Abstract
The effect of 2-week, high-intensity running and a 2-week immobilization on muscle fiber type composition of the plantaris muscle from 18 female, 6-month-old Wistar rats (running, n = 6; immobilization, n = 6; sedentary control, n = 6) was bio- and histochemically investigated. The high-intensity treadmill running began with 20 min (32 m/min, 0% gradient, 75% VO2 max), up to 50 min/day. Right hind limbs were immobilized by an external fixation procedure for 13 days. Muscle mass of the plantaris muscle in the immobilized groups was reduced by 16% in comparison with the sedentary control group. High-intensity running and immobilization increased both mRNA and protein levels of matrix metalloproteinase type 2 (MMP-2) in plantaris. Running and immobilization decreased the percentages of transverse sectional area of fast-twitch glycolytic (FG) type IIb fibers, running increased relative cross-sectional area of fast-twitch oxidative glycolytic (FOG) type IIa muscle fibers, whereas immobilization increased relative cross-sectional area of slow-twitch oxidative (SO) muscle fibers (type I). Our results suggest that both high-intensity running and immobilization are enough to induce overwhelming changes in plantaris.
Highlights
The skeletal muscle is an adaptive tissue that rapidly undergoes changes after both overuse and disuse, as well as under pathological conditions
No differences existed in animal body weights between the two experimental groups at the beginning of the experiments, but 2 weeks of immobilization resulted in a decrease in plantaris muscle weight
The primary finding of the present study was that the plantaris muscle of female rats, the type IIb fibers, undergo changes in response to high-speed running or immobilization
Summary
The skeletal muscle is an adaptive tissue that rapidly undergoes changes after both overuse (i.e., intense exercise, high-speed running) and disuse, as well as under pathological conditions. Overuse and disuse might both result in significant damage to the skeletal muscle morphologically, biochemically, and functionally[1]. Matrix metalloproteinases (MMPs) are a family of at least 24 proteolytic enzymes that belong to a large group of zinc proteolytic enzymes. MMPs are crucially involved in the turnover of extracellular matrix (ECM) components[2]. MMP-2 was shown to play a key role in maintaining structure and activity of basement membrane (BM) components during muscle pathologies such as inflammatory myopathies[3,4]. While the role of MMP-2 in development, growth, and repair of skeletal muscles has Carmeli and Haimovitch: Immobilization and High-Speed Running
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