All-out battle this Wednesday morning in Ile-de-France, in the Meuse, the Vosges or even the Haut-Rhin. Météo France has placed 18 departments on orange alert due to the snowfall and ice expected during the day. Beyond disruptions in transport, these flakes mark the installation of cold on the territory. And with them, the return of shivering for some, while others will sport a light outfit and a smirk.
Muscles, metabolism, morale… Why are we not equal in the face of the cold? While some are layering up as winter approaches, others don’t seem to really need to cover up. A finding of inequality repeatedly reported in the scientific literature, under various aspects. To understand our differences, we must first understand where the feeling of cold comes from and how the human body heats up and heats up. Embark.
First, a matter of sensors
On the surface of the skin is nestled a multitude of sensors, called “free nerve endings”. Particularly dense on our face, they collect and transmit thermal information to the brain. From there, a set of neurons participate in the regulation of body temperature, through various mechanisms – if it’s hot, we sweat, and if it’s cold, we shiver, among others. Shivering, the involuntary contraction of muscles, is the fastest way to warm up. Muscle fibers produce heat when they move, and even when at rest.
Muscles, firewood
Athletes with bodybuilder tendencies, stilts or healthy… Our muscle mass is not evenly distributed according to our way of life and our genetics. For example, men will naturally tend to have more muscle mass than women. Conversely, women have, on average, a thicker layer of fat – up to twice as much. If this insulates, it would above all have the disadvantage of delaying the feeling of having warmed up.
“The fact that women’s insulating layer of fat is thicker means that the heat that these muscle contractions generate potentially takes longer to reach the outer layers of the skin, where the famous free nerve endings are located”, specifies Adam Taylor, Professor of Anatomy at Lancaster University, in a post published in The Conversation.
Gender, but especially genes
But muscle mass and gender aren’t the whole story. In 2021, a team of Lithuanian researchers showed that a genetic variation could be at the origin of the differences in reactions to cold. This is present in women, and in men, in equal proportions. 16% of the population, or about 1.5 billion people, do not have the ACTN3 gene, also called the “speed gene”.
In the absence of ACTN3, the body does not make actinin 3, a protein that influences muscle contraction. These people, who are found more in northern countries or in Asia, would have a different structure and muscular activity, which gives them different sporting abilities… And a muscular response to cold with above-average performance, according to the results of this study, published in the journal The American Journal of Human Genetics and involving about forty people.
Auxiliary heating, boiler room, and condominium
Beyond our ability to warm ourselves, our “auxiliary heating”, we also do not all have the same “boiler room”. Apart from protecting itself from weather-related variations, the body constantly maintains its temperature, largely through metabolic activity, the work of our cells. Real factories, the latter produce all kinds of chemical transformations.
This effervescence produces heat: 50°C, on average, according to a CNRS and INSERM study, published in 2018. And we don’t all have the same metabolism. Again, a question of lifestyle, and genetics – men for example have a higher metabolism. The production of hormones and testosterone in particular, or even to the thyroid and blood circulation, intervenes. Habit and mental health also act. A tired or depressed person will be less able to bear the feeling of cold.