You finish a workout feeling great. Maybe you tried a new exercise, increased the weight, ran farther than usual, or returned to the gym after taking some time off. Immediately afterward, everything seems fine. Then you wake up the next morning. Getting out of bed feels harder. Walking down the stairs suddenly becomes an event. Your legs feel stiff. Your shoulders are tender. Muscles you didn't even realize you trained seem to hurt. And sometimes the second day feels even wor