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AIS Chapter 9 Heat. Heat Exchange During Exercise. Increased core temperature Anterior hypothalamus Commencement of sweating Increased skin blood flow. Cold exposure Posterior hypothalamus Increase heat production Shivering Decrease heat loss Decreased skin blood flow.

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Presentation Transcript
the hypothalamus the body s thermostat
Increased core temperature

Anterior hypothalamus

Commencement of sweating

Increased skin blood flow

Cold exposure

Posterior hypothalamus

Increase heat production

Shivering

Decrease heat loss

Decreased skin blood flow

The Hypothalamus 下視丘—The Body’s Thermostat
heat exchange during exercise1
Heat Exchange During Exercise
  • Evaporative heat loss: Most important
  • Convective heat loss: Small contribution
  • Radiative heat loss: Small contribution
body temperature increase during exercise
Body Temperature Increase During Exercise
  • Increase in body temperature with work rate
    • Linear across wide range of temperatures
heat exchange during exercise effect of ambient temperature
Heat Exchange During Exercise: Effect of Ambient Temperature
  • As ambient temperature increases:
    • Heat production remains constant
    • Lower convective and radiant heat loss
    • Higher evaporative heat loss
heat exchange during exercise effect of exercise intensity
Heat Exchange During Exercise: Effect of Exercise Intensity
  • ↑exercise intensity, ↑ heat production
    • Lower convective and radiant heat loss
    • Higher evaporative heat loss
exercise in hot humid environments
Exercise in Hot/Humid Environments
  • Cardiovascular responses
    • ↑skin temperature, ↑cutaneous blood flow
    • ↑heart rate to maintain cardiac output
    • ↑sweat rate, ↓plasma volume, ↑plasma osmolality
  • Thermal responses
    • ↑ Peripheral and core temperature
  • Hyperthermia: esophageal temperature >~40 C in well-trained subjects
    • An independent cause of fatigue
    • ↓ Self-selected exercise pace
exercise in hot humid environments1
Exercise in Hot/Humid Environments
  • Metabolic responses
    • ↑anaerobic metabolism, ↑blood lactate
    • ↓ADP rephosphorylation (ADP  ATP), ↓muscle blood flow, ↑respiratory exchange ratio
    • ↑glycogen usage, ↑glycolysis
thermal assessment in athletes
Thermal assessment in athletes
  • Heat generation and dissipation during exercise highly individual
  • Ingestible thermometer
  • Rectal thermometer
  • Esophageal thermometer
  • Data analyzed in conjunction with heart rate, sweat rate, rate of perceived exertion, thermal sensation, performance data
acclimatization of heat
Acclimatization of heat
  • Passively: sustained passive heat exposure
    • Not recommended
  • Actively: physical training in warm to hot conditions
    • Limit heat dissipation, promote heat storage
  • Initial adaptations: ↑plasma volume, ↑cutaneous blood flow, ↓heart rate, ↓perception of effort
  • Subsequent adaptations: ↓resting core temp, ↓exercise core temp, earlier onset of sweating, ↓sweat secretion
acclimatization of heat1
Acclimatization of heat
  • Duration: ~ 2 weeks, large individual difference
    • Elite endurance runners already partially heat acclimatized
  • Athletes predominantly train and compete in worm to hot environments  already heat acclimatized
  • Focus: practice pacing and heat management strategies
    • May require 2 weeks
  • Require planning to ensure that tapering not limit adaptation
    • Similar efforts to those of competition
heat management strategies
Heat management strategies
  • Acclimation: what to do in cold environment
  • AIS prepare for Olympics in Asia
    • 7-8 weeks, 60-90 min exercise in heat tent, once per week prior to departure
    • Further 10 days in competition venue
    • Gradually increase exercise intensity in heat
    • Exposed to heat, but allow adequate recovery between sessions
  • Training in spring to prepare for summer competitions
    • 1-2 sessions/week train outdoors at noon, or in hot rooms/gyms
heat management strategies1
Heat management strategies
  • Hydration: <2% body weight loss during exercise
    • Calculate dehydration (%): (preBW – postBW) x 100/ preBW
    • Calculate sweat rate (L/hr): (PreBW - postBW + fluid consumption – urine output) / Time
    • Urine specific gravity: <1.010 (well hydrated), 1.010-1.020 (minimal dehydration)
  • Fluid consumption schedule according to dehydration and sweat rate
  • Ad libitum drinking 50-70% sweat loss during ex
heat management strategies cooling
Heat management strategies: Cooling
  • usually ↓core temp ~0.5 C
  • Ice jackets
  • Water immersion, can be used during breaks
    • < 10 min at < 15 C
    • 20-30 min at 25-28 C: more popular
  • Crushed ice ingestion 冰沙
    • 7.5 ml/kg ice ↓core temp 0.7 C, improve performance
  • Ice towels
  • forearm/ and hand immersion
    • 20 min at 10 C ↓core temp 0.6 C
commercialized ice sports bar
Commercialized ice sports bar

http://www.powerice.com/product-info/