What physiological changes occur in hot conditions? (2)
- changes in circulation to increase peripheral blood flow:
- sympathetic NS signals skin arterioles to dilate and divert blood to peripheries to cool core
- increase HR, contractility and Q to compensate in BP fall - increase in sweating (evaporation) through the stimulation of eccrine sweat glands to secrete sweat
What physiological changes occur in cold conditions? (3)
- behavioural related changes
- reverse process of heat reponses
1. peripheral vasoconstriction: peripheral artieries constrict to maintain blood closer to core, acts to limit heat loss via skin.
2. non-shivering thermogenesis: sympathetic NS stimulates metabolism to generate heat = increased energy use
3. shivering: rapid involuntary cycling of contraction/relaxation of skeletal muscles to generate warmth similar to exercising.
What is the physiological range of core temperature? (6)
normal range = 31-41 deg.
> 45 = possible death without treatment
40 = profound clinical hyperthermia (heat stroke)
38.5 - 39.5 = mod. hyperthermia (heat exhaustion)
36.5-37 = normothermia
33-25 = mod. hypothermia
<24 = possible death without rewarming
How is the thermoregulatory response controlled? (3)
- temperature changes measured by thermoreceptors in the blood as it passes through the hypothalamus and peripheral temperature sensors in the skin, abdominal viscera, spinal cord and greater veins
- Hypothalamus collates efferent signals
- Stimulates processes to cope with heat change (sympathetic ns)
What is conduction? How does it relate to human thermoregulation?
direct heat transfer from one molecule to another through a liquid, solid or gas
requires direct contact
depends on:
- temperature gradient between the surface
- thermal qualities of the surfaces
when exercising our muscles create heat which is conducted out to surrounding tissue and blood
What is evaporation? How does it relate to human thermoregulation?
loss of heat as water heats and converts into a gaseous form
- aided by convection
sweat allows heat to evaporate away from the skin - must evaporate not drip or be wiped away
- primary source of heat loss during exercise
Affected by water vapour pressure of the surrounding air and the gradient between the skin and the surrounding air
How does heat affect exercise performance? (endurance, short sprints, repeated sprints)
endurance performance decreased
- competition for blood supply may limit supply to musculature
- decreased VO2 max, LT2 and time to exhaustion
Short sprints are unaffected
Repeated sprints performance decreased
- decreased glycogen stores
- similar to endurance
Describe cardiovascular drift
Occurs when exercise continues for any length of time in the heat. HR increases even when exercising at a fixed intensity due to:
- continued competition for blood supply
- additional sweating causing plasma volume losses
- plasma is shifted from blood to tissues
- loss of plasma volume -> decreases EDV (decreases preload) and compromises Q
What is acclimation?
using artificial means to expose the body to various conditions
How does cold affect exercise performance? why?
overall decreased performance
- muscle require warm temp. to perform optimally
- decrease in muscular force
- decreased function of small muscles in peripheries
- as fatigue sets in and work rate decreases the ability to create heat decreases
- catecholamines form part of the sympathetic response to the cold; vasoconstriction to fatty tissues to maintain warmth means that access to these fuels is more difficult -> greater use of glycogen stores
- shivering increases VO2 required for a given intensity
Describe critical temperature theory
At approx 40deg most people will voluntarily cease exercise.
Possibly a protective mechanism related to:
- critical temp of brain
- circulatory maintenance
- protect proteins from destruction
The CNS may act directly to inhibit motor recruitment and force production
also consider psychological factors
What are the adaptations to cold conditions?
Limited ability to adapt to the cold. any adaptations are likely to occur during resting exposures.
Behavioural changes have a greater benefit e.g. clothing
What are the adaptations to hot conditions in 5-10 days? how does it affect performance?
- lowered salt content of sweat - dilute sweat preserves extracellular electrolyte concentrations
What are the adaptations to hot conditions in 7-10 days? how does it affect performance?
- improved cutaneous blood flow - transports metabolic heat from deep tissues to bodies shell
- increased sweat output - maximizes evaporative cooling
- lowered sweat threshold - evaporative cooling begins sooner
- more effective distribution of sweat over skins surface - optimum use of surface area for cooling
How would you design an acclimatization program for heat performance? (time frame, temp, intensity, length of session etc.)
- 7-14 days
- 30-35 deg. humidity to match venue
- short, mod. intensity (30-35 min @ 75% VO2 max)
- long, low intensity (60min @ >50% VO2 max)
- interval or continuous
- ideally every day but no more than 2-3 days between sessions
- dry heat better than humid
What are the adaptations to hot conditions in 3-6 days? how does it affect performance? (1)
- increased plasma volume - appropriate circulation to skin and muscles to meet demands of metabolism and thermoregulation; greater CV stability during exercise
What are the adaptations to hot conditions in 5-10 days? how does it affect performance? (1)
- lowered salt content of sweat - dilute sweat preserves extracellular electrolyte concentrations
What are the adaptations to hot conditions in 7-14 days? how does it affect performance? (6)
- improved cutaneous blood flow - transports metabolic heat from deep tissues to bodies shell
- increased sweat output - maximizes evaporative cooling
- lowered sweat threshold - evaporative cooling begins sooner
- more effective distribution of sweat over skins surface - optimum use of surface area for cooling
- decreased reliance on CHO during exercise
- lowered Tcore, Tskin and HR for standard exercise
What physiological changes occur with exercise in the heat? and why? (7)
- working muscles and increased metabolism increased heat load
- Tcore raised and heat balance maintained at a higher level
- HR, contractility and Q increase to account for demands: blood needs to be diverted to peripheries to enhance cooling, decreased supply of O2 blood to working muscles
- blood supply decreased to non-essiential tissues (digestive system, liver, kidneys)
- HLa- clearance decreases since hepatic blood supply is reduced
- greater contribution from anaerobic energy sources due to competition for blood supply to muscles
What is pre-cooling and what are some methods?
Lowering resting Tcore prior to exercise to delay time to critical temp. Improves the sensation of thermal stress Increases exercise performance Methods: - cooling jackets - ice slushies - cold towels - cold water immersion (CWI)
What effect does heat acclimatisation have on exercise performance? (6)
- PV better maintained
- HR remains more stable
- time to reach critical Tcore improved/delayed
- ability to withstand higher Tcore
- improved endurance and team sport performance
- improved time to exhaustion
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Physiological adaptations to endurance13
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Physiological adaptations to anaerobic training20
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Enzymes9
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Physiological adaptions to strength, speed, power15
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Limits to human performance16
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Thermoregulation during exercise21
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Altitude and exercise16
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Ergogenic Aids19
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Sex Differences20
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Development and Ageing5
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Fatigue and Overtraining25
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Recovery20
