Muscle throbbing in the left arm may be a harbinger of the following conditions: First, it may be a harbinger of excessive fatigue in the left upper extremity, if the patient uses the left upper extremity excessively, resulting in excessive fatigue of the muscles here, muscle throbbing and shaking will often occur at the initial stage, followed by obvious muscle pain and weakness; second, this condition may be a harbinger of cramps, after the patient is affected by excessive excitement Second, this condition may be a precursor of cramps, after the patient is affected by excessive excitement, fatigue and other factors, it is possible that the muscles in this area will produce long-term tension. This is the first time that the muscles in this area may throb, followed by muscle spasms, also known as cramps; third, it may be a harbinger of peripheral nerve disease, for example, when there is a nerve root type cervical spondylosis or peripheral nerve compression, there may be such a harbinger first; fourth, it may be a harbinger of epilepsy, some patients due to the influence of the brain’s internal occupancy, bleeding and other factors, may cause abnormal discharge inside the brain. In this case, it is possible that the upper extremity of one side may jump first, followed by a generalized seizure.