Correlations Between Vertical Ground Reaction Force, Sagittal Joint Angles, and the Muscle Co-Contraction Index During Single-Leg Jump-Landing

Impact and lower extremity joint angles during landing are factors that can increase the risk of anterior cruciate ligament injuries. However, the correlations between these factors and lower extremity muscle activation during the flight phase, which may affect these factors, are unknown. The present study aimed to clarify the correlations between the peak vertical ground reaction force (pVGRF), sagittal joint angles during the landing phase, and the vastus medialis (VM) and semitendinosus (ST) muscle co-contraction index (CCI) during the flight phase in single-leg jump-landing. Fourteen healthy, physically active volunteers (age, 22.6 ± 2.7 years; height, 164.4 ± 7.6 cm; body weight, 58.9 ± 8.9 kg; body mass index, 21.7 ± 2.3 kg/m2 ) participated. All subjects performed a single-leg jump-landing task. The pVGRF variables and the sagittal joint angles during the landing phase were measured. The CCI between the VM and ST during the flight phase was measured. The correlations between the VGRF variables, sagittal joint angles, and CCI were assessed using Spearman’s rank correlation coefficient. The knee flexion angle at the pVGRF was negatively correlated with the magnitude of pVGRF (ρ = -0.609, P = 0.021). The knee flexion angle at the pVGRF was negatively correlated with the CCI during the flight phase in single-leg jump-landing (ρ = -0.627, P = 0.016). An excessive CCI between the VM and ST during the flight phase might be indirectly related to a greater landing impact after a single-leg jump.