Originally Posted by trirmk
That can't be accurate. The determinants of power have nothing to do with HR, and using weight alone won't help at all either. It's only the HR monitor and nothing else that he has to estimate power? What monitor is this exactly? I'm curious to look it up.
Heart rate certainly is related to power output. For a given individual, the more power output, the higher the heart rate will be. Accuracy is a relative term. For some applications, the cheap $300 power meter sold by Polar would be considered crude. For others, it would be overkill.
It would be a fairly straightforward task to take a sample population and test them for heart rate at various output power levels. You can analyze the data to generate an algorithm that provides a best-fit power output based on heart rate and weight. Chances are your results will be fairly close for the 'average' person. You could probably do even better if you include VO2max values as a third variable in the algorithm.
Of course, the algorithm will end up being much less accurate for elite athletes and couch potatoes, but that's probably not the target market. I doubt that the HRM manufacturer claims any great accuracy any more than they do for calorie estimates based on heart rate and weight or the calorie expenditure function found in cycle computer.