Power = energy/time
Watt – the rate of energy conversion or transfer – one joule per second
Calorie – the amount of energy needed to raise the temperature of one kilogram of water by one degree celsius
Joule – energy expended (or work done) in applying a force of one newton through a distance of one meter (1 newton meter or Nm)
1 calorie = 4.184 kilojoules (kJ)
kcal – as seen on food containers – eqivalent to 1 Calorie not 1000 calories – see Wiki
Recommended daily calorie intake (UK NHS)
average male – 2500 kcal
average female – 2000 kcal
Power output of a human
As you can imagine this is hugely variable from a couch potato toddler to a peak performance male adult athlete, therefore it is easier to approach the problem from the amount of energy a body takes in via food assuming that the person’s weight stays constant i.e all the food taken in is used to keep the human being living and moving.
Remember a lot of the potential energy taken in is used to keep us alive before we start doing traditional ‘work’.
one day: t = 86400 seconds (24x60x60)
average male intake: 2500 kcal = 10460 kJ
10460kJ / 86400s = 0.121 kJ/s or 121 Joules/second = 121W
Of course this varies hugely during the day – on average, you burn less than 80 calories an hour whilst asleep (dependent on your Basal Metabolic Rate (BMR))
In the Tour de France riders will be consuming up to 6000 calories a day and using up to 400W to tackle the steepest climbs!
Arm, legs or both?