Variability of the Sprint Step Movement Pattern and Its Association with Hamstring Injury Risk

<b>Background:</b> This study investigated how kinematic parameters vary during repeated 50 m sprints and their relationship with movement stability and hamstring injury risk among sprinters at different competitive levels. <b>Methods</b>: Eighteen male Polish National Team sprinters (nine elite, nine sub-elite) performed four 50 m sprints, with measurements of step length, frequency, ground contact time, and flight time taken using the OptoJumpNEXT system across the entire track. The fastest and slowest trials were analyzed, and a 26-question survey examined participants' hamstring injury history and prevention strategies. <b>Results:</b> Results showed that elite sprinters posted faster times, higher step frequency, shorter ground contact times, and increased step velocity, indicating more stable, consistent sprint mechanics. About 89% of athletes reported previous hamstring injuries, mainly during the late swing phase or between 40 and 50 m. The highest injury rate occurred during the fourth repetition, highlighting fatigue as a key risk factor. Elite sprinters mainly increased speed through higher step frequency and shorter ground contact times, while sub-elite athletes relied more on longer step lengths. <b>Conclusions</b>: Overall, elite sprinters exhibit more stable and efficient movement patterns, which may reduce the risk of hamstring strain injury. In contrast, the greater variability and fatigue seen in sub-elite athletes could heighten their injury vulnerability.