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Effect of swim exercise training on human muscle fiber function
R H Fitts1, D L Costill, P R Gardetto
1Department of Biology, Marquette University, Milwaukee, Wisconsin 53233.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 1, 1989
Summary
Collegiate swim training alters muscle fiber function, increasing slow fiber speed and decreasing fast fiber speed. Intensified training further reduces fast fiber speed, with effects reversing upon detraining.
Area of Science:
- Exercise Physiology
- Muscle Biology
- Biochemistry
Background:
- Skeletal muscle adaptations to training are crucial for athletic performance.
- Understanding fiber-type-specific responses to swim training is essential for optimizing conditioning protocols.
- Previous research has focused on endurance or strength training, with less emphasis on the specific demands of competitive swimming.
Purpose of the Study:
- To investigate the effects of a typical collegiate swim-training program and a short-term intensified training period on the contractile properties of slow-twitch (type I) and fast-twitch (type II) muscle fibers.
- To analyze changes in peak tension (Po), calcium sensitivity (pCa-force relationship), and maximal shortening speed (Vmax) in response to different swim training stimuli.
- To explore potential underlying molecular mechanisms, such as myosin expression, responsible for observed functional adaptations.
Main Methods:
- Single muscle fibers (type I and type II) were isolated from the deltoid muscle of collegiate swimmers.
- Fiber contractile properties, including peak tension (Po), force-velocity relationships (pCa-force), and maximal shortening speed (Vmax), were measured using mechanical testing.
- Fibers were analyzed before and after a 10-week typical training period, a subsequent 10-day intensified training period, and a detraining phase.
- Mitochondrial content was assessed via citrate synthase activity.
Main Results:
- Swim training increased mitochondrial enzyme citrate synthase activity but did not alter peak tension (Po) in either fiber type.
- Type II fibers were larger than type I fibers; however, 10-day intensified training reduced type II fiber diameter.
- Swim training shifted the pCa-force relationship in type I fibers, indicating altered calcium sensitivity, and significantly modified Vmax in both fiber types (increased in type I, decreased in type II).
- Intensified training further decreased type II fiber Vmax, while detraining normalized Vmax in both fiber types.
- Myosin expression changes are proposed as the mechanism for altered Vmax.
Conclusions:
- Collegiate swim training induces functional adaptations in muscle fibers, altering calcium sensitivity and shortening velocity without changing peak force.
- Intensified training imposes further specific adaptations on fast-twitch fibers, impacting their shortening velocity.
- These adaptations suggest a plasticity in myosin expression, enabling fibers to better match the demands of swim training, with reversibility upon detraining.