Michael on the top deck near the front of the ship

The blue track on the left of the picture is a 400 metre running track that circles most of the top deck.
There are scheduled exercise walking groups that use the track at various times during the cruise, but you can of course exercise there anytime you want.
I went for an 8 km run one day (so 20 laps) which is quite pleasant, as long as the wind isn't too strong.
It's very nice going for a walk there during sunrise, as the deck is relatively deserted and you can enjoy the beautiful view as you get your exercise for the day.
If you're a bit of a runner or walker, you may get a little frustrated by people not obeying the signs on the track - walkers keep the left, runners to the right - but it's usually not a big issue.
You also have to be a bit careful running around on the deck at the front it can pitch quite a bit, so as you take a stride you might feel like the deck is dropping away from you!