One arm is thick, one arm is thin mainly due to the following reasons: First, it may be that the usual sports functional exercise and did not do the balance training of the upper limbs, mainly to one limb exercise, will cause the exercise side of the limb muscle growth, strong, will be manifested as the case of arm thickness. Second, it is possible that one arm suffers from diseases such as osteoarthritis, which may cause joint pain and soreness. Therefore, patients often avoid using the affected limb, and in most cases will use the healthy side of the limb for household chores and daily life, which will cause muscle hyperplasia on the healthy side, while the affected side, due to less use, may experience muscle atrophy, and will show unequal thickness of both upper limbs.