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

Rehydration  Achieving Euhydration before exercising in a hot environment protects against heat stress because it: Delays dehydration Increases sweating during exercise Diminishes the rise in core temperature Recommendation ml (13-20 oz) 20 min prior to exercise

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

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

Rehydration Factors affecting consumption –Flavor, sweetness –Temperature –Color –Carbonation –Viscosity

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

Sodium during Rehydration

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

Hyponatremia

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

Treatment IV rehydration with saline –Glucose Oral rehydration as effective

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.

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

Heat Acclimation Results in: Core temperature reduced Heart rate at any given workload is reduced Stroke volume increases Due to expansion of plasma volume Extent of Heat acclimation Training status Duration of exposure Rate of internal heat production

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

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

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

Heat Illnesses Heat Syncope –Fainting –Lightheadedness –End of exercise Should stop exercising and rehydrate

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

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

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