Intermittent inspiratory muscle training induces fiber hypertrophy in rat diaphragm.
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.
Bisschop
A
A
Faculty of Physical Education and Physiotherapy, Department of Neuropathology, Katholieke Universiteit Leuven, Belgium.
Gayan-Ramirez
G
G
Rollier
H
H
Gosselink
R
R
Dom
R
R
de Bock
V
V
Decramer
M
M
D000222:Adaptation, Physiological; D000251:Adenosine Triphosphatases / Q000032:analysis; D000818:Animals; D001835:Body Weight; D001945:Breathing Exercises; D003964:Diaphragm / Q000033:anatomy & histology / Q000737:chemistry / Q000166:cytology* / Q000502:physiology; D004558:Electric Stimulation; D006651:Histocytochemistry; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000737:chemistry; D009929:Organ Size; D011312:Pressure; D051381:Rats; D017208:Rats, Wistar; D012132:Respiratory Muscles / Q000033:anatomy & histology / Q000502:physiology
D000251:Adenosine Triphosphatases