i'm 17 stone and i've started the c25k this morning, i must admit i didn't do the whole 30 mins but i did warm up on the xtrainer for 10 mins and cool down on the bike for 10 mins after, next week i will start it properly. Just watch your knees! and noisy treadmills, i had two this morning - dunno if it's just my size but the big guy on the other one wasn't making a noise :/