Max-Force Generation Point:
It's the max-force generation point we mentioned earlier-that's the place on an exercise's stroke at which the target muscle can generate the most force-and more force equals more mass.
That point, say many scientists, is the spot where the most muscle fibers are stressed to the max because they are perfectly aligned for action. So if you overload that max-force point correctly, it's where the most growth stimulation occurs.
Where is that sweet spot on the curl's stroke? Right below the point at which your elbows are bent at 90 degrees, between the bottom and the midpoint. (There has to be some stretch in the muscle for ideal fiber alignment and therefore max-force production; in fact the closer you get to full contraction, the less force you can produce because of fiber crowding and bunching.)
Now imagine Arnold doing a cheat curl. He would lean forward, bend his arms slightly and heave the heavy barbell to his shoulders. Almost all of the overload occurred right at the max-force point-between the arms-straight-position and the midpoint.