Alterations in Quadriceps Voluntary Force Control Following Anterior Cruciate Ligament Injury

Abstract

Although quadriceps strength is important following ACL injury, maximal activation of the quadriceps is rare during sporting situations and activities of daily living. Furthermore, functional stability of the knee joint depends on both adequate strength and the ability to produce force accurately. Previous studies assessing quadriceps force control following ACL injury have utilized constant sub-maximal isometric target forces. However, during most functional activities the quadriceps muscles are required to produce fluctuating force levels. Thus, the use of a testing protocol involving a cyclical or varying target force may better approximate quadriceps forces during functional activities. PURPOSE: To examine submaximal quadriceps force control in individuals with an ACL injury using a cyclical force target. METHODS: Eighteen (18) individuals (12M/6F; 29.8 ± 8.7years) within 8 months of unilateral isolated ACL injury (69.5 ± 42.5 days post-injury) and 18 healthy controls (12M/6F; 29.2 ± 6.8years) participated in the study. Participants performed an isometric quadriceps contraction to match an increasing force ramp from 5% to 25% body weight (BW), after which the ramp gradually reduced from 25% to 5% BW (0.10Hz). Four trials of 60s with 60s rest in between were performed. The root mean square error (RMSE) of quadriceps torque relative to target torque was determined, and compared between groups and limbs using a 2x2 ANOVA with repeated measures on limb. Sub-regional analysis assessed accuracy of force control over an increasing (ascending RMSE) and decreasing (descending RMSE) force ramp. RESULTS: There was significantly greater overall RMSE in both limbs of the ACL group compared to healthy controls (3.36 ± 1.8 %BW INV limb; 3.28 ± 1.2 %BW UNINV limb; 2.40 ± 0.61 %BW CONT; 2.40 ± 0.58 %BW UNINV CONT P=0.032). The ACL group had significantly higher descending RMSE in both limbs compared to healthy controls (3.92 ± 2.8 INV limb; 3.39 ± 1.6 UNINV limb; 2.43 ± 0.61 CONT; 2.36 ± 0.52 UNINV CONT P=0.035). Ascending RMSE did not differ between the ACL and control group limbs (P>0.05) CONCLUSIONS: There are significant bilateral deficits in submaximal quadriceps force control after ACL injury, compared to healthy controls, potentially contributing to altered knee function after ACL injury.