The muscle pain under the thumb may be caused by the following: 1. Overexertion. For example, if the patient does excessive hand gripping, it may cause muscle fatigue of the intrinsic hand muscles here and in other parts of the hand, and then there will be muscle pain in the area; 2, injury related to this area. Because the hand is often used and often in contact with the outside, it is subject to some excessive vibration or impact, which leads to muscle-related damage, and then there will be pain here. If the thumb is stretched excessively, it may cause a strain and lead to pain; 3. Long-term pressure on the thumb. If the hand is propped up on the ground for a long period of time, it can cause ischemia and pain. In addition, prolonged pressure on the hand or wrist may cause the median nerve to become stuck, which may also cause pain in this area.