The Effects of Training on Muscle Structure and Function in the Human Triceps Surae

Abstract

<p>The relationship between fibre structural adaptation to strength and endurance training and the fibre physiological adaptations to these training procedures has been unexplored in humans. Methodological difficulties in fibre identification have prevented these investigations since traditional fibre classification techniques utilize various enzymes which are inactivated during fixation for electron microscopy. However, myoglobin is unaffected by glutaraldehyde fixation.</p> <p>In this study, structural and functional properties of the triceps surae were studied to determine the effects of endurance and strength training on: 1. the relationship between the fibre volume of sarcoplasmic reticulum and transverse tubules (SR) to the time to peak torque (TPT) of the isometric twitch; and 2. the relationship between fibre volume of mitochondria to muscle fatiguability. Needle biopsies were obtained from the gastrocnemii and soleus muscles and fibre types were classified for electron microscopy analysis on the basis of their myoglobin content. Electron micrographs were taken from the interior of 35 type I and 35 type II fibres of each muscle and were analyzed blindly by a stereological short-line test. Contractile properties were obtained from the isometric twitch in the triceps surae complex and separately from the gastrocnemii and soleus.</p> <p>Structural and contractile properties were examined in two subject groups: 1. a cross-sectional group made up of 6 subjects each of active controls, strength athletes and endurance athletes (N=18); and 2. a longitudinal training group (N=7) whom, in a unilateral training model, exercised one leg with a strength protocol and the other leg with an endurance protocol for 16 weeks.</p> <p>The results indicated that TPT was greater (p<.05) following chronic strength vs. endurance training (119.0 vs. 95.3 ms respectively) but TPT was decreased (p<.01) by 24% and 16% following short-term strength and endurance training respectively. The fibre volume of SR was not altered by strength or endurance training in either cross-sectional or longitudinal training groups. Resistance to fatigue at an absolute load was increased by 1.7 fold after short-term strength training and by 3.5 fold after short-term endurance training. Mitochondria volume was unaffected by either training protocol in the gastrocnemii but lower (p<.05) in type I fibres of the soleus after short-term strength (5.76%) vs. short-term endurance training (7.26%).</p> <p>It was concluded that functional adaptation to strength or endurance training may occur independent of fibre organelle volume adaptation to these training programs.</p>