Proceedings of The Physiological Society

University College Cork (2004) J Physiol 560P, PC10

Communications

THE EFFECT OF AN ACUTE BOUT OF NON-FATIGUING INSPIRATORY MUSCLE LOADING UPON DIAPHRAGM AND INTERCOSTAL SURFACE EMG AND MUSCLE PERFORMANCE IN HEALTHY HUMANS

Hawkes,Emma Zoe; Nowicky,Alexander ; McConnell,Alison ;

1. Department of Sports Science, Brunel University, Middlesex, United Kingdom. 2. Department of Health Sciences, Brunel University, Middlesex, United Kingdom.


Volianitis et al. (2001) reported that maximal inspiratory pressure was increased by 10% following prior inspiratory loaded breathing at 40% maximal inspiratory pressure (MIP). The aim of the present study was to characterise the effect of an acute bout of non-fatiguing inspiratory muscle loading on the activation of the diaphragm and intercostals using surface electromyography (EMG). Twelve healthy volunteers gave informed consent to participate in the study, which was approved by Brunel University ethics committee. We recorded surface EMG from the diaphragm, where electrodes were placed in the lowest intercostal space at the posterior-axillary line, and the intercostals, in the 6th intercostal space at the mid-clavicular line, during measurement of MIP at residual volume. Mouth pressure was measured during a maximal inspiratory effort, performed against an occluded airway. After baseline measurements, subjects performed two sets of 30 loaded inspiratory efforts set at a resistance of 40% of the subjects initial MIP (Volianitis et al. 2001). A decreased breathing frequency was adopted, in order to avoid hyperventilation and consequent hypocapnia. Measurements were taken immediately after the first and second set of loaded breathing, and 15 min after cessation of the breathing task. Data presented as means ±S.E.M., and compared using paired t tests. MIP reached (mean ±SEM) 111 ±4.1% (P<0.05) of baseline values after the loaded breathing protocol, returning to near baseline levels after 15 min. During maximal inspiration both diaphragm and intercostal root mean square (RMS) amplitude increased significantly above baseline after the first loaded breathing set (141 ±18.7%, P<0.05 and 143 ±33%, P<0.05, respectively) and in the diaphragm by a further 2% and in the intercostals by an additional 24% after the second set. After 15 min RMS amplitude was still elevated from baseline in both the diaphragm and intercostals (155 ±30%, and 148 ±25.5%, respectively). The significant increase in MIP and RMS amplitude after loaded breathing suggests a potentiation in neuromuscular pathways of the inspiratory muscles. The increased intercostal RMS may also imply that diaphragm activity during loaded exercise is lightened by the recruitment of extra-diaphragmatic muscles and the augmentation of MIP provides evidence of increased synergistic coordination. In addition, an increase in synaptic excitability at either the motor cortex and/or the spinal phrenic motoneurons may have been responsible for facilitation during the inspiratory efforts.

Where applicable, experiments conform with Society ethical requirements