It can be a challenge to stay in shape when you can't even afford to go to the gym. Your options are limited to doing work outs at home or going for a jog in the park, and that's a shame because there are few better ways to keep motivated than to join a class of like-minded people. Well, today we've got a great tip for you. If you're really determined to lead a more active lifestyle, you may be interested to check out some of the discounts Groupon is offering on various fitness courses. For