The human body is a machine. A biological machine, capable of working at a certain rate. For example an 80 kg man may be able to run up a flight of 50 steps, each step 16 cm high, in 20 seconds. He does a useful amount of work equal to the increase in gravitational potential energy,
The rate at which the man does useful work is
although of course, since the human body is a machine less than 100% efficient, the rate at which it consumes energy is a great deal more than this, since a lot of energy is wasted as heat.
In a single day and average man might consume about 12000 kJ of energy as food. In a day there are 60*60*24=86400 seconds so the human body consumes energy at the rate of about
The rate at which the human body consumes energy depends on what it is doing. Obvious strenuous activities demand a lot more power to be produced than non strenuous activities. The energy produced by the human body during various activities is shown in the table below.
|
Activity |
W1) |
|
Reclining |
83 |
|
Seated relaxed |
104 |
|
Standing relaxed |
126 |
|
Sedentary activity (office, dwelling, school,laboratory) |
126 |
|
Car driving |
144 |
|
Graphic profession - Book Binder |
153 |
|
Standing, light activity (shopping, laboratory,light industry) |
167 |
|
Teacher |
171 |
|
Domestic work -shaving, washing and dressing |
180 |
|
Walking on the level, 2 km/h |
198 |
|
Standing, medium activity (shop assistant, domestic work) |
209 |
|
Building industry - Brick laying (Block of 15.3 kg) |
225 |
|
Washing dishes standing |
261 |
|
Domestic work - raking leaves on the lawn |
306 |
|
Domestic work - washing by hand and ironing(120-220 W) |
306 |
|
Iron and steel - ramming the mould with a pneumatic hammer |
315 |
|
Building industry -forming the mould |
324 |
|
Walking on the level, 5 km/h |
360 |
|
Forestry -cutting across the grain with a one-manpower saw |
369 |
|
Volleyball |
418 |
|
Calisthenics |
470 |
|
Building industry - loading a wheelbarrow withstones and mortar |
495 |
|
Bicycling Golf Softball |
522 |
|
Gymnastics |
574 |
|
Aerobic Dancing Basketball Swimming |
624 |
|
Sports - Ice skating, 18 km/h |
648 |
|
Agriculture - digging with a spade (24 lifts/min.) |
674 |
|
Skiing on level, good snow, 9km/h Backpacking Skating ice or roller Tennis |
729 |
|
Handball Hockey Racquetball Cross Country Skiing Soccer |
835 |
|
Running 12 min/mile Forestry - working with an axe (weight 2 kg. 33 blows/min.) |
900 |
|
Sports - Running in 15 km/h |
990 |