Effects of fatigue are more pronounced on the uninjured side during single-limb jumps 2 years after an acute Achilles tendon rupture.

PURPOSE: Achilles tendon rupture (ATR) is a serious lower limb injury that may result in persistent deficits in strength and endurance of the calf muscles. Compensatory mechanisms at proximal joints are known, but the effects of fatigue are less studied. The aim was therefore to evaluate the effect of a fatigue protocol on lower limb kinetics during performance of single-limb drop countermovement jumps (CMJ) in individuals with a history of a unilateral ATR. METHODS: Thirty participants were recruited on average 2 years after ATR. Drop CMJs were performed on each side before and after a fatigue protocol, and peak power values for the hip, knee and ankle joints were calculated, as well as jump height and duration. A mixed model analysis of variance was used to evaluate inter-limb differences pre- and post-fatigue during the landing (eccentric) and push-off (concentric) phases of the involved (INV) and uninvolved (UNinv) side. RESULTS: The fatigue protocol had a greater effect on peak ankle joint power of the UNinv side across both phases (by a mean [95% confidence interval, CI] of 1.06 [0.58-1.54] W/kg) compared to the INV side (0.51 [0.03-1.00] W/kg; p = 0.039). Moreover, greater fatigue-induced changes in ankle joint power were found during landing (by a mean [95% CI] of 1.13 [0.64-1.61] W/kg) compared to push-off (0.45 [0.04-0.93] W/kg; p = 0.011), across both sides. A trend towards increased knee joint power was seen as a response to fatigue across both sides and phases (p = 0.062), with no change at the hip. CONCLUSIONS: Rehabilitation following ATR should emphasize progressive reliance on the INV side across the rehabilitation continuum by incorporating strength, endurance and training under fatigued conditions. This approach may help reduce compensatory reliance on the UNinv side, potentially lowering the risk of overuse‑related injuries. LEVEL OF EVIDENCE: Level III.