Effect of superimposed local vibration on neuromuscular fatigue during high-intensity intermittent isometric contractions in healthy adults

Afferent stimulation with local vibration during low or moderate submaximal voluntary contractions has been shown to transiently enhance muscle force development. However, the effects of superimposed local vibration (SLV) during high-intensity fatiguing contractions remain unclear. This study investigated whether SLV applied to the quadriceps tendon during a high-intensity intermittent isometric task would affect muscle force development and neuromuscular fatigue. Fifteen participants performed 20 isometric knee extensions (15-s effort/15-s rest) at 70% of their maximal voluntary isometric contraction (MVIC) on two separate days, randomly assigned to either a control condition (CON) or with SLV (100 Hz, 2-3 mm) applied during contraction. Performance was assessed using the torque time integral (TTI), time to task failure (T_FAILURE), and quadriceps electromyographic (EMG) activity. Neuromuscular fatigue was evaluated via MVIC and twitch force evoked by femoral nerve stimulation before and up to 30 min after the task. No significant differences were observed between conditions for TTI (<i>P</i> > 0.635, <i>d</i>_z = 0.015) or T_FAILURE (<i>P</i> = 0.679, <i>d</i>_z = 0.109). Following the fatiguing protocol, MVIC decreased immediately and partially recovered by 30 min (<i>P</i> < 0.001, <i>d</i>_z = 1.587), whereas potentiated neuromuscular responses remained reduced throughout recovery (<i>P</i> < 0.007, <i>d</i>_z = 0.758), with no differences observed between conditions (all <i>P</i> > 0.208). Central neural activation parameters, including voluntary activation and normalized EMG activity, remained unchanged (all <i>P</i> > 0.073). These findings indicate that SLV does not enhance torque sustainability, delay fatigue onset, or mitigate neuromuscular fatigue during high-intensity intermittent isometric contractions in healthy adults.<b>NEW & NOTEWORTHY</b> This study investigated the effects of superimposed local vibration (SLV) during a fatiguing intermittent isometric protocol involving high-intensity contractions [70% maximal voluntary isometric contraction (MVIC)]. SLV did not alter the torque-time integral or the duration of exercise before task failure. In addition, neuromuscular fatigue responses evaluated up to 30 min after exercise were comparable between conditions. These findings indicate that intermittent SLV does not enhance the capacity to sustain force or mitigate fatigue during high-intensity isometric exercise in healthy adults.