But who sweats more? The fittest or the fattest people?

We all have millions of sweat glands all over our body, with the greatest concentrations on our feet, around the groin and the underarms. Sweat glands are responsible for keeping us cool as sweat evaporates reducing skin temperature and eventually core body temperature. During exercise this becomes increasingly important to help prevent heat stress, exhaustion and decreases in performance.

People with greater percentage of body fat tend to sweat heavily as the body fat provides an insulatory affect to the body. Heat transfer by other methods is compromised and sweating rates are high amongst obese and overweight individuals. Also the high body mass to surface area ratio of obese individuals means their effectiveness of heat transfer is reduced compared to leaner athletes, so their core body temperature does not decrease as quickly, further increasing their need to sweat. Generally obese individuals are not conditioned to exercise, if this is the cause of the increase in body temperature, so the cooling response (sweating) is not as efficient.

Athletes on the other had also record relatively high sweat rates, especially in hot environments. Thus is seen as a positive result of acclimatisation. When athletes train and compete in hotter conditions their bodies adapt to improve their thermoregulation, or effectiveness of cooling. While athletes can record very high sweat rates the concentration of sodium within the sweat is reduced, so as to limit the electrolyte changes within the athlete. Also athletes who are acclimatised to hot conditions will begin sweating at lower body temperatures to ensure exercising body temperature does not rise rapidly.

Acclimatisation can occur in as little as 10 days. For athletes training in cooler environments and competing in hot conditions, heat chambers or arriving at the competition venue early to acclimatise can be crucial to their success. Also, utilising similar local environments such as that used by marathon runners Michael Shelley & Lisa Weightman in Cairns in the build up to the 2010 Commonwealth Games (in Dehli, India) can improve sweat rates, improve early onset of sweating and reduce sodium concentration of the sweat all to aid performance.

For anyone aiming to acclimatise in cooler weather begin with short training sessions in hot conditions and over a 10-14 day period gradually increase the training load up to normal durations and intensity as the body adapts.

While individual differences do exist, the average sweat rate is 1.2-2.5 litres per hour. Between sports different sweat rates are seen as runners will typically sweat more than cyclists. In many sports protective padding, clothing and other equipment can limit air flow to skin further reducing the cooling effects of sweating, resulting in increased sweat losses as the body attempts to continue to reduce core body temperature.

Of course intensity of exercise, the training status of the athlete and the climate play a big part in the overall fluid loss due to sweating in all activities The highest recorded sweat rate during exercise is 3.7 litres/hour, recorded by marathon champion Alberto Salazar in his preparation for the 1984 L.A. Olympic Games.

So who sweat’s more? Probably the trained athlete during a hard exercise in hot conditions, but if the 2 individuals were to go for a low intensity 30min walk together the fatter person would sweat more, due to increases in core body temperature and reduced effectiveness of their thermoregulation.