Journal of Applied Physiology, Vol 64, Issue 3 1114-1120, Copyright © 1988 by American Physiological Society

ARTICLES

Functional and structural adaptations in skeletal muscle of trained athletes

S. E. Alway, J. D. MacDougall, D. G. Sale, J. R. Sutton and A. J. McComas
Department of Physical Education, McMaster University, Hamilton, Ontario, Canada.

Twitch contractile and ultrastructural characteristics of the human triceps surae were determined in six male strength-trained athletes, six endurance-trained athletes, six active controls, and seven sedentary controls of similar height and age. Twitch contraction time in the triceps surae complex was 20% longer in strength-trained and sedentary groups than in endurance-trained or active control groups. In the 15 subjects peak twitch torque and one-half relation time in the triceps surae were 22.6 +/- 7.9 N.m and 91.1 +/- 18.3 ms, respectively. Mean fiber area in the gastrocnemius was approximately 1.6-, 1.7-, and 2.5-fold greater in the active control, endurance-trained, and strength-trained groups, respectively, relative to the sedentary group. Despite these large differences in fiber areas, the fiber fractional volume of the sarcoplasmic reticulum-transverse tubule network averaged 3.38 +/- 0.86% and 5.50 +/- 0.94% in type I and type II fibers, respectively, in all subjects. The fractional fiber volume of cytoplasm and lipid were similar for all four groups. However, mitochondrial volume was approximately 30% lower in both fiber types of the strength-trained group relative to the other groups. This implies that with exercise-induced hypertrophy, the sarcoplasmic reticulum, cytoplasm, and lipid components increase proportionately with contractile protein, whereas the mitochondrial fraction does not. The proportion of type I fibers in the soleus, medial gastrocnemius, and lateral gastrocnemius was 75.2 +/- 8.3, 58.5 +/- 6.1, and 52.4 +/- 4.2%, respectively, and was similar in all subject groups. The results demonstrate that twitch duration is prolonged in strength-trained athletes relative to endurance athletes.(ABSTRACT TRUNCATED AT 250 WORDS)

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