face it, this is you.
lets get this straight from the get go, i do believe there is a use for treadmills and stationary cycles in limited cases and definitely a use for rowing machines, but ellipticals should all be burned.
So ill start with this, Chronic cardio, in this article Mark Sission (most of you might know that im big on the primal blueprint) gives evidence to show that chronic cardio or prolonged raised heart rate (roughly 65-80%) causes plenty of problems:
"This kind of training (and diet) raises cortisol levels, increases oxidative damage, systemic inflammation, depresses the immune system and decreases fat metabolism. About the only thing good it does is improve cardiac muscle strength – and even then you get to the point of diminishing returns fairly quickly."
Cortisol is a catabolic hormone for those of you who didnt know, catabolism is " The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy."
In this instance its the breakdown of muscle into energy to fuel the cardio. i.e. YOU'RE LOSING ALL YOUR GAINS MAN!
So at this point the major problem is prolonged raised heart rate around the 80% level but that doesn't include walking so for people in bad neighborhoods, in cities in apartments treadmills and stationary cycles could be good, for low heart rate fat burning exercise, fat burning being the point at which you're moving but can hold an easy conversation without getting short of breath, unless you're super excited about what you're discussing like me, luckily all i have to do is type.
"BUT I WANT DAT CONDITIONING!!1!1one1!1!" im glad you brought that up, the best form of conditioning besides strength conditioning with stuff like kettle bells and and circuit training is SPRINTS. short, intense, ramp up the metabolism, doesn't release cortisol, what's not to love? the best part? they get easier over time (keep making it harder, folks, pro tip) they don't take much time, and coupled with a primal/paleo diet you melt the fat right off.
so in essence, on the subject of "cardio" you want to stick to the polar ends of the stick, walking and sprinting, easy and super light and in high volume, and short, intense, and low volume, coupled with a good diet THAT will get rid of that pesky fat, and thats without even talking about strength training.
The only "cardio" machine i will ever use is the rowing machine because of its practical real world skill benefits (call me old fashioned but fantasizing about rowing a ship to an enemy port to pillage just gets me fired up and motivated to train) but i only do it for maybe 1000m just to get warm but i hardly even have access to them.
get outside, take a walk, climb a tree, and just be happier, you'll get better gains from sprinting than long drawn out cardio sessions and it will take less time meaning more time for sun bathing, tree climbing and walking around with friends.