Contractile and histochemical properties of young and old medial gastrocnemius muscle after suspension hypokinesia/hypodynamia.
In order to determine if the atrophic process was different in the young and in the aged fast twitch medial gastrocnemius muscle, in which the aging process is clearly apparent, hindlimb hypokinesia/hypodynamia (H/H) was induced on rats. After 3 weeks, we measured speed-related indices, tension indices and tension producing capacities. Fiber type composition and fiber cross-sectional area were also determined. The body weight and muscle weight decreased. The ratio of muscle weight to body weight was greater in the 3-month-old control group than in the 22-month-old group. However, the ratio was not altered by H/H. In both groups, contraction time, half relaxation time and twitch tension did not vary with H/H but maximally developed tension and force generated per gram of muscle were decreased. For the histochemical analysis, the medial gastrocnemius muscle was divided in its red and white parts. Fiber type composition remained the same after H/H in both parts of the muscle and in both groups of age except for an increase of the FOG fiber type proportion in the red part of the old group. Fiber cross-sectional area increased with age and decreased after the suspension except for the fast fibers in the white part of the aged muscle. The most affected group in fiber cross-sectional (SO-FOG-FG) area after suspension was the white part of medial gastrocnemius in the young group. The suspension atrophy appeared to be independent of age in the medial gastrocnemius at the contractile level whereas atrophy was greater at the histochemical level in the young muscle. With age, fiber cross-sectional area increased particularly in the red part of the muscle.
Simard
C
C
Physical Activity Sciences Laboratory, Laval University, Quebec City, Canada.
Lacaille
M
M
D000375:Aging; D000818:Animals; D005260:Female; D006651:Histocytochemistry; D009068:Movement; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains