Leg Extension
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Machine knee-extension isolating all four quads; a rotary (open-chain) movement with specific knee-joint alignment notes.
Detail
The leg extension is described as an excellent exercise — and, contrary to popular belief, NOT for "cutting up" (definition). It is a rotary motion, so check the axis of rotation. Because the knee is a hinge joint, ensure proper alignment of the patella with the axis of rotation of the cam, and proper alignment by a slight inward rotation of the quads (hip rotation) so the extension is performed in a vertical plane. When the lower back is pressed against the back pad it is difficult to fully extend the knees without developing hamstring tension. Locking out is not very dangerous because the resistance force is pushing the shins down. All four quads are involved. Aligning legs in the same plane and breathing are important. It is the body-part (isolation) quadriceps exercise (e.g., 3 sets after squats and leg press), and is used as the pre-exhaustion exercise before squats. It occupies the "contracted" position of the Positions-of-Flexion quad chart.
Key facts
- Primary Muscles: all four quadriceps (rectus femoris + three vasti).
- Rotary motion — align patella with cam axis; slight inward quad rotation for vertical-plane extension.
- Locking out is not dangerous (resistance pushes the shins down).
- Pre-exhaustion exercise before squats; "contracted" position in the quad chart.
Connections
- Quadriceps — all four quads (isolation).
- Rectus Femoris — 2-joint quad.
- Knee Joint Range of Motion — hinge-joint alignment.
- Pre-Exhaustion System — leg extensions before squats.
- Squats — the structural exercise it pre-exhausts.
Sources
Exercise guides
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Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.