Effect of fatigue on neuromuscular and biomechanical variables after anterior cruciate ligament reconstruction: a systematic review

INTRODUCTION: This systematic review is aimed to evaluate the outcomes of published studies on the topic of fatigue-induced neuromuscular and biomechanical changes after anterior cruciate ligament (ACL) reconstruction.EVIDENCE ACQUISITION: The identification of studies involved a search across three databases - PubMed, Scopus, and Sportdiscus - until July 2023. The key terms utilized were fatigue, anterior cruciate ligament, biomechanics, electromyography, and landing. Included in the analysis were studies that examined the impact of fatigue on neuromuscular or biomechanical variables in individuals with ACLR, with comparisons drawn to either the contralateral side or healthy controls.EVIDENCE SYNTHESIS: Fourteen studies, involving 396 athletes (245 males, 151 females; mean age 23.43 years) met the inclusion criteria. Among these studies, eleven employed general fatigue protocols, and three used peripheral protocols. The tasks varied across the studies, including single-leg landing tasks, maximum voluntary isometric contraction tests, forward jump, and squat. Despite differing tasks, the findings regarding the impact of fatigue on lower limb kinematics, kinetics, and surface electromyography muscle activation patterns were inconsistent. However, in the majority of cases, the response to fatigue was similar between individuals who had undergone ACL reconstruction (ACLR) and healthy.CONCLUSIONS: The main finding of this systematic review was that fatigue changed things sometimes, however, fatigue did not change biomechanics and activity patterns differently in patients after ACLR vs. controls. General fatigue protocols did not produce enough stimulation to show deference between ACLRs and controls. Future studies should focus on different fatigue protocols (such as sport-specific protocols) and more challenging landing tasks.