Effects of thermoregulation in the Cold
Effects of Altitude physiological functions of the body
- As altitude increases, the barometric pressure and the oxygen partial pressure decrease. This means that any athletic performance critically dependent on oxygen for metabolism, i.e., any event lasting longer than roughly two minutes, might be adversely affected. By contrast, because the air at high altitude is less dense than at sea level, jumping, sprinting, and other activities in which air resistance needs to be overcome might be enhanced when competing at high altitude.
- The most important physiological adaptations to living at high altitude are increased ventilation of the lungs, increased blood hemoglobin, and enhanced extraction of oxygen by the tissues. Maximal cardiac output is not usually affected by altitude.
- Although acclimatization to or residence at high altitude is required for optimal endurance performance at high altitude, the value of high altitude training for endurance performance at sea level has yet to be proven.
- Nutrition for athletes at altitude can be a major problem, and weight loss will be significant at moderate to high altitudes. The amount of weight loss is generally dependent on the absolute altitude.
Higher altitudes have dramatic effects on sport performance. At the 1968 Mexico City Olympics (altitude = 2,300 m) the decreased air resistance contributed to improved sprinting and jumping performances; Bob Beamon's Mexico City long jump record stood for nearly a quarter of a century, and is the classic example. The decreased air resistance at Mexico City undoubtedly helped Australian Ralph Dobell to set an Olympic record in the 800 m run. However, at longer race distances, performances were progressively worse in Mexico City than at lower altitudes.
An additional observation in Mexico City was that in the endurance races most of the top performers had lived most of their lives at high altitudes or they had trained for long periods at high altitude. The defeat of Jim Ryun, the favorite and world record holder in the 1,500 m by Kip Keno of Kenya and the defeat of Ron Clark, the world record holder in the 5,000 m and 10,000 m, again by high altitude residents, were clear examples of the importance of living and training at high altitude. In fact, Ron Clark finished 6th in the 10,000 m in a state of collapse. The winning time was two minutes slower than his world record! The first five place getters were athletes who were residents of high altitude or had lived there for some considerable time.
What is it about training at high altitude that might be expected to enhance performance? Because endurance performance depends largely on aerobic (oxygen dependent) metabolism and very little oxygen is stored in the body, the presumed benefit of high altitude training must include effects on the transport and utilization of oxygen. Oxygen transport and utilization requires a series of closely integrated links involving the lungs and breathing, the transfer of oxygen from the pulmonary alveoli to the blood, the carriage of oxygen by the blood in association with hemoglobin, the pumping of oxygenated blood around the body by the heart, the distribution of the oxygenated blood to the working muscle and, finally, the extraction of the oxygen and its use in metabolism by working muscles. The maximum ability to deliver, extract and utilize oxygen is referred to as one's maximal oxygen uptake or VO2max.
Effects of water on the physiological functions of the body
Dehydration
Sweating is the way in which the body maintains its core temperature at 37 degrees centigrade. This results in the loss of body fluid and electrolytes (minerals such as chloride, calcium, phosphate, magnesium, sodium and potassium) and if unchecked will lead to dehydration and eventually circulatory collapse and heat stroke. The effect of fluid loss on the body is as follows:
Carbohydrates
Carbohydrate is stored as glucose in the liver and muscles and is the most efficient source of energy as it requires less oxygen to be burnt than either protein or fat. The normal body stores of carbohydrate in a typical athlete are:
- 70kg male athlete - Liver glycogen 90g and muscle glycogen 400g
- 60kg female athlete - Liver glycogen 70g and muscle glycogen 300g.
During hard exercise, carbohydrate can be depleted at a rate of 3-4 grams per minute. If this is sustained for 2 hours or more, a very large fraction of the total body carbohydrate stores will be exhausted and if not checked will result in reduced performance. Recovery of the muscle and liver glycogen stores after exercise will normally require 24-48 hours for complete recovery.
During exercise there is in an increased uptake of blood glucose by the muscles and to prevent blood glucose levels falling the liver produces glucose from the liver stores and .
Consuming carbohydrate before, during and after exercise will help prevent blood glucose levels falling too low and also help maintain the body's glycogen stores. Many athletes cannot consume food before or during exercise and therefore a formulated drink that will provide carbohydrate is required.
Fluid absorption
There are two main factors that affect the speed at which fluid from a drink gets into the body:
- the speed at which it is emptied from the stomach
- the rate at which it is absorbed through the walls of the small intestine
The higher the carbohydrate levels in a drink the slower the rate of stomach emptying. Isotonic drinks with a carbohydrate level of between 6 and 8% are emptied from the stomach at a rate similar to water. Electrolytes, especially sodium and potassium, in a drink will reduce urine output, enable the fluid to empty quickly from the stomach, promote absorption from the intestine and encourage fluid retention.
