Author(s): TIMBERT, T., MARTIN, A., AMIEZ, N., COMETTI, C., PAIZIS, C., Institution: UNIVERSITY OF BURGUNDY, Country: FRANCE, Abstract-ID: 311

INTRODUCTION:
Local vibration is an afferent-targeted intervention that, when superimposed on submaximal contractions, can modulate force output. Previous studies suggest that the effects of superimposed local vibration (SLV) on force production are intensity-dependent (1). Beyond force modulation, brief local vibration has also been shown to transiently increase corticospinal excitability (2). However, whether SLV modulates corticospinal excitability across different contraction intensities, and at spinal or cortical levels, remains unclear. Therefore, this study aimed to investigate the effects of SLV on spinal and cortical excitability during submaximal contractions performed at different contraction intensities.
METHODS:
Fourteen participants performed submaximal knee extension contractions (6s, separated by 45s of rest) across three sessions at 30%, 50% and 70% of maximal voluntary isometric contraction. Contractions were performed either under control conditions (CON) or with SLV applied to the quadricipital tendon (100 Hz, 2-3 mm). Vastus lateralis background electromyographic activity (bEMG) was recorded during contractions. Single stimulations included maximal M-waves (MMAX), motor-evoked potential (MEP), and thoracic MEP (TMEP), with MEP and TMEP matched at 30% of MMAX during CON. Per condition, 2 MMAX, 6 TMEP, and 10 MEP were collected. Condition and contraction intensity order was randomized.
To account for peripheral changes, spinal excitability was assessed by normalizing the peak-to-peak amplitude TMEP to MMAX, and cortical excitability by normalizing MEP to TMEP.
Linear mixed model with Condition (CON vs. SLV) and Intensity (30%, 50%, 70%) as fixed effects were applied to knee extension force, bEMG, and normalized neurophysiological responses (MMAX, MEP, TMEP).
RESULTS:
Knee extension force and bEMG did not differ between conditions (all p > 0.299). MMAX was unaffected by SLV (p = 0.827), contraction intensity (p = 0.491), or their interaction (p = 0.962). Spinal excitability (TMEP) showed no main effect of Condition (p = 0.386), Intensity (p = 0.083), or interaction (p = 0.978). Similarly, cortical excitability (MEP) was not influenced by Condition (p = 0.548), Intensity (p = 0.235), or their interaction (p = 0.910).
CONCLUSION:
Superimposed local vibration did not modulate cortical or spinal excitability across contraction intensities, suggesting that brief SLV does not alter the overall balance between excitation and inhibition within the corticospinal pathway. Future studies should examine longer SLV exposure durations or fatiguing conditions to better characterize its neuromodulatory effects.
(1) Spiliopoulou et al., “Tendon vibration during submaximal isometric strength and postural task”, Eur J Appli Physiol, 2012.
(2) Rosenkranz et al., “Differential effect of muscle vibration on intracortical inhibitory circuits in humans”, J Physiol, 2003.