The twist

The power of a backhand comes from the twisting, or rather, untwisting of the body, which creates a wave of energy flowing from the ground, through the hips and core, and out to the fingers.

This idea of a twist or whip is actually pretty common across sports - it's the same principle that golfers and batters use to power their swings, that soccer players use to kick the ball, and that volleyball players use to slam the ball. Arms are little, with little muscles. The power has to come from the large muscles of the body, ie, the core and legs, while the whipping motion allows the disc to accelerate through the entire throw.

So to start the backhand, you need to first wind up your body. Take a moderate step out, and twist so that the disc is far behind you.

You lose the additive advantage of the twist if you unwind your body all at the same time. You want to untwist one section at a time, so that the power and momentum of each part can fuel the next. The legs go first - they grip into the ground to power the uncoiling, and then the hips rotate, and moving upwards through your core, and finally the shoulders open up, the arm extends and the wrist snaps.

Easier said than done, especially if you have been used to throwing with only your arm, so get in front of a mirror and watch your throwing motion. Then practice - first slowly, and exaggerate each step of the untwisting, and then speed it up. You don't even have to actually throw the disc at this point - just practice the motion and keep watching the mirror to check your form. And when you feel confident that you can coordinate your body for the (un-)twisting, then go out with a friend and practice hucking.