What’s too hot for the human body? Study offers new insights on thermoneutral zone

There is a particular range of temperatures in which the human body doesn’t have to exert more energy or increase its metabolic rate in order to maintain its ideal core temperature of 37 degrees Celsius. That’s the thermoneutral zone.

Various studies indicate the zone’s lower limit is 28 degrees Celsius. Below this, the body starts to exert more energy – with one of the key ways being shivering, when muscle groups involuntarily contract to generate heat.

When the bar goes up, the body uses different mechanisms to cool down, such as sweating. But while the lower limit of the zone has been established, the upper limit is somehow still uncertain. One study suggests 32 degrees Celsius could mark the limit as it’s when humans start to sweat.

Both Temperature And Humidity Affecting Results

According to new research from the University of Roehampton in England, the body may fail to get rid of excessive heat and function optimally when outside temperatures rise above 40 degrees Celsius.

Researchers conducted a set of experiments to find the zone’s upper limit likely lies between 40 and 50 degrees Celsius. Additional research into the temperature range is expected to better inform policies on working conditions, international travel, medication and sports.

For the study, the researchers recruited 13 healthy volunteers aged between 23 and 58 years. They were exposed to five different temperature and humidity conditions. Interestingly, there was some evidence that humidity also plays a large role in the metabolic rate.

Several metrics got recorded throughout each condition and at baseline, including sweating rate, breathing rate, heart rate, movement levels, blood pressure, core and skin temperatures, and volume of air inhaled and exhaled per minute.