1. Exercise in the Cold and Hot

2. Piokilotherms vs Homeotherms
Piokilotherms: at mercy of the elements
Homeotherms: can function independent of the environment
Ability to maintain constant temperature

3. Normal body temperature: 36.5-37.5°C
During exercise can increase to 40°C with no ill effects
Core temp: temperature of the hypothalamus, temperature regulator of the body
Thermal gradients: temperature differences from one point to another the lead to movement of heat
Temperature always equilibrates from hot to cold

4. Temperature Regulation
Metabolism
Shivering
Nonshivering thermogenesis
Metabolic Rate
Heat loss

5. Metabolism
Heat is produced naturally during normal metabolic reactions
Most reactions lose ~75% of energy as heat
At BMR heat loss is ~100 kcal/hr
BMR is porportional to ¾ power of body weight (surface rule)

6. Shivering
Main mechanism for increasing heat during negative heat balance
Involuntary muscle contraction
Maximum shivering can increase body’s heat production 5X

7. Preshivering tone can increase heat production 50-100%
An effective way to increase body temperature b/c no work is done by the muscles and most of the energy is expended is heat
Increases Q by increasing SV via increased venous return
Limits: glycogen depletion, hypoglycemia, fatigue, ex., hypoxia, drugs (alcohol and barbiturates)

8. Nonshivering thermogenesis
Increased thyroxin secretion (thyroid) and catecholamine secretion (adrenals) increase metabolic rate
Thyroxin increases the rate of all cells
Cats., esp norepi. release FFA, increasing metabolic rate

9. Metabolic Rate (Q10 and food)
Q10 is rate of a physiologic process at a particular temperature to the rate at a temperature 10°C lower
Increased metabolic rate can be self-perpetuating (dangerous)

10. At high temperatures, hypothalamus loses ability to cool the body
Rate of temperature increases faster at higher temperatures
Metabolic rate temporarily increases following food intake, esp. proteins

11. Heat Loss
Radiation
Conduction
Convection
Evaporation

12. Radiation Loss or gain in the form of electromagnetic waves
At rest, in a comfortable environment, radiation accounts for 60% of total heat loss
Varies with body position and clothes
Human skin, regardless of color, absorbs ~97% of radiant energy that strikes it

13. Conduction Transfer of heat from a body to an object
Or, heat transfer within an organism down a thermal gradient
~3% of total heat loss at room temperature occurs this way

14. Convection Conduction of heat to air or water
Amounts to ~12% of all heat lost at room temperature
Heat is conducted to water or air, moves so that other molecules can be heated
Faster in water or air?

15. Greater in the wind (air movement)
Wind chill effect
Can also occur in the circulatory system
Heat moves with the blood from the core to the periphery
As skin temp. incr., heat loss to environment increases
Rate is affected by blood flow and temperature gradient (core/periphery)

16. Evaporation ~25% of heat is lost this way in a comfortable environment
Quantity of heat absorbed by sweat as it evaporates: latent heat of vaporization
Body loses 0.58 kcal/gm H2O evaporates
Only means of cooling at high environmental temperatures
Critical for exercise

17. If body cannot lose heat this way, body temp. increases rapidly
Sweat is only effective if it evaporates
High humidity: evaporation reduced or prevented
Effective evaporation also hampered by little air movement

18. Women have a lower sweating capacity than men do
Process occurs by sweating and insensible water loss: ventilation, diffusion through skin, does not include sweat, urine, and feces
Sweat rates are at 0 when temperature is low

19. Hypothalamus and temperature regulation
Temperature regulatory center
Set-point it tries to keep
Sweating normally occurs at 37°C
Set-point can change in response to dehydration, starvation, and fever
Responds to heat primarily through heat-sensitive neurons in the preoptic area of anterior portion

20. More cold than heat receptors in the skin
Thermoregulators transmit impulses to the spinal cord, to hypothalamus, initiates response
Ant. Hypothalamus stimulates the sweat glands, evaporative heat loss
“Hunting Reflex” primarily in hands and feet

21. Exercise in the Cold Clothing Oxygen Consumption Ventilation Heart
Muscle Strength
Metabolic Changes

22. Oxygen Consumption Maximum uptake is unaffected by the cold
Submax. VO2 increases in the cold
Why?

23. Ventilation Increases in the cold, particularly if exposure is sudden
Abrupt exposure can lead to gasping reflex

24. Heart
Changes in cardiac performance more common in men
Incidence of arrhythmias increase in cold
Muscle Strength
Strength decreases with lower muscle temp.

25. Metabolic Changes Increase use of CHO as substrate
Light ex: glycogen depletes faster
Max ex: depletion is independent of temp.
Prolonged exposure to cold: hypoglycemia, suppresses shivering, core temp drops, lactate higher
Fat metabolism suppressed, even though cat. response is higher

26. Acclimatization and Habituation to Cold
Acclimatize: physiologic compensation to environmental stress over time
Habituation: lessening of the sensation associated with an environment
Shivering threshold
First test of acclimatization
Cold-acclimatized people maintain heat production with less shivering, more nonshivering thermogenesis

27. Hand and Feet temperature
Second test for acclimatization
Acclimatized: maintain almost normal temperature
Habituation also plays a role
Ability to sleep in the cold
Third and final test
Seems to depend on extent of nonshivering thermogenesis induced by increased secretion of norepi

28. Hypothermia
Depresses the CNS, lose ability to shiver, sleepiness, coma, death
Lower temp: lower cellular met. rate, further lowering temp.
Profound effects on the CV system
Central BV decreases; plasma sequestration, inadequate fluid intake, cold diuresis

29. Risk factors cold exposure Lack of protective clothing Leanness
Inadequate fluid intake
High wind chill
Use of alcohol &/or drugs
Use of snow to relieve thirst
Glycogen depletion

30. Frostbite Caused by ice crystal formation within the tissue
Occurs in exposed skin
Can lead to tissue death

31. Exercise in the Heat

32. Plasma volume decreases during exercise in the heat
becomes acute at intensity increases
decrease of plasma volume is made worse by loss of body fluids through sweating
may not be enough blood to adequately perfuse all areas during exercise in the heat

33. central blood volume may decrease and cause a decrease in cardiac filling pressure
results in increased HR in attempt to compensate for lower SV
submax. HR increases also
@ max levels, skin vessels vasoconstrict to help maintain blood pressure and Q

34. negative response on heat transfer
circulatory regulation takes precedence over temperature regulation in this case
VO2 max is not impaired in the heat unless the person was experiencing thermal imbalance before beginning the exercise

35. Sweating Response
primary means of heat dissipation during exercise (evaporation)
in heat, sweating is very important b/c body tends to gain rather than lose heat by radiation, conduction, and convection
during exercise, sweating is related more to intensity than environmental temperature

36. Acclimatization to heat
first two weeks of heat exposure results in lower heart rate, core temperature, RPE, and skin temperature at rest and during exercise
primary physiological adjustments are increased peripheral heat conductance, plasma volume, and sweating, decreased core temperature at onset of sweating, and improved distribution of sweat over the skin

37. CV Adaptations
acclimatization induces a 3-27% increase in plasma volume, if acclimatization is done with exercise training
increased plasma volume helps to maintain SV, central blood volume, and sweating capacity
also increases in vasopressin, renin, and aldosterone in early days

38. blood flow to the skin decreases
decreased skin blood flow helps to maintain central blood volume, which is vital for maintaining BP, SV, and muscle blood flow during exercise
core temperature is lower during exercise
decrease in skin blood flow is accompanied by a large increase in sweating and evaporative cooling capacity

39. Sweating Response
acclimatization increases this response almost 3X, from ~1.5 l/hr to 4 l/hr
accompanied by a more even distribution of sweating
sweat losses of sodium chloride decrease b/c of increased secretion of aldosterone

40. Thermal Distress
includes dehydration, heat cramps, heat exhaustion, heat syncope, and heat stroke
hyperthermia is caused by an imbalance between heat gain and heat loss

41. Dehydration loss of fluid from the body
can decrease sweat rate, plasma volume, Q, VO2 max, work capacity, muscle strength, and liver glycogen
at fluid deficit of 5% of BW, symptoms include discomfort, and alternating states of lethargy and nervousness
level >7% is extremely dangerous

42. at levels >10%, ability to walk is impaired, and is accompanied by discoordination and spasticity
as 15% is neared, the person experiences delirium, shriveled skin, along with decreased urine volume, loss of ability to swallow food, and difficulty swallowing water
>20% the skin bleeds and cracks

43. thirst does not keep up with fluid requirements
physical fitness helps prevent this
during prolonged exercise, can develop hyponatremia, caused by excessive sodium loss in the sweat without adequate replacement

44. Heat cramps
characterized by involuntary cramping and spasm in muscle groups used during exercise
it occurs in people who have exercised and sweated heavily
often the individual is conditioned and acclimatized
fluid and electrolyte replacement, rest, some say magnesium helps

45. Heat exhaustion
rapid, weak pulse, hypotension, faintness, profuse sweating and psychological disorientation
results from acute plasma volume loss and inability of the circulation to compensate for the concurrent vasodilation in the skin and the active working muscles

46. Treatment have person lie down in cool area administer fluids
rest and drink plenty of fluids for next 24 hr.
not allowed to participate for rest of the day

47. Heat syncope
related to heat exhaustion, but can occur without major sweat loss
typically, it occurs after exercise when the individual stops moving and blood pools
can occur secondary to heat exhaustion or independently

48. Heat stroke
failure of hypothalamic temperature regulatory center; represents a major medical emergency
principally caused by failure of the temperature regulatory center in hypothalamus, which causes failure of the body’s heat loss mechanisms

49. characterized by a high core temperature, hot, dry skin, and extreme CNS dysfunction
associated with increases in plasma norepinehprine, epi, and endotoxin levels that have been associated with vascular collapse
risk is greatest in high temperatures, humidity, hottest time of the day, and on days with little wind

50. Treatment cool person with tepid water
ice packs on the groin, neck, and axilla
send to hospital ASAP

51. Prevention ensure athletes are well-conditioned avoid overheating
be aware of early symptoms of heat stress: thirst, fatigue, lethargy, and visual disturbances
athletes should not train harder than normal intensity
should not compete if have an illness accompanied by a fever

52. schedule practice during the cooler times of the day
modify or cancel sessions when the wet bulb temperature is 25.5°C or greater
plan regular fluid breaks
supply a drink that is cold and contains some CHO and electrolytes

53. hyperhydrate before activity
fluid replacement should be encouraged during the early stages of practice and competition
athletes should be weighed every day before and after practice. If a 2-3% decrease in weight, should consume more fluid, if 4-6%, should decrease activity levels, 7% loss, consult a physician

54. Rhabdomyolysis Myoglobin excretion is increased
Myoglobin is cleared by the kidneys
Kidneys shut down, especially with heat
Can lead to death
Occurs with excessive exercise
Rare
May be a predisposition, latent metabolic disorder
Diuretics contribute to this
CHO as well, but a rare possibility