I am looking at doing my cardio/road work about 7 days a week as i have some weight to lose. i don't really run/walk because of bad knees and shin splints. I like biking mostly at the gym and could committ to it 6-7 days a week. how much time a day do i need to put in that the weight will start coming off and i will build up my stamina. Most people recommend 45-60 minutes. is that sufficient at a good pace?