Every time you work out, you inflict microscopic damage on your muscles, which is then repaired naturally by your body with a tiny new layer of muscle tissue. As these layers are formed, you build visible muscle. You don’t need to have muscle soreness every time you work out in order to see progress. In fact, it’s not advisable to push yourself to the point where you’re sore after every workout. In general, if you’re sore for 2-4 days, you’re in the safe zone. If you’re experiencing DOMS for more than 4 days, you may have gone too hard.