Hi Becky: I am a mom here on Weplay and a former collegiate Div. I volleyball player and college coach. I would recommend for arm strength to strengthen the core, chest, back and shoulders. These muscles all work together to produce a quick swing. Strengthening the rotator cuff muscles will also help. I have a volleyball strength training program on my website. I own female athletes first.com. Go and click on conditioning programs. Strength translates into speed and power. Make sure they have the correct mechanics on the swing to help prevent injury.

by quicker do you mean not waiting or waiting for the ball? if so, a good drill is to have them not swing at the ball at all when they get a set and have it hit them on there head. they will have to jump at the right time to hit the ball. if you want a better snap, have them hit it with their arms, but they will have to snap there wrists because the goal is to have the ball bounce off the ground and go under the net. if you mean faster arm swing by speed, have them do windmills with their arms

Becky,
Use resistance training techniques taught and closely supervised by a physical trainer.

Almost everything?

Just kidding. Thanks for the nod.

Well first hit it off a tee then throw then slow pitchs accelerate and they will get better with some practice!