Lorenzo Blasi, 25, works part-time as a lecturer in fitness at Barnet College, north London

"I started training when I was 11 or 12 and I have only stopped training once since. That was for two weeks when I was 21. It was hell. I only stopped because an expert had told me to. I had damaged my back and was told I might do some permanent damage if I carried on. I felt terrible not being able to train. Really moody and miserable.

I do see myself as addicted to exercise. But, unlike some, I also feel that I can control it, and I wouldn't say that it has ruined my life.

There is a physiological side: I get a definite high - not a euphoric high, but I feel as if I have achieved something. I feel strong and as if I'm walking on air. If I don't train, I am left with a lot of energy and feel quite agitated; I end up fidgeting with my fingers and very restless.

When I was a teenager I wanted to be a professional footballer more than anything else. Even when I wasn't training, I would be doing sit-ups or push-ups in my room. So I have always done extra training.

When I reached 17 or 18, people began to say I was training too much and I was going to burn myself out, but I didn't really take much notice. My aim was pretty focused - that come the weekend and the next time I played football, my game would be better. If I didn't play well on Saturday, then I would push myself even harder the next week.

Now, my weekly programme involves a mix of weights for muscle tone, aerobics, cycling, step aerobics, running and swimming. It's about three hours a day, excluding the part-time job I do, which also involves fitness. I left a job working for a car dealer because I wasn't able to exercise - in that way, exercise does control me.

A sports person is supposed to peak around 27. From 30, you're on your way down. You hear stories, particularly of body builders, who find it hard to give up as they get older - I'll have to wind down gradually. I exercise for myself, so that even when I'm 40 I'll be able to go for a run. I can't imagine life without exercise."NICK WALKER