Diaphragm and intercostal surface EMG and muscle performance after acute inspiratory muscle loading

We examined the effect of an acute bout of submaximal non-fatiguing inspiratory loading (IL) on maximal inspiratory pressure (MIP), and on the activation of the diaphragm (DI) and intercostals (IC) using surface electromyography (sEMG). After baseline measurements, 12 healthy subjects performed two sets of 30 inspiratory efforts at a load equivalent to 40% of their initial MIP. MIP and maximal DI and IC sEMG activity were recorded after the first and second set of IL, and 15 min after task cessation. After IL, MIP reached (±S.E.M.) 111 ± 4% (P = 0.032) of baseline values, and during MIP, DI and IC root mean square (RMS) sEMG amplitude increased significantly above baseline (143 ± 21%, P = 0.039 and 137 ± 33%, P = 0.016, respectively). The significant increase in MIP and RMS amplitude after IL suggests that MIP efforts were initially submaximal, and that prior loading enabled full activation. The changes in DI and IC RMS amplitude may also reflect an improvement in the synergy between them during these maximal efforts.