Thermoregulation During Exercise

Introduction

• Theme: Maintaining body temperature at rest and during exercise
• Importance: Information doesn't typically fall under bioenergetics, neuromuscular, or cardiorespiratory units

Body Temperature Regulation

• Goal: Maintain a constant internal body temperature
• Normal Range: 97 - 100°F (average now closer to 98°F)
• Critical thresholds: Above 104°F or below 93.2°F

Internal Mechanisms

• Heat Production: Metabolism, muscle contraction, shivering
• Heat Loss: Radiation, conduction, convection, evaporation
  • Conduction: Direct contact with cooler objects
  • Convection: Gas or liquid moving across skin (e.g., wind)
  • Radiation: Infrared rays (60% of heat loss at rest)
  • Evaporation: Major during exercise (80% of heat loss during exercise)
  • Insensible Water Loss: Evaporation during breathing (10% of daily heat loss)

Environmental Factors

• Humidity: Reduces pressure gradient for heat loss
  • High humidity: Harder to lose heat, sweat rolls off
  • Low humidity: Risk of dehydration
• Temperature: Ambient temperature affects heat gain/loss
• Critical Temperature: ~104°F (degradation of proteins, nervous system affected)
  • Proteins include enzymes, receptors, and myelin

Hypothalamus: Body's Thermostat

• Thermoreceptors: Central (monitor blood temperature in brain) and peripheral (monitor external temperature)
• Pre-optic Anterior Hypothalamus (PAH): Responds to temperature changes
  • Responses: Sweating, dilation/constriction of blood vessels, shivering, hormonal changes (e.g., catecholamines)

Cardiovascular Response

• Competition for Blood Flow: Between muscles and skin
• Stroke Volume: Decrease due to blood diverted to skin, sweating
• Heart Rate: Increases to compensate for decreased stroke volume
• Limitations: Performance affected by limited blood flow to muscles

Fluid Balance and Sweat Rate

• Sweat Rate: 1 liter/hour per square meter of body surface area
• Dehydration: 2% body weight loss affects performance
• Thirst Mechanism: Kicks in at ~2% body weight loss, already dehydrated
• Electrolyte Loss: Sodium in sweat important for muscle function
• Hormones: ADH and aldosterone help retain sodium and water

Heat Disorders

• Heat Cramps: Muscle cramps due to electrolyte loss
• Heat Exhaustion: Profuse sweating, fatigue, pale/cool skin
• Heat Stroke: No sweating, rapid pulse, confusion, emergency situation

Preventive Measures

• Environmental Awareness: Schedule exercise during cooler times, wear light, loose clothing
• Hydration: Drink fluids regularly, don't wait for thirst
• Acclimation and Acclimatization
  • Acclimation: Short-term (~10-14 days), body learns to sweat earlier
  • Acclimatization: Long-term (months/years), body fully adapts to new environment
  • Benefits: Reduces strain on cardiovascular system, decreases inflammation
• Training: Use interval training to enhance adaptation

Renin-Angiotensin-Aldosterone Pathway

• Purpose: Regulate blood volume and pressure
• Trigger: Dehydration causes decrease in blood volume/pressure
• Process: Kidney releases renin, liver releases angiotensinogen → Angiotensin I converts to Angiotensin II → aldosterone released to retain sodium and water
• Effect: Increases blood volume and pressure, negative feedback loop

Conclusion

• Understand and mitigate heat-related challenges during exercise
• Focus on maintaining hydration, appropriate clothing, and adaptation strategies