If someone is riding for the purpose of getting fitter, a heavy bike works better than a light bike. But, assuming that the wheels and tires are of equal weight and quality, the performance difference between a 19 pound bike and a 29 pound bike on typical roads is so small that it is difficult to measure.

Of course, if you were climbing a mountain that took an hour, those 10 extra pounds would be meaningful. There is a difference between pushing 200 pounds of rider and bike up a hill, compared with 210 pounds. But, if that rider is trying to get fitter, that extra work will help him get fitter even faster.