Calories to Watts

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.

__________________
Happiness is when your bike is worth more than your car......a lot more !

serenaslu

Watts is power, KCals is energy. You either have to convert Kcals to watts-hour:

1 KCal = 1.163 watt-hour

or Watts to KCal/hour or any other power=energy/time.

Try:
http://www.joshmadison.com/software/convert/
for a nice freebie units converter.

ric_stern/RST

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

ric

__________________
http://www.cyclecoach.com

Perro Loco

On occaision, at work I use an excercycle-( I can't remember the brand at the moment) it gives calories per hour and calories burned. Is this really Kcals not calories? - Usualy on a mid level resistence you get ~ 1,000 calories/hour.

ric_stern/RST

i'd assume that it meant kcal. however, 1000 kcal/hr = ~ 278 W -- that's quite a hard effort (that's about 42 km/hr for me during a TT).

ric

__________________
http://www.cyclecoach.com

Perro Loco

I can only do it for about 20 minutes. I doubt it is super accurate. I am currently not in great cycling shape (work has been prohibitive for the last several months-recently moved settling in.....) but have started back again.
The other night I was able to maintain ~ 28 Km/ hour into a headwind on a flat for ~ 15- 20 minutes before sensibility took over. me and bike weigh about 90 kg (yeah, I know need to drop some weight, get rid of that steel frame...) so it might not be way off.

ric_stern/RST

sounds like it's way off. keep up the good work though and you'll be cycling faster and for longer

ric

__________________
http://www.cyclecoach.com

Perro Loco

Thanks, typo on my last sentence-I agree I thought it was way off.

jp111

Ric,
Thank You for your reply.

__________________
Happiness is when your bike is worth more than your car......a lot more !