I have to inject to play badminton, my DSN explained that my muscles are releasing glucose and if there's no insulin in my body then the glucose has no where to go but stay in my blood, she said this especially happens with exercise where you stop/start, or I suppose where you sometimes exert yourself more. So I usually inject a couple of units before I play, I do find though that I tend to go a bit low after afterwards so watch for that - i usually bolus less at the next meal.