ISB clinical biomechanics award winner 2019: Knee extensor fatigue resistance in individuals following anterior cruciate ligament reconstruction.

Background: Individuals following anterior cruciate ligament reconstruction demonstrate quadriceps weakness throughout the post-operative recovery and at the time of returning to sport. This is often accompanied with patterns of quadriceps fatigue resistance. As such, fatigue may be an identifier of individuals with delayed recovery. The purpose was to assess quadriceps fatigue in anterior cruciate ligament reconstructed patients at the time of return to sport in comparison to healthy controls.

Methods: A total of 215 individuals, 120 following anterior cruciate ligament reconstruction (21.0 (2.9) years, 63 Female, 5.96 (0.48) months post-surgery) and 95 healthy controls (21.5 (8.4) years, 49 Female), participated in this study. All participants completed a 30-s knee extensor maximum voluntary isometric contraction. Knee extensor strength, limb symmetry index, and fatigue (%) were compared between groups. Between-limb fatigue comparisons were made through the Fatigue Index Limb Difference = [(Involved Limb Fatigue Index) - (Uninvolved Limb Fatigue Index)].

Findings: Individuals following anterior cruciate ligament reconstruction (18.7 (10.9)%, -5.6 (11.2)) demonstrated lower values of unilateral fatigue and Fatigue Index Limb Difference compared to healthy participants (22.5 (8.2)%, P = .002; 2.2 (7.9), P < .001). For anterior cruciate ligament reconstructed patients, there was a weak, negative, significant relationship between the involved limb strength and fatigue (r = -0.184, P = .048). There was no relationship between limb symmetry and Fatigue Index Limb Difference (r = 0.137, P = .142). For Healthy individuals, there was a positive, moderate relationship between limb symmetry and Fatigue Index Limb Difference (r = 0.400, P < .001).

Interpretation: Individuals following anterior cruciate ligament reconstruction demonstrate fatigue resistance compared to healthy active controls and greater resistance to fatigue in their involved limb compared to their contralateral limb.