LEC4,5: Thermal Environment

Question 1

Two competitive circulatory demands

Answer 1

1. oxygen transport
2. blood flow to the periphery for cooling

Question 2

General responses to exercise in the heat

Answer 2

Submaximal exercise requires similar cariac output

As blood volume decreases (dehydration), stroke volume is proportionately reduced

Q is maintained by increasing HR

Vascular constriction and dilation: in order to compensate for cutaneous and muscle blood flow we see constriction of splanchnic and renal vessels

Possible explanation for liver and renal complications
resulting from exertional heat stress

Vasoconstriction in the viscera increases total peripheral resistance and maintains blood pressure

In severe exercise, the need to maintain Q will take precedence over diversion of blood to skin for cooling

During prolonged submaximal exercise in the heat:
- we see greater reliance on anaerobic metabolism than in cooler conditions
- results in earlier accumulation of lactate, encroachment on glycogen reserves, premature fatigue

Question 3

Why would we see an increase in blood lactate concentration increase?

Answer 3

• greater reliance on glycolysis – more production
• decreased plasma volume
• decreased lactate uptake by liver
• possibly decreased uptake by muscle

Question 4

Heat Production During Exercise

What does 1 kcal equate to?

Answer 4

Energy needed to raise temp of 1 L of water by one degree C (specifically 15ºC to 16ºC)

Question 5

Heat Production During Exercise

1 Liter of O2 uptake is equivalent to?

Answer 5

~4.83 kcal

Question 6

When efficiency is low (usually less than (blank)) so
most energy is released as (blank)

Answer 6

30%, heat

Question 7

Heat production during exercise

Answer 7

At rest:
VO2 = 0.250 L/min or ~1.2 kcal/min (~1700 kcal/day)
Moderate exercise:
VO2 = 2.00 L/min or ~10 kcal/min
Hard exercise:
VO2 = 3.00 L/min or ~15 kcal/min
Maximal exercise:
VO2 = 4.00 L/min or ~20 kcal/min
Efficiency is low so ~ 70% is released as heat

Question 8

Sweat evaporation transfers about (blank) kcal/ml

Answer 8

0.6 kcal/ml or 580 kcal/L

Max sweat rate is about 30 ml/min
Max heat loss is then about 18 kcal/min

Question 9

Factors influencing sweat evaporation

Answer 9

1. Surface exposure
2. Ambient temp
3. Relative humidity
4. Convective air currents

Question 10

What contributes to uncompensable heat stress?

Answer 10

1. Metabolic rate
2. Encapsulation
3. Environmental exposure

Question 11

Common Themes in Thermal Research

Acute exposure

Answer 11

What are the initial responses to environmental stress in someone not acclimatized?

Question 12

Common Themes in Thermal Research

Chronic exposure or adaptation

Answer 12

How does the body adapt to repeated exposure?

Question 13

Common Themes in Thermal Research

Performance Issues

Answer 13

How do different environmental conditions affect our ability to work or perform?

Question 14

Common Themes in Thermal Research

Individual variability in response

Answer 14

Why do some people tolerate exercise in challenging environments better than others?

Question 15

Common Themes in Thermal Research

Countermeasures

Answer 15

How can we protect individuals from negative effects of exposure to challenging environments?

Question 16

How can sweat loss measured?

Answer 16

Sweat loss is usually estimated by change in nude body mass before and after the experimen

Question 17

How is sweat rate measured?

Answer 17

Sweat rate is usually estimated by collecting the volume of sweat at a particular site

Question 18

Core Temperature

Rectal probe

Answer 18

Flexible probe usually inserted approximately 15 cm

Question 19

Core Temperature

Esophageal

Answer 19

Flexible proble, usually inserted through nostril, down back of throat into the esophagus

Question 20

Core Temperature

Tympanic

Answer 20

Inserted into ear canal near eardrum

Question 21

Core Temperature

Telemetry “pill”

Answer 21

Swallowed in advance of measurement period to allow passage into small intestine

Question 22

Skin Temperature

Standard sites

Answer 22

arm, chest, calf, thigh
Individual temperature values may be combined to estimate weighted mean skin temperature

Tsk = 0.3Tchest + 0.3 Tarm + 0.2Tthigh + 0.2Tcalf

Question 23

Uncompensable Heat Stress

Exposure Time is affected by 3 factors:

Answer 23

1. Initial Core Temperature
2. Final Core Temperature
3. Rate of Change in Core Temperature

Question 24

Heat Balance During Exercise

Heat production caused by (blank) while heat loss or storage caused by (blank)

Answer 24

Muscle contraction and environment

Evaporation, environment Radiation, conduction, convection

Question 25

Exercise ALWAYS results in an (blank) in core temperature

Answer 25

increase

Question 26

Normal ceiling for safe exercise is (blank)

Answer 26

40 degrees

Question 27

Ability to exercise in uncompensable heat stress conditions (failure to thermoregulate) appears to be greater in (blank)

Answer 27

aerobically fit

Question 28

Abnormally high core temp eventually (blank) exercise performance regardless of fitness

Answer 28

impairs

Question 29

Critical temp of (blank)usually coincides with fatigue

Answer 29

38 - 40 degrees

Question 30

Heat Balance Equation

S = M ± Wk ± R ± C ± K - E (W.m-2)

Answer 30

S – gain or loss in heat storage
M – metabolic heat production
W – external work performed
R – radiative heat exchange
C – conductive heat exchange
K – convective heat exchange
E – evaporative heat exchange