Q: how long does it take to gain a pound of muscle in my buttocks? I have muscular legs but a sagging flat out of shape but. I ride a bike nearly 100 miles three time a week.

A: Heavy cardio such as biking is not conducive to building muscle that are not directly involved in the movement (in your example, your buttocks, which don't do much while biking compared to quads or calves). And one pound is A LOT for a relatively small muscle group like your buttocks. As usual, the amount of muscle built will depend as much on your diet as on the exercise. Without proper nutrition you will have only small, if any, gains. But if you're interested in what exercises target your glutes specifically, check out the lunges, the squat, and the deadlift in the Essential Exercises section of my site. Note that all 3 of those exercises (especially the lunge and the squat) also will severely stress leg muscles which may interfere with your biking routine. If you had to pick one exercise for your buttocks, I would recommend the lunges. Hope that helps!