New research shows sweating may not depend on sex, but on the ratio between body surface area and mass.
Have you ever wondered why you sweat during a good workout? The human body has an internal heat regulation system that some have likened to a furnace: it produces heat and then releases it through a variety of physiological processes. One of them is sweating.
Our normal body temperature varies between 36.5-37.5 °C, or 97.5-99.5 °F. When the outside temperature increases, it sends signals to the brain's hypothalamus - sometimes referred to as the body's thermostat. The hypothalamus responds to changes in temperature by making physiological adjustments to keep that ideal inner temperature.
On a hot summer day - or during an intense session at the gym - the temperature receptors on our skin send signals to the hypothalamus, which in turn "tells" the body to start cooling itself off by producing sweat.
Until now, it was believed that men and women respond differently to rising heat because of sex-dependent physical characteristics.
But new research - conducted by scientists from the University of Wollongong in Australia and Mie Prefectural College of Nursing in Japan - challenges this conventional belief.
The researchers - led by Sean Notley - hypothesized that the heat response would change depending on the ratio between body surface area and mass - not depending on gender. A secondary hypothesis was that larger individuals would sweat more in order to adjust to increasing heat.
The findings were published in the journal Experimental Physiology.
When it comes to sweating, gender does not matter, but body size does
The study evaluated vasomotor and sudomotor functions in 60 healthy participants of various body shapes and sizes - 36 males and 24 females.
The participants completed two tasks in compensable conditions of 28°C (82.4 °F) and 36 percent relative humidity: they rested for 20 minutes, and then cycled at a steady, heat-producing pace for 45 minutes. Participants also cycled at a higher intensity.
Under these conditions, the body naturally tries to keep the body temperature from rising by sweating and increasing the blood flow to the skin.
Notley and colleagues evaluated the forearm blood flow and the body's vascular conductance.
The trials revealed that the mass-specific area was indeed a significant factor that determined vasomotor and sudomotor responses in men and women. Mass-specific area accounted for 10-48 percent of the individual variability in the body's response to heat.
The researchers considered morphological differences between genders, but gender-dependent differences explained less than 5 percent of the changes noticed between individuals.
Therefore, the study concluded that the way our body responds to heat depends on morphological changes, but not on gender. The same body temperature changes occurred in all of the participants, irrespective of their sex.
Furthermore, the study found that females and males with a smaller body size - who have more surface area per body mass kilogram - lose heat by increasing blood circulation rather than sweating.
By comparison - and as hypothesized - larger people were found to rely more heavily on sweating.
"Gender has long been thought to influence sweating and skin blood flow during heat stress. We found that these heat loss responses are, in fact, gender independent during exercise in conditions where the body can successfully regulate its temperature."