A Work Workout

As mentioned, my working hours are long, and it has left little time to do solid exercise. Re-joining a gym in Gotanda just hasn't proved to be cost or time-effective. I've been for a few runs along the river on the weekends, and I guess if I really cared, I could go for early-early morning runs before work. My office is on the 7th floor so I can use the stairs instead of taking the lift. I can do butt-clenches in my chair, I suppose.

Does anyone have more suggestions for sneaky exercise at work?