I have good news and I have bad news regarding indoor cycling classes. Let's start with the bad news because I want to end on a positive note.
As a longtime master instructor in the indoor cycling industry for the past 15 years (meaning I've certified and educated a large number of instructors at conferences and workshops), I have found that the really good instructors who are well-versed in exercise science and practice effective, cycling-specific training techniques are unfortunately in the minority.
The fitness world has morphed the original intention of indoor cycling and Spinning® into aerobics classes on bikes, and has resorted to gimmicks and non-stop movements in their quest to keep students interested. But don't despair—there are good instructors out there who are more like coaches.
Let's examine the reason for this.
There is a schism between the "fitness" and "cycling" worlds that doesn't need to exist. Many instructors who cater just to the "fitness" community claim that they don't need to practice cycling-specific techniques because their students aren't cyclists, and aren't interested in performance improvement, but are interested instead in weight loss and having fun. Hence, they bring into the cycling studio techniques and movements they use in other group exercise classes.
Cyclists look at those crazy moves done in a typical "Spinning" class, shake their heads and vow never to step foot in there.
A "cycling-specific" class taught by a cyclist is often looked upon by the fitness crowd as elitist and boring. It doesn't have to be this way. Cycling-specific doesn't have to mean staying seated for 30 minutes or more without changing position, and it is not necessary to do Zone 2 training in a 45-60-minute class—that is what leads some to believe that cycling training is boring.
Cycling-specific simply means honoring the rules of biomechanics and proper cycling technique that have been found to be scientifically sound after decades of research on proper position, pedaling mechanics and optimal power output. There is no sport that has been studied as much as cycling—cycling boasts over 100 years of scientific study!
What is important to realize is that the same type of training that improves a cyclist's performance would be far more beneficial to the non-cycling population as well. The rules of biomechanics do not change between a cyclist and a non-cyclist, and they do not become less true because one moves from an outdoor road bike to an indoor bike. While there are a few differences with an indoor bike, such as a fixed gear drive train with a heavy flywheel, and the fact that most of the bikes do not move in any way (flex or bend), for the most part, you would still ride both bicycles in the same way.
Training using proper cycling techniques indoors would create adaptations in the non-cyclist's body that lead to greater fat burning and increased caloric consumption than they experience in their aerobics-on-a-bike classes. These non-outdoor-cycling indoor cyclists would find they have greater strength and endurance, better fitness, and would ultimately increase their weight loss if they stopped the madness and just rode the bike like a real bike.
How would we know? It all comes down to power output. Anything that would reduce a rider's power output (as all these crazy moves tend to do) reduces the effectiveness of the workout. Additionally, the additional fluff of aerobics-type moves does absolutely nothing to increase fitness, and in fact, may even lead to a decrease in their fitness potential. Many of these popular moves are not only less effective, but they are also quite dangerous.