According to Cleveland ClinicThe quad muscles can be divided into five segments. The rectus femoris, which runs from your hip bone down until your patella or kneecap, is the first segment. It’s responsible to extend your knee and recruit your hips during a lunge. Livestrong. The vastus intermedius can be found just beneath the rectus. Its primary function, which is to assist with knee extension and it’s located in the middle of your thigh, is the vastus intermedius.
The vastus medialis muscle is the next quad muscle being used. It is the largest quadriceps muscle and can be found on the outside of your thigh. Healthline). The vastus lateralis’s job is to support your movement from a squatting to standing position and extend the lower leg (similarly to the other segments). The vastus medialis (the quad muscle on the inner side of your thigh) is the smallest. Its primary function is to extend your knees (just like the rest, the quad squad), but the large portion of the vastusmedialis just above your knee can also help stabilize you, Livestrong says.
Cleveland Clinic says that the newest quadriceps muscle was discovered. It is known as the tensor or vastus intermedius lateralis. It lies between vastus intermedius medialis and vastus vastus medialis. Its function is still being studied.