I attend a spinning classes on tuesdays and thursdays at my gym. There is a different instructor in each of the classes, and the style is very different. The tuesday class is definately a strength building class as most everything is slow, steep climbs. The thursday class is mostly endurance, varying from sprints to climbs. They are a great suppliment to riding, esp when the weather's bad. Not to mention the drill seargent figurehead keeps the motivation way up. :thumbup: