Abstract
BACKGROUND: Motor training with audible cues can improve motor performance; however, few studies have examined the effect of synchronized audible cues during exercise. This study aimed to determine the immediate effects of terminal knee extension (TKE) exercise with audible cues on motor unit behavior, including motor unit action potential (MUAP) and motor unit firing rate (MUFR). The test-retest reliability and minimal detectable change (MDC) were evaluated. METHOD: Thirty healthy adults were randomly enrolled to two groups: TKE exercise with audible cues and without. A Trigno-Galileo sensor of electromyography (Delsys, Inc.) was used to collect vastus medialis (VM) muscle activity during a single-leg squat test before and after TKE exercise. Metronome beats (60 beats/minute) were assigned to provide rhythm during TKE exercise in audible-cue group. In the control group, participants performed TKE exercises at a self-paced speed. After 3 days, 15 participants voluntarily returned to test VM activity again. A two-way mixed ANOVA (2 × 2; group × time) was used to examine main and interaction effects, and independent t-tests were used to compare mean changes between groups. ICC and Spearman correlation tests were used to analyze test-retest reliability of MUAP and MUFR parameters. RESULTS: After TKE exercise, the final data from 27 participants (13 experimental, 14 control) were analyzed. Both groups exhibited a decrease in peak and average MUAP. A significant reduction was observed (p = 0.03) in group without audible cues. The MUFR did not significantly change following TKE exercise in either group. Moderate test-retest reliabilities were 0.70 and 0.58 and MDC were 0.82 mV and 0.65 mV for the peak and average MUAP, respectively. CONCLUSION: Incorporating rhythm may promote neuromuscular control and cause preserves to the MUAP of VM muscle, but not to MUFR. TKE exercises synchronized with metronome beats may be an effective strategy to promote VM function in individuals with knee dysfunction because of its safety, low cost, and ease of use during rehabilitation. Evaluating TKE with audible cues in individuals with knee dysfunction also warrants further investigation. TRIAL REGISTRATION: NCT06565325 (21 August 2024, first available on ClinicalTrials.gov).