Maximal shortening of inspiratory muscles: effect of training

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Abstract
Normal subjects can increase their vital capacity by appropriate training. Whether that change can be achieved by greater maximal shortening of the inspiratory muscles without concomitant increases in peak static inspiratory pressures was tested. Healthy volunteers (16) participated in the study; 8 were randomly assigned to make 20 inhalations to total lung capacity, held for 10 s with the glottis open, each day for 6 wk; the remainder served as nontraining controls. Before and after the 6-wk study period, multiple determinations were made of lung volumes and of curves relating lung volume to maximal static inspiratory (and expiratory) pressure. Control subjects had no significant changes from base line in any variable. In the training group, the mean vital capacity increased 200 .+-. 74 ml (P < 0.05) or 3.9 .+-. 1.3% (P < 0.02), without a significant change in residual volume. After training, the mean maximal inspiratory pressure at the airway opening (PI) at a lung volume equal to the base-line total lung capacity was 27 .+-. 8 cmH2O in this group (vs. 0 before training; P < 0.02). Values of PI in the mid-vital capacity range did not change. In response to appropriate training stimuli inspiratory muscles can contract to shorter minimal lengths, a capacity potentially important in progressive pulmonary hyperinflation.