Spend an hour on one cardio machine vs. two or three different ones?
I like to keep my cardio sessions an hour long and at a fairly high intensity. I understand that it's recommended to change the routine so that the body doesn't get too accustomed to only one type of work-out. That is why, if I choose to do an hour an the elliptical today, I will do an hour on the stair master next time, then an hour on the treadmill the following time, etc. However, I often see people break down their cardio session (whether it's 30, 40, or 60 minutes long) among different cardio equipment. Most people I know who do an hour of cardio do 20 min. on the elliptical, 20 min. on the treadmill, and then 20 min. on the stairclimber, or a similar combination. Would this be more effective than staying on only one of those for the entire 60 minutes?
My reasoning is, since it's important to constantly keep the heart rate up, that staying on one machine the entire duration definitely minimizes the amount of time (no matter how short it may be for some) that the heart rate drops between switching machines. I also think that since I've already suffered through the warm-up and survived it once, I might as well just keep going as opposed to doing it all over again on whatever machine I choose to hop on next. I also understand that, while it's great to use different machines to exercise different body parts, I don't see a problem with using only one machine one day, as long as I use a different one next time, and keep mixing things up that way...
Are there any other reasons besides those that I should consider breaking down my 60-min. cardio into two 30-min. or three 20-min. sessions on two or three different cardio machines? Sometimes I think I would make it easier on myself (mentally, at least) if I divided my cardio work-out that way, but I'm actually afraid that it may not be as effective in terms of total calorie burning, heart rate, etc. Ideas??