Current Gymbucks earning period: 7/30/12 - 9/23/12
Next Gymbucks redemption period: 9/27/12 - 10/07/12 (Holiday lines!)
Gymbucks are a coupon for $25 off a $50 purchase (before shipping and after discounts are applied). They are earned on ever $50 purchase made through a certain 'Earning' period. Then you can redeem them on $50 purchases during a 'Redemption' period.
You can use them online or in the store. Online - during checkout just put in the code and pin number located on the back of the gymbuck or at the top of the online order receipt. Its instant use and is very easy to do :)
Instore the gymbucks need to be stapled to the receipt and handed over to use.