Re: Calories to Watts
Originally Posted by jp111
I have a trainer this winter that measures watts, but, last riding season I had a Polar HRM, and no way of knowing watt output for recorded rides. All I have is the calories used, time, dist, HR, ect. I have found the formula to convert watts to KCalorie, but not KCalorie to watts. Is it possible ? I would like to have some idea of power output from this past season, to get an idea of where to improve next.
as a ball-park estimation you can directly convert kcal to kj on a 1:1 ratio (i.e., 500 kcal = 500 kj) for when you want to convert kcal to watts -- this is because although there is 4.18 kcal to 1 kj humans are around 20 - 25% efficient when cycling (so vaguely everything cancels out).
In other words if you *accurately* knew that you'd expended (e.g.) 500 kcal and ridden for (e.g.) 1-hr then you'd have averaged 139 W = (500 kcal / 3600 secs) * 1000.
However, given that the Polar can only estimate energy expenditure based on HR, it isn't accurate (or else power meters would be a waste of money). and given that you're using a trainer (and not a power meter) i'd say that you can't make any comparisons about power and/or energy expenditure -- due to the inaccuracies of all the equipment you're using