30 minutes of daily activity heats up your metabolism and keeps your body burning calories. 1 That’s why Nutrisystem recommends regular exercise as an essential part of your weight loss plan. But when you’re just starting a new workout program or when you exert yourself more than usual, you might experience sore muscles—maybe enough to make you want to skip a day or two of activity. The Cause of Sore Muscles According to the American Council on Exercise (ACE), there are two kinds of sore muscles that are correlated with physical activity. “Immediate muscle soreness quickly dissipates and is the pain you feel during, or immediately after, exercise. Delayed muscle soreness signals a natural adaptive process that the body initiates following intense exercise.” 2 Delayed muscle soreness (DOMS) happens about a day or two after your workout and typically goes away after 72 hours, says ACE. This is a common experience for people who work out, both new and experienced exercisers alike.