If you're not vinyasa-ing this lunchtime, at least get up out of your seat and take a brisk walk (NOT to KFC) or check out what classes are on at local gyms. If not for your physical wellbeing, it will make you feel super self-righteous to arrive back in the office with a post-exercise glow!
UPDATE! Ambika's lunchtime vinyasa yoga class is FABULOUS! It passes in no time - I could go another hour and still feel invigorated. I leave feeling lighter, longer and more at peace with the world (even in Collins Street at lunch hour!)