Environmental Exercise Physiology

The human body is able to withstand large amounts of stress, and then adapt to that stress. The environment can become a stress for the human body, particularly while under the effects of training stress.

The environmental stressors that inflict the highest levels of stress on the human body include altitude, hot and cold climates, humid climates, as well as pollution in the air and jet lag.

If correctly controlled, the human body is able to recover from and adapt to these stressors, to the point that performance is able to be enhanced due to exposure to these stressors.

However, if the stress of the exposure to the environment is too intense or prolonged, adaption will not occur, and may result in injury or disorder of the human body. In such circumstances, treatment would involve rest and recover, as well as medical intervention in extreme circumstances.



Altitude, as it pertains to effecting the human body can be described as any elevation above 1524m (5000 ft).

Components which contribute towards the effect of altitude on the human body:

 Atmospheric Pressure

The atmospheric pressure decreases as altitude increases, however, the percentage of gases in the air remain constant.

Air always contains 20.93% oxygen, 0.03% carbon dioxide and 79.04% nitrogen. The pressure that oxygen molecules exert is directly related to atmospheric pressure. As this partial pressure of oxygen changes, so the transfer of oxygen from the air into the body is decreased, making breathing more laboured.

 Air Temperature

Air temperature decreases by 1°C every 150m. As the air cools, the humidity of the air would decrease, and the evaporation from the body would increase. This would increase the breathing rate and result in a quicker rate of dehydration.

 Solar Radiation

Less ultraviolet light is blocked due to the reduced atmosphere and lowered water pressure

These aspects all contribute towards the following short-term physiological responses:

 Respiratory Responses

Increased respiratory rate

  1. lower oxygen uptake per breath
  2. Increased carbon dioxide build-up in muscle and blood stream

Decreased oxygen uptake into the blood (92% saturation at altitude, 98% at sea-level)

  1. Lower partial pressure of oxygen
  2. Dehydration of alveoli, lower oxygen diffusion

Decreased oxygen uptake into muscles due

  1. Lower pressure gradient due to decreased oxygen in bloodstream
  2. Higher concentrations of carbon dioxide in muscle and bloodstream

Cardiovascular Responses

Decreased Blood Volume

  1. Lowered plasma volume, leading to thickening of blood
  2. Increased haematocrit (red blood cell concentration) to increased haemoglobin levels

Increased Cardiac Output

  1. Compensates for decreased partial pressure of oxygen
  2. Initially due to increased heart rate

Metabolic Adaptations

Higher Lactic Acid Production

  1. Oxidative pathways are limited due to lowered oxygen availability
  2. Shift towards anaerobic metabolisms

Lowered Maximal Capacity

  1. Unable to utilise oxidative energy system effectively
  2. Maximal exercise requires activation of all energy systems

Reduced Maximal Oxygen Uptake

  1. Only affected from an altitude of 1600m
  2. VO2max decreases at a rate of 11% for every 1000m above 1600m



  1. Erythropoiten levels increase, increase RBC production
  2. Leads to higher haemoglobin levels and thereby a higher haematocrit
  3. Requires that the recommended dietary intake of iron is met to achieve increased RBC production


  1. Tendency towards type I fibre utilisation
  2. Lowers muscle cross sectional area
  3. Increases capillary density
  4. Muscles increase ATP production from oxidative pathways


  1. Increased carbon dioxide removal due to increased ventilation
  2. Little improvement in muscle oxygen uptake
  3. Decreased ability to train at maximal intensities


High intensity training levels will decrease at altitude, and prolonged stays at altitude will result in a decrease in higher intensity performance levels.

Aerobic capacity can be increased due to increased eurythropoietin production, thereby increasing RBC production and oxygen carrying capacity.

The best training aerobic adaptations are achieved when athletes who live at altitude, carry out 3 to 4 week bouts of intense training at altitudes below 1500m, and especially at sea-level. This allows for both the altitude-induced increase in RBC count, as well as the high intensity adaptations achievable only at sea-level. Research has shown an average 2-3% increase in performance in athletes that practice this; however, the effects are lost with 3 months of returning from living at altitude. Training in cold environments has also been found to decrease altitude acclimatisation, as heat acclimatisation has been shown to augment altitude acclimatisation.

In order to achieve the adaptations of altitude training which would improve performance, athletes are advised to move to an optimal altitude of 2400m for a period of 4 weeks. The athletes are then advised to move back to sea level for a period of 3 weeks in order to allow for maximal performance gains.


If an athlete lives at sea-level, they will require a period of acclimatisation in order compete at maximal levels at altitude. The following measures will allow for maximal acclimatisation:

  1. Move to altitude 3 to 4 weeks prior to the start of the competition or event
  1. Use an iron supplement if diet or natural levels are low
  1. Modify training intensity and volume when at altitude
  1. Focus on aerobic training in the first week, 75% to 80% of sea-level aerobic intensity
  2. Increase intensity during second week, introducing anaerobic conditioning gradually
  3. Train at maximal aerobic levels during week 3. Maintain anaerobic intensity, increasing rest between interval runs.
  4. Taper and/or recover in week 4 in preparation for event or competition


These illnesses usually occur at altitudes above 1500m and are common at altitudes above R2400m.

Mountain Sickness

This is an acute response and is common, especially at high altitudes.

Symptoms include:

  • Headaches
  • Nausea
  • Lethargy
  • Vomiting
  • Disturbed sleep patterns

Symptoms may begin after a few hours of exposure, peak during day 1 and 2 and resolve after 4 days.

High Altitude Pulmonary Oedema (HAPE)

A more severe response to altitude exposure, and is often looked upon as a medical emergency

Symptoms include

  • Symptoms of mountain sickness
  • Coughing
  • Dyspnea (blue discolouration of the lips)
  • Frothy sputum
  • Chest pain
  • Tachypnea
  • Respiratory distress
  • Pulmonary rales

Prevention of Altitude Illness

  1. If ascending over 2400m, ascend gradually at between 300-600m per day
  2. Certain medication may prevent illness, E.g. Acetazolamide

Points for Discussion

  1. Will altitude exposure improve anaerobic performance?
  2. What is the optimal approach for avoiding acute responses to altitude? E.g event at altitude as part of an extended competition.
  3. Which athletes will achieve the best gains through altitude exposure?
  4. Can prolonged exposure and or training at altitude place an athlete at risk of overtraining?
  5.  How effective is erythropoietin (EPO) as an ergogenic aid?


The human body, during rest, usually does experience more than a 1°C rise in temperature. The body temperature is regulated at 37°C through constant feedback from the neural and endocrine systems. The hypothalamus plays the most significant role in the body of regulating temperature.

Other factors that regulate temperature include; the external climate, internal metabolic functions, intense physical exercise as well as illness.

Body temperature is very basically a balance mechanism regulating heat production and heat loss.

There is a continuous exchange between the body and the environment through convection, conduction and radiation. The body can both gain and lose heat through these mechanisms. The body also gains heat through metabolic reactions, and loses heat through evaporation.



A major by-product of energy production within the body is heat. When heat production exceeds dissipation, the body temperature will rise. During intense physical activity, the metabolic energy production may rise to levels in excess of 20 times the resting levels. Only 25% of the energy is used to generate muscle movement, the rest being heat. This metabolic heat is transferred from the muscle into the blood stream through the process of convection, and then moves towards the core. The body needs to dissipate this heat to avoid hyperthermia and tissue damage.

It does this by increasing heart rate and blood flow to the extremities. It also dilates the blood vessels to allow for greater blood flow and increased convection.  The final mechanism is through sweating, where heat is transferred through the circulatory system to the skin surface and then into sweat onto the surface of the skin which evaporates.



The skin surface comes into direct contact with a cooler object, transfer heat way from the body. E.g. immersion in water


The transfer of heat from working muscles to the skin surface. The heat is dissipated to air surrounding the body. This requires the following conditions in order to be effective:

  • The air temperature must be cooler than the body temperature
  • Superficial body fat must not be excessive
  • Clothes must not be tight-fitting
  • The air must be passing over the skin surface effectively, I.e. there must be a breeze.


This involves the heat given off by the body. This is also dependent on the air temperature being cooler than the body temperature, and the ability of the heat to escape.


An image of moisture being evaporating from material.

In warm environments and during exercise, this is the most effective form of heat dissipation. At rest is accounts for 20% of heat loss, however, when the environmental temperature exceeds 20°C, this percentage rises to 80%. Factors which determine the extent of heat loss through evaporation include:

  • Sweat rate (Conditioned athletes produce up to 30ml of sweat per minutes
  • Air velocity
  • Water vapour pressure gradient (determined by humidity)


Full acclimatisation to heat requires at least 5 to 10 days of repeated bouts of exercise in a hot environment. The intensity of the training needs to be reduced to below 70% of the usual training intensity to avoid disorders associated with hyperthermia.

Adaptations that occur to allow for acclimatisation include:

  • Increased sweat rate
  • Onset of sweating at lower body temperatures
  • Increased plasma volume
  • Sodium and chloride retention (promotes water retention)
  • Lower core body temperature due to more effective heat dissipation
  • Lower heart rate during physical activity
  • Reduced perception of heat stress
  • Delayed fatigue

There is no difference in acclimatisation between men and women.

If conditions are more humid, acclimatisation will occur at a faster rate as the conditions are more stressful.


Humidity drastically inhibits the body’s ability to dissipate heat. Heat loss through evaporation and conduction is reduced due to the reversal of heat and fluid transfer gradients.

Fluid loss becomes especially important to monitor as the body is transferring much of the fluid to the periphery, and since evaporation is slowed, the process is accelerated. Drinking cooler fluids will assist is lowering core body temperature.

Assessing Fluid loss through weight loss

Weigh yourself naked (with an empty bladder) before you train.

  1. Keep track of how much you drink (Litres).
  2. Weigh yourself naked after your session.
  3. Subtract your post-session weight from your pre-session weight (Kg).
  4. Add to that number the amount of fluids you consumed in litres. For example, if you lost 0.3kg and drank 0.7ml of fluid, your total fluid loss equals 1L.
  5. Divide your hourly fluid loss by four to determine how much to drink every 15 minutes. In the example above, you would need to drink 250ml every quarter-hour.

Clothing Guidelines in Humid Environments

It is important to give the body the best opportunity to sweat, and remove the sweat off the skin as quickly as possible. This can be achieved through the following

Wear minimal clothing

  1. Clothing must be loose fitting
  2. Clothing must breathe and must be absorbent
  3. Moisture-wicking clothing is preferable


Heat Cramps

This condition is caused due to the loss of sodium and potassium associated with heavy sweating. It will occur most commonly in poorly conditioned individuals or in highly humid environments.

Signs & Symptoms

  •  Skeletal muscle spasms


  • Move individual to a cooler environment with good air movement to encourage evaporation
  • Provide individual with fluids, especially electrolyte or saline solutions


  • Effective hydration during activity
  • Balanced diet


This will usually accompany more severe heat disorders, and will occur in warm, especially humid conditions.

Signs and Symptoms

  •  Fatigue and Lethargy
  • Irritability
  • Loss of coordination
  • Faintness
  • Disorientation


  • Cool fluid replacement
  • Electrolyte solutions


  • Adequate hydration before and during activity

 Heat Exhaustion

A more serious heat illness which is associated with a combination of high levels of intense exercise in hot environments and poor hydration. The cardiovascular system becomes unable to supply blood to vital organs.

Signs and Symptoms

  •  Elevated core body temperature
  • “Goose-bumps”
  • Headaches
  • Fatigue and lethargy
  • Dizziness, fainting and disorientation
  • Hypotension
  • Rapid pulse
  • Nausea and vomiting
  • In-coordination


  • Move to a cool, shaded area
  • Remove clothing which is unnecessary
  • Elevated feet to avoid shock
  • Actively lower body temperature with cold clothes or sponges (Especially under armpits, on stomach and in groin).
  • Begin oral or IV hydration
  • Monitor vital signs and transfer to hospital when stable


  • Avoid competition during extreme conditions
  • Acclimatise prior to competition
  • Hydrate adequately before and during event
  • Wear clothing which breathes and is appropriate for conditions

 Heat Stroke

A very serious form of heat illness which may be life-threatening, and is classified as a medical emergency. It is a thermoregulatory failure of the body due to extreme heat stress, and is often, but not always, associated with an absence of sweating while exposed to extreme conditions.

Signs and Symptoms

  •  Extremely high core body temperature
  • Rapid pulse and respiration rate
  • Hypotension
  • CNS Symptoms due to lack of blood to brain
  • Combative behaviour
  • Dizziness and disorientation accompanied with instability
  • Convulsions
  • Coma

Treatment and Prevention

  •  As per heat exhaustion, except the illness represents a medical emergency, and the individual must be placed under medical care as soon as possible.


When training in cold conditions, the physiology of the body differs considerably. The muscles become less effective, with decreased force production a slower contraction speed. Fatigue is also more likely is body heat is not retained either through warm clothing or effective adaptations as a result of conditioning.

The body uses the following mechanisms to generate or retain heat:


An involuntary muscle contraction in response to extreme cold which will result in increased heat production.  Shivering will impair performance as it reduces muscle coordination.


A sympathetic nervous system response which causes the release of adrenaline. This causes a greater metabolism of glucose and free fatty acids. It occurs most commonly in young children.

Increased Thyroid Production

The hypothalamus, in response to the cold stimulus will stimulate the thyroid gland to release higher levels of thyroxine, increasing the metabolic rate

Periphyral Vasoconstriction

The sympathetic nervous system stimulates the smooth muscle tissue to constrict in the periphery and dilate in the core. This causes blood, and the heat it carries to move away from the periphery and lowers heat loss

Anatomical Factors with impact on heat loss

1. Body size

A larger individual will retain more heat than a smaller individual. Children do not retain heat very well.

2. Body Composition

Higher levels of subcutaneous fat will result in greater insulation and therefore greater heat retention.

3. Sweat Rate

Individuals with higher sweat rates will retain heat less effectively than those with low sweat rates.

Environmental Factors which impact on heat loss

1. Wind Velocity

The greater the air movement, the greater the loss of heat through convection, radiation and evaporation. This is known as the wind chill effect.

2. Lower Ambient Temperature

The lower the temperature, the more the body has to work to retain heat. This will firstly increase sweating, increasing heat loss. Secondly, it will increase the rate of fatigue, which will ultimately result in the bodies heat retention mechanisms becoming less effective.


Disorders and injuries associated with training in cold environments are usually a result of prolonged exposure to extreme conditions. The main condition is hypothermia, which will occur when the core body temperature drops below 35°C. It can be classified into 3 levels:

CategoryCore Body TemperatureSigns and SymptomsTreatment
Mild33-35°CShivering, hunger, lethargy, confusion, muscle spasms, difficulty with motor tasks, slurred speech, slow reflexes and irregular gait pattern.Insulate with dry clothingContinue mild exerciseWarm fluids
Moderate30-33°CShivering may not be present, semi-conscious, confused actions and irrational behaviour, extreme fatigue, irritable and depressed, memory loss, poor coordination, muscle stiffness, slurred speech and a slow, irregular pulse.Heat with warm shower, hot-water bottles or body contactGive warm air and liquidsProvide medical care when stable
SevereLess than 30°CLoss of consciousness, dilation of pupils and a fait or undetectable heart beatTransport immediately for medical careInsulate torso during transport

Two physiological phenomena that are useful to know about in severe hypothermia are:

  1.  Afterdrop: this is defined as a continued fall in the core temperature, after removal from the cold stress, which may even occur during rewarming. It is due to heat redistribution within the body. The importance of this is that even when re-warming has started the patient may be at risk of cardiac arrest.
  2.  Circum-rescue collapse: this is when a hypothermic victim is found with stable vital signs but then collapses during or soon after rescue. It is thought to be caused by a massive drop in blood pressure or precipitation of ventricular fibrillation on handling of the victim. This phenomenon was initially described in maritime rescue but it has also been seen with rescue of hypothermic victims in the mountain environment.

 Preventing Cold Injuries

  1. Avoid excessive exposure to cold wind
  2. Wear adequate clothing for conditions
  3. Acclimatise to conditions (10 days is ideal)
  4. Ensure adequate nutrition and hydration before and during activity
  5. Wear layers during activity to draw sweat from skin
  6. Wear head covering and cover mouth
  7. Avoid alcohol as it dilates blood vessels and increases heat loss


Whenever an individual trains outdoors, they face the risk of being exposed to various pollutants and toxins, particularly if the individual trains in a highly build up or industrialised area.

These pollutants can deprive the body of the oxygen it requires for energy production, as well as irritate the breathing passages. This will result in decreased performance, as well as the possibility of developing various breathing disorders, including asthma, chronic bronchitis and even cardiac disease.

Prevention or Management of Exposure

  1.  Train or compete away from areas known to have high levels of air pollution.
  2. If an individual has a hypersensitive breathing tract, then they must either take a preventative bronchodilator prior to physical activity, or keep their inhaler on them if they enter areas with high levels of pollution
  3. Exercise-Induced Asthma may develop in individuals who train or compete over a long period of time in an area with high pollution levels. In such cases, these individuals may be treated with preventative bronchodilators prior to participating in physical activity.


Jet lag is becoming an increasingly prominent factor in professional athletes, due to most sports becoming more global in nature, and demands to compete in various countries in order to earn income increase.

Jet lag is brought about due to a disturbance in the body’s circadian rhythm. The circadian rhythms are cycles of the physiological systems which regulate body temperature, heart rate and hormone secretions. This determines the body’s response to internal and external stimulation. The circadian rhythm is synchronised with light-dark cycles, social interactions and environmental factors like air temperature.

A disruption in the circadian rhythm will result in the following symptoms:

  •  Fatigue
  • Insomnia or sleep disturbances
  • Headaches
  • Irritability
  • Constipation
  • Impaired athletic performance

Factors that determine the extent of “Jet Lag”:

Distance Travelled and Speed of Travel

Crossing only 2 time zones may result a disruption in circadian rhythms, however, the more time zones that are crossed, the greater the disruption. A higher rate of crossing will also result in a greater disruption.

Direction of Travel

Travelling east (essentially backwards) is more disruptive than travelling west. This is due to the fact that the body prefers a longer circadian rhythm, and is better equipped to cope with a delay in the cycle than a shortening of the cycle.

Exposure to Synchronisers

Circadian rhythm synchronisers include daylight, regular meals, social interactions, moderate physical activity and most importantly establishing a regular sleep-wake cycle. The sooner an individual is exposed to these synchronisers, the sooner they will be able to synchronise with the local environment.


The type of food an individual ingests may result in the stimulation of certain hormones.

Serotonin: This hormone encourages sleep, and slows the body’s cycles down. It is released when starchy or sweet foods are ingested.

Adrenaline: This hormone stimulates the body’s cycles, and it released when high protein foods are ingested.

Individual Differences

Circadian rhythm differs between individuals, making certain individuals more likely to wake up earlier and go to sleep earlier, and certain individuals to wake up later and go to sleep later. The early riser has been found to adapt better to east travel, while the late riser shows a better adaptation to westward travel.

An individual’s personality has also been found to influence adaptation, with extroverted or highly motivated individuals adapting better to jet lag than introverts. This is thought to be due to the extra effort the motivated individuals put into overcoming disruptions in rhythm, as well as their tendency to stimulate their cycle through social interaction.

 Reducing the Effects of Jet Lag

Arrive in competition environment early (1 day for every time zone crossed travelling east, and half a day for every time zone crossed travelling west)

  1. Adjust eating, sleeping, work or exercise schedules by 1-2 hours over a 5 day period in the direction of the new time zone.
  2. Arrange flight in order to arrive as close as possible to the local bed time
  3. Eat high protein/low carbohydrate meals for 3 days prior to travel and during travel, attempting to follow the meal schedule that will be followed at the destination. Once at the destination, eat low protein/high carbohydrate meals and use tea and coffee to aid synchronisation.
  4. Fluid intake can have extensive effects on the rhythm. Alcohol should be avoid as it disruptions sleep cycles and delays adaptations. Tea or coffee should be avoid while travelling, and large amounts of caffeine-free liquids, especially water, should be consumed to prevent dehydration.
  5. East-bound traveller should avoid bright light, movies and socialising until breakfast of the arrival day. Upon arrival, adjust to local schedule immediately through exposure to bright sunlight, social interaction, meals and training schedule.
  6. Set watch and adjust sleep, meals and social interaction to local times as soon as travel begins.