There was a experiment done in the 80's to effectivly measure the strength of the the quad muscle.
the machine used was a leg extension, the seat angled back and hip secured to ensure no other muscles were involved in the movement, tested each leg indivdually, isometrically at varying angles of the knee joint, the machine was connect to a PC measuring force output.
What was obvious was peak force was measured at full contraction, what was a suprise was that most subjects tested where found that the dominant leg was fractionally weaker.
the tester contibuted this to the dominant leg recieving too much work over time, he came to the conclusion that, in strength, "less is more"
Fred Hatfield was one of the ones tested, along with many others.