There are 3 main reasons for the lack of strength in the left arm: 1, due to nerve damage in the left arm, such as damage to the brachial plexus nerve, radial nerve, median nerve, ulnar nerve and other nerves, resulting in a decrease in nerve function, which may lead to a significant decrease in muscle strength in the left arm and a lack of strength. 2, due to neurogenic cervical spondylosis, which is due to a cervical spine area with This is due to a herniated disc or bony stenosis in the cervical spine, which causes extrusion and stimulation of the nerve roots, resulting in ischemia of the nerve roots and affecting normal nerve conduction, and therefore may lead to a lack of strength in one arm. 3, it may be due to excessive fatigue and strain of the left arm muscles, ligaments and other soft tissues, and accompanied by cold, resulting in an increase in local lactic acid and inflammation and other metabolic products, which may also lead to a local feeling of The weakness, that is, the lack of strength related performance.