increased duration of hamstring activity, and alterations to hamstring/quadriceps synchronization relative to initial foot-ground contact during the late swing phase of the stride cycle.