Hip and knee kinematics, center of pressure position, and ground reaction force are associated with Achilles tendon force during jump landing

PurposeJump-landing exercises are often performed during the rehabilitation of Achilles tendon (AT) injuries. However, the factors that affect the AT force (ATF) during landing are unclear. This study aimed to determine the kinematics and ground reaction force (GRF) variables associated with the peak ATF during a drop vertical jump (DVJ).MethodsThe landing phase of DVJ was evaluated in 101 healthy participants (46 males, age: 21.2 +/- 1.4 years old) using a three-dimensional motion analysis system with two force plates. ATF was estimated from the ankle flexion angle and moment. Univariate and multivariate regression analyses were performed with the peak ATF as the dependent variable. The vertical GRF (VGRF), center of pressure (COP), forward trunk leaning, hip/knee/ankle joint angles at peak ATF, and sex were used as independent variables.ResultsIn the univariate regression analysis, larger VGRF (beta = 0.813), more anterior COP position (beta = 0.214), smaller knee flexion (beta = -0.251) and adduction (beta = -0.252), smaller hip flexion (beta = -0.407), smaller forward trunk lean (beta = -0.492), and male sex (beta = -0.282) were significantly associated with a larger peak ATF. Multivariate analysis revealed that larger VGRF (beta = 1.018), more anterior COP position (beta = 0.320), a larger knee (beta = 0.442), and smaller hip flexion (beta = -0.205) were associated with the larger peak ATF.ConclusionsThe VGRF, COP position, and knee and hip flexion were independently associated with ATF. Modifying these factors may be useful in managing tendon loading during jump-landing exercises.