In most of the cases, how long will the muscle pull last depends on the location of the muscle and it also depends on the impact and severity of the injury. Under normal circumstances, symptoms of mild back muscle pull show improvement in about one to two weeks and show complete recovery in about 4 to 6 weeks. Moderate to mild pulled muscle in legs take about 8 to 10 weeks to heal completely. Symptoms of severe pulled muscle (usually grade III strain) persist until the tear in the muscle is surgically repaired. In some cases, the symptoms may persist even after the repair is done.