Influence on Strength and Flexibility of a Swing Phase–Specific Hamstring Eccentric Program in Sprinters' General Preparation

Hamstring injuries are common in sprinters and mainly occur during the terminal swing phase. Eccentric training has been shown to reduce hamstring injury rate by improving several risk factors. The aim of this study was to test the hypothesis that an additional swing phase-specific hamstring eccentric training in well-trained sprinters performed at the commencement of the winter preparation is more efficient to improve strength, ratio, optimum angle, and flexibility than a similar program without hamstring eccentric exercises. Twenty sprinters were randomly allocated to an eccentric (n = 10) or a control group (n = 10). Both groups performed their usual track and field training throughout the study period. Sprinters in the eccentric group performed an additional 6-week hamstring eccentric program, which was specific to the swing phase of the running cycle (eccentric high-load open-chain kinetic movements covering the whole hamstring length-tension relationship preformed at slow to moderate velocity). Isokinetic and flexibility measurements were performed before and after the intervention. The eccentric group increased hamstring peak torques in concentric at 60° · s(-1) by 16% (p < 0.001) and at 240° · s(-1) by 10% (p < 0.01), in eccentric at 30° · s(-1) by 20% (p < 0.001) and at 120° · s(-1) by 22% (p < 0.001), conventional and functional ratios by 12% (p < 0.001), and flexibility by 4° (p < 0.01), whereas the control group increased hamstring peak torques only in eccentric at 30° · s(-1) by 6% (p ≤ 0.05) and at 120° · s(-1) by 6% (p < 0.01). It was concluded that an additional swing phase-specific hamstring eccentric training in sprinters seems to be crucial to address different risk factors for hamstring strain injuries, such as eccentric and concentric strength, hamstring-to-quadriceps ratio ratio, and flexibility.