Not all exercise sessions are made equal. If you're just doing 10 pushups or 7 minute circuits for 6 months, you're still very much in the beginner phase.
It took me a few years of consistent intense training to really get into the groove of things. I've been at it for about 9 years now. This is the intensity that I aim for (mind you, this is not me in the video): http://www.youtube.com/watch?v=LAhNyvTF5Uw
After that level of intensity on a consistent basis for a few years, you adapt to it. While you may feel tired, you gain energy from it as well.
I did much more than 10 push-ups or 7 min circuit training each session for those six months (and those six months isn't the only time I've exercised, just one of the longer uninterrupted streaks of it). Don't patronize me.
Not trying to patronize you at all, and I apologize if it came off that way. I'd say that most people in the tech/hacker community aren't too well acquainted with consistent, dedicated exercise. It wouldn't be unreasonable for someone to have the belief that after 6 months of 7 minute circuits, their body should be well adapted to intense workouts. Since I don't know who you are or where you stand on the experience spectrum, I took an educated guess, and apparently was wrong.
It took me a few years of consistent intense training to really get into the groove of things. I've been at it for about 9 years now. This is the intensity that I aim for (mind you, this is not me in the video): http://www.youtube.com/watch?v=LAhNyvTF5Uw
After that level of intensity on a consistent basis for a few years, you adapt to it. While you may feel tired, you gain energy from it as well.