Elliptical Trainer and calories burned

i have recently bought an elliptical trainer, enjoying using it , i usually do 30 minutes each time.
The calories burned according to that is usually 535 but when i log it on here its says 300 calories, which do you thing is right or is it somwhere inbetween?

thanks

Here is an interesting exchange I had a few years ago with a physiologist at Cybex:

I use a Cybex 750AT [this is a brand of elliptical http://www.amazon.com/CYBEX-750AT-Total-Body-Trainer/dp/B002VL5KME I love this thing!!] at the gym. I am not a super athlete. I get my heart-rate up to ~150 and hold it there for ~45m. At the end of the workout the 750AT tells me I’ve burned ~800 cal -- equivalent to an 6 mile run!! When I run my heart rate is likely to be about the same, suggesting the same metabolic burn-rate, but it would take me 60 min to burn 800 cal, assuming my slow 10 min miles.

Can this possibly be right?

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His reply:

Thank you for your recent email regarding your use of the Cybex 750 Legacy Treadmill.

Quite honestly, your question is a bit complicated – hopefully, you weren’t seeking a “yes or no” answer.

The only means of measuring calories directly is to lock you in a sealed room with a water bath, and measure the rise in temperature of the water as you expend energy. This is referred to as direct calorimetry. Obviously, we cannot do that.

Everything else is an indirect measure. This includes the algorithms on treadmills, heart rate monitors, and any other device which professes to inform you of caloric output. Our treadmills use a formula established by the American College of Sports Medicine, which takes into account the speed of the treadmill and its incline. We could use heart rate as an indicator, but since most people don’t wear heart rate monitors, and grasping the sensors while running is difficult and leads to computation errors, it is impractical for us to do so. In the end, we do our very best to establish an accurate prediction of your caloric output by employing a well-established, scientifically supported, prediction equation.

Regarding the correlation between heart rate response and energy expenditure, we have made some interesting discoveries of our own. In a recent study conducted by the Department of Kinesiology at the University of North Carolina at Charlotte, we compared heart rates on two different devices – our Arc Trainer and a popular elliptical trainer – at normalized metabolic workloads. We established maximum oxygen consumption for subjects on both devices, and then had subjects exercise at 55%, 65%, and 75% of their VO2max. What we discovered, was that at each percentage, the heart rate on the Arc was significantly lower (p <.05) than the elliptical. Despite the equivalent metabolic workloads, heart rates were lower on the Arc.

How do we explain this? Biomechanically, the forces generated on the Arc create joint torques which effectively activate the large hip extensor muscles, the Glutes and hamstrings, which lowers the overall muscular stress, resulting in a lower heart rate (see pressor response), while maintaining metabolic output. The biomechanics of the elliptical are such that virtually all of the torque loading is placed on the knee joint, creating very high muscular stress on the quadriceps, with very little on the glutes and hamstrings. This results in a higher heart rate with no additional elevation of metabolic output. Kind of fascinating, really.

How does this relate to your running? A good deal of muscle activity during running goes towards management of shock on initial contact (heel strike). Our treadmills are designed in such a way that they dissipate the shock when your heel strikes the deck, reducing the stress on the muscles that are working to manage that shock. Furthermore, the deck then stiffens in the middle and at the tail, in order to allow you to efficiently generate ground reaction forces which propel you through the air. Overall, it’s a very efficient system. Consequently, if you’re managing your run according to your heart rate response, you may find that you can run a bit faster on the 750 than you would outdoors, at a comparable heart rate. Thus, the increased caloric burn.

We are currently engaged in research to examine metabolic outcomes on the 750 and other modalities. Until I have more specific scientific evidence, I’m afraid this explanation is all that I can offer. Nevertheless, it’s questions like yours which help us to continue to investigate human performance and how our products can best contribute to its enhancement.

Please feel free to contact me with any other questions.

Best regards,