With recent advancements in the fields of musculoskeletal and simulation research, we are now able to calculate individual muscle forces during high velocity, single-leg landing sporting tasks where knee injuries are known to occur. Results from this simulation research have shown that the relative contribution of the gastrocnemius is significantly elevated relative to the hamstrings during the impact phase of single-leg landing. These findings represent a paradigm shift in the literature, challenging over 30 years of clinical research, which have presumed that the hamstring muscles were the primary muscle group supporting the knee during single-leg landing sport tasks.
Through a joint research project with The University of Western Australia’s School of Sport Science, Exercise and Health (SSEH) and the department of Mechanical, Aerospace and Biomedical Engineering at the University of Tennessee, full body three dimensional motion capture data was collected from six amateur Western Australian rules footballers conducting two different single-leg jump landing tasks while marking a football. This motion capture data was then used to create a full-body, 37 degree-of-freedom musculoskeletal model’s scaled to each participant’s anthropometry. Using static optimization and computed muscle control in the advanced musculoskeletal software OpenSim, muscle driven simulations of these sporting movements were generated, providing the literature new insights associated with how muscles function to support the knee and lower limb during single-leg jump landing tasks where injuries are known to occur.
Results from this research showed that the gastrocnemius muscle produces significantly more force than the hamstring to generate the joint compression forces needed to support the knee during the single leg landing tasks. These results represent a paradigm shift in the literature, which have presumed from cadaveric and electromyography literature, the hamstrings were the key muscle group utilized to support knee during high velocity sporting activities. Specifically, clinical estimates of hamstring strength/muscle activation have been used as primary measures to assess everything from an athlete’s knee injury risk, return to play following injury as well as gage the effectiveness of knee and ACL injury prevention training protocols.
Within this manuscript, we have also provided an empirically verified a mechanical model explaining these results. The primary goal of the neuromuscular system during any task (i.e. standing, walking, landing, etc.) is to prevent the centre of mass from falling to the ground. Together with the quadriceps and hip extensors, the gastrocnemius muscles are used to generate support moments, which are moments of force acting against gravity to keep your body upright. Being a biarticular muscle, the gastrocnemius serves a secondary role, elevating joint compression during single-leg landing, which is used to stiffen and support knee from external loading, reducing an athlete’s risk of injury in sport.
- Dr Jeff Reinbolt and Dr Kristin Morgan, The University of Tennessee, Knoxville, TN