Principles of Skeletal Muscle Adaptations

Some questions and answers on the principles of skeletal muscle adaptations during training and exercise.

1. Analyze the influences on muscle fiber type with reference to genetics and training.

• Sports do not influence average muscle fiber type; athletes excel at different activities because of their muscle fiber types
• Genetics influences muscle fiber type
• Training influences muscle biochemistry
• Myosin isotomes do not change due to training, its genetically determined
• Endurance athletes cannot become a sprinter and vice versa
• Intermediate transitions can happen, IIa to IIa and vice versa

2. Does endurance training cause adaptations in muscle structure?

• Doesn’t effect cross-sectional area of muscle or muscle fibers
• Adaptations include increased mitochondria proteins and increased glycolytic enzymes, therefore 2 X increase oxidative metabolism
• Intensity and duration of training affects degree of adaptations
• Degree of involvement of motor unit in person’s training affects adaptation

3. Does resistance training show specific adaptations in fiber-type?

• Yes, repressed fastest MHC’s (myosin heavy chains) and increased expression of intermediate MHC’s
• Resistance training makes cross-bridges cycle at a slower rate and therefore maintaining force of contraction
• Resistance training decreases endurance capacity
• Both training forms increases strength and endurance when trained concurrently

4. Does a decrease in physical activity change muscle structure?

• Large reduction in usage of motor units or decrease load against motor units contractions
• Decrease muscle and muscle fiber cross-sectional area
• Decreased in metabolic proteins that support endurance performance
• Marked atrophy from loss of myosin from myofibril pool
• Decrease in specific tension because decrease ability of atrophied muscles to make cross-bridges

5. How does gender affect skeletal muscle differences?

• Men have greater muscle mass and muscle cross-sectional area
• Men have greater max force and max power capabilities
• Endocrine differences between gender is reason for muscle differences
• Cultural component as woman are often denied same level of physical activity as men
• Most of the differences are accounted to because of differences in muscle mass between genders