Background: The single leg squat on a 25 degree decline board has been described as a clinical assessment tool and rehabilitation exercise for patients with patellar tendinopathy. Several assumptions have been made about its working mechanism on patellar load and patello-femoral forces but these are not substantiated by biomechanical evaluations.
Objective: Objective of this study was to investigate knee moment and patello-femoral 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, 25 (with/without backpack 10kg) 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 2-D inverse dynamics.
Results: Knee moment increased by 40% at decline angles of 15 degrees and higher while 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. Patellar tendon and patello-femoral force both increased with higher decline angles but beyond 60 degrees patello-femoral force rose steeper than tendon force.
Conclusions: Single leg squats at decline angles above 15 degrees all result in the same forty percent increase in maximum patellar tendon force. In knee flexions over 60 degrees patello-femoral forces increase more than patellar tendon forces. Higher tendon load can be achieved by the use of a backpack with extra weight.
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