there both low impact but walking still burns almost 2 times the calories than biking 110 to 55..and running 5 times, should i deflate my tires to make it more dificult? i stay in the first gear, had a hip replacement so cant run anymore.... ive been on a very low cal diet since my surgery, and have been biking 100 miles a week on a beach cursier, but since ive been able to walk im doing 50 miles walking and have lost 2 x the weight than i did biking...same diet less weight...i can never run agian but will harder biking be better than walking to get in real shape?