How long do muscle spasms usually last?

Depends: That depends....A muscle spasm may last a few seconds in the face or arms, but could last much longer in the back. Usually though the spasm is short-lived but the resulting inflammation causes pain for much longer. Alternating hot/cold, staying hydrated, taking anti-inflammatory meds, stretching, and massage can all help.

Seconds to a few min: Muscle spams tend to be brief and intermittent. They are rarely the primary problem, but the body's inefficient way of trying to protect an injured or dysfunctional area. An example would be low back spasms in the setting if a disc herniation.