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Energy of an effort
How many kilojoules a ride is, and how many kilocalories you burned to ride it.
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Energy of an effortFondoLab
2581
kcal
- Work
- 2160 kJ
- kcal an hour
- 860
- kcal per kJ
- 1.20
3:00:00 of riding at 200 W is 2160 kJ of work. At 20% gross efficiency your body burned about 2581 kcal to do it: 1.20 kcal for every kJ on your head unit.
| Efficiency | kcal | kcal per kJ |
|---|---|---|
| 18% | 2868 | 1.33 |
| 20% | 2581 | 1.20 |
| 22% | 2347 | 1.09 |
| 24% | 2151 | 1.00 |
How we got this
The formula with your numbers in it, then every constant we used and where it comes from.
The working
- Work = power × time = 200 W × 10800 s = 2160 kJ
- Burned = work ÷ efficiency = 2160 kJ ÷ 0.20 = 10800 kJ = 2581 kcal (1 kcal = 4.184 kJ)
The numbers and their sources
A number marked FondoLab default is our judgement, not a study's finding; we say so rather than borrow authority.
| Number | Value | Basis |
|---|---|---|
| Gross efficiency | 20%, adjustable from 15% to 25% | The share of the energy you burn that ends up as work on the pedals; the rest is heat. Trained riders measured 19.8% on average in the lab, lower at low power. Energy burned rises in a straight line with power, so riders at higher power show a higher efficiency. [1][2] |
| Kilojoules and kilocalories | 1 kcal = 4.184 kJ | The definition of the calorie. It is why the rule of thumb "kJ on your head unit ≈ kcal burned" works: at an efficiency of about 24% the two cancel out. At a more typical 20%, you burn about 1.2 kcal for every kJ.
FondoLab default |
References
-
Moseley L, Jeukendrup AE (2001). The reliability of cycling efficiency. Medicine and Science in Sports and Exercise 33(4):621–627. doi:10.1097/00005768-200104000-00017
Laboratory reliability study · Seventeen trained men (74.6 kg, VO2max 61.9 mL/kg/min) on a cycle ergometer at 80 rpm, three identical graded tests from 95 to 305 W in 35 W steps. · Read by us: Abstract
Measured gross efficiency, the share of the energy a rider spends that comes out as work on the pedals, from oxygen uptake and carbon dioxide output.
- Gross efficiency averaged 19.8% (± 0.6%) over the three tests, and varied by about 4% from test to test.
- It was lower at 95 and 130 W than at 165 W and above, and lower at 165 W than at 235 W.
-
Ettema G, Lorås HW (2009). Efficiency in cycling: a review. European Journal of Applied Physiology 106:1–14. doi:10.1007/s00421-009-1008-7
Review · Laboratory studies of cycling efficiency in riders of every level. · Read by us: Abstract
Argues that gross efficiency, work done over total energy spent, is the most relevant measure of cycling efficiency.
- Energy spent rises in a straight line with work rate, at every level of rider. Work rate explains about 91% of the variation in energy spent, cadence about 10%.
- Gross efficiency depends strongly on work rate, mostly because the energy spent at zero work weighs less as work rate rises. That largely explains why elite riders, who ride at higher power, show a higher gross efficiency.
Read more: How many carbs per hour on a gran fondo?
60, 90 or 120 grams an hour? What the research says about carbohydrate on long rides, and how to set your own target.
On your race
Fueling planner: carbs, fluid and caffeine stop by stop for your race
More calculators
- Carb loadingGrams of carbohydrate a day to load before a race, from a meta-analysis of 181 studies.
- Carbohydrate budgetMuscle and liver glycogen against what a ride burns: when you run empty, and what to eat or how much to ease off.
- Caffeine doseCaffeine in mg for your body weight: the dose that helps endurance, and EFSA's safe limits.