# Muscle power: Correlation

Prices it moves with, and why

Source page: https://www.materialinsights.org/energy/e_muscle/correlation/

Muscle power from people and draught animals has no market price; its cost is food, fodder and wages. It persists in farming and transport where machines and fuel are costly, and shrinks as incomes and mechanisation rise.
 No public price Muscle power has no public monthly price series: Paid as wages and feed, not traded as energy.

#### What its price moves with

 Commodity [Ri Rice](https://www.materialinsights.org/commodities/rice/)Food fuel

Human muscle runs on food, and staple grains such as rice and wheat are the cheapest calories. Food prices therefore set the cost of manual labour in poorer regions. Higher wages also raise its cost.
 Not enough overlapping price history to measure.

 Commodity [Mz Maize](https://www.materialinsights.org/commodities/maize/)Fodder

Draught animals such as bullocks and horses need grain and fodder. When feed is costly, the case for replacing animals with tractors and engines grows. Mechanisation and costly fodder have cut draught animal numbers in India.
 Not enough overlapping price history to measure.

 Energy [Agr Energy in farming](https://www.materialinsights.org/energy/e_agri_energy/)Substitute

Diesel tractors, pumps and threshers replace human and animal muscle on farms. Cheaper machines and diesel, often subsidised, have pushed farm mechanisation across India. Each tractor replaces many hours of human and animal work in the field.
 Not enough overlapping price history to measure.

 Energy [EV Electric and hybrid vehicles](https://www.materialinsights.org/energy/e_evs/)Substitute

Electric rickshaws and e-bikes are replacing cycle rickshaws and pedal bikes in Indian cities. Falling battery costs make motor power cheaper than muscle for short trips. They also earn drivers more per day with less effort.
 Not enough overlapping price history to measure.

 Energy [Oil Crude oil](https://www.materialinsights.org/energy/crude_oil/)Substitute

Fuel prices set the cost of engines that compete with muscle in transport and farming. High oil prices slow the move away from muscle power in poorer regions. Cheap fuel speeds up the switch.
 Not enough overlapping price history to measure.

How to read these numbers

**Correlation of monthly changes** (the number in the coloured pill) compares how much each price moved, month by month, since 2006 or the first month both series exist. It runs from −1 to +1: near +1 the two usually rise and fall in the same months, near 0 there is no link, and a negative number means they tend to move in opposite directions. Above 0.7 is strong, 0.4 to 0.7 moderate, 0.2 to 0.4 weak.

**12-month changes** compare year-on-year moves, which shows whether two prices share the same cycles even when the month-to-month noise differs.

**Price function** is a straight-line fit of the two prices on logarithmic scales: price ≈ k × (partner price)^β. β is how much this price moves, in per cent, for a 1% move in the partner over the whole period, and R² is the share of the variation the fit explains. Two prices that both drift up with inflation can fit well without any real link, so read it together with the monthly correlation.

**Lead or lag** checks whether the monthly correlation is clearly higher when one price is shifted by 1 to 6 months.

Correlation is not cause. The reasons on each card explain the economic link; the numbers show how strongly it has shown up in prices. Proxy series are US producer price indexes or related prices and can blur the real link.

Data: World Bank Commodity Price Data (Pink Sheet), October 2026; US Bureau of Labor Statistics producer price indexes, IMF primary commodity prices and US EIA prices via FRED, Federal Reserve Bank of St. Louis, retrieved November 2026. Calculations by this site.

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_muscle/index.md)
- [Overview](https://www.materialinsights.org/energy/e_muscle/overview/index.md)
- [How energy resides](https://www.materialinsights.org/energy/e_muscle/resides/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_muscle/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/e_muscle/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/e_muscle/geography/index.md)
- [Impact on nature](https://www.materialinsights.org/energy/e_muscle/nature/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_muscle/links/index.md)