1. However, when the researchers subdivided the samples according to the exercise habits of volunteers, the results changed significantly. They found that after the age of 40, men and women who exercise regularly have thinner epidermis and healthier skin, but thicker dermis. Structurally, their skin is closer to their twenties and thirties, which is quite different from people of the same age, even those over 65.
Second, after the results came out, the researchers realized that other factors, such as diet heredity and lifestyle, may also affect the skin difference between the fitness group and the rest group. To further confirm, the researchers set up a group to collect skin samples from the hips of sedentary volunteers and let the group move. At the initial stage of the study, the skin of these volunteers over 65 years old was consistent with their age. Then they started a very concise endurance training, practicing twice a week, running or riding a bike at a moderate and strenuous speed, and persisting in exercise for at least 30 minutes at their highest level of aerobic metabolism. This training lasted for three months, and then the researchers took a biopsy of their skin again.
Third, but at this time, their skin samples look completely different. The outer and inner skin are close to people in their twenties and forties. It is not clear why exercise changes the skin composition, but in an independent part of this study, the researchers examined the changes in the content of specific substances produced by muscle work. This substance is called muscle hormone, and it is now known that it will enter the blood and activate cells, thus changing the muscle itself. In this study, the researchers found that after exercise, the content of a muscle hormone named IL~ 15 in volunteers' skin samples increased significantly. After three months of exercise, the content of IL 15 in their skin samples increased by nearly 50% compared with the original study.