Long hours sat in front of a computer?
Too tired to exercise when complete work?
Busy concentrating on your work?
Have you thought about Exercising at work
Stretches whilst at your desk
Have a walk out of the office at lunchtime
Legs stretch whilst sat down
Walk, Cycle, Run to work
Start some work fitness activities
Make a reason to talk to some office staff in the building
Walk up the stairs rather than using lift every time