Lying triceps extensions have always been among the premier exercises for filling out your upper arms, but you may not be getting the full effect. Pointing your guns perpendicular to the floor when you lock the weight out gives your triceps a break—the load transfers to your elbow joints. It’s just like the top position of a bench press, and it doesn’t stimulate the triceps.
Instead, move your arms back a bit so they’re about 45 degrees to the floor. When you bend your elbows, the weight will come down below the back of your head, giving the triceps a greater stretch. When you extend your elbows, you can still lock out the weight, giving you the benefit of training through a full range of motion, but your tri’s will stay engaged because your arms are at an angle rather than vertical. The pull of gravity will focus the load squarely on the triceps.
Another Advantage - Because the weight never sits directly on the joints, this extension won’t aggravate your elbows.