StrengthBeginner

Leg Extension

Pure quad isolation on a fixed machine. The only exercise that hits the rectus femoris through full knee extension without hip help.

GIF · Demo Leg Extension

What is the leg extension?

The leg extension is an open-kinetic-chain knee extension. You sit, hook your shins under a roller pad, and straighten the knees against resistance. It isolates the four quadriceps heads, especially the rectus femoris which gets minimal stimulus from squats since it crosses the hip. It's a key accessory for athletes who need quad size or for anyone returning from knee work. Not a replacement for squats, a complement.

How to do the leg extension

Adjust the machine

Set the back pad so your knee aligns with the machine's pivot. Shin pad sits just above the ankle bone.

Anchor your hips

Sit fully back, grip the handles, press the lower back into the pad. Hips don't leave the seat at any point.

Extend, don't kick

Drive the toes up and the shin forward in a controlled 1 to 2 second push to full lockout. Squeeze the quads hard at the top.

Lower on 3 seconds

Resist the weight all the way down to a deep knee bend, around 90 degrees or more. Slow eccentric drives growth.

Coach tip

Point the toes slightly outward to bias the inner quad (VMO), slightly inward to bias the outer quad. Use the bias your knees need.

Common mistakes

Hips lifting off the seat. If the hips rise, the hip flexors are helping. Lower the weight and re-anchor.
Half reps. Stopping short of lockout misses the strongest contraction. Lock the knees fully each rep.
Banging the stack. Dropping the weight crashing back skips the eccentric. Slow descent or no growth.
Roller pad on the shin too low. Set too far down the shin, it pinches the achilles. Just above the ankle bone is right.

Variations & progressions

Easier

Single-leg extension

Work one leg at a time with half the stack. Lets you correct side imbalances and focus the contraction.

Harder

1.5 reps

Full extension, halfway down, back to full, then all the way down. Doubles time under tension at the top.

No machine?

Sissy squat or reverse Nordic

Bodyweight knee-dominant variations that bias the rectus femoris through hip extension while the knee flexes. Brutal.

How to program it

Three protocols by goal. Pick one per cycle and aim for progression on load or distance.

Goal	Sets × Distance	Load	Rest
Hypertrophy	4 × 12-15	60-70% 1RM	75 s
Pre-exhaust before squat	2 × 15	Light, 40% 1RM	60 s
Quad finisher	3 × 20 with 3 s eccentric	50% 1RM	60 s

Log every rep

Add the leg extension to your ZON program

Track load, distance and progression in one timeline.

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Leg Extension FAQ

Is the leg extension bad for the knees?

Old myth. Loaded knee extension is one of the most studied and effective ways to strengthen the quad and protect the joint, including post-ACL rehab. The risk comes from going too heavy too soon, not from the movement itself. Stay in a comfortable range and progress gradually.

Should I do it before or after squats?

After, for most people. Squats train more muscle for less time, do them fresh. Use the leg extension as an accessory to add quad-specific volume once the heavy work is done. Pre-exhaust (light extensions before squats) is a niche tool, not the default.

How far down should I go?

As far as the machine allows while keeping tension, usually 90 degrees of knee flexion or deeper. Cutting the range short above 90 wastes the deep stretch position where the rectus femoris grows most.