Intercostal electromyographic responses to multi-site chest wall vibration at an optimal frequency

High-frequency mechanical vibration facilitates respiratory muscle activity via muscle spindle afferents. Although synchronised multi-site chest wall vibration enhances ventilation, the associated intercostal electromyographic (EMG) responses and their contribution to ventilatory changes remain unclear. This study investigated the effects of multi-site chest wall vibration on intercostal muscle activation and ventilation in healthy adults.

Twenty healthy adults underwent phase-synchronised chest wall vibration delivered to four or eight intercostal sites during inspiration and expiration. Surface EMG of inspiratory and expiratory intercostal muscles, tidal volume (VT), respiratory rate, and thoracoabdominal motion were recorded. EMG amplitudes were normalised to maximal voluntary contraction (%MVC), and ventilatory variables were compared across conditions.

Multi-site chest wall vibration significantly increased intercostal EMG activity during inspiration and expiration. Eight-site stimulation elicited greater EMG responses than four-site stimulation in both directly stimulated and adjacent intercostal muscles (4th inspiratory intercostal: 17.65 vs. 11.59%MVC; 3rd: 15.35 vs. 10.54%MVC; p < 0.01). These changes were accompanied by increases in VT (0.86 vs. 0.65 L, p < 0.01), minute ventilation (9.63 vs. 7.33 L/min, p < 0.05), and rib cage displacement (183.6 vs. 157.7%, p < 0.05), without changes in respiratory rate or abdominal motion. Changes in intercostal EMG were positively correlated with VT (inspiratory: r = 0.524; expiratory: r = 0.439; p < 0.01).

Synchronised multi-site chest wall vibration enhances intercostal muscle activation and ventilation, likely via spatial summation of proprioceptive input, increasing respiratory motor output. This approach may represent a promising non-invasive strategy to augment ventilation.