Use deep knee flexion for the three vasti, then recognize why rectus femoris needs a different hip position and movement.
Vastus lateralis — The outer sweep of the thigh, from high on the thigh bone down to the kneecap — the part that flares when you lock the knee hard.
Vastus medialis — The inner mass, reaching lowest of the four into the teardrop just above the inside of the knee.
Vastus intermedius — Hidden between those two, lying flat against the front of the thigh bone.
Rectus femoris — The strap straight down the middle, and the only one starting on the pelvis rather than the thigh bone — so it crosses the hip as well as the knee.
Straightens the knee
Sit with one leg out in front and lock the knee straight. The whole front of the thigh hardens at once: four heads pulling on the kneecap through a single tendon.
Controls the knee folding under load
Lower yourself slowly toward a chair and stop just before you land. The front of the thigh burns while the knee is still bending — the quadriceps paying rope out rather than pulling it in.
Lifts the thigh, through rectus femoris only
Standing, lift one knee toward your chest against your own hand. The strap down the middle of the thigh tightens right up near the hip — the one head with a job at both ends.
Frequently asked questions
How deep should I squat?
Deeper generally grows more quadriceps: depth trials show greater increases at several points along the front of the thigh when the range stays controlled.[1] Controlled is the whole condition. Use the deepest position in which the foot stays flat, the knee tracks in line with it, and the pelvis does not tuck under at the bottom. Raising the heels slightly gets many people past an ankle limit rather than a thigh one — which is why it makes depth easier without making it a contest.
Is it bad if my knees pass my toes?
No rule forbids it, and deep knee flexion cannot happen without some of it. The question worth asking is whether the knee tracks consistently with the foot and whether the load feels tolerable there. A knee collapsing inward, or a twist to escape the bottom position, tells you more than any imaginary line drawn at the toes.
Do deep squats train all four quadriceps heads?
Not equally. The three vasti cross only the knee, so knee depth is exactly what they want. Rectus femoris crosses both joints: squatting deep shortens it at the hip while lengthening it at the knee, and the two largely cancel. A reverse Nordic keeps the hip extended while the knee bends, so it is long at both ends. That is an anatomical inference about position, not a claim that reverse Nordics grow more muscle.
Can I isolate the teardrop above my knee?
No. Reviews do not support reliably isolating the VMO — the lowest fibres of vastus medialis — from the rest of that muscle using a special stance, foot angle, or partial range.[2] It grows when the quadriceps as a whole is trained through a full, loaded range, which is the same answer as for every other head.
One common mistake
• Forcing the knees into one universal path.
• Knees may travel beyond the toes during a deep squat; the important question is whether they track consistently with the feet and the load is tolerated.
• Collapsing inward or twisting to escape the bottom is more concerning than crossing an imaginary toe line.
What's normal
A burn that arrives early in a set and a heaviness afterwards that stairs will find for you — going down more than up. Two days of soreness across the front of the thighs is common after unfamiliar deep work.
How sore is normal? →Stop if you notice
Pain inside the knee that sharpens the deeper you go, or a knee that gives way, locks, or swells within a day of training. Grinding that hurts, as opposed to a joint that is merely noisy.
These guides are general information, not medical advice. Stop for sharp or persistent pain, and consult a qualified professional before beginning any exercise program.