Execution of Leg Sets

[bigla2004]

That's an entirely different issue related to performing the exercise "improperly" meaning in a way that predisposes the low back to injury, not an issue with the normal recruitment patterns used to execute the lift.

Have you been lumping squat, leg press and hack squat (machine) together in terms of quad activation over the course of the movement (ROM)?...

-S

I have been for squat & hack squat as the movements are more similar than the leg press in execution.