《黄帝内经·灵枢·刺节真邪》
天气寒冷，则地冻结，水成冰；人体阳气沉伏于内，则皮肤密致，腠理闭合，汗液不出，血气凝滞，肌肉坚涩。
寒则地冻水冰，人气在中，皮肤致，腠理闭，汗不出，血气强，肉坚涩。
When the weather is cold, the earth freezes and the water turns into ice; when the yang qi of the human body sinks inward, the skin becomes dense, the pores close, sweat does not come out, the blood and qi stagnate, and the muscles become hard and dry.