Alterations in human muscle fibre type distribution induced by acute exercise

Abstract

Fibre type distributions in the vastus lateralis muscles of six male subjects (age 18 to 22 years) have been compared at rest and during exercise. Exercise consisted of one leg cycling at 60% VO2 max (one leg) for 120 min. The increased contractile activity was associated with a 28.8% (p less than 0.05) decrease in the distribution of Type I fibres in the exercised leg. This change in fibre type distribution was manifested early in the exercise (15 min), and was also evident in muscle samples obtained after 60 and 120 min of activity. Reductions in the Type I fibre distribution was accompanied by an increase in the Type II fibres, specifically the Type IIA distribution (p less than 0.05). Comparable alterations in the specific fibre distribution were also found in the non exercising leg. These observations indicate that alterations in the muscle cell induced either directly or indirectly by the increased contractile activity interact with normal pre-incubation conditions to effect changes in the stability of the myofibrillar ATPase reaction. Specifically, it appears that a percentage of the Type I fibre population becomes acid labile and alkali stable.

Influence of exercise on the fiber composition of skeletal muscle

“…(1983) after 15 rain of moderately intense exercise. The question arises as to what produced the disparity between our results and those of Ball et al (1983). The type, duration, and intensities of exercise were too similar for these to be a likely cause of the discrepancy.…”

“…The high intensity exercise studies are different from those of Ball et al (1983). Muscle glycogen decreased in all experiments.…”

“…Exercise induced changes in ionic composition of muscle, for example K +, are relatively small when compared to those that inactivate myosin from white or red muscle (Sreter et al 1966). The observation of Ball et al (1983) of changes in fiber composition of both the active and inactive leg is difficult to rationalize with a locally induced modification ofpH or ionic composition.…”

“…The times for obtaining the muscle samples were also similar with our first sample during prolonged exercise being taken after 5 or 20 min of exercise whereas that of Ball et al (1983) was obtained after 15 rain of exercise. Thereafter the times for obtaining muscle samples during exercise were similar with the exception that we obtained final samples after 3 h of exercise in some subjects as compared to 2 h by Ball et al (1983). Since both experiments studied man and obtained samples from VLM, species and muscle differences Means +_ SD for number of rats in parentheses.…”

“…The report of Ball et al (1983) prompted us to re-examine biopsy samples that had been obtained from the VLM of subjects in earlier studies of motor unit engagement patterns during different intensities and durations of exercise. Initially no attempt was made to discern whether shifts in the percent fiber composition occurred in these samples.…”