Relationship between explosive lower limb strength and impact force during landing in healthy young individuals.

Excessive peak vertical ground reaction force (VGRF) during landing is a risk factor for anterior cruciate ligament injury. Identifying the physical characteristics associated with peak VGRF is essential for injury prevention. The relationship between peak VGRF and maximum voluntary contraction (MVC) of the thigh muscle is weak, possibly because MVC does not reflect the muscle strength exerted at the knee joint posture and timing when peak VGRF occurs. This study explored the relationship between peak VGRF during landing and the rate of torque development (RTD), a measure of the rapid generation of muscle force, assessed at three different knee joint flexion angles. RTD and MVC of the quadriceps and hamstrings were measured in 36 physically active adults (18 males) using an isokinetic dynamometer at 30° and 60° knee joint flexion angles, simulating the joint angle at landing, and at a conventional 90° knee joint flexion angle. Results showed a significant negative correlation between hamstring RTD at 30° knee flexion and peak VGRF (r =  -0.71, p = 0.001), but no significant correlations were found with others. Therefore, it is important to assess muscle strength at the posture and timing when peak VGRF occurs to reduce peak VGRF and prevent injury.