The Endocrine System and Exercise

Muscle Fatigue and Fuel Sources

• Muscle fatigue is caused by the accumulation of H+ ions, which can lead to muscle pain
• Normal muscle pH range is slightly alkaline, between 7.35 and 7.45
• Muscles can use carbohydrates, fats, and proteins as fuel sources
• H+ ions cause muscle pain by activating pain receptors

Delayed-Onset Muscle Soreness (DOMS)

• DOMS is primarily caused by micro-trauma to muscle fibers and surrounding connective tissue

Sodium Bicarbonate and Caffeine

• Sodium bicarbonate helps fight fatigue by buffering excess H+ ions
• Caffeine reduces muscle soreness by blocking adenosine receptors, which reduces pain perception
• The International Olympic Committee (IOC) sets an upper limit of 12 μg/mL for caffeine intake in urine

Impaired Muscle Function and Fatigue

• Impaired muscle function during fatigue is primarily caused by the accumulation of H+ ions and lactic acid
• Lactic acid buildup in muscles impairs muscle function by reducing pH levels

Hormonal Responses to Exercise

• Epinephrine and norepinephrine are released during exercise to increase energy availability
• Cortisol levels increase during overtraining, leading to muscle breakdown and impaired recovery
• Hyperthyroidism increases metabolic rate, while hypothyroidism decreases it
• Resistance training increases the release of anabolic hormones, such as testosterone
• Testosterone is responsible for increasing muscle size through protein synthesis

Fluid Balance and Hormones

• Sweating reduces blood plasma volume, which can lead to dehydration
• Aldosterone is responsible for maintaining blood plasma levels
• Myokines are involved in muscle remodeling and repair
• Leptin levels decrease during high-intensity exercise
• Growth hormone increases fat metabolism
• Cortisol levels decrease when working at less than 50% intensity
• Hyperthyroidism is associated with weight loss and decreased body size