4 - Thermal Stress and Exercise Flashcards
What are some of the factors affecting thermal balance during exercise?
radiation - happens no matter what (important at rest)
conduction - need two things in contact
convection, evaporation (respiratory and sweat), metabolic storage, environment, core temperature
Why does surface area matter for the body’s cooling strategies?
more SA = more cooling
important for all 4 (evaporation, radiation, convection, conduction) - ignores density
What thermal factor is the biggest contributor to heat stress in FPE?
metabolic heat - not external factors
What are the 2 competitive circulatory demands?
oxygen transport and blood flow to the periphery for cooling
How does evaporation affect blood pressure during exercise in the heat?
sweating (from plasma) creates a drop in blood volume (dehydration), reducing strove volume, which then increases HR
How are vascular constriction and dilation affected due to exercise in the heat?
constriction of splanchnic and renal vessels to compensate for cutaneous and muscle blood flow - vasoconstriction in the viscera increases total peripheral resistance and maintains blood pressure - also trying to conserve blood volume by reducing blood flow to the gut/redirecting blood flow
During prolonged submaximal exercise in the heat, what are some responses that we see?
greater reliance on anaerobic metabolism than in cooler conditions, resulting in earlier accumulation of lactate, encroachment on glycogen reserves (glycogen depletion may lead to fuzzy thinking), premature fatigue
Why does blood lactate concentration increase during prolonged submaximal exercise in the heat?
greater reliance on glycolysis (more production), decreased plasma volume, decreased lactate uptake by liver, possibly decreased uptake by muscle
How many kcals burned during submaximal exercise in the heat are due to heat vs. useful exercise?
about 75-80% of kcals are lost as heat (so if we’re burning 5kcal at 1L O2, 4kcals are heat and 1 is useful)
How much does core temperature increases during different exercise conditions?
hard exercise - PT - 1 degree/30 min
maximal exercise - PT - 1 degree/5-7 min
treadmill exercise (30min @ 70% VO2max) - 2-2.5 degree increase in 30 min
How is efficiency calculated, and what is it normally at?
efficiency = energy equivalent of work done / energy consumed during work
usually less than 30% - most energy released as heat
What is the average rate of heat gain in protective clothing?
about 2 degrees per hour
How many kcals is equivalent to 1L of oxygen uptake?
~4.83 kcal
