For quad growth
For quad growth, the two are close. Leg extension rates slightly higher: more of the work on the quads, easier to progress.
Belt squat gives more stretch.
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
Belt Squat. Loads the legs from the hips, so the quads work hard with no weight on the spine.
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.
For quad growth, the two are close. Leg extension rates slightly higher: more of the work on the quads, easier to progress. Belt squat gives more stretch. 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.
Belt squat needs a machine, so for most people it’s a gym exercise. Leg extension needs a machine, so for most people it’s a gym exercise.
Belt squat: it rates Excellent for joint and recovery cost in our research rubric, against Strong for leg extension.