For quad growth
For quad growth, leg extension rates higher on our research criteria: easier to progress, easier on the joints.
Sissy squat gives more stretch.
Both are good choices that train the quads the same way, so they swap freely. Rotating between them every few weeks is an easy way to vary your training.
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.
Sissy Squat. The knees travel far forward and stretch the quads hard, but it’s tough to load and stresses the knees.
For quad growth, leg extension rates higher on our research criteria: easier to progress, easier on the joints. Sissy squat gives more stretch. Both are good choices that train the quads the same way, so they swap freely. Rotating between them every few weeks is an easy way to vary your training.
Leg extension is easier: it’s easy to learn, while sissy squat takes some practice.
Leg extension needs a machine, so for most people it’s a gym exercise. Sissy squat needs no equipment, so you can do it anywhere.
Leg extension: it rates Strong for joint and recovery cost in our research rubric, against Good for sissy squat.