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  • Title: Intermittent inspiratory muscle training induces fiber hypertrophy in rat diaphragm.
    Author: Bisschop A, Gayan-Ramirez G, Rollier H, Gosselink R, Dom R, de Bock V, Decramer M.
    Journal: Am J Respir Crit Care Med; 1997 May; 155(5):1583-9. PubMed ID: 9154861.
    Abstract:
    The effects of 8 wk of moderate load intermittent inspiratory resistive loading on diaphragm contractility, and histochemistry of the diaphragm, scalenes, and gastrocnemius were studied in rats. A resistance was placed in the inspiratory port of a Hans-Rudolph valve, through which each animal breathed during 30 min/d, 5 times/wk (loaded group, n = 10). These rats were compared with animals breathing through the same device without inspiratory resistance (control group, n = 10). During loading, animals generated mean inspiratory pressures of -3.2 +/- 1.7 cm H2O with a TI/Ttot of 0.69 +/- 0.06, resulting in a tension-time index of 0.050. At the end of training, the diaphragm mass increased in loaded animals (0.17 +/- 0.01% body mass) compared with control animals (0.15 +/- 0.01%, p < 0.01), while scalene and gastrocnemius mass remained unchanged. Diaphragmatic force as well as fatigue resistance were similar in both groups, whereas time to peak tension was significantly (p < 0.01) shorter in loaded rats (18.8 +/- 1.7 ms) compared with control rats (21.2 +/- 1.8 ms), half-relaxation time remaining unchanged. Finally, hypertrophy of diaphragmatic type IIa (+19%, p < 0.01) and IIx/b (+12%, p < 0.05) was present in the loaded group. Histochemistry of the scalenes remained unchanged, whereas type IIx/b hypertrophy (+12%, p < 0.001) was observed in the gastrocnemius internus. We speculate that the latter was due to multiple escape maneuvers. We conclude that intermittent inspiratory muscle training: (1) caused fast twitch fiber hypertrophy in the diaphragm; (2) did not produce any effect in the scalenes.
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