Exertion will cause numbness in the left hand, indicating that there is nerve damage in the process, usually no symptoms of numbness indicates that the damage is not particularly serious, clinically there are several possibilities: 1, exertion refers to the cervical spine low head easily induced cervical spondylosis appears, especially neurogenic cervical spondylosis, easy to produce numbness in the left hand. 2, exertion belongs to each finger wrist joint range of motion too much, resulting in these parts of the muscle strain, Strain, after the muscle parts of the nerve jamming, clinically more common are ulnar neuritis, forearm jamming syndrome or carpal tunnel syndrome, etc.. Regardless of which of the above causes of left hand numbness, indicating that the symptoms of strain must be removed, strain accumulates over time the above symptoms of left hand numbness will become more and more serious, gradually to twenty-four hours will have the symptoms of left hand numbness.