Millis,
Do you have a smartphone? You can study while exercising - at least during cardio. I watch old Thursdays With Ron videos on
MGMAT's Vimeo website at my gym - some of them require paper and pen but if you can find a topic that you can go along with without that and just try to pick up tricks and skills this can be valuable.
I know it's tough to do the exercising and the GMAT prep at the same time but there are a few options. I'd probably put together a YouTube playlist or check out Vimeo for some valuable videos. You could even use that as your "MBA" prep time - watch some of the old webinars posted here from the consultants that put together some great stuff. I find it really difficult to follow just audio GMAT stuff but you can find some video stuff that will help. I wouldn't abandon it all together, though, as if you give up everything but the GMAT stuff you're going to burn out!
Good luck.