One of the worst and most overused ways to measure how hard you’ve worked has got to be calorie expenditure. Over the last 11 years I have had the conversation with dozens of clients who are disappointed with their workout because their watch told them they hadn’t worked hard enough.
For many activities, calories burnt does not give you an accurate measure of Work Done or Intensity. The fact is that for many people the calorie goal they are chasing, probably doesn’t have any real relevance.
Take away notes if you’re short on time:
- Calories burnt during exercise are not comparable to calories eaten
- Devices will vary greatly in their results
- Each person is an individual and personal devices can not account for that accurately
- Devices do not accurately account for the type of exercise you are doing
- Look at how much work you did and how long it took to determine how hard you have trained.
- Heart rate is NOT a measure of intensity
- Focusing on numbers can lead to an athlete attaching too much self-worth to that number
Why looking at calories all the time can be bad for your training:
Using a wearable device when exercising can have a positive effect on motivation and accountability and can be an excellent way for people new to exercise to get the ball rolling. Where they become a problem though is if the person gives that data too much weight. It’s the same for any measurement whether it be calories, body weight, weight lifted, distance ran etc. These things are all useful, but when you attach too much emotion to an arbitrary number you risk creating a negative response. Your self-worth and happiness should not be dictated by whether your watch tells you that you did a good job or not. There is no such thing as a wasted workout. Every session is doing you benefit and a positive can be found even from the worst workout.
If you only look at one measure, then there is only one way to have a positive outcome.
What is a calorie?
A calorie is a unit of measurement used to state the amount of energy stored inside food or used by the body. 1 kilocalorie is measured as the amount of energy required to heat 1ml of water by 1 deg C.
By hooking our bodies up to complicated VO2max machines in the lab we can accurately measure the amount of energy required to complete a given task. Outside of the lab however this is attempted to be repeated by using portable devices which measure speed, distance and heart rate. This type of measurement has many flaws which can lead to great inaccuracies in results.
(Currently there are some great looking new portable V02 max devices coming out, but let’s assume you don’t have one.)
What doesn’t calories account for?
The calorie measure doesn’t accurately account for the type of exercise you are doing. An easy example could be skipping compared to running. Because you are standing in the same spot, speed and distance are removed from the equation.
Even when GPS is used, distance doesn’t measure your force output. You might be pushing a 100kg sled 50m or you might be jogging 50m. A device which only looks at distance/time will not know the difference. Some devices add heart rate to the equation to counter this but again this is limited.
Heart rate is also a flawed measure of work and intensity. Whilst it has been used for years, heart rate is only a correlate. This means that while heart rate and intensity may have some connection, it is not always about how hard you are working. A great example is riding on a roller coaster. Your heart rate might be through the roof! But you’re not doing anything.
Furthermore each device calculates calories differently using different equations to ESTIMATE calories. Some of these are better than others. This was demonstrated excellently for myself just last week when running with a friend. Over 10km my device told me I had burnt approx. 500 calories whist his said over 800! Now these were just simple phone apps calculating distance, elevation gain and time but if they have such a massive discrepancy it’s clear that neither of those results can be accurately compared to the calories we had eaten in our food.
A better way to measure work & intensity:
The best way I know of to compare two sessions is to look at Work.
Work =Force x Distance
Essentially if you measure the amount of force used (ie, body weight or external weight moved) and then multiply by the distance you have moved it, you can determine the amount of work done. The beauty of this is that it is measurable, observable and repeatable. It doesn’t have to involve a complex equation either if you would like to keep it simple.
The next step is to measure intensity. Intensity is exactly equal to Power.
Power = Work/Time
This can be measured as simply as timing how long it took you to complete a set amount of work or alternatively how much work you completed within a set time period.
If you don’t want to work out the maths – simply repeat the same set amount of work and time how long it took you to complete. The faster you did the workout, the greater the power output. The greater the power – the higher the intensity.