Sweating under strenuous exercise

article adapted from The Science Teacher Oct 1998 Most of the data presented in this article comes from the American College of Sports Medicine.

Water loss during strenuous exercise can be up to 2-3 litres per hour during hot conditions. Even at temperatures of around 10 ^oC soccer players can lose 2 litres of sweat during a ninety minute game. Performance is diminished as the body is forced to cope with a lower blood volume and low blood pressure.

The concentration of salts in the body is critical for normal body function. This is particularly true for elite athletes required to perform at peak levels. The concentration of sodium is particularly important and this could change in response to dehydration due to sweating or ingestion of fluids.

Research suggests that the reduction of water in a person's body has serious consequences on athletic performance. In one study subjects performed 5,000 m runs in 19 minutes and 10,000 m in 40 minutes. When athletes were dehydrated by approximately 2% of their body mass, their running speed decreased by 6-7% at both distances. At 4% dehydration levels performance reduced by 20-30%. At 7% dehydration collapse was likely.

Decrease in performance due to dehydration results from:
- decrease in blood volume;
- increase in the concentration of sodium in the body fluids;
- decrease in cardiac output per beat;
- an increase in core body temperature.

The composition of sweat is 0.88 - 1.3 g/L of sodium but although sodium is lost in the process of sweating the concentration of sodium, in body fluids, increases due to the fact that water is also lost.

Energy, during long term exercise of between 1 to 4 hours, is provided by the oxidation of glucose and fats. Sugar intake is recommended during activities lasting more than 1 hour with an intake of no more than 60-75 grams per hour.

Monitoring water and sodium loss, as well as sugar intake, is a major key to optimal athletic performance in events lasting between 1 to 4 hours. For this reason drinks such as Gatorade are produced and marketed to athletes.

Would these drinks be of any benefit to people who are not active or who exercise for less than 30 minutes in aerobic exercise?

Dehydration experiments during exercise can be easily conducted. A simple way of measuring water loss during exercise is to use a set of bathroom scales and measure the mass of athletes before and after exercise.

Design an experiment to measure the amount of water lost during a game of soccer or a chosen sport.

Is the amount of fluid lost during a game related to the body mass of an athlete?

Is the amount of fluid lost during a game related to the ambient temperature?

Is the amount of fluid lost during a game related to the humidity?