Quadriceps

The four heads of the quadriceps merge into a common tendon that inserts on the tibia via the patellar tendon. The rectus femoris is the only biarticular one in the group: it crosses both the hip and the knee, so it also participates in hip flexion. The vastus lateralis forms the outer part of the thigh, the vastus medialis the inner part (the classic 'teardrop' above the knee), and the vastus intermedius lies beneath the rectus femoris, deep down.

The squat is the king of quadriceps exercises, but it's not the only one. The 45-degree leg press, lunges, Bulgarian split squats, leg extensions, and hack squats are all effective exercises. The high-bar squat with a narrow stance emphasizes the quadriceps. The leg extension is the only exercise that completely isolates the quadriceps without involvement from glutes and hamstrings, and it's particularly effective for the rectus femoris when performed with full ROM.

The quadriceps are a large, resilient muscle group that tolerates high training volumes. For growth, work with a wide rep range: heavy sets of 6-8 reps on compound exercises and sets of 10-15 on isolation exercises. Squat depth matters: descending at least to parallel ensures the quadriceps work through their full ROM. If you cut the squat in half, you're leaving stimulus on the table.