The quadriceps, or quadriceps femoris, is made up of four muscles: the rectus femoris, the vastus intermedius, the vastus medialis and the vastus lateralis. These muscles make up the front of the thigh and extend downward over the knee.
According to the National Institutes of Health, the rectus femoris originates on the illium, the uppermost bone of the pelvis, and continues down the middle of the thigh. Because it connects at the hip, it is responsible for parts of hip flexion, especially when the leg remains straight. The other three muscles originate from the femur and function to straighten the knee as well as keep the patella, or kneecap, in place. The vastus intermedius lies on the front of the leg below the rectus femoris, while the vastus medialis lies on the inner part of the thigh, and the vastus lateralis lies on the outer part.
The muscles of the quadriceps are crucial to human mobility, as they allow walking, running, squatting, jumping, standing from a seated position and other movements to take place. Maintaining the strength and flexibility of the quadriceps is important not only to athletes, but also to anyone who wishes to maintain or enhance mobility. According to About.com, engaging in simple strengthening, stretching and balance exercises is the best way to keep your quadriceps functioning smoothly for years to come.