A2 Flashcards
State the normal physiological range for core body temperature
37±0.5 degrees celsius
What is thermoregulation?
Increased blood and internal temperature
Impulses go to hypothalamus
Vasodilation occurs in skin blood vessels so more heat is lost across the skin
Sweat glands become more active, increasing evaporative heat loss
Body temperature decreases
What are the four ways the body thermoregulates in hot and cold environments?
Conduction, convection, radiation, evaporation
Outline conduction
Heat can be conducted through the body’s surface and to the clothing and/or the air (or water) that is in direct contact with the skin. Conduction accounts for less than 2% of heat loss.
Outline convection
Involves moving heat from one place to another by the motion of air (or water) movement. Cyclists gain a cooling effect through convection.
Outline radiation
Transfer of energy waves (sun, fireplace, radiator) sent by one object and absorbed by another. The body absorbs radiant heat energy when temperature of the environment is higher than skin temperature.
Outline evaporation
Conversion of sweat from liquid water to vapor (evaporative cooling). Is the most important avenue for heat loss from the body. As sweat evaporates from the skin, a cooling effect is achieved, thus releasing heat from the body.
Describe the formation of sweat and the sweat response
Body contains between 2-4 million sweat glands
Sweat production depends on density of sweat glands and amount of sweat per gland- back and chest have greatest sweating rates.
Sweat glands are located over most of the body and release a solution containing water and minerals through small opening in the skin onto the surface of the body.
When this solution evaporates, it effectively cools the skin and regulates body temperature.
Sweating during exercise reflects increase in body temp.
Also influenced by amount of moisture in air.
Discuss the significance of humidity and wind in relation to body heat loss.
Humidity plays a major role in heat loss
Affects perception of thermal stress
When high (regardless of temperature), limits evaporation of sweat
Convection involves moving heat from one place to another by the motion of air (or water) movement. Less wind, less convection, and vice versa.
Outline the importance of wind chill in relation to body heat loss.
Wind increases the rate of heat loss (via convection) because the warmer insulating air layer surrounding the body continually exchanges with the cooler ambient air.
The wind chill index illustrates the cooling effect of wind on exposed skin leading to a dangerous exposure (frostbite).
Discuss the physiological responses that occur during prolonged exercise in the heat.
Increased vasodilation to assist with cooling
Reduced muscle blood flow in high temperatures resulting in increased glycogen breakdown in the muscle and higher levels of muscle and blood lactate in comparison to the same exercise performed in a cooler environment.
Reduced blood volume due to excessive sweating. Thus a reduced cooling ability of circulating blood.
An increase of body temperature results in a lower venous return (rate of blood flow) to the heart, and a small decrease in blood volume from sweating.
A reduction in SV causes the HR to increase to maintain cardiac output. Elevated heart rate (This phenomenon is called Cardiovascular drift)
Explain cardiovascular drift
An increase of body temperature results in a lower venous return to the heart, a small decrease in blood volume from sweating. A reduction in stroke volume causes the heart rate to increase to maintain cardiac output.
Include reference to blood viscosity.
Describe how an athlete should acclimatize to heat stress.
Performing training sessions in similar environmental conditions (heat and humidity) for 5 to 10 days results in almost total heat acclimatization.
Initially, the intensity of training should be reduced to avoid heat-related problems in these conditions.
The total daily exercise-time in the heat should reach 90-100 minutes.
Discuss the physiological and metabolic adaptations that occur with heat acclimatisation.
Increased plasma volume
Increased sweat response (rate of sweating)
Decreased electrolyte content of sweat (thinner sweat)
Minerals in body to balance amount of H20 in your body and pH levels
Reduced rate of muscle glycogen utilization
Decreased heart rate at a given work load and stress
Lower core and skin temperature
Heat-related disorders
Heat cramps
Heat exhaustion
Heat stroke
Hyperthermia (a symptom of heat stroke) – core body temperature has risen dangerously high
What is the cause of heat cramps?
intense, prolonged exercise in the heat
muscle fatigue
sodium loss in sweat
What are the signs and symptoms of heat cramps?
pain
involuntary spasms of active muscles
low serum Na+
How do you prevent heat cramps?
stop exercise; rehydrate
massage/light stretching
What are the causes of heat exhaustion?
Increasing negative water balance
What are the signs and symptoms of heat exhaustion?
Fatigue/exhaustion
Loss of movement coordination/dizziness
Flushed skin
Reduced sweating
High core temperature
How do you prevent heat exhaustion?
Remove subject to shaded/air-conditioned area
Hydrate before and during exercise
Acclimatised
What are the causes of heat stroke?
Thermoregulatory failure
Dehydration
What are the signs and symptoms of heat stroke?
Core temperature >41 degrees celsius
Lack of sweating
Disorientation/twitching/seizures/coma
How do you prevent heat stroke?
Immediate whole body cooling
Acclimatise
Adapt activities to climatic constraints
Treatment of heat cramps
move to cooler location and administer fluids or saline solution
Treatment of heat exhaustion
move to cooler environment, elevate feet; give saline if conscious or intravenous saline if unconscious
Treatment of heatstroke
rapidly cool body in cold water or ice bath or with wet towels; seek medical attention
How can athletes minimise the impact of heat related disorders?
Acclimatise - to get used to the temperature/humidity and environment before the competition
Tapering - reducing intensity and duration of training leading up to competition
Stretching/massaging (heat cramps)
Wear light weight clothing
Stop exercising
Hydration
Avoid direct sunlight
How is muscle function effected by exercising in the cold?
- cooling a muscle causes it to contract with less force
- Normal muscle fibre recruitment patterns are altered for force development
- This can affect the efficiency of the muscle’s actions
- Muscle flexibility is reduced
- Both muscle shortening velocity and power decrease
- Small muscles in the periphery, such as fingers, can be severely affected, reducing dexterity and the ability to perform fine motor skills
How are metabolic responses effected by exercising in the cold?
- Prolonged exercise is marked by gradual depletion of carb stores and inability to maintain blood glucose
- Shivering increases glycogen breakdown during exercise
- Shivering relies on fat (lipids), blood glucose, muscle glycogen and protein as energy sources
- Carb intake may be required for prolonged exercise in the cold
- Hypoglycaemia (low blood sugar) suppresses shivering
- Individuals use more energy exercising in the cold than in the heat
- Free fatty acid (FFA) as a fuel source reduces due to vasoconstriction, as blood flow to subcutaneous fat stores is reduced
How does the body conserve heat?
Shivering involves rapid involuntary cycle of contraction and relaxation of muscles.
Non-shivering thermogenesis is stimulation of metabolism. Increasing the metabolic rate increases heat production
Peripheral vasoconstriction reduces blood flow to skin.
Induce vasoconstriction of skin and skeletal muscles circulations.
Decreased blood flow decrease convective heat loss
Induce shivering involuntary, rhythmic muscle contractions heat production.
Decrease muscle contractibility.
Lower HR (due to peripheral vasoconstriction).
Also, joints become stiff due to synovial fluid becoming viscous, which hampers performance
Relationship between cellular metabolism and the production of heat in the human body
Cellular metabolism – all chemical reactions taking place within the body, including respiration of working cells during physical exercise.
Only a small part of the energy (ATP) the body produces is used for physiological functions such as muscle contractions – usually less than 25%
The rest is converted to heat
All active tissues produce metabolic heat
(Body temperature can increase as a result of exercise.
During exercise, respiration releases energy in the muscles
To keep your body temperature from rising too high, your heart pumps the heat in your blood from your muscles to your skin
The skin produces sweat which evaporates from the surface of the skin to cool your body.
Meanwhile, this decreases O2 supply to skeletal muscles lowering performance)
What is frost bite?
Frostbite is damage to skin and tissue, continued cooling and freezing of cells leading to destruction of cells. Similar to burns. Also, as circulation decreases, cell die due to lack of oxygen and nutrients.
How is frost bite caused?
It is caused by exposure to freezing temperatures – typically any temperature below -0.55C (31F).
What are the risks?
Can be intensely painful. Deep frostbite can lead to tissue loss of fingers, toes and even parts of limbs.
What is hypothermia?
A serious situation where the core temperature of the body falls from 37C, down to 35C or less.
A low body temperature, decrease in respiratory rate and volume.
How is hypothermia caused?
If someone is exposed to extreme cold and/or inadequately protected
What are the risks of hypothermia?
Mild Hypothermia - symptoms such as shivering, numb hands and other extremities and reduced manual dexterity.Complex skills such as skiing become more difficult, the victim may also feel tired and may argue and become uncooperative.
profound hypothermia – unconsciousness and death
What are the precautions you should take when exercising in the cold?
The principle barrier is clothing, the amount of insulation offered by which is measured in a unit called a clo. Generally each 0.6cm of clothing adds 1 clo of insulation.
The insulating effect of clothing is reduced when it becomes wet.
Clo unit is a measure of insulator capacity provided by any layer of trapped air between the skin and clothing.
Stay dry, because being wet reduces the effect of insulation.
Not overdressing due to having too much insulation and therefore producing too much sweat.
Hands and face should also be covered to prevent frostbite.
Hydration
Why does swimming in cold water represent a particular challenge to the body’s ability to thermoregulate?
Water has a very high volumetric heat capacity. Raising the temperature of a cubic centimetre of water by 1°C takes more than 3200 times as much energy than you’d need to heat the same volume of air by the same amount.
This means that the layer of water surrounding your body heats up only very slowly, the temperature gradient between the water and you stays very steep, so the rate of heat loss remains high.
Worse, because water is very dense, even a slight current will penetrate through clothes and between the hairs on your skin.
This displaces the water you have already warmed up. On the other hand, air is easier to trap in a stationary boundary layer that can be warmed up and this acts to reduce the steepness of the temperature gradient.
Water has a much higher thermal conductivity than air. This means that water conducts heat much better than air does, and heat loss via conduction when immersed in water is greater.
Finally, the presence of water currents results in an increased rate of convective heat loss.
Why is the body surface area to body mass ratio important for heat preservation?
Individuals with higher body mass tend to have a smaller ratio of surface area (skin) to body mass
This leads to decreased rates of heat loss.
Children, who tend to have a higher surface area to volume ratio, conversely lose heat more rapidly.
