From birth to adolescence, a person’s height grows continuously, but after puberty the body basically stops growing taller. However, the height of the same person in the same day is different in the morning and in the evening, and it is always slightly higher in the morning when you first wake up than in the evening. One wonders why the height of a person changes throughout the day. It turns out that it has to do with the relaxation and contraction of the joint tissues and ligaments that make up the body’s height. Height is the total height of the human body in a standing position, and it consists of four parts: the head, the spine, the pelvis and the lower limbs, which are connected by joints and ligaments. The spine is the most closely related to the body’s height changes throughout the day. Because it is the central axis of the body, it consists of 24 vertebrae, a sacrum and a coccyx, which are connected by ligaments, intervertebral discs and intervertebral joints. The intervertebral discs are disc-shaped cartilage located between the two vertebrae, strong and flexible, in addition to connecting the vertebral body, but also to withstand the pressure, slowing the impact to protect the brain marrow, and facilitate the movement of the spine in various directions. After working and studying during the day, the whole body muscles, joints and ligaments are in a state of tension and compression, and the vertebrae are tightly pressed together. But through a full night’s sleep and rest, the elastic intervertebral discs are relaxed without pressure, so that the spine becomes slightly longer because of relaxation, and the interesting phenomenon of “taller in the morning and shorter in the evening” appears.