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Seated Knee Extension (Bodyweight)

Draftstrength55%beginner⬤ strong evidence

View FHIR resourceFHIR R4 ActivityDefinition — the interoperable form of this exercise

Why Include This

This is an open-kinetic-chain quadriceps strengthening exercise, the most isolated way to load the quadriceps (especially the vastii and VMO) without needing equipment. Quadriceps strength is a robust predictor of physical function and is consistently reduced after knee injury, surgery, immobilization, and with age. Progressive quadriceps strengthening is a core, guideline-supported intervention for knee osteoarthritis, where it reliably reduces pain and improves function (a first-line recommendation in OARSI/ACR guidelines), and OKC knee extension is well established for restoring quadriceps strength and controlling arthrogenic muscle inhibition after ACL reconstruction and other knee injury. Because resistance here is only the weight of the shin and foot, it is a low, controllable load well suited to early rehab and deconditioned older adults, and the terminal-range hold specifically recruits the vastus medialis, which is relevant for patellofemoral tracking. One honest caveat: near-full-extension OKC loading increases patellofemoral joint stress, so patients with anterior knee pain often work through a mid-range (roughly 90 to 45 degrees) arc rather than locking out.

Evidence basis: strong

Positions & Range of Motion

Start: seated tall against the chair back, thigh fully supported, foot flat, knee bent ~90°
End: knee straightened so the leg is nearly parallel to the floor, quadriceps (especially the VMO above/inside the kneecap) firmly tightened and held ~2 s at the top
Range of Motion: knee extension from ~90° flexion to near-0° (full extension)

How to Perform

Sit tall on a sturdy chair with feet flat. Straighten one knee to lift the foot until the leg is nearly parallel to the floor, hold briefly at the top, then lower under control. Bodyweight of the shin/foot provides the only resistance.

Watch on YouTube↗

Opens a YouTube search for “Seated Knee Extension (Bodyweight)”

Equipment:chair

Starting position: seated

Coaching Cues

1
Sit tall against the chair back with your thigh fully supported and hands resting at your sides or on the seat.
(verbal)
2
Squeeze the thigh and slowly straighten your knee, leading with the top of the foot until the leg is nearly level.
(external-focus)
3
Pause and firmly tighten the muscle just above and inside the kneecap for a 2-second hold at the top.
(verbal)
4
Lower slowly over 3 to 4 seconds rather than letting the leg drop; keep the movement smooth and controlled.
(verbal)

Evidence-Based Dosing & EMG Data

Recommended Dosing

2 to 3 sets of 10 to 15 repetitions per leg, with a 2-second hold at end range, most days of the week; progress load or reps once the target range is completed without fatigue or knee pain.

EMG Activation Data

Vastus medialis activity increases toward terminal extension, supporting the end-range hold; rectus femoris contribution is relatively reduced in sitting because the flexed hip shortens it (active insufficiency).

Muscles Involved (10)

Primary Movers

Quadriceps Femoris— Prime mover of open-chain knee extension against the weight of the shin and foot.

Vastus Medialis— Active knee extensor across the arc; emphasized in terminal range, though it cannot be selectively isolated from the rest of the quadriceps.

Vastus Lateralis— Contributes to knee extension throughout the arc.

Vastus Intermedius— Deep monoarticular knee extensor active across the full range.

Stabilizers

Iliopsoas— Borderline: helps hold the flexed thigh seated, but the chair provides most of that support, so demand is low.

Lengthened / Stretched

Semimembranosus— Stretched across the knee as it straightens.

Biceps Femoris — Long Head— Stretched across the knee as it straightens.

Semitendinosus— Stretched across the knee as it straightens.

Hamstrings (Group)— Antagonists that lengthen at the knee and eccentrically control the lowering phase.

Synergists & Assistors

Rectus FemorisSynergist— Biarticular; contributes to knee extension but at a length disadvantage with the hip flexed in sitting.

Easier Variations ↓

Short-arc quad (bolster)

Place a rolled towel under the knee and extend only through the final 30 to 40 degrees to full straight, reducing load and patellofemoral stress.

Seated isometric quad set

Keep the foot on the floor and simply tighten the quadriceps to gently press the knee straight, holding without lifting the shin.

Harder Variations ↑

Ankle-weight knee extension

Add a light ankle weight (or a loaded bag over the foot) to increase resistance as bodyweight becomes easy.

Eccentric-emphasis / single-leg tempo

Lift with both efforts but lower on one leg, or extend the lowering phase to 5 to 6 seconds to overload the eccentric portion.

Target Movements (2)

Knee ExtensionTibiofemoral Joint

Knee FlexionTibiofemoral Joint

Why This Exercise Matters

Everyday activities this exercise helps you do — essential means it directly trains the capacity the task needs:

Pushing Up from Chairessential Squat to Standessential Stair Climbing

Goals This Helps With

Rehab, performance, prevention, and mobility goals this exercise supports — essential means it's a cornerstone:

Knee Osteoarthritisrehab Patellofemoral (Knee) Painrehab⚠Fall Preventionprevention

Research Notes

claude-researched 2026-07 (home/bodyweight), panel-verified muscle roles + rationale. Sources not yet linked.