Biomechanical analysis of the single-leg decline squat

<jats:p><jats:bold>Background:</jats:bold>The single-leg squat on a 25° decline board has been described as a clinical assessment tool and as a rehabilitation exercise for patients with patellar tendinopathy. Several assumptions have been made about its working mechanism on patellar load and patellofemoral forces, but these are not substantiated by biomechanical evaluations.</jats:p><jats:p><jats:bold>Aim:</jats:bold>To investigate knee moment and patellofemoral contact force as a function of decline angle in the single-leg squat.</jats:p><jats:p><jats:bold>Methods:</jats:bold>Five subjects performed single-leg eccentric squats at decline angles of 0°, 5°, 10°, 15°, 20° and 25° (with/without a backpack of 10 kg), and 30° on a board that was placed over a forceplate. Kinematic and forceplate data were recorded by the Optotrak system. Joint moments of ankle, knee and hip were calculated by two-dimensional inverse dynamics.</jats:p><jats:p><jats:bold>Results:</jats:bold>Knee moment increased by 40% at decline angles of 15° and higher, whereas hip and ankle moment decreased. Maximum knee and ankle angles increased with steeper decline. With a 10 kg backpack at 25° decline, the knee moment was 23% higher than unloaded. Both patellar tendon and patellofemoral forces increased with higher decline angles, but beyond 60°, the patellofemoral force rose steeper than the tendon force.</jats:p><jats:p><jats:bold>Conclusions:</jats:bold>All single-leg squats at decline angles >15° result in 40% increase in maximum patellar tendon force. In knee flexions >60°, patellofemoral forces increase more than patellar tendon forces. Higher tendon load can be achieved by the use of a backpack with extra weight.</jats:p>