Teaching is more active than a lot of jobs, and most of my working day is spent on my feet. But I still find myself needing to exercise, so I try to run at least four or five times a week. The great thing about running is that it's so flexible - you can run anywhere, any time. And there's no commitment involved. Joining a gym makes you feel you have to get the most out of your membership, while playing a team sport means you have to be there for training and matches or you let other people down. But running is something you can fit into your life as and when you have time - you don't have to build your day around it. I don't have a routine. I run at different times of the day, depending on what else I'm doing.
I turn 30 this year, so I'm becoming more aware of the need to keep in shape. Regular exercise is increasingly important as you get older.
Most people are aware of their fitness levels, and I know I'm not as fit as I was five years ago. Having said that, my main motivation for running is simply that I enjoy it - it's no hardship, it's something I look forward to. I've done a couple of half-marathons, but I don't have any ambitions to do a full marathon. I see running as a leisure activity and I don't want to get too hung up on it.
The important thing is not to get uptight if you miss a day, or even a week. When I'm too tired or it's raining, I just don't bother. And I don't run against the clock or set myself targets, I just run until I've had enough. On a school day that means around 30 minutes, but at weekends I do up to an hour. How far I go in that time varies a great deal depending on my energy levels.
I don't really care where I run. It's the exercise I enjoy, rather than the scenery. My school is in central London, not far from the river, so it's always interesting to run on the streets round there. And if I start from home, there's a good park I can use. I'm usually on my own, but sometimes I go with a friend and we'll chat as we run.
As for what goes on in my head, it changes from day to day. Sometimes running clears my thoughts completely and I forget about everything. Other days I might spend the whole time thinking about a problem or coming up with ideas. Either way, when I've finished I always feel better for it.
The children at school know I go jogging, and that's a good thing; it sends out a message that exercise is important. Most of my colleagues try to keep fit in some way. The head and deputy both go to the gym, and I know other teachers also jog.
The fitness bug is definitely catching. It means exercise is often a topic of conversation in the staffroom, and you'd soon get found out if you started easing up. I'm Canadian, and I used to teach at a school in Toronto where we had a staff running club, as well as staff basketball and volleyball evenings. This is my first year at St Paul's, so I've not been brave enough to start anything like that. But I might suggest it one day and see if there's any interest.
Rafal Balik is a Year 4 teacher at St Paul's CE primary school in the London borough of Tower Hamlets. He was talking to Steven Hastings. A "Get Active" column on how teachers get - and stay - fit starts next week in Friday magazine