for longer periods. Maximum sustained power levels during one hour range from about 200 W (NASA experimental group of "healthy men") to 500 W (men's world hour record). Energy input The energy input to the human body is in the form of food energy, usually quantified in kilocalories [kcal] or kiloJoules [kJ=kWs]. This can be related to a certain distance travelled and to body weight, giving units such as kJ/(km∙kg). The rate of food consumption, i.e. the amount consumed during a certain period of time, is the input power. This can be measured in kcal/day or in J/s = W (1000 kcal/d ~ 48.5 W). This input power can be determined by measuring oxygen uptake, or in the long term food consumption, assuming no change of weight. This includes the power needed just for living, called the basal metabolic rate BMR or roughly the resting metabolic rate. The required food can also be calculated by dividing the output power by the muscle efficiency. This is 18–26%. From the example above, if a 70 kg person is cycling at 15 km/h by expending 60 W and a muscular efficiency of 20% is assumed, roughly 1 kJ/(km∙kg) extra food is required. For calculating the total food required during the trip, the BMR must first be added to the input power. If the 70 kg person is an old, short woman, her BMR could be 60 W, in all other cases a bit higher. Viewed this way the efficiency in this example is effectively halved and roughly 2 kJ/(km∙kg) total food is required. Although this shows a large relative increase in food required for low power cycling, in practice it is hardly noticed, as the extra energy cost of an hour's cycling can be covered with 50 g nuts or chocolate. With long and fast or uphill cycling, the extra food requirement however becomes evident. To complete the efficiency calculation, the type of food consumed determines the overall efficiency. For this the energy needed to produce, distribute and cook the food must be considered. Typical speeds In utility cycling there is a large variation; an elderly person on an upright roadster might do less than while a fitter or younger person could easily do twice that on the same bicycle. For cyclists in Copenhagen, the average cycling speed is . The fitness and cadence of the rider, bicycle tire pressure and sizes, gear