Exercise Physiology 2

Temperature Regulation

Normal Body temperature is 37°C. The core of the body remains at this temperature due to a balance between heat entering and heat leaving the body.

HEAT GAIN = HEAT LOSS

Skin temperature is different to body temperature. It is a product of:•Environment

•Clothing

•Quantity of body fluid

•Whether at rest or exercise

Thermal Death Point

Thermal death point is only 7°C either side of the body’s “reference” temperature.

Temperature Regulation Control

The hypothalamus is the body’s thermostat. If the body’s temperature goes above or below 37°C it will react.

The hypothalamus acts as a thermometer inside of the body. It sends messages to the heating and cooling systems of the body, which react to re-establish the normal internal temperature.

Heat balanceHEAT BALANCE

HEAT PRODUCTION HEAT LOSS

Metabolism

Voluntary Exercise

Involuntary Exercise

(shivering)

Radiation

Conduction

Convection

Evaporation

The body loses and gains heat in order to maintain a heat balance.

Heat Loss

Radiation – Heat loss through infrared rays. The greater the difference between the body’s heat and the environment, the greater the radiated heat loss.

Conduction – Transfer of heat through contact

Convection – Transfer of heat by a moving fluid (hot air rises)

Evaporation – Sweating

Exercise in the heatWhen at rest the core body temperature is

37°C. Muscle temperature however, changes between 25°C and 33°C depending on environmental temperature. Muscle temperature increases during exercise.

Exercise in the heat makes it difficult for the body to maintain it’s heat balance, and the body’s water requirement greatly increases.

Through perspiration, the body loses its major cooling aid being water (0.5L to 4.2 L per hour may be lost.)

Sweating is a result of increased muscle temperature. Continuous exercise and inadequate fluid replacement results in rises in core temperature.

For every 1% loss of body weight there is a 0.1°C increase in core temperature.

Symptoms of water loss

1% loss causes thirst

5% loss causes discomfort

7% loss is dangerous

10% loss results in the breakdown of coordination and all movements are difficult.

15% loss results in the athlete becoming delirious

20% loss is the upper limit of dehydration before death.

DEHYDRATION

Increase in pulse rate

Decrease in blood pressure

Decline in circulatory function Increase in core body temperature

Decrease in blood pressure

Heat disorders1.Dehydration – Excessive loss of water which

results in thirst to circulatory problems to muscle meltdown to death

2.Heat Cramps – Involuntary cramping of muscle groups as a result of dehydration

3.Heat Exhaustion – Caused by the inability of the circulatory system to function properly in the absence of sufficient water

Warning signs are:• Profuse sweating

• Paleness

• Fast and shallowing breathing

• Rapid and weak pulse

• Cool and moist skin

• Faintness

• Disorientation

What to do:– Help person to cool off

– Use cool, non-alcoholic beverages

– Rest

– Cool shower, bath or sponge bath

– Lightweight clothing

– Air conditioned room

– If symptoms worsen or last longer than 1 hour seek medical attention

4.Heat Stroke – the temperature regulatory system breaks down and the core body temperature rises over 41°C within ten to fifteen minutes

Warning signs are:– Confusion

– Little or no sweat with red, hot dry skin

– Rapid, strong pulse

– Throbbing headache

– Unconsciousness

– NauseaWhat to do:

– Get person to shady or air-conditioned area

– Cool person immediately using whatever methods you can. For example, immerse in a tub of cool water, cool shower, spray with garden hose or if humidity is low wrap person in a cool wet sheet and fan them.

– Seek medical assistance as soon as possible

Methods for dealing with heat during exercise•Drink plenty of water

•Replace salt and minerals

•Wear appropriate clothing and sunscreen

•Schedule outdoor and indoor activities carefully

•Acclimatisation

•Train with others

•Stay cool indoors

•Monitor those at high risk: infants and children up to 4 years, people 65 years of age or older, overweight people, the ill or those who take medications and people who overexert during work or exercise.

Exercise in the cold

Dangers of exercising in the cold are greater than those for exercising in the heat.

There are only limited means of short-term acclimatisation to reduce the impact of cold on exercise performance.

This includes vasoconstriction, which limits the blood flow to the skin to avoid cold injury.

Shivering is also a form of gaining heat, but it can hinder performance as it fatigues muscle activity and reduces motor skill level.

Methods to reduce the effects of cold while exercising are:

Multiple layers of thin, wind / waterproof, breathable clothing, which may be adjusted to the level of activity. Remove outside layers before sweating commences into thin layers. Cover the head, as it is a very high area of heat loss. Make sure the extremities are covered to prevent frostbite.

If possible train indoors or in areas away from the wind and cold temperatures.

Food increases metabolism and digestion increases heat production. Eat foods containing protein, as it has a high specific dynamic index (SDA) and makes you warmest out of all of the types of food.

Must keep the intake of fluids up, as cold air cannot hold moisture.

Respiration – try to cover the mouth and nose, as cold / dry air must be warmed / humidified eg wear a scarf

Try to exercise in the middle of the day when the air temperature is at its highest and when there is the greatest radiant heat.

If it doesn’t compromise performance, putting on extra fat acts as insulation against the cold conditions eg Susie Maroney

Hypothermia – occurs when the core body temperature is below 35°C. It is characterised by the ‘stumbles and mumbles’.

Results in low blood sugar levels, hypoventilation, acid / base disturbances, loss of protein from damaged cells and eventually cardiac failure

Treatment:

•Remove from cold environment and use dry clothing

•Slow re-warming – use body heat, drinks and pre-warmed air

•No hot showers or baths, warm from inside out and do not massage hands and feet vigorously.

Exercise at altitudeExercise at altitude can have a major effect on

performanceEndurance performance is usually diminished

and anaerobic performance unaffected. This is because ascent to altitude results in lower oxygen in inspired air, and therefore less oxygen delivery to active muscles.

The percentage of oxygen in the air is at the same at sea level, but the total amount of air is less.

A moderate altitude around 15oom can start to affect the athlete, and over 5000m can be extreme.

An increase of altitude results in a decrease of 2°C per 300m, so the cold also has to be dealt with.

Physiological responses to exercise:

Decreased arterial oxygen content

Increased ventilation

Increased CO2 output

Increased stroke volume

Decreased sub-max HR

Decreased VO2 max

Progressive dehydration – increased breathing of colder / dryer air and increased urine.

Overcoming the effects of altitude

Live high / train low – maximise the resting adaptations to altitude and minimise the disruption to training caused by altitude

Daily transit – between high and low altitudeNitrogen houses – decreases O2 in the air by increasing

nitrogen. Mimic high altitude conditions and you can set the height you require

Altitude tents – portable and have a decreased O2.

Acclimatisation at Altitude

Adaptations occur over 2 – 3 weeks:Increased red blood cell concentration – over days due to dehydration and weeks / months due to increased cell production

Partial restoration of plasma volumeIncreased muscle capillarisation Increased muscle enzyme activity

Altitude SicknessThis generally occurs above 3000m and is most likely to happen in:

–Unacclimatised individuals

–After rapid ascent

– In combination with exercise

Symptoms:–Headache

–Dizziness

–Nausea

–Sleep disturbances due to cardiovascular responses to hyperventilation

* Pulmonary / cerebral edema may occur in extreme circumstances and requires immediate return to lower altitudes.

HydrationPrinciples of body temperature regulation

The temperature of a healthy individual is maintained at around 37°C. Changes in external temperature (eg weather) or internal temperature (eg exercise or fever) causes a response in the brain. The hypothalamus in the base of the brain controls and regulates the temperature of the body through ‘shivering / Goosebumps’ to conserve heat accordingly and ‘sweating’ to cool the body. This is called ‘thermoregulation’.

Heat is lost from the body by:

Radiation – heat radiates from the skin to the environment

Conduction – heat is transferred to an object; seat or chair for example

Convection – air currents cause heat loss from the skin

Evaporation – sweating causes heat loss

Dehydration (loss of fluid from the body) causes fatigue in a performer so fluid must be replaced. Continued dehydration results in an increase in pulse rate, higher core body temperature, decreased blood pressure and a gradual decrease in circulatory function. Heat cramps and heat stroke are serious consequences of failure to hydrate the body sufficiently. Thirst is not a good indicator as you are already dehydrated and fluid loss is best measured by immediate weight loss, for every 1 kg of weight loss, 1 L of fluid has been lost. Another indicator of dehydration is the colour of urine (yellow usually means dehydrated, clear means hydrated).

Guidelines for fluid replacement

Water is the ideal fluid replacement

Hydrate before a performance

Rehydrate, if possible, during a performance

Drink after the performance

Sports drinks are ok as they aid fluid absorption, particularly in hot conditions

Wear loose clothing while exercising to help heat loss from the body

Avoid exercise in the hottest times of the day and where there is a high fluid loss on two consecutive days

Avoid alcohol, caffeine and salt as it accelerates dehydration by absorbing fluids and making you urinate more.