Specificity and reversibility of inspiratory muscle training

The purpose of this study was to evaluate the pressure-flow specificity of adaptations to inspiratory muscle training (IMT), in addition to the temporal effects of detraining and reduced frequency of training upon these adaptations.

Twenty-four healthy subjects were assigned randomly to one of four groups (A: low-flow-high-pressure IMT; B: high-flow-low-pressure IMT; C: intermediate flow-pressure IMT; and D: no IMT). Subjects performed IMT 6 d.wk(-1) for 9 wk, and inspiratory muscle function was evaluated at baseline and every 3 wk. Groups A, B, and C were then assigned randomly to either a maintenance group (M) (IMT 2 d.wk(-1) ) or a detraining group (DT) (no IMT). Inspiratory muscle function was reassessed at 9 and 18 wk post-IMT.

At 9 wk, group A exhibited the largest increase in pressure, B a large increase in flow, C more uniform increases in pressure and flow, and D no changes in pressure or flow. Maximum inspiratory muscle power increased in groups A, B, and C by 48 +/- 3%, 25 +/- 3%, and 64 +/- 3%, respectively (mean +/- SEM, P < or = 0.01). Maximum rate of pressure development increased in groups A, B, and C by 59 +/- 1%, 10 +/- 1%, and 29 +/- 1%, respectively ( P < or = 0.01). A decrease in inspiratory muscle function was observed at 9 wk post-IMT in DT. Inspiratory muscle function plateaued between 9 and 18 wk but remained above pre-IMT values. Group M retained the improvements in inspiratory muscle function.

These data support the notion of pressure-flow specificity of IMT. Detraining resulted in small but significant reductions in inspiratory muscle function. Reducing training frequency by two thirds allowed for the maintenance of inspiratory muscle function up to 18 wk post-IMT.