Am. J. Respir. Crit. Care Med., Vol 155, No. 5, May 1997, 1583-1589.
Intermittent inspiratory muscle training induces fiber hypertrophy in rat diaphragm
A Bisschop, G Gayan-Ramirez, H Rollier, R Gosselink, R Dom, V de Bock and M Decramer
Faculty of Physical Education and Physiotherapy, Department of Neuropathology, Katholieke Universiteit Leuven, Belgium.
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.
