As often as the knees will allow. I try for 2-3 times a week. There are others that go more often then that. As much as I really enjoy doing it, I need to do more flat miles. All climbing and no cruising makes for a dull boy. So far this year all my rides except 3 have included GMR in them. But I will say all that climbing has done the legs good. Went skiing today for the first time this season and the legs felt great. It was the tenth run before they actually started to feel like jelly. Years past they felt like that after the 3rd or 4th run the first day of the season. So I guess doing GMR is worth more than just being an incredibly great way to get out into the mountains. It's a way to shorten ones life but give you stronger legs at the same time.