Bro, GVT is actually centered around doing 10 sets of a main compound for the particular muscle group, and then 3 sets of supplementary exercises. The leg extensions are more of an isolation movement. So a leg day under GVT should look like 10 (perhaps squats or leg press) + 3 (e.g. leg extensions) sets for quads and 10 (maybe stiff legged/romanian deads) + 3 (e.g. leg curls/Bulgarian split squats) sets for hams. And 3/4 sets of calves too later on if you have the energy for it. Gotta stick to compounds and heavy (relative) weight for this program. My 2 cents, yeah.