Fiber Types and Metabolic Potentials of Skeletal Muscles in Sedentary Man and Endurance Runners*

Abstract

This description of some of the present knowledge on skeletal muscle fibers, their metabolic potentials, and their interplay with the degree of physical activity has revealed that skeletal muscle of man has a very large capacity for adaptation. Moreover, this adaptability appears to be of utmost importance for the metabolic response as well as for performance. Although all this is true, it should not distract us from the fact that we are lacking the most important information. The questions that need to be answered are: What triggers the changes to take place? Which are the regulatory mechanisms?

Hypothesis on the Pathogenesis of Idiopathic Scoliosis

“…Others believed that the increased myoelectric activities on the convex side were only a secondary effect of the muscles adapting to a higher load demand in larger curves (Zetterberg et al, 1984). This would be consistent with the reported findings of differences in the morphology of the paravertebral muscles between the left and right sides ( Saltin et al, 1977;Spenser & Eccles, 1976;Wong et al, 1980;Yarom & Robin, 1979). However, the increase of type 1 muscle fibres on the convex side can be explained on the basis of muscle denervation ( Ford et al, 1984;Webb, 1973Webb, & 1981Zetterberg et al, 1984), produced by an alteration of the motor drive arising at the spinal cord level, either from altered sensory input at the same level ( Pincott, 1980;Pincott & Taffs, 1982; or from a central mechanism ( Barrack et al, 1984;Dubousset et al, 1982;Michelsson, 1965;Whitecloud et al, 1984).…”

Changes in passive ankle stiffness and its effects on gait function in people with chronic stroke

“…An equally plausible conclusion is that repetitive exercise promoted changes in fiber-type distribution [39][40][41][42], i.e., an increase in the proportion of slow-to-fast twitch fibers; since the former type has a smaller diameter, it may have led to a decrease in the volume of the muscle undergoing passive stretching. Yet another possibility is that the PAS-altering mechanism was via changes in the thixotropic properties of antagonist muscles [43].…”

Cardiovascular Adjustments to Gravitational Stress

“…Disuse atrophy preferentially affects red fibers in general (42) and postural muscles, which contain a high proportion ofred or slow-twitch fibers (288). The atrophy is reversible; muscle mass is restored relatively rapidly (-2 wk) after experimental immobilization, but postural muscles (e.g., soleus) may require 3-4 mo to regain full strength (42).…”