KNR 280 | Thermoregulation | Exam 3

Normal core temperature range (°F/°C)?

96.8–99.5°F (36–37.5°C)

When does heat illness begin?

102°F (≈39°C)

When does hypothermia begin?

< 95°F (≈35°C)

Four environmental heat gain sources?

Radiation, Conduction, Convection, and Metabolic heat (ATP use)

Four heat loss mechanisms?

Radiation, Conduction, Convection, Evaporation (sweat)

Which is the dominant cooling method during exercise?

Evaporation

How does humidity affect cooling?

High humidity ↓ evaporation → ↓ heat loss → ↑ heat stress

Factors affecting heat balance?

Air temp (thermal gradient), humidity, air movement, sunlight, clothing

What happens when air temp > skin temp?

Evaporation becomes the only effective cooling method

What does “thermoregulation is about transferring heat, not cold” mean?

Body must move heat away; cold is just absence of heat transfer

Core temperature measurement sites (rank accuracy)?

Rectal, Esophageal, GI > Tympanic > Oral > Skin

How does vasodilation aid cooling?

Moves warm blood near skin → ↑ heat loss via radiation/conduction/convection

How does exercise intensity affect thermoregulation?

↑ Intensity → ↑ metabolic heat → greater sweat rate and vasodilation demands

How does fitness level affect thermoregulation?

Trained people sweat earlier, more efficiently, and have greater plasma volume

How does dehydration affect thermoregulation?

↓ plasma volume → ↓ venous return (↓ preload) → ↓ SV → ↑ HR → ↓ Q → ↓ VO₂max

Why does cardiovascular drift occur in heat?

As body temp ↑ → plasma ↓ → SV ↓ → HR ↑ to maintain Q (but Q still falls slightly)

What happens to VO₂max in heat stress?

It decreases due to lowered Q (SV ↓, HR can’t fully compensate)

What are the 2 major responses to overheating?

↑ Sweat rate + Vasodilation

What are the two cardiovascular consequences of exercise in heat?

Competition for blood between skin and muscles

Reduced plasma volume due to sweating

What’s the result of these cardiovascular consequences?

↓ Venous return → ↓ Preload → ↓ SV → ↑ HR → ↓ Q → ↓ VO₂max

Define acclimatization

Physiological adaptation to repeated heat exposure

Cardiovascular adaptations to heat acclimatization?

↓ Resting core temp, ↑ plasma volume, earlier sweating onset, ↓ HR, maintained Q

How fast does plasma volume increase with heat training?

Within about 1 week

What role does fat play in thermoregulation?

Insulates (retains heat) but adds non-contributing body mass → more stress

Early sweating onset benefit?

Allows earlier evaporative cooling before core temp spikes

Greater sweat rate benefit?

↑ Evaporative cooling capacity → prevents overheating

Main causes of heat stroke?

Failure of thermoregulation → core >105°F, CNS dysfunction, dehydration

Main signs of hypothermia?

Shivering, confusion, slowed HR and metabolism, potential heart rhythm issues

What is “competition for blood flow”?

During heat stress, skin and muscles both demand blood → ↓ venous return + SV

Key performance effects of heat stress?

↑ HR drift, ↓ SV, ↓ VO₂max, ↑ fatigue rate, ↓ endurance