Sex Differences In Quadriceps Strength And Rate Of Torque Development 6 Months Post ACL Reconstruction

Abstract

Quadriceps weakness is ubiquitous post anterior cruciate ligament reconstruction (ACLR) and is strongly associated with adverse long-term patient outcomes. To date, research is equivocal in healthy subjects that males are stronger than females. However, there has been little work defining sex differences in quadriceps strength post ACLR. Identifying sex differences in quadriceps strength may allow for targeted rehabilitation strategies. PURPOSE: To determine whether sex differences in quadriceps strength and rate of torque development (RTD) exist in subjects 6 months after ACLR. METHODS: Seventy-five subjects (43 M, age 19.5 ± 6.0, Tegner 8.2 ± 1.7) 6 months after an ACLR performed maximum voluntary isometric contractions (MVIC) of the quadriceps. Subjects were positioned on a Biodex System 4 per previously reported literature. The average of four MVIC trials were normalized to the subjects’ body weight. Sex differences in quadriceps strength and RTD in injured and uninjured limbs were compared using analysis of covariance, controlling for age. RESULTS: The males were older (M = 22.6 ± 6.7 years, F = 16.8 ± 3.4 years, p < 0.01) and heavier (M = 79.1 ± 12.5 Kg, F = 66.4 ± 18.6 Kg, p < 0.01) than females. Despite controlling for age and body weight, males displayed higher peak quadriceps strength in the injured limb (M = 2.1 ± 0.6 Nm/Kg, F = 1.7 ± 0.6 Nm/Kg, p = 0.02, Cohen’s d = 0.63) and uninjured limb (M = 3.2 ± 0.8 Nm/kg, F = 2.6 ± 0.6 Nm/kg, p ≤ 0.01, Cohen’s d = 0.76). There were no significant sex differences in the injured limb’s RTD (M = 5.5 ± 2.1 Nm/Kg, F = 5.0 ± 2.4 Nm/Kg, p = 0.65, Cohen’s d = 0.22) but males displayed higher RTD in the uninjured limb (M = 10.4 ± 3.8 Nm/Kg, F = 8.1 ± 3.5 Nm/Kg, p = 0.025, Cohen’s d = 0.59). CONCLUSION: Six months post ACLR, males had greater peak quadriceps strength bilaterally and increased RTD in the uninjured limb compared to females with moderate to large effect sizes. However, there was no significant sex difference in RTD on the injured limb. These data suggest that females may need continued progressive resistance strength training while males may be ready to progress power-based quadriceps training strategies 6 months post ACLR. Addressing the disparity in recovery of muscle strength may reduce long-term impairments associated with osteoarthritis and subsequent ACL injury risk.