Hormonal Control During Exercise

Endocrine Control and Exercise

Learning Outcomes for the Lecture Series

  • Understand and describe the metabolic changes required to maintain exercise.

  • Evaluate roles of key hormones in regulating glucose and fat metabolism during exercise:

    • Insulin

    • Glucagon

    • Cortisol

    • Epinephrine

    • Norepinephrine

    • Growth Hormone

  • Demonstrate understanding of complex hormone interactions during exercise.

  • Describe how hormones influence the breakdown of proteins during exercise metabolism.

  • Understand hormonal control over adaptations to chronic endurance and resistance-type exercise.

Physiological Response During Acute Exercise

  • Central Nervous System (CNS):

    • Regulates physiological responses through somatic and autonomic systems.

    • Maintains cerebral blood flow and oxygen supply.

  • Metabolism Changes:

    • Increases liver glucose output (glycogenolysis and gluconeogenesis).

    • Increases adipose tissue lipolysis and free fatty acid (FFA) mobilization.

  • Skin & Sweat Rate:

    • Increased sweat rate for heat dissipation (max ~2-3 L/h).

  • Cardiovascular Changes:

    • Increased heart rate (max ~200 bpm) and cardiac output (max ~40 L/min).

  • Oxygen Transport:

    • Increased whole-body oxygen uptake (max ~7 L/min or 80-90 ml/kg/min in elite athletes).

Acute vs Chronic Exercise

  • Acute Exercise:

    • Immediate physiologic responses to a single exercise bout.

    • Increased metabolic rate and ATP production.

  • Chronic Exercise:

    • Metabolic adaptations occur over time to improve fatigue management and metabolic efficiency.

  • Key Types of Exercise:

    • Aerobic: Uses oxygen; endurance training.

    • Anaerobic: Absence of oxygen; resistance training.

Substrate Utilization During Exercise

  • Substrate use varies with exercise duration and intensity:

    • 0-3s: ATP (immediate use)

    • 3-15s: Phosphocreatine (quick energy)

    • 15-45s: Glycolysis (anaerobic)

    • >45s: Shift from anaerobic to aerobic pathways.

  • The relative contributions from carbohydrates and fats change with exercise intensity.

Hormonal Responses to Exercise

  • Major Endocrine Glands Involved:

    • Anterior Pituitary Gland

    • Thyroid Gland

    • Adrenal Gland

    • Pancreas

  • Hormonal Effects:

    • Increased growth hormone (GH) leads to elevated fat metabolism.

    • Glucagon promotes glycogenolysis and gluconeogenesis.

    • Insulin facilitates glucose uptake but decreases during exercise to maintain higher blood glucose levels.

  • Responses to Intensity and Duration:

    • Hormonal secretion rates vary based on energy demands, exercise type, and personal fitness level.

Hormonal Interactions During Exercise

  • Hormonal responses during both graded (intensity) and prolonged exercises include:

    • Increased epinephrine and norepinephrine from the adrenal medulla.

    • Cortisol helps mobilize energy while decreasing immune reactions.

    • GH and thyroid hormones modulate energy metabolism and recovery post-exercise.

Role of Glucagon and Insulin

  • Glucagon: Increases as muscle glycogen is depleted to convert liver glycogen to glucose; essential for maintaining glucose levels.

  • Insulin: Inhibits during exercise to prevent excessive glucose uptake, allowing muscle contraction to move GLUT4 transporters to the cell membrane for increased glucose entry.

Protein Catabolism and Recovery

  • Protein may become a fuel source when glycogen stores are depleted.

  • Hormones such as GH and testosterone further facilitate recovery and muscle synthesis post-exercise.

Key Takeaways

  • Exercise induces significant hormonal responses to enhance energy availability and efficiency, ensuring optimal performance.

  • Hormonal adaptations play a critical role in the recovery and physical adaptations from both endurance and resistance training scenarios.