Strenuous exercise-induced alterations of muscle fiber cross-sectional area and fiber-type distribution in steroid myopathy rats.
OBJECTIVE
To investigate the effect of exercise intensity on the muscle histopathology in steroid myopathy rats.


METHODS
Eight-week-old male Wistar rats (n=40) were divided into four groups: a control group (n=4), steroid-only group (n=12), moderate exercise + steroid group (n=12), and a high-intensity exercise + steroid group (n=12). Five weeks after triamcinolone injection, the soleus muscle (SOL) and extensor digitorum longus muscle (EDL) were removed and stained for adenosine triphosphatase (ATPase). The muscle fiber area and fiber type distribution of each fiber type were measured.


RESULTS
In the high-intensity exercise group, the type I fibers in the SOL and the type IIb fibers in the EDL showed significant atrophy. In the fiber distribution of the SOL, type I fibers decreased in the steroid-only group and high-intensity exercise group as compared with the control, whereas there was a significant increase in the moderate exercise group vs. the steroid-only group. In the EDL, type I fibers were significantly greater in the moderate- and high-intensity exercise groups, whereas type IIb fibers significantly decreased in the moderate-exercise group as compared with the steroid-only group.


CONCLUSIONS
In rats with steroid myopathy, high-intensity exercise caused changes such as muscle atrophy. The fiber type distribution of the SOL changed from type II fibers to type I fibers in the moderate exercise group. Intensive exercise, however, resulted in transformation from type I to type II in the fiber type distribution. For the EDL, no significant fiber type changes were observed with high-intensity exercise when compared with moderate exercise.
Uchikawa
Ken
K
Department of Rehabilitation Medicine, National Hospital Organization, Murayama Medical Center, Tokyo, Japan.
Takahashi
Hidetoshi
H
Hase
Kimitaka
K
Masakado
Yoshihisa
Y
Liu
Meigen
M
D000818:Animals; D001284:Atrophy / Q000139:chemically induced; D001835:Body Weight / Q000187:drug effects; D017079:Exercise Tolerance / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018908:Muscle Weakness / Q000139:chemically induced; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology*; D009135:Muscular Diseases / Q000139:chemically induced / Q000209:etiology / Q000503:physiopathology*; D009468:Neuromuscular Diseases / Q000139:chemically induced; D010805:Physical Conditioning, Animal; D010807:Physical Endurance; D051381:Rats; D017208:Rats, Wistar; D014221:Triamcinolone / Q000009:adverse effects* / Q000494:pharmacology
D014221:Triamcinolone