The effect of training on strength and endurance of the diaphragm in quadriplegia.

The diaphragmatic electromyogram was used to detect fatigue of the diaphragm in six chronic quadriplegics while they breathed for 10 minutes against a variety of inspiratory resistances. The maximum static inspiratory mouth pressure was measured at functional residual capacity (Pmmax) and from the electromyogram the critical inspiratory mouth pressure that developed in each inspiration (Pmcrit) below which electromyographic changes of diaphragmatic fatigue do not develop was estimated. The measurements were repeated after 8, 12 and 16 weeks of inspiratory muscle training consisting of inspiring for a period of 30 minutes daily, six days a week, against a resistance just sufficient to produce the electromyographic changes of fatigue. A significant and progressive increase in Pmmax and Pmcrit was found during the training. It was concluded that (1) quadriplegics are predisposed to the development of inspiratory muscle fatigue due to reduced muscle strength and reduction in endurance, and (2) in these patients inspiratory muscle training increases both strength and endurance, and protects against fatigue.