Reliability of transcranial magnetic stimulation-evoked responses on knee extensor muscles during cycling

Abstract

Transcranial magnetic stimulation (TMS) measures the excitability and inhibition of corticomotor networks. Despite its task-specificity, few studies have used TMS during dynamic movements and the reliability of TMS-derived measures has not been assessed during cycling. This study aimed to evaluate the reliability of motor evoked potentials (MEP) and short- and long-interval intracortical inhibition (SICI and LICI) on vastus lateralis and rectus femoris muscle activity during a fatiguing single-leg cycling task. Nine healthy adults (2 females) performed two identical sessions of counterweighted single-leg cycling at 60% peak power output until failure. Five single-pulses and five short- and long-interval paired pulses delivered to the motor cortex, and two maximal femoral nerve stimulations [maximal M-wave (Mmax)], were delivered during two baseline cycling bouts (unfatigued) and every 5 min throughout cycling (fatigued). When comparing both baseline bouts within the same session, MEP{middle dot}Mmax-1 and LICI (both ICC: >0.9) were rated excellent while SICI was rated good (ICC: 0.7-0.9). At baseline between sessions, in the vastus lateralis, Mmax (ICC: >0.9) and MEP{middle dot}Mmax-1 (ICC: 0.7) demonstrated good reliability, LICI was moderate (ICC: 0.5), and SICI was poor (ICC: 0.3). Across the fatiguing task, Mmax demonstrated excellent reliability (ICC >0.8), MEP{middle dot}Mmax-1 ranged good to excellent (ICC: 0.7-0.9), LICI was moderate to excellent (ICC: 0.5-0.9), and SICI remained poorly reliable (ICC: 0.3-0.6). Overall, these results corroborate the cruciality of retaining mode-specific testing measurements and suggest that during cycling, Mmax, MEP{middle dot}Mmax-1, and LICI measures are reliable whereas SICI, although less reliable across days, can be reliable within the same session.