Alterations to Landing Technique and Patellar Tendon Loading in Response to Fatigue

Purpose: Fatigue may contribute to knee joint injuries, such as patellar tendinopathy, by increasing joint loading and altering lower limb landing technique, which in turn may increase tissue loading. This study aimed to investigate the effect of lower limb muscle fatigue on the landing technique and patellar tendon loads generated during the horizontal and vertical landing phases of a stop-jump task. It was hypothesized that muscle fatigue would increase patellar tendon loading and alter the landing technique displayed during the horizontal, but not the vertical, landing phase of the stop-jump task. Methods: Sixteen men, recruited from team sports involving repetitive landing, performed repeated trials of a stop-jump task. During each trial, the participants' ground reaction forces and electromyographic activity of seven lower limb muscles were recorded, three-dimensional kinematics measured, and peak patellar tendon force (F-PT) calculated. Results: When fatigued, participants generated a significantly lower F-PT and F-PT loading rate, despite a higher vertical ground reaction force (F-V) and F-V loading rate, during the horizontal landing phase of the stop-jump task. During the vertical landing phase, participants displayed only minor changes to the kinetics and kinematics of their landing in response to fatigue, although fatigue caused substantial alterations to their lower limb muscle activation patterns during landing. Conclusions: During the horizontal landing phase of the stop-jump task, participants decreased their patellar tendon load when they were fatigued by altering their lower limb landing technique, including a reduced net knee joint extension moment associated with less knee and hip flexion. This decrease in patellar tendon loading when fatigued may be an inherent protective strategy to potentially decrease loading of the tendon during repetitive landing.