Final answer:
Training improves a muscle's capacity to use fatty acids for energy instead of glycogen, fostering better endurance and delaying fatigue through enhanced aerobic metabolism and cellular changes such as increased mitochondrial content and myoglobin levels.
Step-by-step explanation:
Training increases the ability of muscles to metabolize fatty acids for energy, thereby delaying the onset of muscle fatigue. Initially, muscles use stored glycogen to produce energy, but as glycogen levels fall, the liver releases glucose and the metabolism of fat becomes more prominent, especially during low-intensity activities. This shift to utilizing fatty acids allows for prolonged aerobic metabolism which is more efficient than anaerobic glycolysis in producing ATP, the energy currency of cells.
Muscle cells adapt through aerobic training by increasing mitochondrial density, enhancing the circulatory system for better oxygen delivery, and increasing myoglobin content which ensures a steady supply of oxygen to the muscles. These adaptations facilitate a prolonged ability to sustain aerobic respiration, delaying fatigue. Moreover, the training stimulates angiogenesis to improve oxygen supply and waste removal, without significantly increasing muscle mass to maintain a small diffusion area for nutrients and gases.
Endurance training also improves the effectiveness of the circulatory system and enhances oxygen storage via myoglobin, allowing more efficient muscle contractions and less fatigue. All these factors contribute to an increase in endurance and a delay in the onset of muscle exhaustion. Training enhances the muscle's capability to metabolize fatty acids for sustained energy production, delaying muscle fatigue through improved efficiency of aerobic pathways and cellular adaptations.