Center of pressure predicts Intra-limb compensatory patterns that shift demands away from knee extensors during squatting.

Abstract

The persistence of knee extensor moments deficits following anterior cruciate ligament reconstruction (ACLr) may be attributed to difficulty quantifying inter- and intra-limb compensations clinically. Force plate derived center of pressure (CoP_pos) and vertical force (vGRF) may provide valuable information regarding limb and joint loading impairments in this group. This study aimed to determine the: 1) relationship between measures CoP_pos and intra-limb extensor moment distribution during a squat, and 2) utility of using CoP_pos and vGRF to estimate knee extensor moment deficits post-ACLr. Twenty-four individuals, 142 ± 22.5 days post-ACLr, performed bilateral squats. Ankle (aEXT), knee (kEXT) and hip (hEXT) extensor moments were calculated using three-dimensional kinematics and GRF. Moments, CoP_pos and vGRF were identified at peak kEXT. Intra-limb moment distribution was characterized using hEXT/kEXT and aEXT/kEXT ratios. Linear regressions analyzed relationships between CoP_pos and hEXT/kEXT and aEXT/kEXT. Stepwise regressions determined if between-limb CoP_pos ratio predicted between-limb ratios of hEXT/kEXT and aEXT/kEXT. Stepwise regression determined if between-limb CoP_pos and vGRF ratios predicted between-limb kEXT ratio. Results found that CoP_pos predicts intra-limb moment distribution (hEXT/kEXT and aEXT/kEXT); more anterior CoP_pos related to higher moments at the hip and ankle relative to the knee. In addition, between-limb CoP_pos ratio predicts between-limb ratio of hEXT/kEXT and aEXT/kEXT ratios. Together between-limb CoP_pos (52%) and vGRF (18%) ratios explained 70% of the variance in between-limb kEXT ratios (R2 = 0.70, p < 0.001). These data suggest that force plate derived CoP_pos and vGRF may be important for detection of knee extensor moment deficits in individuals post-ACLr.