Unit 3&4 - Exercise Physiology Flashcards
vasodilation and vasoconstriction
If the body needs to lose heat, vasodilation (blood vessels
to the skin surface increase their diameter) takes place, increasing blood flow to the skin so heat loss can occur via sweating
If the body is trying to retain heat, vasoconstriction (blood vessels to the skin decrease their diameter) occurs and less blood is sent to the skin surface so heat loss is minimized. Vasoconstriction can result in a loss of fine motor skills.
CONDUCTION and factors
Heat exchanged by 2 objects in contact
Factors that determine rate at which conduction occurs:
Difference in temp between 2 surfaces (heat flows from hot to cold)
Surface area (↑SA→ ↑ heat loss)
Thermal conductivity of material (metal – good conductor of heat)
CONVECTION
Heat exchange by contact with a fluid that is flowing
This will occur when heat is carried away from body by air or water currents.
RADIATION
Radiation occurs when heat is transferred from a warmer body to the cooler surroundings without physical contact
EVAPORATION
Is the cooling of the body as a result of the vaporisation of sweat
Evaporation of sweat on skin creates cooling effect
As a result, the cooled skin cools the blood travelling to the skin’s surface, maintaining the body’s core temperature
- Evaporation is most effective in dry conditions
As humidity increases, evaporation becomes less effective
- 100% humidity results in no heat loss via evaporation as sweat cannot be evaporated off the skin if the surrounding air is already saturated.
- Body will continue to sweat but no heat loss occurs and core temperature will rise. Dehydration becomes a problem due to large volume of fluid being lost from the body.
Rate of sweating dependent on;
Gender (male more than female)
Number of sweat glands
Body surface area (↑SA = ↑ sweat)
How fit you are (↑fitness = ↑ sweat if all other factors are equal e.g. body SA)
Excessive sweating leads to a loss of body fluids and when level of fluid drops, body’s core temp↑.
It is this gradual dehydration which leads to heat exhaustion and heatstroke
The body’s preferred mechanism of heat loss is dependent upon the following 3 factors;
ENVIRONMENT
Ambient temperature – if above the body’s core temperature, then evaporation is the only method of heat loss. Other methods will result in heat gain.
Forced convection – heat loss via convection will occur if it is windy.
Barriers to convection – clothing will minimise the effect of convection as it will insulate the boundary layer of air.
Temperature radiating surfaces – light clothing will not absorb as much heat as dark clothing
Relative humidity – if 100%, no heat loss via evaporation.
The body’s preferred mechanism of heat loss is dependent upon the following 3 factors;
AGE
Children don’t sweat as much as their sweat glands are not as developed as adults
The body’s preferred mechanism of heat loss is dependent upon the following 3 factors;
PHYSIOLOGICAL STATE
Rate of heat production (how much work the athlete is performing)
Hydration state – will determine rate of evaporation as a reduction in plasma volume leads to a decrease in sweat rate
Heart rate (HR) Stroke Volume (SV) Cardiac Output (Q)
the number of times the heart beats per minute
the amount of blood ejected from the heart each beat
the amount of blood circulating around the body every minute = HR * SV
Double heat load
situation where the body is forced to deal with 2 forms of heat (metabolic heat and environmental heat)
As a result this double heat load creates competition for blood flow
- Muscles and vital organs require blood flow to sustain energy metabolism
- Skin blood flow required to transport heat out to environment to keep core temperature cool. This blood flow cannot deliver its oxygen to the working muscles, impacting on performance.
Cardiovascular drift (cardiac drift)
when heart rate increases in an attempt to maintain cardiac output caused by a decrease in stroke volume
When exercising in the heat, the body directs blood flow to the skin and away from the working muscles to increase heat loss via evaporation
An ↑ in sweat rate → ↓ blood plasma volume.
As a result CARDIOVASCULAR DRIFT occurs;
In an attempt to maintain cardiac output, HR increases.
This increase in HR is relatively smaller than the decrease in SV, therefore cardiac output is reduced.
As a result, skin blood flow ↓ (cooling mechanism) and oxygen sent to working muscles is also reduced, placing extra strain on the body to maintain exercise levels.
A reduction in blood flow to the working muscles increases production of lactic acid
A reduction in blood flow to the skin reduces the rate of sweating, inhibiting the body’s ability to lose heat via evaporation. These changes lead to a rise in core temperature and negatively affect performance
Dehydration
- occurs when the amount of water leaving the body is greater than the amount being taken in
Heat related injuries are progressive – they occur in a certain order.
Stage 1 – Dehydration occurs when fluid replacement does not match fluid loss.
Stage 2 – Heat exhaustion occurs when the dehydrated athlete continues to exercise and continues to sweat thereby losing more fluid. If the athlete fails to replace the fluid lost through sweating, he risks moving to stage =
Stage 3 – Heat stroke occurs when the body stops sweating resulting in the core temperature rising to dangerous, life threatening levels, caused by a lack of evaporative cooling. It is a form of hyperthermia.
explanation summarises the process of heat stress occurring to an athlete exercising in very hot conditions (40°C);
At rest in the heat, conduction, convection and radiation all become methods of heat gain.
As a result HR and SV ↑ to allow the body to send more blood to the skin, creating a cooling effect via evaporation
Commence exercise – HR and SV continue to ↑ as the body must also send blood to the working muscles
Whilst exercising, core body temp starts to↑ which places extra strain on the body’s cooling mechanism – the hotter it is, the more dependant the body is on evaporation
A hot ambient and core temperature creates a double heat load
Players drink fluid in an attempt to remain hydrated
As exercise continues, player continues to drink, however fluid loss > fluid intake resulting in dehydration occurring
Dehydration results in a loss of plasma volume. This affects the amount of blood which can be delivered around the body
As blood volume , the body must try and maintain cardiac output (Q) to ensure enough blood is still sent to the working muscles and skin
HR ↑, however this increase is not as big as the SV. Subsequently, Q leading to less blood flow to the working muscles and the skin
This leads to a reduced performance and an ↑ core body temp – headache, dizziness, nausea
With continued exercise, further sweat loss occurs leading to severe dehydration
With Q, body must now make a decision
Send blood to the working muscles and vital organs?
Send blood to the skin for cooling?
The body chooses muscles and vital organs leading to reduced heat loss via evaporation (dry skin). As a result core temperature rises placing the athlete at extreme risk of unconsciousness, coma or even death if exercise continues
HYPERHYDRATION PRE - EXERCISE
Involves increasing the body’s fluid stores by consuming extra fluid prior to an event.
1L prior to exercise recommended
600ml 3 – 4 hours before the game
400ml just prior to the game to prime the stomach m
Hyponatremia
An abnormally low concentration of sodium (salt / electrolytes) in the blood.
When a person sweats profusely for an extended period of time, drinking too much water can cause problems because the body is losing salt and water in the sweat, but only the water is being replaced
4 ways sports drinks are affective SPORTS DRINKS
Taste good meaning athlete wants to drink more
Provide athlete with rapid supply of energy (high GI) and assist in glycogen sparing
Replace lost electrolytes (particularly effective in ultra endurance activities where massive amounts of sweat loss and electrolyte loss occurs)
Rehydrate the performer
Heat acclimatisation and HOW TO ACCLIMATISE;
when heat tolerance is improved by repeated exposure to hot environments.
The first sessions of heat acclimatisation should last for 15-20 minutes and be combined with light to moderate activity.
It should increase to 45-60min daily for approx 8-9 days with an increase in exercise intensity & duration.
5-10 days living and training in heat is recommended
Should be completed 4-6weeks prior to competition and then 2* per week leading up to competition to maintain benefits
MAJOR ADAPTATIONS TO HEAT ACCLIMATISATION
sweating
↑ blood plasma volume
↑ Sweat rate (sweat glands ↑ size)
Start sweating at lower core temperature
Sweat becomes more dilute & is distributed over the body more effectively – keeps salt in the body
CARDIOVASCULAR
Heat acclimatised athletes exercise with lower core and skin temperatures due to sweating adaptations
Increased blood volume to allow for increased sweating
Humidity define and it will;
Defined as the amount of water vapor that exists in the air
Increase sweat rate
Increase fluid loss
Decrease the effectiveness of cooling via evaporation
Decrease performance, particularly aerobic performance.
Wind chill
is the apparent temperature felt on the skin due to the combination of wind and ambient temperature.
Wind increases the loss of heat via convection as it constantly removes the layer of warm air around the body and the body cools rapidly.
Hypothermia
Hypothermia occurs when the body’s temperature falls below 35°C.
METHODS TO HELP COPE WITH EXERCISING IN THE COLD 4 ways
Experiment with length of warm up
Experiment with layered clothing
Psychological acclimatisation
Ensure adequate fluid replacement as water loss will be increased via the need to humidify dry, cold air before it enters the lungs
when at ALTITUDE
At altitude, there is a reduction in the pressure of oxygen entering the lungs. This reduces the pressure differential between the alveoli and the capillaries with the result being less oxygen diffusing from the alveoli into the blood.
ALTITUDE ACCLIMATISATION
Altitude acclimatisation describes the improved physiological response to altitude hypoxia
LIVE HIGH, TRAIN LOW
This involves daily intermittent exposure to artificial altitude environments whilst maintaining normal training intensities
This method is seen to be more beneficial as it allows players to maintain their training intensity whilst still getting the added benefit of altitude exposure and its associated physiological adaptations.
LIVE HIGH, TRAIN HIGH
Athletes lives at altitude to achieve physiological benefits of decrease in 02 concentration and trains at altitude to obtain adaptations
As a result, reduced benefits in performance due to reduced training intensity over a prolonged period of time – DETRAINING.
train for a period of 3-4weeks