There are problems with this study, causing it to lead to a logical fallacy known as a 'Hasty Generalization'. The lengths of crank arms are not precise enough!

The most important lever in the crank arm mechanism is your knee. That is where the leverage comes from, not so much the arm length. Try some squats and you will see what I mean. If you squat all the way to the floor, its a lot harder than it is if you only squat a few inches. This is because of the leverage in the knee.