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Physiological responses to heat accumulation
surface blood flow is increased at expense to other tissues
EPI release– HR upward drift glycogen use
blood volume cardiac efficiency ( SV, HR)
fatigue
Fluid balance
dehydration impairs endurance performance, – minimal effect on power and speed events
blood volume will skin blood flow and heat dissipation
thirst mechanism doesn’t keep up with dehydration
need for water replacement > than electrolyte replacement
Maintaining fluid balance
fluid intake during exercise will:– minimize dehydration– minimize rise in body temperature– reduce CV stress
[CHO] > 6-8% slows absorption from gut
Sport Nutrition: Sport Drinks
[CHO] affects fluid absorption rate in gut– Gatorade – 6%– Exceed – 7.2%– Coca-Cola – ~11%– Sprite – 10.2%– cranberry juice – 15%– orange juice – 11.8%
ACSM Fluid Replacement Recommendations
Before exercise, drink: – ~500 ml 2 hr before exercise
During exercise, drink:– early and at regular intervals– to replace lost fluids (if tolerated)– over-hydration can result in hyponatremia
After exercise, drink:– excess of that lost during exercise
Acclimatization to exercise in heat
body fluids/blood volume (w/in 3-5 d) skin blood flow rate of sweating (may take up to 10 d) electrolyte loss heat tolerance
Achieving heat acclimatization normal workouts in heat for 5-10 d
Suggested Readings(available at gssiweb.com under Sport Science Exchange)
Murray, R. Fluid replacement: The American College of Sports Medicine Position Stand. GSSE 9(4) SSE#53, 1996. http://www.gssiweb.com
Maughan, R.J. and S.M. Shirreff. Preparing athletes for competition in the heat: developing an effective acclimatization strategy. GSSE 10(2) SSE#65, 1997.http://www.gssiweb.com
The primary mode of heat dissipation during exercise is
a. convection
b. radiation
c. conduction
d. sweat evaporation
What likely is the primary cause of HR drift during moderate-intensity exercise in heat?
a. plasma volume leading to SV
b. Epi release
c. temperature
d. sweating
e. body weight
Recommended