Review Question - QID 214027

The primary energy substrate for anaerobic muscle activity lasting less than 10 seconds is ATP and creatine phosphate.

Muscle energy substrates vary depending on aerobic or anaerobic exercise. It is also influenced by the duration of the exercise. Aerobic respiration is significantly more effective at releasing energy than anaerobic respiration. This is due to the aerobic processes being able to extract most of the glucose molecules' energy in the form of ATP. Conversely, anaerobic processes leave most of the ATP-generating sources in waste products. Anaerobic processes predominate in short exercise duration, whereas aerobic processes dominate endurance exercises. In strictly anaerobic activities lasting <10 seconds, ATP and creatine phosphate are predominately utilized by skeletal muscle. As activities continue, glycogen becomes an energy substrate that is utilized. During aerobic and anaerobic exercise lasting between 1 and 4 minutes, glycogen and lactic acid become predominant substrates utilized by skeletal muscle. Lastly, during strictly aerobic activities lasting >4 minutes, glycogen and fatty acids are the preferred substrate.

Staron et al. summarize the delineation, development, and distribution of human skeletal muscle fiber types. They identified a total of seven fiber types, with most human muscles having mATPase-based fiber types that correlate with the myosin heavy chain content. They conclude that although the major populations of fast and slow fiber are established shortly after birth, subtle alterations take place throughout life.

Laumonier et al. reviewed muscle regeneration mechanisms. They identified three main phases in the process of muscle regeneration: a destruction phase with the initial inflammatory response, a regeneration phase with activation and proliferation of satellite cells, and a remodeling phase with the maturation of the regenerated myofibers. They conclude that therapeutic approaches have limited effectiveness and optimal strategies for such lesions are not known yet.

Incorrect Answers:
Answers 2-4: During aerobic-only activities lasting longer than 4 minutes, glycogen/glucose and fatty acids are the preferred substrate.
Answer 5: Lactic acid has low ATP yield and predominates with exercise lasting a duration of 2-3 minutes.