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Leg Extension
Positions & Range of Motion
- Start
- seated tall on a leg-extension machine, back and hips against the pads, hips flexed ~90°, shins hooked behind the roller resting just above the ankles, knee axis aligned with the machine pivot
- End
- knees smoothly extended to nearly straight (short of hyperextended lockout) with quadriceps squeezed, brief pause
- Range of Motion
- ~90° knee flexion to near-full extension (~0–10° short of lockout), lowering over 2–3 s
How to Perform
An open-kinetic-chain, single-joint knee extension performed on a leg extension machine. Sit tall with your back and hips against the pads, hips flexed to roughly 90 degrees, and hook the shins behind the padded roller so the pad rests just above the ankles. Align the machine's axis of rotation with the lateral knee joint line. Fasten the lap belt if available and hold the seat handles. Extend both knees smoothly until they are nearly straight (stopping short of a hard, hyperextended lockout), pause briefly with the quadriceps contracted, then lower under control back to the start. Keep the movement slow and deliberate rather than swinging the weight up.
Opens a YouTube search for “Leg Extension”
Coaching Cues
- 1
Sit tall with your back flat against the pad and line the knee joint up with the machine's pivot; the roller should rest just above the ankles, not on the shin bone.
(setup) - 2
Straighten the knees smoothly and squeeze the thighs at the top, stopping just short of a forced hyperextended lockout.
(execution) - 3
Lower the weight slowly (about 2-3 seconds) and stay in control instead of letting the plates drop or swinging your torso.
(tempo) - 4
Exhale as you extend the knees and inhale as you lower; avoid gripping the seat so hard that you brace unnecessarily.
(breathing)
Evidence-Based Dosing & EMG Data
General resistance-training guidelines apply, as no leg-extension-specific dosing is well established: for hypertrophy roughly 3-4 sets of 8-12 reps; for muscular endurance/early rehab 2-3 sets of 12-20 reps with lighter load; train the target 2-3 times per week with about 48 hours between sessions, progressing load as tolerated. In patellofemoral rehab, limiting range to the terminal ~45-0 degrees is commonly used to reduce joint stress.
Surface EMG studies of open-chain knee extension consistently show high, well-balanced activation across the quadriceps heads. Contrary to older claims, the vastus medialis (VMO) cannot be selectively isolated from the rest of the quadriceps; VMO-to-vastus-lateralis activation ratios generally stay close to 1:1 across the range, though vastus medialis activity tends to be relatively higher in the terminal (near-full-extension) portion. Rectus femoris activation is somewhat blunted in the seated, hip-flexed position because the muscle is on relative slack. Compared with closed-chain movements like the squat, the open-chain leg extension isolates the quadriceps with minimal hamstring co-contraction. Note that peak patellofemoral joint compression occurs in the more flexed portion of the range while anterior tibiofemoral shear is greatest near terminal extension, which informs range selection in patellofemoral or ACL rehab.
Muscles Involved (9)
Primary Movers
Secondary Movers
Lengthened / Stretched
Easier Variations ↓
Terminal-range knee extension (short-arc)
Work only the last 15-30 degrees to full extension with lighter load. This shortens the lever arm and reduces patellofemoral stress, useful for early rehab or irritable knees.
Isometric quad set
Regress to a static seated quad contraction (or holding the leg at partial extension) with little or no external load to build tolerance before adding machine resistance through range.
Harder Variations ↑
Single-leg (unilateral) leg extension
Perform one leg at a time to increase per-limb load, expose side-to-side asymmetries, and add balance/stabilization demand.
Slow eccentric / tempo emphasis
Add a controlled 3-5 second lowering phase or a brief isometric hold at end range to raise time-under-tension and eccentric loading, or simply progress machine weight for strength/hypertrophy.
Target Movements (1)
Why This Exercise Matters
Everyday activities this exercise helps you do — essential means it directly trains the capacity the task needs:
Goals This Helps With
Rehab, performance, prevention, and mobility goals this exercise supports — essential means it's a cornerstone:
Research Notes
claude-researched 2026-07; muscle/movement links validated against the roster. Adversarial clinical verification pending — do not promote past needs_review without human review.