Abstract
Determining the oxygenation level of skeletal muscle is an effective non-invasive method of evaluating its physiological changes. Nevertheless, the relationship between muscle fiber composition and intramuscular oxygenation is still unclear. In the present study we examined the differences in muscle fiber composition and their relationship to muscle oxygenation levels by comparing power lifters (Training group), who regularly engaged in muscular resistance training, with ordinary healthy people (Control group). The vastus lateralis muscle oxygenation level was measured via near infrared continuous wave spectroscopy, and muscle tissues were collected and used for histochemical analyses in order to calculate muscle fiber compositions. When the rate of decrease in muscle oxygenation after performing a single squat at 50 and 80% of the participants’ maximal lifting weight (MLW) was examined, the rate of decrease was significantly higher at 80% of MLW than at 50% of MLW in Training group, and was significantly higher in the Training group than in the Control group. Moreover, after performing multiple squat movements at 80% of MLW, compared with the Control group, the Training group showed a significant delay in the time it took for their muscle oxygenation level to recover to 50% of its original level at resting time (T1/2). A significant correlation between the occupancy of Type IIa fiber and T1/2, or between an average cross-sectional area of muscle fibers and T1/2 was noted. The present study demonstrated that in the Training group, in a cross-sectional area of Type IIa fiber that had increased, the decreased muscle oxygenation level due to performing squat exercises exhibited a delay in recovery at the resting time, suggesting that the amount of oxygen consumption was increased in the Training group because the crosssectional area of Type IIa fiber was larger, compared with the Control group.
Highlights
Skeletal muscle is composed of several types of muscle fibers such as Type I, Type IIa, and Type IIx, all of which differ in contractile and metabolic characteristics
The physiological reactions of the vastus lateralis muscle in the right thigh caused by performing a squat included a constriction of arterioles and blood capillaries due to an increase in intramuscular pressure associated with muscular contraction, microcirculatory dysfunction, and decreased peripheral muscle blood flow
The changes in the types of muscle fibers recruited were associated with the changes in the capacity of oxygen consumption by mitochondria, which brought about changes in muscle oxygenation
Summary
Skeletal muscle is composed of several types of muscle fibers such as Type I, Type IIa, and Type IIx, all of which differ in contractile and metabolic characteristics. The exercise-induced stimulation from muscular resistance increases muscle mass and strength, changes muscle composition and improves muscle function. This process is thought to be the after-effect of hypertrophy of muscle fiber size, an increase in muscle fiber number, accretion of connective tissue around muscle fiber, or some combination of these [1]. Resistance training under local hypoxia reportedly induces muscle hypertrophy (Type II fiber) and increases muscle strength [2,3,4,5]. The extension of an ischemic interval induced by resistance training attracts hypoxia and affects muscle structure and function
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