Increasing your forearm strength can give a edge on winning a arm wrestling match even if you don’t have that have that usual bulky biceps. You can increase your forearm strength by doing some pushup and wall climbing. Lifting weights should also be good for your forearms. Also work on your deltoids. This is helpful in increasing your endurance limit and tiring out your opponent. Forearm curls can also be an excellent exercise for you.
Make sure you have good and optimum amount of protein in your diet. Proteins help to build muscle. The thing to remember is having artificial proteins or having more proteins than the optimum quantity can damage you liver. So be careful.
Having confidence is another important aspect. This intimidates the opponent and gives you that extra edge to win.
If your opponent is as strong or stronger than you, then rather than trying to put his arm down, put your effort into keeping your arm straight. This will tire out your opponent and also confuse him.
Now that you have your opponent tired, you can put his arm down by getting your arm closer to you. By doing this you can utilize your shoulder muscles too.
Do follow all the above tips if you wish to win over an opponent of equal or more strength.