Cardio machines are very helpful for weight loss. If you use interval training, you can get more results than if you did traditional aerobic cardio. But that's another story for another time. Let's take a look at which machines burn the most calories.

An okay choice: Elliptical Machines.

The biggest reason to choose elliptical machines - you've got a bum knee. I have worked with clients with extreme osteoarthritis and we were able to use these for a decent workout without pain.

But other than that, I am hardly impressed by the elliptical machine for fat loss. If you go into any gym, compare the bodies on the ellipticals to the ones on other machines...most of the time, the people on the ellipticals make no progress from month to month. Sorry, I just don't like these.

But if you have bad knees, or if you are an exception to my experience, feel free to keep rocking the elliptical!

Up next...The Stationary Bike

The bike can be easy on your knees as well, particularly if you are overweight and can't support your bodyweight at this time.

But personally, I like the stationary bikes a lot. The set up allows you to do a large amount of mechanical work during your interval training - and that is what puts Turbulence on the muscle and allows you to increase your post-exercise metabolism. In fact, when I first started designing the interval workouts back in 2001, I used stationary bikes exclusively.

I also think that the bike allows you to work very hard with less risk of injury. Sprinting requires an extensive warm-up due to the explosive nature of the activity.

I recommend starting with the bike unless you are an experienced runner that knows your body well

In addition, here are three more key points about the bike.

a) Stick to the upright version if possible. When using a recumbent bike for intervals, your hips tend to rock too much and your body tries to get into awkward positions in order to push hard against the resistance. That's my experience. The upright bikes are set up better for intervals.

b) For intervals, increase the resistance against your pedalling, and not the speed of your pedalling. I don't like high RPM spinning. I think you'll get more results and do more work when you keep the RPM between 80-100 and work against a harder resistance. Forget that high-RPM spinning stuff...I think it is rough on your hips and knees.

c) When on the upright bike, sit as upright as possible for the recovery intervals or even stand for some of the work intervals. Just avoid a rounded over posture as that can be hard on your low back.

And the winner is...The Treadmill.

The treadmill can burn almost 20 calories per minute of exercise during your workout. That's a big burn, but of course only advanced fitness levels can achieve that - but hopefully you fit that category now or you will someday with consistent training and nutrition.

Some tips: Don't go crazy on using an incline (as that can lead to tight calves), but if you are able to run at more than 10mph, use a 1% incline to help offset the need for more speed. The last thing you want to do is end up in a crazy video on YouTube with you flying off the end of a treadmill into an elliptical machine.

So as with all types of sprinting, be careful.

Honorable mentions go to...The Rowing Machine and Stairmaster...these can be used in place of other machines for variety and are still effective. Better yet, if you are able, use your body as the best fat burning machine. I highly recommend bodyweight circuits for interval training. These are fun, effective, and perhaps even better at sculpting your body.