Symmetry of squatting and the effect of fatigue following anterior cruciate ligament reconstruction

Purpose: To evaluate weight-bearing and joint symmetry during the double-leg squat exercise at baseline and after fatigue in patients who have undergone anterior cruciate ligament reconstruction (ACLR) compared to uninjured controls. Methods: Ten males who had returned to sport after primary ACLR participated along with ten uninjured male controls. Lower limb kinematic, kinetic and ground reaction force (GRF) data were collected during double-leg squats at baseline and after a generalised fatigue protocol. Symmetry indices were calculated for hip and knee external flexion moments and the vertical GRF (weight-bearing symmetry) at maximum squat depth. These were compared between ACLR and control groups before and after fatigue using ANOVA models. Results: The ACL group preferentially unloaded the reconstructed limb at baseline, but changed to a more symmetrical load distribution to perform the squat exercise in the fatigue condition. This same loading pattern was seen at both the knee and hip joints. The control group did not show any effect of fatigue. For both groups, symmetry indices were closer to zero (which indicated perfect symmetry) in the fatigue condition. Conclusions: When prescribing squat exercises, it should be recognised that initially, patients with ACLR tend to unload the affected knee. More symmetrical loading patterns may be achieved by inducing bilateral fatigue. When fatigued, loading symmetry was similar between this patient group and controls. This is relevant information for those who implement rehabilitation training programmes.