If you’ve ever been to a spinning class, they can be intense.  I swear they always have spinning type classes on the major TV weight loss shows.  But realistically speaking, at my local gym, they only have early morning classes and quite frankly they do it in a dark room that is only meant for spinning, because the machines can’t so easily be pulled in or out in so many ways.  But realistically speaking, you go at a certain speed and they push you to keep going at that rate to burn a ridiculous amount of calories every hour on a regular basis in general terms. 

In general terms, you actually exert yourself not only in cardio methods, but also in other ways, so you are always working new parts of your body and you are always burning more calories in so many ways.  Essentially speaking, you are always working to burn off more calories and lose more weight.  They use the dark room only for a reason, and all in all, all the methods and tools used are used for a reason.  If done correctly, cycling can easily be one of the most effective methods of cardio in general.