I recently started spinning class when it got too dark to ride outside in the evenings. The first class was really tough - I could hardly do the standing at all even though I do stand on my bike. After a few times, I felt a lot stronger and standing was not a problem. I never experienced any muscle soreness at all. I am lucky that we have two really good spin instructors. They are really encouraging and very "up" type individuals. They never interfere with our bikes or "our" rides. With the new people, they just make sure the bikes are set up correctly. Although I haven't had a chance to get out on my bike much lately, when I have, I have really noticed a difference in my strength. I just love spinning and I really look forward to the classes.