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:
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 BALANCE HEAT PRODUCTION HEAT LOSS Metabolism Voluntary Exercise Involuntary Exercise (shivering) Radiation Conduction Convection Evaporation Heat balance The body loses and gains heat in order to maintain a heat balance.
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 heat When 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.
Increase in pulse rate
Decrease in blood pressure
Decrease in blood pressure
DEHYDRATION Decline in circulatory function Increase in core body temperature
Heat disorders Dehydration – Excessive loss of water which results in thirst to circulatory problems to muscle meltdown to death Heat Cramps – Involuntary cramping of muscle groups as a result of dehydration Heat Exhaustion – Caused by the inability of the circulatory system to function properly in the absence of sufficient water Warning signs are:
Fast and shallowing breathing
Rapid and weak pulse
Cool and moist skin
What to do:
Help person to cool off
Use cool, non-alcoholic beverages
Cool shower, bath or sponge bath
Air conditioned room
If symptoms worsen or last longer than 1 hour seek medical attention
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:
Little or no sweat with red, hot dry skin
Rapid, strong pulse
What 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
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 altitude Exercise at altitude can have a major effect on performance Endurance 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 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 altitude
Nitrogen 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 volume
Increased muscle capillarisation
Increased muscle enzyme activity
Altitude Sickness This generally occurs above 3000m and is most likely to happen in:
After rapid ascent
In combination with exercise
Sleep disturbances due to cardiovascular responses to hyperventilation
* Pulmonary / cerebral edema may occur in extreme circumstances and requires immediate return to lower altitudes.
Exercise Under Water
Effects of Pollution on Exercise Many cities in the world have severe pollution problems, which have a negative effect on performance – there is little you can do. However, try: Exercise in large parks away from major traffic areas where possible Exercise at times that correspond to low traffic periods
Travel and Sports Performance Additional stress may be placed on athletes and their bodies because of the effects of travel and different environmental conditions at the destination. Jet Lag Your body has a normal rhythm of sleep and wake which is often disrupted when you travel across many time zones – this can have a negative effect on performance. Ways to prevent the negative effects of jet lag:
If possible plan your trip so that you have several shorter legs of the journey – once you have adjusted to one place move on to the next. This is obviously time consuming and expensive and may outweigh the negative effects.
When travelling by air drink plenty of water and avoid alcohol and caffeine. Dehydration is a symptom of jet lag due to the air conditioned planes.
Before you leave or when you arrive at your destination try and adjust your sleep-wake patterns to match your destination.
Try and plan to arrive at your destination in the morning and then stay awake for the remainder of the day, sleeping in the dark. Avoid napping as it will prolong your adjustment to the time zone.
Expose yourself to sunlight as the chemicals in the body that effect sleep are affected by sunlight.
If possible exercise lightly for the first few days until your body has adjusted.
Travel and Sports Performance Overseas trips, international competitions or training camps often provide nutritional challenges for athletes – poor planning often results in poor performance. The following tips can help you prepare:
pack a small supply of your favourite convenient foods, they are not often available overseas
organise meals in advance
be sure to make nutritious CHO rich choices when travelling
airlines often have ‘athlete’ meals – organise in advance to have extra bread rolls and fruit juice and take along your own water bottle
when travelling by road do not rely on petrol station food
avoid or minimise alcohol intake when travelling (particularly on long flights or in air-conditioned buses or trains)
when travelling overseas be prepared to try different CHO foods as traditional ones are not always available
when travelling to exotic locations drink bottled water
‘Travellers trot’ is common in athletes when they travel to countries with suspect water supplies. In this case it is imperative to maintain adequate fluid intake (bottled water is best), avoid milk and cheese and gradually introduce foods once symptoms settle. Suitable food choices include; white bread (toast) or rice, broth, low fibre cereals with low fat milk, dilute fruit juice, soft drinks, cordial or sports drinks