Quadriceps is the large muscle group on the front of your thigh that straightens your leg at the knee. When you kick a soccer ball, climb stairs, jump for a rebound, or stand up from a chair, your quadriceps are doing most of the work.

The name comes from Latin words meaning “four heads” because this muscle actually consists of four separate muscles that work together as one powerful unit. You can feel your quadriceps tighten if you sit in a chair and try to straighten your leg without lifting your foot off the ground.

Athletes who run, jump, or bike develop strong quadriceps because these activities demand powerful leg extension. When someone's legs feel tired after climbing several flights of stairs, it's usually their quadriceps that are burning. Physical therapists often have patients strengthen their quadriceps after knee injuries because these muscles help stabilize and protect the knee joint.

People usually say “quads” for short, as in “my quads are sore from yesterday's practice.”