The thing about a break is that you don’t have to work. That’s kind of the very definition of a break. You get a couple of minutes where you don’t have to think about your job. Your responsibilities are on hold, you’re not needed, and you can think about something else. Plus, you can do anything you want on a break. Maybe you’ll just use it to eat lunch, but heck, you could go jump rope in the park for 30 minutes if you wanted to. You could work on your novel. You could go pet every dog you see on the sidewalk. You could call your mom and ask her how she’s doing. 

The point is that the time is your time. You can use it as you please because you are released from your duties. This certainly doesn’t mean that you should be working while you’re on your break. Then, by definition, it’s not a break.