Biomechanical analysis of the single-leg decline squat

Background: 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.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, 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.Results: 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.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.