At the gym today I decided to change my intervals from one minute to 30 seconds. So I was doing 30 minutes of 30 seconds on 30 seconds off, at 10mph.

After I was done I asked a personal trainer there his opinion on it & he said it's better to do them by minutes because by the time you're getting into the sprint it's over - which is exactly what I was thinking.

However he gave me a bit of advice & said said that rather than jumping on jumping off all the time, to do it by fast sprint then slow it down to 5mph slow jog for a minute, then back up & down & so on. Then gradually I'd want to increase from 5 & 10mph to 6 & 11mph etc.

It immediately sounded way better because you're still interval training at a high rate, but not totally stopping. Remaining active at all times.