(12) COMPARISON OF HAMSTRING MUSCLE ACTIVATION AND COORDINATION BETWEEN HAMSTRING INJURED AND UNINJURED LEGS DURING REPEATED SPRINTING

Purpose: This study aimed to examine differences in hamstring muscle activation and coordination patterns between injured and uninjured limbs during repeated submaximal sprinting on a treadmill in individuals with a history of hamstring strain injury. Methods: Eight athletes (age: 22.7 ± 3.5 years; male: n = 5; height: 173.2 ± 4.5 cm, weight: 74.6 ± 13.6 kg, return-to-play duration from injury: 3.9 ± 2.9 weeks) participated in this study. After demographic data collection, participants performed a 100m sprint on a track to measure their maximum sprint speed. Each participant then completed five repeated sprints at 90% of maximum sprint speed (ranging from 22.7 to 25 km/h) on a high-speed treadmill. Each sprint lasted 10 seconds followed by a 5-second rest interval. During the repeated-sprint protocol, electromyography (EMG) signals were recorded from the biceps femoris long head (BFlh) and semitendinosus (ST) at a sampling rate of 2000 Hz. Additionally, shank angular velocity was recorded to determine three running phases: stance phase, early-swing phase, and late-swing phase. EMG signals were normalized to the peak value of maximal voluntary contraction (MVC), which was recorded before the repeated-sprint protocol using an isometric hamstring contraction test. EMG data were processed using a custom Python script to calculate the peak and mean root mean square(RMS) values of BFlh and ST across the three phases. Muscle coordination was assessed using the BFlh/ST ratio, calculated from either peak or mean RMS values across the three phases. An independent t-test was used to evaluate differences in EMG activity and coordination between the injured and uninjured limbs. Results: The statistical analysis revealed that BFlh peak (p=0.035), and mean (p=0.045) RMS values were significantly greater in the injured limb during early swing-phase. Additionally, a significant difference in mean muscle coordination values (BFlh/ST ratio, p=0.03) was observed between the injured and uninjured limbs during the late-swing phase (see Table 1). Conclusions: The previously injured limb exhibited different hamstring muscle coordination patterns compared to the uninjured limb during repeated-spring performance. Specifically, during the early-swing phase, the injured limb demonstrated greater BFlh activation than uninjured limb. Additionally, regarding muscle coordination, during the late-swing phase, the injured limb demonstrated greater BFlh activation relative to ST compared to the uninjured limb. Practical Applications: Current hamstring injury prevention and rehabilitation strategies primarily focus on enhancing eccentric strength (e.g., Nordic Curls) and flexibility. However, neuromuscular control changes following injury are commonly observed, and should be considered in prevention and rehabilitation strategies to reduce re-injury. Acknowledgements: none