I have a jumping in my left arm?

Muscle twitching: The cause of the involuntary fasiculations are many. If you have been working out or using your arms a lot, the muscles may be tired. How much caffeine have you had? Are you on medications? Are you dehydrated? Try massaging the area and applying a warm compress. Drink more water. Eat plenty of fruits and vegetables to avoid a nutritional deficiency. Go see your doctor if the twitching continues