LEC6: Thermal Limits

Question 1

One of the ways we naturally defend against heat stress during physical work is that we (blank)

Answer 1

slow down

Question 2

Critical Internal Temperature

‘Critical’ core temp that accelerates fatigue and is associated with (blank)

Answer 2

exhaustion

Question 3

high body (and brain) temp leads to fatigue through (blank)

Answer 3

impaired arousal or voluntary muscle activation

Question 4

Brain Function During Hyperthermia

Answer 4

Ratio between low (α = 8-13 Hz) and high frequency (β = 13-30 Hz) brain waves changes with hyperthermia

β waves decrease (similar to sleep) suggesting reduced arousal during hyperthermia

Altered brain activity associated with increased core temperature

Altered brain activity associated with increased RPE

Question 5

Psychophysical contributors to hyperthermic fatigue and exhaustion

Exercise Hyperthermia Pathway

Cheung and Sleivert, (2004)

Answer 5

1. ↑ in temperature in the brain
2. ↑ in α/β waves
   a. ↓ arousal
   b. ↑ RPE
3. Both lead to ↓ in voluntary activation
4. Fatigue/exhaustion

Cheung and Sleivert, (2004)

Question 6

Hyperthermia-induced changes in brain blood flow and metabolism

Exercise Hyperthermia

Cheung and Sleivert, (2004)

Answer 6

1. ↑ in temperature in the brain
2. ↑ metabolism in focal areas of the brain
3. Cerebral glycogen depletion
4. Fatigure / Exhaustion
5. Hypoglycemia
6. Cerebral glycogen depletion
7. Fatigue / Exhaustion
8. Hyperventilation and ↓PCO2
9. Cerebral vasoconstriction and ↓Cerebral blood flow

Cheung and Sleivert, (2004)

Question 7

Effects of elevated body temp on gastrointestinal tract blood flow

Exercise Hyperthermia

Cheung and Sleivert, (2004)

Answer 7

1. ↓ Gut blood flow
2. Endotoxemia
   a. ↑Cytokines
   i. CNS Impairment
   b. Free Radical Species
   i. Contractile protein damage

Both i’s lead to fatigue/exhaustion

Cheung and Sleivert, (2004)

Question 8

Cardiac Output

Answer 8

Q = HR x SV = MAP/TPR

Q = cardiac output
HR = heart rate
SV = stroke volume
MAP = mean arterial pressure
TPR = total peripheral resistance

Question 9

What does “Central Pressure” describe?

Answer 9

Where MAP can meet the need for venous return

Question 10

As blood volume decreases
(dehydration), stroke volume (SV) is
proportionately (blank)

Answer 10

reduced

Question 11

Vascular constriction and dilation is used for what?

Answer 11

Compensate for cutaneous and muscle blood flow

Question 12

Vasoconstriction in the viscera increases
(blank) and
maintains (blank)

Answer 12

Total Peripheral Resistance (TPR), blood pressure

Question 13

Exposure Time

Initial Core Temperature

Answer 13

Heat acclimation, hydration, menstrual cycle phase, MOPP level

Question 14

Exposure Time

Final Core Temperature

Answer 14

Aerobic fitness, hydration, state of encapsulation

Question 15

Exposure Time

Rate of Change in Core Temperature

Answer 15

Clothing characteristics, environment, body composition, fluid replacement, rate of heat production (work and rest schedules), cooling