Exercise- KNOWLEDGE IS POWER

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Hi, Am quite new to this. Bought an elliptical trainer and was doing 30 mins and the default was that I burned 351 cals. I just bought a heart rate monitor and did 30 mins and I only burnt 213 cals!!! No wonder I wasn't losing weight as I was eating back my exercise calories. At least I know now and on a positive note I would have built up my fitness and muscle over the last month. I will also have to intensify my workout to burn more cals in a shorter time. Just wondering if anyone has the same experience. I know that some of the main issues with not losing weight are underestimating calories and overestimating exercise. KNOWLEDGE IS POWER.