There are two main reasons why it hurts to sleep on a hard bed: 1. Because the body does not adapt when sleeping on a hard bed, and does not conform to the normal physiological curvature of the body, it is easy to cause the body’s muscle tissue to be in a state of excessive fatigue, more lactic acid and inflammation and other metabolic products of the accumulation of more, will stimulate the peripheral nerves around, so there will be a painful performance. 2. When the mattress is thin and cold, it will lead to more tension in the muscular tissues of the body, a decrease in blood circulation and a decrease in arterial blood supply, which will lead to a decrease in local energy, electrolytes and nutrients. As a result, excessive fatigue of muscle tissues can easily occur. In addition, the decrease in venous return leads to a further accumulation and increase in metabolites, which leads to an increase in peripheral nerve irritation and an increase in pain.