Kcal is simply a measure of energy expenditure, and is there to provide an *estimate* of the amount of energy that you have used.
As the data comes from a HR monitor it's likely going to be wildly inaccurate. To determine energy expenditure correctly, this needs to measured in a lab setting, as expired respiratory gases need to be analysed.
A good ballpark figure can be obtained for energy expenditure from an accurate power meter (e.g., Power Tap hub, SRM cranks), as power = energy / time. Thus, energy = power x time, giving an answer in kj, which is then divided by 4.18 to get an answer in kcal, with Kcal being the figure that most people use (at least here in the UK).
Most (all trained, and even most untrained) cyclists fall into ~ 20 - 25% efficient when cycling, such that if you multiply the the above kcal expenditure by ~ 4 you arrive back at the same figure in kcal as kj, i.e., if you have a power meter and it said you expended 1000 kj on your ride, you also expended ~ 1000 kcal (as opposed to 239 kcal).
To correctly calculate your efficiency, you'd have to be in a lab, and have your expired respiratory gases analyses and have your power accurately determined.
As an aside your efficiency increases, as your absolute power increases, and your efficiency decreases as your absolute cadence increases.
Accordingly, the 992kcal your watch measured, 'would be' 992 kj. if for instance that one obtained from one hour of cycling (purely used for illustrative purposes only), you'd have ridden at an average power output of 275.5 W. For an average sized male (~70kg) on a TT bike, on a flat circuit, that would equate to ~ 43 km/hr (as a ballpark figure).
The energy figure you is unlikely to be accurate. if it was accurate, there'd be no need to have power meters!
Therefore, i wouldn't base any weight loss plans on this figure as it's likely to be completely erroneous. However, you could use it as some sort of tracking number that you record in a training diary. Assuming that the figure increases (i don't know how they exactly estimate energy expenditure) as you ride at a higher intensity and/or longer volume, you'd be able to see that now you can expend 992 kcal per ride, whereas two months later you might be able to burn 1500 kcal.
Ric
