Conceptual framework for strengthening exercises to prevent hamstring strains.

High-speed running accounts for the majority of hamstring strains in many sports. The terminal swing phase is believed to be the most hazardous as the hamstrings are undergoing an active lengthening contraction in a long muscle length position. Prevention-based strength training mainly focuses on eccentric exercises. However, it appears crucial to integrate other parameters than the contraction type. Therefore, the aim of this study is to present a conceptual framework based on six key parameters (contraction type, load, range of motion, angular velocity, uni-/bilateral exercises, kinetic chain) for the hamstring's strength exercise for strain prevention. Based on the biomechanical parameters of sprinting, it is proposed to use high-load eccentric contractions. The movement should be performed at a slow to moderate angular velocity and focused at the knee joint, while the hip is kept in a large flexion position in order to reach a greater elongation stress of the hamstrings than in the terminal swing phase. In this way, we believe that, during sprinting, athletes would be better trained to brake the knee extension effectively in the whole range of motion without overstretch of the hamstrings. Finally, based on its functional application, unilateral open kinetic chain should be preferred.