.png){kind=small}
Critical Power & W'
Some Insights into the use of CP
This isn't the only way, but it is a way of using research and applied practice together, here I just want to share some insights into why and how.
A metric I’m sure you have heard before. It’s increasingly becoming a popular method to determine training zones and as a performance monitoring tool. It is used extensively withing research literature from your classic physiology papers to the applied practice papers.
Here we are going to just explore some avenues of how CP and W’ can be used as a performance/analytic tool as well as a performance marker. Yes, you can use other methods, metrics and ways. Is this better? Well…That depends, First lets explore some questions first. Often a framework I use when dealing with metrics/markers/assessments, as a lot of these can promise so much when in reality, they deliver so little. As with anything there must be a reason, some form of value from testing and as a Physiologist/applied practitioner I am able to measure a vast array of things, but just because I can, does not mean I should.
Frame Work
[1] What is the purpose and what am I looking to achieve?
[2] What is the validity of this measure? Am I actually measuring what I want to measure?
[3] What information will it provide?
[4] Is the information going to positively inform practice and decision making?
[5] Can I quantify what is ‘good & bad’?
[6] Is it sensitive enough to detect change?
[7] Will athlete adherence be likely?
[8] What does the research and anecdotal evidence say about it?
This is not ranked in any particular order, but If you can’t answer many of these well, maybe just have a double think about it.
The main think really, is helping you gauge/monitor a change in performance towards the athletes goals. Testing should be gear towards that. You can have classic lab-based assessments, or more performance-based assessments. As you know, the best measure of performance, is performance itself. If working with a sprinting, you would include some form of sprinter assessment I you catch my drift!
I’m not going to go too much into depth on this, but I will share some key references, some bits of work, which will likely appear in every piece of full published work. Critical Power demarcates the boundary between the severe and heavy intensity domain, Representative of the highest power reflecting the highest oxidative rate of ATP, without a deterioration of metabolic homeostasis. In short the highest aerobic power we can maintain.
There isn’t a timestamp associated with this as such. It depends on [1] testing method for starters more on this later [2] the most obvious is your training status. It can be from 20-45 minutes or more, or less. One of the elements supporting this marking, is the amount of physiology supporting it aerobic determinants. Mitchell, et al., 2018 (Critical power is positively related to skeletal muscle capillarity and type in muscle fibres in endurance-trained individuals) though muscle biopsy’s noted that type 1 muscles fibres and capillary contacts to those muscles fibres were higher correlated with CP support by the review as well here Goulding and Marwood (2023) Interaction of factors Determining Critical Power.
There has been much debate as to whether maximal lactate steady state better representees this steady state power see Jones 2018, but often it is down to methodological issues Caen et al. (2024) Critical Power and Maximal Lactate Steady State in Cycling: “Watts” the Difference?
But for this article let's stick with CP.
The most simplistic method is often called the ‘3 and 12’ where you aim to average the highest amount of power for a 3 and 12-minute effort separated by 30-40 minutes of riding.This allows you to calculate CP and W’ in the simplest ways, just go to the calculator link here and type in your values. You can do them on separate days if this is your first time there is minimal difference (we have a paper coming out on this soon) and if it’s your first time, you will often have some improvement in the second time as you become more familiar with pacing that effort.
This is just a learning effect and is always normal.So why use this over the 20-minute test?If you do a lot of TTs that are 10 miles, It’s likely still going to be useful for you to add this in, as it's very close to your performance demands! Aside from assessing CP, it all gives us W′ as the ‘prime’ is the symbol, it’s not called work prime or anaerobic work it’s W′.
In short, W′ is representative of the work you can complete above CP, it helps us predict exercise tolerance. This helps us understand your CP/ W′ in which there is an optimal balance, as W′ has a fatigue cost associated with it. Think of it as your matchbox, it is the size and of it. It is this extra insight, compared to other traditional methods of testing that helps us track and monitor your training response. It also then comes into the modelling of the reconstitution of W′, But we will cover more of that at a different time.
However, CP has a large proportion to do with its recovery, so for Crit/cross and MTB, there is a balance between CP and W′. W′ is quite complex, and much of the literature is still unsure in terms of its physiological origin. But what we do know, is it isn’t solely a marker of anaerobic capacity, trust me, there is a large involvement of O2. But for now, here are some quick easy charts if you use WKO5, and you can use our online calculator as well, which also as an interval power/duration predictor as well. If you want to learn more about calculating it, see our article.
I you want to learn a little bit more, then head over to my researchgate profile and take a look at some of my part published conference papers. In which we look into the W'bal moddeling side of things and what is correlated with intermitent exercier performance until failure!
Insights Series
Coming soon