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Contractile adaptations in the human triceps surae after isometric exercise
S E Alway1, J D MacDougall, D G Sale
1Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1989
Summary
High-intensity isometric training improved muscle contraction speed in the triceps surae. However, this enhancement in muscle function was not directly linked to changes in the sarcoplasmic reticulum-transverse tubular network within muscle fibers.
Area of Science:
- Exercise Physiology
- Muscle Biology
- Cellular Ultrastructure
Background:
- Skeletal muscle adaptations to training involve changes in contractile properties and cellular structure.
- The role of the sarcoplasmic reticulum-transverse tubular (SR) network in modulating muscle contraction speed is crucial.
- Isometric training at maximal voluntary contraction (MVC) intensity is a potent stimulus for muscle adaptation.
Purpose of the Study:
- To investigate the ultrastructural and twitch contractile characteristics of the human triceps surae following prolonged isometric training.
- To determine if changes in the SR-TT network correlate with alterations in muscle contraction dynamics after training.
Main Methods:
- Seven sedentary subjects underwent 16 weeks of unilateral isometric training at 100% MVC.
- Muscle biopsies were analyzed for fiber type, fiber area, and SR-TT network volume density.
- Twitch contractile properties (contraction time, relaxation time, peak torque) were measured before and after training.
Main Results:
- Isometric training significantly decreased twitch contraction time by ~20% in the triceps surae.
- Type I and II fiber areas increased in the soleus, and type II fibers in the lateral gastrocnemius.
- No significant changes were observed in one-half relaxation time, peak twitch torque, or fiber type percentages.
- The volume density of the SR-TT network did not significantly change in the gastrocnemius, but increased in soleus type I fibers.
- Correlations between SR-TT network changes and twitch dynamics were not statistically significant.
Conclusions:
- Isometric training at 100% MVC induces faster muscle twitch contraction times in the triceps surae.
- These functional improvements are not directly explained by alterations in the SR-TT network's volume density.
- Muscle fiber hypertrophy occurs, but the SR-TT network's role in modulating contraction speed adaptations requires further investigation.