I also tend to check out the commentary track(s) immediately after viewing the film. But rather than work out, I tend to fill the time with another hobby -- looking at the cinematography! Since the commentary is not constantly advancing plot, my eyes feel free to wander the frame and notice new things. I remember David Fincher complaining on the Fight Club track that a little appearance (by 'Ricky' in the hallway as Norton is ushered out of his job by security men) was universally missed by people. It wasn't important, but it was a detail nonetheless. My thought is that he should be happy people are missing things like that. It means that even upon repeat viewings we are still wrapped up in the story and are drawn to the subject of the frame. But when listening to the commentaries, I can feel free to view the film from a different mindset -- and enjoy all of the framing and photographic details to a fuller extent whilst still soaking in all of the spoken information. Bring on more commentaries!