Well, there are different moves in armwrestling and even though the different moves use the basic same muscles, the order of importance changes depending on the position you are pulling from or the technique you are trying to use. Here are the important muscles and what they are used for.
Forearm- Hand supination, pronation, and wrist flexion, also "rising" wrist strength when in a backpressure (hammercurl) position, and of course strong fingers for obvious reasons
Shoulder- Rotator strength for side pressure and to aid in keeping a lock
Biceps/Brachi- bicep is mostly used in hooking, brachialis is used heavily for back pressure and top rolling, with a combo of both being used in a drag hook, or a rotator controlled hook
Lats- used to stay tight, or to keep a strong lock when sliding the elbow across the pad to get better position for the technique you are trying to execute...
Tricep - used for a shoulder press, that should be the only time though. Armwrestling is nicknamed pulling, because you are almost always pulling, not ever pushing, most of your pressure should be directed at the table corner closest to your arm you are not using. (IE. if pulling with the right arm, you generally will pull toward the corner of the table where your left elbow is resting)
Anyway congratulations to Alcatraz for getting 2nd in his classes at the big Ottawa tournament. I have seen you post on the armwrestling board so I knew you'd be at C.O.A.C. today. I like how you said todd didn't get that size from endurance training, back about 7 or so years ago, he was a 198 puller, then about 4 years ago he was up to about 260 when he went against Voevoda lol