Objective  To study the interaction of risk factors for muscle injury, including the strength, length, velocity, power of the hamstrings, so as to explore the biomechanical mechanism of the time phase of hamstrings strain during sprint running.

  Methods   The data of three-dimensional kinematics and force-plate were collected during the running of subjects, and the lower musculoskeletal model along with the muscle function model were set up, then the static optimization algorithm was programmed so that the biomechanical data of single muscle of the lower limb were quantified.

  Results   The hamstrings sustained the high stress and were in the high-speed centrifugal contraction state during the middle stage of the swinging phase of the hamstrings, and produced the power peak of per area for negative work during the full gait. The length and stress peak of hamstrings appeared at the ending stage of the swinging phase. Besides, under the condition of maximum extension during the initial touchdown, the hamstrings sustained the high stress and did the high-speed concentric contraction, and meanwhile produced the power peak of per area for positive work. The mechanic index of biceps femoris muscle exceeded other muscles remarkably.

  Conclusion   The middle and ending stage of swinging phase is the likely strain phase for hamstrings; while the biceps femoris muscle is the likely strained one among the muscles of hamstrings.