Assessment of Diaphragm and External Intercostals Fatigue from Surface EMG using Cervical Magnetic Stimulation

This study was designed: (1) to test the reliability of surface electromyography (sEMG) recording of the diaphragm and external intercostals contractions response to cervical magnetic stimulation (CMS), (2) to examine the amount and the types of inspiratory muscle fatigue that developed after maximum voluntary ventilation (MVV) maneuvers.Ten male college students without physical disability (22.1±2.0 years old) participated in the study and each completed a control (quiet breathing) trial and a fatigue (MVV maneuvers) trial sequentially. In the quiet breathing trial, the subjects maintained quiet breathing for five minutes. The subjects performed five maximal static inspiratory efforts and received five CMS before and after the quiet breathing. In the MVV trial, subjects performed five maximal inspiratory efforts and received five CMS before, immediately after, and ten minutes after two sets of MVV maneuvers performed five minutes apart. Maximal inspiratory pressure (PI_max), sEMG of diaphragm and external intercostals during maximal static inspiratory efforts and during CMS were recorded. In the quiet breathing trial, high intraclass correlation coefficients (ICC=0.95-0.99) were observed in all the variables. In the MVV trial, the PI_max, the EMG amplitude and the median power frequency during maximal static inspiratory efforts significantly decreased in both the diaphragm and the external intercostals immediately after the MVV maneuvers (P0.05). It is concluded that the sEMG recordings of the diaphragm during maximal static inspiratory efforts and in response to CMS allow reproducible sequential assessment of diaphragm contractility. MVV maneuvers resulted in inspiratory muscles fatigue, possibly central fatigue.