Your Muscles (for Kids) - Nemours KidsHealth When you make a muscle in your arm, you tense your biceps (say: BYE-seps) muscle. When you contract your biceps muscle, you can actually see it push up under your skin. Your quadriceps (say: KWAD-ruh-seps), or quads, are the muscles on the front of your thighs. Many people who run, bike, or play sports develop large, strong quads.