Lecture 4 - Environmental Challenges to Physical Fitness

Question 1

How is excess heat lost? [4 ways]

Answer 1

Radiation - [primary way during rest] emitting infrared rays, dilation, redskin. the transfer of heat without the aid of a medium (solid, liquid, gas) from a high temp object to a lower one due to emission of infrared radiation e.g. blood acts as a carrier of heat -> increased flow of blood (vasodilation) to the surface of the skin enables rapid transfer of heat from the body to external environment

Evaporation - [primary way during exercise] sweat used as a cooling mechanism. Sweat is secreted onto the surface of the skin, water molecules in sweat evaporate using excess heat as the source of energy for this vaporisation. humidity decreases sweat evaporation rate this is why it makes it feel hotter than it is

Convection - wind-chill, warm air rises from the blanket covering the body. the blanket of air that surrounds our body gets heated up due to excess heat or normal body temp. warm air rises [due to low density] and cool air takes its place, this movement of air takes away excess heat. use of a fan increases the rate of convection; reason why it feels colder than it actually is when it is windier

Conduction - heat moving from a high temperature to a low temperature e.g. ice collars/vests, water sports. heat is transferred across the tissues - blood->blood vessel wall ->muscle->connective tissue-> skin

Question 2

what is the effect of humidity on the body?

Answer 2

• Reduces the rate of sweat evaporation, hence lowers the ability to thermoregulate
• Leads to increased sweat rate, hyponatremia [salt levels decrease past the threshold] , vicious cycle

Question 3

What are the consequences of HYPERthermia?

Answer 3

• High heart rate
• redistribution of blood flow to skin, respiratory system [muscles are not receiving blood so causes impaired performance]
• impaired performance
• possible heat exhaustion or heat stroke
• possible death
  note - HYPOthermia < 35C, HYPERthermia > 40C

Question 4

What are the symptoms when core body temp > 40C?

Answer 4

• Nausea, headaches
• Intense sweating
• Cramp
• Confusion
• Loss of Appetite
• Higher heart rate

Question 5

Dehydration levels

Answer 5

0.5% weight loss - thirst
2% weight loss - more thirst, discomfort, appetite loss
5% weight loss - difficulty concentrating
8% weight loss - dizziness, laboured breathing in exercise, confusion
10% weight loss - decreased blood volume, possible kidney failure
>10% weight loss - very real risk of death

Question 6

Properties of heat acclimatisation

Answer 6

• requires 7-21 days
• increased plasma volume
• earlier onset of sweating [threshold]
• higher sweat rate [gain or slope]
• reduced salt loss in sweat
• reduced blood flow to the skin
• increased synthesis of heat shock proteins [protect the enzymes you already have]

Question 7

How does altitude (hypobaric hypoxia) affect the body?

Answer 7

• frost bite, HYPOthermia
• the oxygen pressure is lower so:
  - increases the stress at any relative work rate
  - reduces maximal work rate possible
  - alkalosis [breathing out more CO2, which is acidic;
  pH level shifts to alkaline side ] due to high
  ventilation rate
• total gas pressure is lower
  - Cerebral oedema - brain inflammation
  - Pulmonary oedema - Lung inflammation

Question 8

what the outcomes of HYPERbaric environments [scuba diving]

Answer 8

pulmonary injury

the bends [embolisms caused by compressed N2 expanding on ascent

Nitrogen narcosis

• N2 increase in blood due to compressed nature of scuba gas
• loss of brain function - possible death

Question 9

what are the effects of micro-gravity (space travel) environments?

Answer 9

• bones and muscles are strong because they must stand up and work against gravity
• time in microgravity environments leads to loss of bone mass/density and muscle mass/ functional strength
• the heart becomes weaker as it does not have to pump blood against the gravity