Fiona-
Ah, it has been a long weekend so I have not had a chance to get on the board. If you are doing those sprints, you are working all the muscles in your legs, your butt, and your lungs! I read your post and I thought it was such a great example for people who say they have no time to exercise. Who can't take a couple minutes out of their day while they're making tea and run a few sprints! I think thats GREAT!!
Keep up the good work!!!
Linda