There is a hard strip inside the arm may be caused by physiological reasons such as muscle spasm, or it may be caused by trauma, arm soft tissue scarring, adhesion, phlebitis, tumor lesions and other reasons. 1. Muscle spasm: due to poor posture caused by arm muscle tension, spasm, touching the arm can be felt inside a hard bar, generally belongs to the physiological phenomenon. 2. Trauma: due to strenuous exercise or collision caused by arm muscles, injury, local hematoma formation, the patient may appear to have a hard bar inside the arm. 3. arm soft tissue scarring, adhesions: common in the past, old soft tissue injuries, in the healing process, the local muscle and other soft tissue healing scar tissue, patients may appear to have a hard bar inside the arm. 4. Phlebitis: due to phlebitis caused by bacteria and other pathogens infecting the veins, patients may have a hard strip inside the hand. 5. Tumor lesions: such as arm myofibroma, the abnormal proliferation of local tumors caused by muscle hardness, touching the hard stripes change. There may be other reasons why there is a hard strip inside the arm, it is recommended that the patient go to the hospital in time to improve the examination and give further treatment or therapy after the cause is clear.