Quadriceps Rate of Torque Development Is More Impaired Than Strength 4 to 12 Months Post-ACLR in Collegiate Athletes

Abstract

Background:

Quadriceps neuromuscular impairments are common after anterior cruciate ligament reconstruction (ACLR). Quadriceps function is typically characterized by peak torque (PT) assessment, and reported as limb symmetry index (LSI). Even when PT LSI is restored, high reinjury rates and abnormal biomechanics persist. Quadriceps rate of torque development (RTD) may have significant functional relevance, but direct comparisons of PT and RTD recovery post-ACLR are lacking.

Hypothesis:

Quadriceps RTD LSI will recover more slowly than PT LSI post-ACLR.

Study Design:

Longitudinal cohort study.

Level of Evidence:

Level 3.

Methods:

42 athletes 4, 8, and 12 months post-ACLR completed maximal and rapid voluntary isometric knee extension contractions with both limbs. RTD was calculated as torque-time curve slopes from onset to 100 ms (RTD_0-100), 100 ms to 200 ms (RTD_100-200), onset to 200 ms (RTD_0-200), and 20% to 80% of PT (RTD_20-80). Between-limb differences were assessed with paired t tests (Bonferroni adjusted P < 0.003). Linear mixed models assessed the effect of time and variable on differences in PT and RTD LSIs and variable-by-time interactions. Least square mean differences and 95% CIs between PT and RTD LSIs are reported.

Results:

Significant between-limb asymmetries were observed at all timepoints (P < 0.001) for all PT and RTD variables. No variable-by-time interactions were detected. There was a main effect of both time (P < 0.001) and variable (P < 0.001). RTD_0-100 LSI was not significantly different than PT LSI (P = 0.36). RTD_100-200, RTD_0-200, and RTD_20-80 LSIs were less than PT LSI by 10.4% (6.0, 14.9), 7.3% (2.8, 11.7), and 15.7% (11.2, 20.1), respectively (P < 0.002).

Conclusion:

In collegiate athletes, RTD impairments are greater than PT impairments from 4 to 12 months post-ACLR, but the specific RTD metric is important.

Clinical Relevance:

Increased focus on the development and implementation of interventions to improve quadriceps RTD, beginning earlier post-ACLR, is warranted.