Author(s): BERBENNI, T., GROSSIO, L., GALIGANI, M., GAMBARETTI, G., GARBARINI, F., RAINOLDI, A., BOCCIA, G., Institution: UNIVERSITY OF TURIN, Country: ITALY, Abstract-ID: 2151

INTRODUCTION:
Fatigue impairs explosive force production and compromises performance in many sport-specific actions. It is commonly defined as a time-related reduction in voluntary force-producing capacity arising from peripheral and/or central alterations. At the cortical level, voluntary movements are preceded by the Movement-Related Cortical Potential (MRCP), a slow negative potential detectable via electroencephalography (EEG) and known to be sensitive to fatigue. However, the contribution of electrocortical activity to fatigue-induced reductions in rate of torque development (RTD) remains unclear. The present study investigated cortical and peripheral changes induced by repeated rapid isometric contractions.
METHODS:
Nineteen healthy volunteers (10 females, 9 males) performed 120 rapid isometric knee extensor contractions while 64-channel EEG recorded cortical activity and high-density surface electromyography (HD-sEMG) recorded muscle activation of the vastus lateralis and medialis. Torque was quantified in 25 ms epochs (from 25 ms to 150 ms), together with root mean square (RMS) and conduction velocity (CV) derived from HD-sEMG, as well as MRCP amplitude for each contraction. Before and after the fatiguing task, maximal voluntary torque (MVT) was recorded, and femoral nerve electrical stimulations (M-wave and octet) were delivered to evaluate peripheral contractile function. The best 20 of the first 30 and last 30 contractions were averaged to obtain PRE and POST measurements.
RESULTS:
MRCP amplitude was significantly reduced at POST (p = 0.0002, n2p = 0.57). Similarly, voluntary torque and RMS (normalized to MVT and M-wave amplitude, respectively) were significantly reduced from 100 ms to 150 ms (p = 0.007, n2p = 0.08; p = 0.0179, n2p = 0.04). M-wave-normalized CV remained stable over time. Octet-evoked torque, normalized to MVT, showed an early increase within the first 25 ms (P = 0.0001, d = 1.561) and subsequently (50, 75ms) returned to pre-fatigue levels (p = 0.0537; p = 0.4166). Neural efficacy (i.e., the ratio between voluntary and evoked torque) significantly decreased at POST (p < 0.0001, n2p = 0.23).
CONCLUSION:
Repeated explosive contractions induced an impairment in RTD. However, the preservation of CV and evoked responses suggests that peripheral muscle properties did not account for this impairment. The reduction in neural efficacy and MRCP amplitude instead points toward diminished net neural drive and altered cortical motor preparation as primary contributors to the decline in explosive force production.