What is the first aid for a spasm of the muscles?

Muscle spasms are typically seen in heat cramps, when exercising on hot days and you are not used to it. In that case, drink a fluid with sodium and other electrolytes such as Gatorade (preferably dilute regular Gatorade with half water, or use G2).

For chronic spasms, heat pads may be beneficial to relax the muscle. Talk to your doctor if it gets severe, muscle relaxers may be prescribed, or they may be able to identify underlying conditions.