For quad growth
For quad growth, hack squat rates well ahead on our research criteria: 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
Hack Squat. Deep knee bend under stable, heavy load: the quads are clearly the limiter.
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 cycling, hack squat rates well ahead on our research criteria: more carry-over to cycling, more injury protection.
For quad growth, hack squat rates well ahead on our research criteria: 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.
Hack 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.
About the same: both rate Strong for joint and recovery cost in our research rubric.