Exercise Thermoregulation, Fluid Balance, and Rehydration
Chapter 10Part 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• 400-600 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
Hyponatremia
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
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