Muscle power
Human and animal work, fuelled by food that plants made from sunlight.
Natural sources · Solar-derived flows · No. 10
- Natural sources
- Origin: Indirect solar
- Renewable: Yes
A working adult sustains only about 75 watts, yet about two-thirds of the world's farmers still rely on hand tools.
Chart: Illustration: Muscle power
Where it comes from
Plants turn sunlight into food and fodder, and muscles turn that chemical energy into work: about 75 W for a working adult.
About 8.2 billion people and some 400 million draught animals supply it, with hand and animal labour most common in sub-Saharan Africa.
Three things to know
- A horse can sustain about 750 W for a few hours, against about 75 W for a person.
- Only about 30 million of the world's farmers use machines; most of the rest work with hand tools.
- In sub-Saharan Africa in the late 1990s, 65% of cultivated land was prepared by hand and only 10% by tractor.
The journey
- 1 SunlightGrows crops, grass and fodder
- 2 FoodEaten by people and working animals
- 3 MusclesAt best a quarter becomes work
- 4 WorkPloughing, carrying, pedalling and lifting