Gymbucks are earned during specific earning periods. They are a coupon for $25 off a $50 purchase that you receive for spending $50 during the earning period. The redemption period for gymbucks is usually 10 days long.
Coupons are usually 20% off and can be found in parents and parenting magazines. If you sign up for a rewards card, they sometimes email coupons as well plus you can earn $5 for every $250 spent. It takes a long time for me to earn but it's always nice to get a few bucks once on a while.