How much is a W’ of 20 kJ

A well trained cyclist may have an anaerobic capacity W’ between approximately 20 to 30 kJ. This is only a number but what does it represent and what can you achieve with this energy boost ?
Let us first of all distinghuish between the energy that you consume and the work that you produce. The energy you consume comes mainly from oxidation of stored fat and/or sugars and also from extra intake of sugars. This energy is expressed in calories. When exercising the caloric energy is converted into mechanical work, expressed in joule. The nice thing is that 1 calorie is equal to 4.18 joule, but the bad news is that this conversion is extremely inefficiënt and that only about 23 % of the calories becomes useful joules, the rest 77% is wasted energy in the form of heat that has to be eliinated mainly by sweating. After all producing 20 kJ of work needs the burning of 20 kCal of sugars or fats.

Energy input 20 kCal

100 ml of Coca cola contains 42 kCal.
20 kJ of work can be achieved through the burning of only 48 ml cola, or from 1 small piece of Turkish delight.

Sometimes a boost of much less than 20 kJ is enough to finish off your adversaries.

What can you achieve with 20 kJ of extra energy ?
Supose the lift is out of service and you need to climb the stairs up to your apartment. A person of 70 kg will need to produce 20 kJ in order to climb to the 10th floor of his building.

However when the heat is on in the final of a climbing stage all front riders have used up a part of their W’ and the differences may be much less that the full amount of W’
Let us take the example of stage 18 in the Tour de France 2022. The final climb is to the col of Hautacam
Vingegard, Van Aert and Pogacar are leading. Altough Vingegard is leading the general ranking with 3’26 advantage over Pogacar, they still want to end with a ‘coup de theatre’
Van Aert attacks, Vingegard stays with him and Pogacar feels he is not good enough to follow.
Van Aert rides to exhaustion, while Pogacar can not afford to do the same. Suppose Van Aert produces only the very small extra amount of 5 kJoule of energy. This extra boost of work results in an extra altitude gain of 7 m, or a distance gain of 89 m on a 8% slope.
In conclusion, Van Aert commits suicide but kills Pogacar and launches Vingegard by using only 5 kJ extra energy.