Exercise Thermoregulation, Fluid Balance, and Rehydration

1. Exercise Thermoregulation, Fluid Balance, and Rehydration Chapter 10 Part 2

2. Rehydration • AchievingEuhydrationbefore exercising in a hot environment protects against heat stress because it: • Delays dehydration • Increases sweating during exercise • Diminishes the rise in core temperature • Recommendation • 400-600 ml (13-20 oz) 20 min prior to exercise

3. Adequacy of Rehydration • Body weight changes • Extent of water loss from exercise • Adequacy of rehydration during and after exercise or athletic competition. • 16 oz water loss/1 lb weight loss

4. Adequacy of Rehydration • Urine and hydration: • Dark yellow urine with a strong odor = inadequate hydration • Large volume, light color, without a strong odor = adequate hydration

6. Rehydration • Factors affecting consumption • Flavor, sweetness • Temperature • Color • Carbonation • Viscosity

7. Sodium and Rehydration • Sodium added to a rehydration beverage • Provides more complete rehydration. • Why? • Maintains plasma osmolality: • Sustains the thirst drive • Leads to greater fluid ingestion • Thus, • More rapidly restore lost plasma volume during rehydration

8. Sodium during Rehydration

9. Hyponatremia • A sustained low plasma sodium • Osmotic imbalance across the blood–brain barrier • Rapid water influx into the brain. • Swelling - encephalopathy • Symptoms (mild to severe) • Confusion, convulsions, collapse, and coma

10. Hyponatremia

11. Hyponatremia

12. Occurrence • Most cases (> 8 hrs) • Ultra marathon • Prolonged triathlon events • Plasma sodium concentrations (Noakes) • 7-10 hours, 4 cases • 115-125 mmol/L • Fluid intake – 6-12 L

13. Treatment • IV rehydration with saline • Glucose • Oral rehydration as effective

14. Acclimatization • Improving heat tolerance • Physiologic adaptations of body • Repeated exposure to heat stress • Requires exercise in a hot environment • Exercising in the heat for 1 hour or more • Daily for 9 to 14 days.

15. Acclimatization • Cardiovascular changes by • Plasma volume expansion, first 1-3 days • Sweating mechanisms • Longer, up to 10 days or more. • Sweat earlier and at a greater rate • Sweat is more dilute • This causes skin temp to drop • Increases the thermal gradient from the core to the skin

16. Heat Acclimation • Results in: • Core temperature reduced • Heart rateat any given workload isreduced • Stroke volume increases • Due to expansion of plasma volume • Extent of Heat acclimation • Training status • Duration of exposure • Rate of internal heat production

18. Age Differences in Acclimatization • Older individuals have: • A decreased sensitivity of thermoreceptors • Limited sweat gland output • Altered structure and function of the skin and its vasculature • A decreased recovery from dehydration

19. Other Factors • Children • More sweat glands, less sweat • Longer acclimatization • Gender • Men sweat more. • Women show heat tolerance similar to men. • Body fat • Insulation

20. Heat Illnesses • Heat Edema • Unacclimated person • Profuse sweating • Red face • Sodium retention • Swelling feet, legs • Not a problem

21. Heat Illnesses • Heat Syncope • Fainting • Lightheadedness • End of exercise • Should stop exercising and rehydrate

22. Heat Illnesses • Heat cramps • Involuntary muscle spasms that occur after intense physical activity • Usually high sweat rates • Electrolyte imbalance • Stop exercise and rehydrate

23. Heat Illnesses • Heat exhaustion • Most common heat illness • High sweat rate • Syncope, cramps • Headache, blurred vision, • Fast heart rate and breathing • Mild confusion, agitation, poor coordination • Stop exercise, rehydrate and get to a cool place

24. Heat Illnesses • Heat stroke • Most serious and requires immediate medical attention • Second leading cause of death in athletes • Delirium, memory loss • Seizures, coma, confusion, weakness • Symptoms-dry skin, no sweating • Get person to hospital • If not, • Ice baths (have to bring down temperature) • Cold water enema