A pulled musclemedically known as a strainoccurs when muscle fibers are stretched too far and sometimes tear.
Summary
A pulled muscle usually starts to heal in a few days.
With proper care, most people will fully recover from a pulled muscle.

Tfilm / Getty Images
2016;3(1):15. doi:10.1186/s40634-016-0051-7
Harvard Health Publishing (Harvard Medical School).Muscle strain.
2009;1(5):392-395. doi:10.1177/1941738109343156
Penn Medicine.Strains.