Biomechanical analysis of the single-leg decline squat.

BACKGROUND The single-leg squat on a 25 degrees 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. AIM To investigate knee moment and patellofemoral contact force as a function of decline angle in the single-leg squat. METHODS Five subjects performed single-leg eccentric squats at decline angles of 0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees and 25 degrees (with/without a backpack of 10 kg), and 30 degrees 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. RESULTS Knee moment increased by 40% at decline angles of 15 degrees and higher, whereas hip and ankle moment decreased. Maximum knee and ankle angles increased with steeper decline. With a 10 kg backpack at 25 degrees decline, the knee moment was 23% higher than unloaded. Both patellar tendon and patellofemoral forces increased with higher decline angles, but beyond 60 degrees, the patellofemoral force rose steeper than the tendon force. CONCLUSIONS All single-leg squats at decline angles >15 degrees result in 40% increase in maximum patellar tendon force. In knee flexions >60 degrees, patellofemoral forces increase more than patellar tendon forces. Higher tendon load can be achieved by the use of a backpack with extra weight.