Myth: Toe Direction Targets Vastus Medialis/Lateralis
Training the quads isn't complicated. Of course you might think differently given that there are plenty of bogus tips out there on where to point your toes while doing knee extensions and how to manipulate stance width on squats to supposedly isolate different heads of the quadriceps.
Here's the problem with that. Muscles respond to torque. Introducing an action that doesn't use the target muscle will not increase torque, period.
A muscle acts only on joints that it crosses. But it's "toes out" to hit medialis, and "toes in" to hit lateralis on the leg extension, right? Not exactly. More like "toes out" to tear your MCL and "toes in" in to tear your LCL.
Your knee only bends one way, so train it that way. Introducing external rotation at the hip on squats (toes out) also won't do your quads any good. Instead, your glutes will likely end up taking on the brunt of the training load. Of the four heads of your quadriceps, only the rectus femoris crosses the hip. However, it's responsible for flexion at the hip... not rotation.
If you want to increase the size of your quads, your best bet is to manipulate the knee angle and center of gravity location associated with compound movements like squats, lunges, split squats, etc.
Quad vs. Glute Dominant Lunge Pattern
Additionally, ditch the old "knees behind toes" cue. Let your knees track over your toes every time you lunge and squat when targeting quads.