1. Environment Brooks Ch 22 OUTLINE Environmental Heat Environmental Cold
Body temp and Heat Transfer
Exercise in Heat
Acclimatization to Heat
Environmental Cold
Exercise in Cold
Heart, muscle and metabolic responses to cold
hypothermia

2. Environmental Temperature
People have an ability to live and work in very hot and very cold environments
Able to tolerate these variable environments by tightly regulating our internal (core) temperature - homeotherms
We utilize behavioral and physiological means to regulate our core temperature
normal core temp oC
core - defined as temperature of the hypothalamus
Experimentally - rectal and esophageal temperatures are used for core temperature
Oral temperature is influenced by breathing cold air
Tympanic temperature is influenced by head skin temperature

3. Core Temperature Heat balance - fig 22-2
At temperatures above 41oC the interior of many cells begin to deteriorate
At temperatures below 34oC cellular metabolism slows greatly, leading to unconsciousness and cardiac arrhythmias
During exercise core temp can exceed 40oC - rise is proportional to intensity
While the core remains relatively constant
skin temperature is influenced by the environment, metabolic rate, clothing and hydration state - fig 22-1
Heat balance - fig 22-2
directed by hypothalamus - thermostat
peripheral receptors in skin and hypothalamus
heat and cold receptors
Initiates heat production (shivering) or dissipation (evaporation) to regulate core temperature - fig 22-6
Clothing and air movement across the skin affect capacity for heat loss

4. Heat Transfer Radiation Conduction
heat in form of electromagnetic radiation - 60% of heat loss at room temperature at rest
Sun is largest source of radiant heat
Conduction
transfer through direct contact
Rate of transfer depends on temperature gradient and conductive properties of surface
Convection - conduction to/from air or water
Depends on body surface area exposed to surrounding medium and the flow of that medium - wet suit ?
more rapid in water (~25 times)
heat loss is much greater in wind and moving water
Wind-chill index fig 22-3

5. Heat Loss
Evaporation
quantity of heat absorbed by sweat as it evaporates from the skin
1 gm sweat = Joules (.58kcal)
sweat is only effective for cooling if it evaporates
max sweat rate is ~ 1.5 L/hr in sedentary untrained individuals
Can improve to 4 L/hr with exercise acclimatization to hot humid environment
Sweating results in loss of H2O, Na+, Cl-, urea, lactate and K+
Important to replace these following exercise in the heat which involves excessive sweating
Sweating still occurs during swimming

6. Exercise in Heat Core temp inc with exercise intensity
Fig high environ temp adds to metabolic heat stress of exercise
Cardiovascular effects
depends on bodies ability to dissipate heat and maintain bld flow to active ms
during exercise (acute)
plasma vol dec
Due to inc BP and loss of fluid from sweat
dec central bl vol results in dec filling pressure and a compensatory inc HR
HR inc not viable at higher intensities
near max - vasoconstrict periphery
To maintain BP and CO - triage
No change in VO2 max unless subject started with a thermal imbalance

7. Exercise in Heat Sweating Response
Primary means of heat dissipation during exercise
Sweat rate related more to exercise intensity than environmental temp
Pre-cooling body prior to exercise may improve performance
Ventilation may be affected by temperature during rest and exercise
Dr. Matt White (SFU)
Sedentary exposure to warm bath, increasing core temperature by 2 oC
Observe inc HR, Ventilation and R value with no change in VO2 -
indicate thermal rather than metabolic stimulus for these changes
Aaron Chu - compare values during exercise with/without rise in core temp

8. Acclimatization Acclimatization Acclimation
adaptations produced by a change in the natural environment
Acclimation
adaptation to laboratory environment
heat and exercise are both required for optimal adaptational responses
Acclimation in first 2 weeks
dec HR, core temp, perceived exertion, skin temp at rest and submax exercise
Table 22-2
inc plasma vol (range %)
inc sweat capacity ( L per hour)
dec core temp at onset of sweating
dec skin blood flow - improve distribution of sweat over skin
reduce losses of minerals (sweat and urine)

9. Individual Variation Majority of physiological adjustment in 4-6 days
does not occur without exercise
intense exercise most effective
humidity specific adaptation
atheltes a little faster in acclimatizing
sweat rate and mineral changes take up to two weeks to adapt
Loss of Acclimatization occurs in absence of heat and physical fitness
physically fit retain benefits longer than sedentary individuals

10. Dehydration Dehydration - loss of body fluid
Moderate levels of dehydration will impair CV and temperature regulation - impact performance - fig 22-9
A fluid loss of 5% of body weight will cause irritability, fatigue and discomfort. This level of dehydration is common in football and distance running.
Dehydration levels > 7% are extremely dangerous. At this level salivating and swallowing are difficult.
Dehydration levels > 10% there are coordination problems and spasticity.
At 15% the person experiences delirium and shriveled skin.
Above 20% dehydration death will occur.

11. Exercise In Cold
Rare except when survival is at stake for people to exercise with cold core temp
Protective clothing and high metabolism of exercise usually prevents drop in temp
Work, however, has lower metabolic output, long hours and may create an increased risk in cold environments
Movement in cold
Numbing of exposed flesh
Cumbersome protective clothing
Manipulation with hands difficult
Anaesthetizes sensory receptors in hands
Clothing-layers and breathability important
Must balance insulation value with heat production of exercise
Additional clothing after exercise important
Metabolism drops, heat loss remains high
Shivering inc metabolic costs
Increases perception of effort
May also impair movement patterns
Agonist and antagonist contract

12. CV responses in Cold O2 consumption
VO2 max - unaffected by cold
Submax VO2 increases at lower intensities (*work*)
Due to higher heat loss
Inc skin and ms blood flow during exercise
Greater thermal gradient and heat loss
Wet clothing in wind % higher VO2 requirements
Table exercise in cold
Shivering - Inc VO2 utilization
May also be inc in non-shivering thermogenesis - due to inc catecholamines (stress) and leptin
Swimming in cold water
Reduced VO2 peak at higher intensities- fig 22-7

13. Exercise in Cold
Exercise can partially replace heat production of shivering during cold
Peripheral vasodilation with exercise - reduces insulation in body
Exercise followed by cold exposure - higher threshold for vasocontriction and shivering
Ventilation
Inc ventilation - especially with sudden exposure - gasping reflex
Hyperventilation, tachycardia, peripheral vasocontriction, hypertension
Reduced blood CO2 - vasocontriction in brain - confusion, unconsciousness
Heart
Cold - peripheral vasocontriction - Inc central blood volume - inc BP
Arrythmias - inc in cold
Inc afferent impulses to hypothalamus and cardiovascular control center
Inc adrenal epinephrine
Ventricular fibrillation - leading cause of death in people with hypothermia

14. Cold Exposure Muscle strength
Ms strength and peak power dec as ms temp decreases - dec enzyme activity
May require inc motor unit recruitment to compensate for reduced output
May also see reduced ms blood flow
Combine to inc lactate production and reduce clearance - early fatigue
Metabolic Changes
Inc use of carbohydrates
Ms glycogen reduced faster in light exercise - augments inc in lactate
Prolonged exposure - hypoglycemia
Suppresses shivering, core temperature drops
Fat metabolism depressed even with catecholamine rise
may be due to reduced subcutaneous circulation
These problems are compounded by fatigue, sleeplessness and underfeeding

15. Acclimatization to cold
Shivering threshold
Maintain temperature without shivering, or with less shivering
Experiment - three week exposure - inc thyroid hormone - tissues more sensitive to Nor epinephrine and Epinephrine
Uncoupled ox phosphorylation
Heat released without ATP formed
Leptin - released from Adipose
Stimulates Sympathetic NS
Temperature of hands and Feet
Unacclimatized - temp dec progressively
Acclimatization - maintained
Intermittent vasodilation in periphery
Habituation as well, become more tolerant
Sleeping Ability in the cold
Depends on non shivering thermogensis
Aborigines (Australia) - vasocontriction of periphery - sleep in cold without covering

16. Hypothermia
Hypothalamus ceases to control body temp at extremely low temperatures (< 30 oC)
CNS depressed
Lose ability to shiver
Sleepiness - - -> coma
Reduced metabolic rate --> dec temperature
Cardiovascular
Central blood volume decrease
Exacerbated by
inadequate fluid intake
Plasma sequestration
Cold diuresis
Hypothermia is possible during endurance exercise events
Heat loss greater than production
Glycogen depletion - blood glucose declines, CNS functioning declines