Leg Curl

Move · Resistance Training · Movement, Typed Supps

Bending the knee against resistance is the one hamstring job that squats and deadlifts never ask for.

Stage by stage

Set-up (Hip angle sets length): Seated machines hold the hip flexed and the hamstrings long; lying and standing versions start them shorter, and that difference matters more than the load selected.
During the set (Isolated knee flexion): With the hip fixed the movement is pure knee bending, the hamstring action hinge patterns barely load; gastrocnemius assists because it crosses the knee.
Lowering phase (Eccentric strength built): Controlled lowering at long muscle length is the quality linked with lower hamstring strain rates in sprinting sports.
Months later (Knee flexor hypertrophy): Size and eccentric strength build in the knee flexors, complementing rather than replacing hinge-based hamstring work.

Muscles trained

Primary: hamstrings
Secondary: calves

Intensity

3.5 METs (Resistance (weight) training, multiple exercises, 8-15 repetitions at varied resistance).

Time to effect

Weeks: Hamstring strength and the mind-muscle connection improve fast, since most people rarely train knee flexion directly.
Months: The back of the thigh visibly fills out, and eccentric strength (controlling the weight down) improves, which matters for sprinting and change-of-direction sports.

Related supplements

Creatine Monohydrate

Common myth

"Leg curls are just an accessory move, not worth serious lifters' time." In reality: Because the hamstrings act at both the hip and the knee, compound lifts like deadlifts and squats train them without ever fully lengthening the muscle under load. Leg curls fill that gap, and research on hamstring strain prevention specifically credits exercises that load the muscle at longer lengths, which is exactly what a controlled leg curl does.