I have a question. Now I of course realize an exact answer here is impossible, I mean it obviously would require an in depth study that involved a myriad of controlled variables like the individual, the specific cardio machine, etc etc... but I'll frame it real generic. Which one of these, A or B, would result in a higher/longer metabolic burn rate for the day, and when done over a period of months, result in a larger reduction of excess body weight, all else being equal like diet. A) 30 minutes on the exercise machine where you are busting your ass off and on for the majority of the session and you can't wait till its over. A level where reading a magazine is pretty much out of the question and you actually feel the work/pain in your muscles or B) Say 50 minutes or more on the same machine but at a much less painful level where you still get your heart-rate up to 120ish and keep it there, but its more enjoyable and you can read or just listen to music or whatever. The exact number of minutes in my example are for simplicity purposes only, just to convey the principles involved behind what I'm basically asking. It could be 7 minutes of ball busting vs.15 minutes of tolerable yet brisk exertion. And again I know an exercise physiologist could probably dedicate several years and 100 graphs to figure out the optimum mix, the ratios of time duration to physical difficulty, and even that would of course depend on the individual and what they felt like at the time, but just generally... Personally I prefer the longer session at an easier pace than the shorter session in pain. But is the shorter session more effective? As it stands, I do either/or depending on the day. But am I wasting my time on the easy days even though I go longer?