Strength and Biomechanical Contributions to Vertical Ground Reaction Forces in a Single Limb Landing Task

Abstract

Reducing dynamic joint loading is a key strategy included in injury prevention landing mechanics programs. Previous research has noted the importance of increased knee flexion to reduce vertical ground reaction forces (vGRF), and the relationship between strength asymmetry and asymmetrical landing mechanics following injury. PURPOSE: To determine if and how landing kinematics at the hip, knee, and ankle, as well as quadriceps strength contribute to vGRF in a single limb landing task. METHODS: Thirty-four physically active males (Age: 27.6 ± 4.6yrs; Height: 177.74 ± 7.15cm; Mass: 84.31 ± 11.83kgs) completed a single limb drop landing off a 45.7 cm box onto a force plate. A 3D motion system was used to collect dominant (DOM) and non-dominant (NON) hip flexion at initial contact, peak knee flexion (PKF), knee flexion at initial contact (KFIC), peak ankle flexion, ankle flexion at initial contact and, peak vGRF. DOM and NON quadriceps strength (IKQS) was collected using an isokinetic dynamometer at 60°/s. Simple linear regression models were run for each limb to detect independent contributions to vGRF. Backward stepwise multiple linear regression was used to determine the best model to predict vGRF. RESULTS: KFIC independently accounted for 11.8% (p= 0.047) of the variance in DOM vGRF. No DOM limb multiple linear regression model was significant. KFIC and PKF independently accounted for 15.7% (p=0.021) and 16.5% (p=0.017) of the variance in NON vGRF, respectively. KFIC and IKQS as a multiple linear regression model accounted for 18.9% (p=0.043) of variance in NON vGRF. CONCLUSION: KFIC, on DOM and NON limbs, is the best sagittal plane kinematic predictor of vGRF, in a single limb drop landing task in physically active males. Despite IKQS not being an independent significant predictor on either limb, it improved KFIC prediction of vGRF on the NON limb. This study highlights how active males use sagittal plane knee motion and quadriceps strength to influence vGRF in a single leg landing task, as research has shown women are more likely to use hip and knee kinematic strategies. Active individuals with weak quadriceps and a stiffened knee at initial contact are likely at risk for injuries associated with increased impacts during single limb landings.