Power Training Terminology Explained: CTL The Most Important Training Number?

By Martin Sigrist

Takeaway: CTL = Chronic Training Load and is a simple rolling average of the last 7 weeks training that tells you, precisely, how fit you are. It is the most important number in training as if you can raise it and still show signs of improvement you will maximise your chances of reaching your potential.

This is one of an occasional series that will explain a key power based training term. This will cover CTL, or chronic training load.

CTL in Plain English

CTL is a number that provides an objective measure of your fitness. It’s calculated as a rolling average of your last 7 weeks training and is expressed in the same units as TSS. So a CTL of 100 means you have been averaging the equivalent of riding one hour as hard as you can every day for the last 7 weeks.

CTL is the most important number in bike training. The higher it is then the quicker you will become fitter and the more likely you are to achieve your ambition. Understanding CTL also helps achieve peak fitness for an event as it allows you to “taper” immediately beforehand, allowing you to start at the ideal combination of peak fitness and freshness.

(Chronic, by the way, is used in the medical sense of long term. Personally I think CTL would be better named “long term training load” and I always think of it that way myself.)

CTL Overview

Previously I have discussed TSS a number that gives each workout a score to show how hard it was. However one workout will not make you a better rider. That requires months and years of training.

CTL is a number that helps you measure the consistency of your training and the overall direction it is heading.

It’s measured in the same units as TSS. Indeed it is calculated directly from TSS and is a moving average of your TSS scores over the last 7 weeks. So if you do 700 TTS per week for seven weeks your CTL will be 100. In this case you will be training at the equivalent of riding one hour as hard as you can every for an hour every day.

The goal of a training plan is to get CTL as high as possible. So week on week should see a gradual rise in CTL, called a ramp. Different riders will be able to sustain different “ramps” the key limiters being the time available for training and the capacity to recover from and adapt to training.

The only way to find out your limits in terms of CTL and ramp is experience. This is one reason why CTL is the most important number in training. It is the best way to determine, with precision, if you are training in the most effective and productive way possible. Other measures of training load such as time spent, miles ridden or even time in HR zone are far less accurate and far less useful.

CTL Example

To help understand CTL below is a graph of my CTL over the last 5 or so years. It shows how each year CTL moves up through the season to reach a peak and then comes down as I take it a bit easier for a while.  (It also shows how the last year has been a bit of an exception due to the pandemic and other factors.)

The graph also shows my power PBs for 5, 20 and 60 minutes.  It’s noticeable how they coincide with the peaks of CTL. To an extent this is inevitable, as some will have occurred in an event I was training for.

However it is mainly because raising training load makes you fitter. That’s the whole purpose of training, if you just keep doing the same thing day after day, week after week you may plateau.

Target CTL

While everybody is an individual it can be useful to have some sort of target CTL in mind. The article below provides a useful ready reckoner for this purpose.

https://help.trainingpeaks.com/hc/en-us/articles/230904648-Suggested-Weekly-TSS-and-Target-CTL

ATL – Acute Training Load

Just for completeness its worth knowing that power based training also refers to “ATL”. This is “acute” training load where “acute” means “short term”. It’s simply the average TSS for the last week. This can be useful in detailed training planning, typically there will be a few weeks when ATL is higher than CTL so moving the overall average up and then a bit of recovery when it is lower.

ATL will also be lower than CTL during a pre event taper.

How to Use CTL

1. Know your CTL. There are many training products that will tell you this if you upload your ride data to them. Or simply just keep a daily log of TSS and use a spreadsheet to calculate it. Simply being aware of your CTL and the direction in which it trending  should help inform you as to whether your training plan is optimal or not.
   
2. Let CTL guide your recovery needs. If your CTL is going up it is natural to feel tired. However if you are able to regularly hit your workout targets, are able to keep moving CTL up it and seeing your performance improve it means you are in the zone in terms of balancing the needs of recovery with those of training. Again this is another reason why CTL is so powerful and so useful. Used intelligently it will allow you to explore the limits of your potential without being at risk of overtraining.
   
3. Taper. CTL is a 7 week average so it will remain high even if you take it easy for a few days. In the week leading up to a significant event you can let your average come down a bit and CTL will remain high. The best way to do this is do workouts with short hard efforts that will keep your fitness at peak but allow muscles to be fully rested.  (As noted above ATL will be lower than CTL.)
   
4. Spike. The flip side to tapering is to spike, having a week or two which pushes CTL up quickly. This is the purpose of a training camp and you can use CTL and ATL to simulate the effects of being on one if you cannot actually go away. (ATL will be quite a bit higher than CTL.) Blocks of 3-5 days of hard training with an easy day between can result in a step change in fitness and can be a means to breakthrough if you feel you are on a plateau.
   
5. Consider when to change your FTP base for calculation. CTL and TSS are both relative to FTP. So if your FTP improves you should, in theory, change it to keep the numbers consistent. If you are at a stage of training when you are seeing rapid gains every month then this is something you should do. However if there are only small changes in FTP it is not, in my opinion, sensible to keep changing it but rather wait until the end of a season and do so then.
   
   The key reason for this relates to my view that mindset is critical to becoming the best that you can be. It can be rewarding seeing CTL moving upward, changing your FTP might result in your CTL going down. While strictly speaking this is accurate if there is any risk it will reduce motivation I do not think it is worth doing mid-season. Far better IMO to increase it at the end of the season. This will immediately give you a SMART goal that will motivate you for next year. Simply replicate your CTL from this year and you will, by definition, be getting fitter and should see yet more improvement.

Email me on [email protected] if you want more info on this or any topic I have raised. I make take a while but I will get back to you.)

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Now among the world’s fittest sexagenarians Martin Sigrist started riding on doctor’s orders in 2005 and had to push his bike up his first hill. Next year he soloed the Tour de France. He has since experienced every form of road cycling from criterium to ultra endurance. His ongoing mission is to use the latest in science and technology to fight a, so far successful, battle against Father Time.