Leg Curl (Hamstring Curl)

The leg curl trains knee flexion: all three hamstring muscles cross the hip and knee (2-joint muscles); here knee flexion is performed with the hip joint stabilized. To reduce involvement of the gastrocnemius, keep it in plantar flexion while doing knee flexions (pointing the toes takes the gastroc out). Variations:

• Prone (lying) Leg Curl — align the axis of rotation (the knee should not be on the pad); stabilize by tightening the abs; if the glutes are tightened too much the quads elevate above the padding; relax the ankle and feet; check feet placement (feet to the sides emphasizes the upper hamstrings).
• Incline Leg Curl — beware of knee hyperextension.
• Seated Leg Curl — a good substitute for the prone leg curl for those with lower-back problems.

SAFETY NOTE: use care with RM loading (hamstring curl can cause injury). Sartorius and gracilis are weak knee flexors. The prone leg curl is the "contracted" position of the Positions-of-Flexion hamstrings chart.

• Primary Muscles: Biceps Femoris, Semitendinosus, Semimembranosus.
• Knee flexion with hip stabilized; plantar-flex the ankle to reduce gastroc involvement.
• Variations: prone, incline (watch knee hyperextension), seated (low-back-friendly).
• Use care with RM loading.

• hamstrings — the three knee flexors.
• gastrocnemius — secondary knee flexor (minimized by plantar flexion).
• two-joint-muscle — hamstrings cross hip and knee.
• rm-loading-caution — injury risk with RM loading.

The three variants are now structured exercise records in spine/leg-curl.json: ex.lying-leg-curl, ex.incline-leg-curl (carrying the knee-hyperextension caution), and ex.seated-leg-curl.