Mechanics of hamstring function in sprinting

Hamstring strain injury is commonly reported as one of the leading causes of injury in many competitive sports, resulting in significant performance, health and financial implications. Despite a growing body of research, little change has been observed in the prevalence of hamstring strain injury, suggesting the current areas of knowledge may be incomplete. The purpose of this study was to develop a suitable musculoskeletal model to examine hamstring function during sprinting and its relationship with hamstring strain Injury. Experimental data was collected on one male participant running at submaximal and maximal speeds (overground and treadmill). The open-source software, OpenSim, was used to construct, evaluate, and optimise a 3-dimensional musculoskeletal model suitable for sprint running. To successfully simulate sprinting, adjustments were made to a generic model including ranges of motion, anthropometrics, and muscle parameters. The final model was shown to produce realistic estimates of movement and muscle performance. The choice of optimisation method was shown to be important, with direct collocation achieving a dynamically consistent and viable solution, presenting a feasible framework for the investigation of ballistic movements. Hamstring function and joint moments were shown to significantly increase with running speed, supporting the suggestion that hamstring injury risk significantly increases with running speed. Other findings emphasised that the terminal swing is a critical period when the hamstring is at most risk of injury. Investigating multiple strides revealed high variability in hamstring muscle function, showing large changes in the relative load between the hamstring muscles. Previous sprinting research is often limited to a single representative stride, providing a narrowed view on hamstring muscle function. Future research may need to include multiple running strides to better understand the relationship between muscle function and hamstring strain injury. Finally, the effects of altering muscle strength and fibre length on hamstring function were quantified. Findings reveals that adjusting biceps femoris long head fibre length resulted in minimal changes to simulation performance and hamstring function. Reductions in hamstring or gluteal strength, or increases in quadriceps strength, resulted in poorer simulation performance and large changes to hamstring muscle function. Reduced simulation performance was characterised by large changes in the pelvic orientation, supporting the suggestion of pelvic instability as a risk factor for hamstring strain injury.