Metric; a system or standard of measurement

Introducing the kJ measurement*

def; A kilojoule is a unit of measure of energy; it’s the metric, up to date terminology used in science AND on sources of nutrition

A calorie (aka kcal) is the measurement of potential energy that is available from food

Are they the same, yes basically. They can be converted back and forth. 

What does this croissant have to do with the topic of kJ?


Fitness/CTL, Form/TSB, Fatigue/ATL, TSS; are useful and we’ve been using them to build, adapt and perform. 

There comes a point though, where various factors prevent or reduce optimization of performance based on those alone.  When increasing CTL volume no longer happens, when the TSB should stay the same.   How do you improve performance further, make gains without adding just volume or just intensity?

The performance we’re looking for is;

3. Aerobic endurance, going fast for longer

2. Aerobic power, going faster for a moderate amount of time

1. Anaerobic pure power, going fast, for a short time

Where do they all fit in;

  1. Is dependent on strength, the muscles ability to contract with force, anaerobically 
  2. Is measured by the maximum aerobic power available for 3 to 8 minutes, before the lactic acid environment prevents optimal muscle contraction 
  3. Endurance is a measure of the muscles to continue to contract over time. 

All of these contribute to performance and required in differing degrees of importance depending on the type of riding you do and plan to do. 

Now we can bring in the power of the kiloJoule, kJ!

It’s not a super power, but you may think of it that way when wielding it to produce results!

Here’s the take, the spin, the different way of looking at energy production and usage. 

Energy is required to to produce your results, through every ride. 

kJ is the workload produced and the energy required based on that; the intensity, let’s call that power or watts and the heart rate associated with that intensity.  How do you prepare to supply that energy?


Total kJ needed = your workload, based on a power meter and HRM x 30-35%/#hrs of the ride

This gives you kJ/ hour. To calculate how much workload/energy needed on a long ride:

#seconds x avg. power / 1000 = kJ/hr.

Here’s the math, for example: 

A 3 hr ride is 3x60x60 = 10,800 x 100W (avg,) = 1080000/1000 = 1080kJ, workload or energy utilized by the body.

That can be compared to other rides and used to calculate fuel for the intended workload. 

A more precise method, since avg watts and HR varies is to look at past rides and see the kJ metric. Use that to calculate future rides, x 30%

As an example for you, I’ve gone to my ride of the 100km PacPop this year;  

Starting from home the ride workload as monitored and recorded was 1887 kJ for 4.25 hrs at 123w avg. 444kJ x 30% is 133 / hr.   

With that, I know to have breakfast, egg on toast. I can aim for over halfway, 60 km to have that date bar waiting at the checkpoint since I’ll have used stored glycogen and breakfast by then. Keeping in mind that the average doesn’t take into account the hard burn at the start. 

360 kcal per date square will get me to the finish easily but they’re so good I may have 2!

Rules in general 

  • 2 hrs maximum stored glycogen. More like 80 minutes if you’re pushing hard off the start.
  • Also note that 1 gram of glycogen has 2.7 grams of water with it for those folk concerned with an increase of weight overnight. 
  • Aerobic metabolism is more efficient in that it can continue indefinitely compared to anaerobic metabolism.   
  • If you choose to ride fasted, then you have 80 minutes assuming that the store shelf was replenished.  Or ride aerobically, below threshold to use all energy sources available in your body; fat being an energy source for the slow burn. 
  • Fluids with even small quantities of carbohydrate, rinsed in the mouth, is associated with improved high intensity endurance performance. Always leave a little in your WB!

How to do it – the steps to take, do it now!

  • Put the kcal or kJ metric on your monitor screen;  then use it
  • Prepare for the ride, make your nutrition choices prior to the workout
  • No need to eat in the first hour unless preceded by a swim, or run. 
  • Fasted? eat after an hour depending on intensity, aerobic or anaerobic. 
  • Know how many kJ are in your bar or WB. If you plan to eat a bar or have a gel, have a bottle with plain water or one with only elytes, available to help the nutrients absorb. Your gut can only absorb so much at any time since your skeletal muscles are working hard and need the blood flow.
  • Gels are best, work for you optimally in the last 10 to 20 km to the finish on the bike, OR to use on the run after an hour.   And you can calculate how many you need in 1, 2, 3, 4 or 5 hrs.

The croissant picture at the top, is an example of the type of nutrition you or I may choose!
The energy in kJ is 1699. Conversion from kcal is x 4.184

Micronutrients, minerals available in a croissant as well; Magnesium, Calcium, K and Na, Iron

Macronutrients protein; 8.2g and lipid; 21g

@ Thomas Haas has the right idea! A croissant is a great choice pre or during a ride at the cafe stop.

Now What? Based on this knowledge*

*What will you be doing in the future to use this metric effectively?  

Monitor your ‘burn’ during the ride to prevent depletion of your resources, AND to improve your performance;

Increase your kJ per ride, meaning that within any distance ride, you will be producing more Workload!

This information garnered from CTS TrainRight podcast presenter Adam Pulford

Coach Be