For quad growth
For quad growth, the two are close. Single-leg leg press rates slightly higher: more stretch, easier on the joints.
Leg extension keeps more of the work on the quads.
Both are good choices, and they train the quads differently. Using both across your week covers more of the muscle than either alone: in studies, varied exercises grew parts of a muscle that one exercise missed. (Fonseca et al., 2014; Costa et al., 2021)
The research score comes from these, scored by hand from the studies. Lifter scores appear once an exercise has 10 ratings. How scores work
Leg Extension. The only exercise that fully loads the rectus femoris: it grew all three of its regions in one trial, where Smith squats didn’t. Lean back to stretch it more.
Single-Leg Leg Press. One leg at a time on a stable sled: a deep knee bend, no balance demand and easy to load in small steps.
For quad growth, the two are close. Single-leg leg press rates slightly higher: more stretch, easier on the joints. Leg extension keeps more of the work on the quads. Both are good choices, and they train the quads differently. Using both across your week covers more of the muscle than either alone: in studies, varied exercises grew parts of a muscle that one exercise missed.
About the same: both are easy to learn.
Leg extension needs a machine, so for most people it’s a gym exercise. Single-leg leg press needs a machine, so for most people it’s a gym exercise.
Single-leg leg press: it rates Excellent for joint and recovery cost in our research rubric, against Strong for leg extension.