Muscle fatigue at the end of the day is a completely natural process, especially if the day was associated with heavy physical labor. Most often, the lower back, arm and leg muscles hurt from fatigue. But there comes a time when a person begins to notice that the lower back hurts even at rest, while walking the pain intensifies and radiates to the arm or leg. It becomes increasingly difficult to bend over, it is almost impossible to relax the back muscles, even in a lying position.