Words Matter! The Effects Of Instruction On Quadriceps Rate Of Torque Development After ACL Reconstruction

INTRODUCTION: Emerging evidence suggests that evaluating quadriceps rate of torque development (RTD) is critical after anterior cruciate ligament reconstruction (ACLR). However, agreement on how to best evaluate this metric of explosive strength after ACLR remains elusive. Previous work in healthy cohorts shows that short duration (1 s) “fast” contraction efforts result in significantly higher RTD compared to “hard and fast” 5 s contractions. The influence of verbal instruction and contraction duration remains unexplored in ACL populations and the majority of ACL research derives RTD from "hard and fast” trials intended to measure peak strength. Identifying which protocol elicits higher measures of quadriceps RTD after ACLR will help standardize testing procedures and provide practitioners with valuable insight on how to best evaluate explosive strength. PURPOSE: To evaluate differences in maximal quadriceps RTD measured during “fast” (1 s) (Protocol A) compared to “hard and fast” (5 s) (Protocol B) contractions in individuals after ACLR. METHODS: 20 participants (20.6 ± 2.0 years) 1-5 years from ACLR (3.0 ± 1.2 years) performed “fast” (1 s) and “hard and fast” (5 s) maximal effort isometric knee extensor contractions on an isokinetic dynamometer. Torque data was sampled at 1500 Hz and filtered using a fourth-order, low-pass Butterworth zero-lag digital filter with a 50 Hz cut-off frequency. RTD was calculated as the slope of the torque-time curve during the first 50 ms, 100 ms, and 200 ms from contraction onset. RTD was averaged across trials. Paired samples t-tests, mean differences, and effect sizes were calculated to compare differences in mean RTD. RESULTS: Table 1 TABLE 1: - The Influence of Test Protocol on Quadriceps Rate of Torque Development Time Epoch Protocol A(N·m/s) Protocol B(N·m/s) p ES (Cohen’s d) Mean Difference (N·m/s) 0 - 50 ms 764.1 ± 305.5 515.2 ± 299.7 < .001 0.94 (0.40 - 1.46) 248.8 (124.5 – 373.2) 0 - 100 ms 827.7 ± 327.8 629.2 ± 304.5 < .001 0.88 (0.35 - 1.39) 198.6 (92.8 – 304.3) 0 - 200 ms 653.3 ± 248.2 560.9 ± 199.8 .002 0.79 (0.27 - 1.28) 92.4 (34.7 – 150.1) Data are presented as mean ± standard deviation for the anterior cruciate ligament (ACL) involved limb. Effect sizes and mean differences include the 95% confidence intervals. p ≤ 0.05; ES = effect size. CONCLUSION: "Fast" (1 s) contractions elicit higher maximal quadriceps RTD compared to “hard and fast” (5 s) in individuals after ACLR. Practitioners looking to measure maximal quadriceps RTD should consider using independent testing trials focused on short duration “fast” contraction efforts.