Why do girls always have cold knees?

Girls always feel cold easily in winter, especially their knees. In fact, it is because of the differences between men and women, and the amount of heat they receive is different. In addition, girls nowadays don’t like to do sports, and the blood supply to the muscles of the limbs is insufficient, which causes the knees to be cold for a long time. The best way to solve this phenomenon is to exercise regularly, exercise your arterial system and increase blood supply. We will use the following theory to scientifically explain why girls are prone to cold hands and feet.

1. Women have a larger relative surface area of ​​their bodies and lose more heat under the same circulation conditions. Women's hands and feet are generally smaller than men's. According to the viewpoint of biogeometry, the smaller the body size, the larger its relative surface area. That is to say, the relative surface area of ​​women's hands and feet in contact with the outside world (that is, the surface area divided by its average mass, the standard unit is square meters/kilogram) is larger than that of men. Under normal circumstances, most of the human body is covered with subcutaneous fat, which plays a role in keeping warm and storing energy. Due to the influence of estrogen, women's fat layer is much thicker than men's, which to a certain extent offsets the greater heat loss caused by women's larger relative surface area than men. However, due to frequent activities and physiological needs in the hands and feet, a large amount of fat cannot be accumulated. That is to say, even under the same circulation conditions, women lose more heat per unit mass in their hands and feet than men.

2. Women’s arterial perfusion is weaker than men’s, resulting in less heat supply to the extremities. Due to hormonal reasons, women's muscles are not as developed as men's, especially the upper limb muscles, which is very obvious. (There are also social factors involved. Many girls are very afraid of "growing muscles"). By randomly selecting young men and women of the same age and living conditions after puberty and measuring the inner diameter of their brachial artery in their upper arms with B-ultrasound, it can be concluded that the inner diameter of the brachial artery in men is larger than that in women, which is a statistically significant difference. Please note that arterial perfusion and blood pressure are not the same concept. In the extremities, the main source of skin temperature is blood. The greater the irrigation flow, the more heat it brings and the higher the skin temperature. vice versa. However, women who do physical labor rarely have the problem of cold hands and feet. The reason is that long-term physical labor rebuilds the arterial system, increases the blood supply to the limb muscles, and also relatively increases skin perfusion.

3. Different endocrine conditions lead to different densities of microvascular beds. Estrogen causes the density of women's subcutaneous blood vessels to be higher than men's, which is why women's skin generally looks more moisturized than men's. The problem is that the microvascular bed is also the main area for heat dissipation. At the same temperature and humidity, we have already explained above that body shape causes different amounts of heat loss in men and women. Here we should also mention that the heat dissipation efficiency is also different. Women have a higher heat dissipation efficiency due to the higher density of their microvascular beds. Under the same temperature and humidity, the subcutaneous microvascular beds in women's hands and feet close earlier than men to reduce heat loss. But microcirculation is the main source of heat for the skin of the extremities. If the microvascular bed is closed, the heat supply to the extremities will be greatly reduced.

In summary, girls’ cold hands and feet have a physiological basis. Of course, there are many social factors. For example, women are generally less active than men in winter, which leads to less heat production. Women who engage in physical labor or exercise for a long time have fewer cold hands and feet. These are all influencing factors.