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Note: Several cycling training terms used throughout this post are trademarked by TrainingPeaks, including Training Stress Score®, Normalized Power®, and Intensity Factor®. Additionally, terms including Acute Training Load, Chronic Training Load, Training Stress Balance, and Efficiency Factor are featured in TrainingPeaks software. In some cases, metrics that represent similar concepts are used in other apps.
Topics Covered In This Episode:
- How is CTL calculated?
- The difference between fitness and CTL
- What’s missing from the CTL metric
- How to interpret CTL
- What are typical CTL scores for different athletes
- Additional metrics you should be tracking to measure performance gains
- See a chart of target CTL scores here
- Podcast Episode: How To Improve Your Cycling FTP
- Podcast Episode: How To Train VO2 Max
- Article: Cycling Training Terms and Acronyms Explained
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What Is Chronic Training Load (CTL) And How To Use It To Improve Performance
By Chris Carmichael,
Founder and Head Coach of CTS
Chronic Training Load (CTL) is one of the key metrics athletes and coaches track on the Performance Manager Chart in TrainingPeaks software. It is commonly thought of as a measure of an athlete’s “fitness”, as opposed to fatigue or form (the ability to perform). Strava displays a similar metric and refers to it as “Fitness” in the “Fitness and Freshness” graphs. Although CTL is important and valuable, it is often misinterpreted and misused. Here’s a guide to Chronic Training Load and how to use it to improve real-world performance.
What is Chronic Training Load (CTL)?
CTL represents a weighted average of daily Training Stress Score (TSS) over the past 42 days. This means recent workouts are given more emphasis than the sessions from six weeks ago. CTL is often thought of as an athlete’s fitness level, but it is probably more accurate to consider it the “amount of training you have been sustaining”.
Equating CTL to “fitness” can be misleading. CTL is a measure of training load calculated from a very specific power-based metric (TSS). However, many athletes interpret “fitness” to mean performance, as in: high fitness results in high performance. As a result, athletes sometimes overvalue a high or increasing CTL. If you want to go faster, climb better, or win a sprint, you may need to let CTL decline. In other words, if you want real-world performance to improve, you may need to let your modeled “fitness” go down.
Factors that skew CTL
CTL is a good measure of sustained training load but a few factors can skew the value and lead to misinterpretations.
Training Stress Score (TSS) aims to account for intensity and duration within a single metric. This makes it easier to compare the training stress from a short, high intensity workout against a long, moderate pace endurance ride. You can read a comprehensive guide to TSS For this article, the important part is that a TSS of 100 represents the training stress from 60 minutes at Functional Threshold Power (FTP).
CTL is heavily affected by training volume because long moderate-intensity rides are great for racking up high daily TSS. High training frequency (i.e. riding 6 days/week vs. 3 days/week) keeps CTL elevated because it reduces the number of TSS=0 days. That means someone who just rides a lot at one steady pace could appear very fit (i.e. high CTL) but have very limited real world performance.
Accuracy of Functional Threshold Power
The accuracy of several training metrics all hinge on the accuracy of the FTP value entered into training software and bike computers. The calculation for TSS compares your normalized power to your FTP to determine how “hard” you’re going in relation to your maximum sustainable power output. If your FTP is set too low, meaning your FTP improved and you haven’t updated the values, then your hourly and daily TSS values will skew high.
Factors that limit CTL
CTL cannot continually increase. Athletes have limited training time and can only go so hard. Athletes reach a CTL plateau when they bump up against their maximum weekly training hours. For CTL to continue rising, TSS would have to increase. But without more hours they can only increase TSS by increasing intensity. However, redirecting training focus to improve specific areas like power and time to exhaustion at VO2 max, or anaerobic capacity, typically brings CTL down. (more on this later).
So, at some point, “fitness” as measured by CTL dissociates from “performance” because CTL cannot increase anymore but specific real-world performance metrics (and outcomes) can.
What is a good CTL?
There is no good or bad CTL, but there are some typical CTL levels for different types of athletes. The chart below contains some very broad ranges for weekly training hours and target CTL values for different groups of cyclists.
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The cited CTL range for road racers is 40-175 across a span of 6 to 25 weekly training hours. That’s a massive difference. In practice, CTS Coaches typically see CTL values around 40-100 for century and non-competitive gran fondo riders. Masters racers, MTB cross-country, and age group gran fondo competitors are often in the 70-120 range, and ultraendurance mountain bike and gravel racers sometimes go a bit higher.
However, it’s important to reiterate that the absolute number is less important than how you built it, the rate at which it’s changing, and what you’re doing with it.
When should CTL be highest?
Frequent and long, moderate intensity rides are a great way to ramp up to a high CTL. Workouts featuring long, sustained subthreshold intensities – like Tempo, SweetSpot Tempo, and SteadyState intervals – ramp up CTL, too. This type of generalized aerobic endurance- and FTP-building training is characteristic of the Base Period of the year.
You can think of a high CTL at the end of a base building period as a visual representation of aerobic foundation you have to work with. You have built up your conditioning to the point your aerobic engine can sustain a large training load. But it’s not very specific to any event or race demands. Now it’s time to focus that large capacity for workload on training for specific demands.
Improving performance beyond CTL
Keeping CTL high over time means keeping daily TSS high. The higher your CTL the more dramatically it will drop after just a few extra rest or low-TSS rides. This drop is natural, and necessary for improving actual performance, because rest allows time for adaptation and supercompensation, leading to higher power outputs and speed on the bike.
Similarly, a change in training focus can affect daily TSS values and the frequency of high-TSS days. Workouts with very short, very high intensity efforts can create a big training stimulus. However, the TSS for these workouts may be low because the total time at high intensity was short and the remainder of the ride was at very low intensity. Training blocks featuring high intensity interval workouts may also include more rest days or recovery rides per week. As a result, weekly TSS can drop off even though you’re completing high quality and effective workouts.
CTS Coach Adam Pulford recently illustrated this in this Instagram post. After months of maintaining a high CTL, he had a period of increased travel and less training, and his CTL dropped significantly. Upon returning to training he set his highest 20-minute power of the year. He also covers this in the Youtube video and podcast on this topic.
Other metrics that indicate performance gains
So, let’s say CTL is maxed out, plateaued, or dropping due to increased training specificity. What metrics should you use to measure “fitness” gains? All the metrics below can be improved without an increase in CTL, and sometimes with a reduction in CTL.
- Power output at specific intensities: Training blocks focused on increasing FTP, increasing power at VO2 max, increasing anaerobic capacity.
- Power durations: In addition to raising power outputs at specific intensities, it’s important to extend your time-to-exhaustion at those intensities. In other words, if you can hold your FTP for 20 minutes now, train to increase the duration to 30 minutes at the same power.
- Segments, placings, and outcomes: Eventually, all these improvements in metrics need to translate to meaningful improvements on the road, track, or trail. Did you make the front group? Are you placing higher in races? Are you setting new segment PRs? Do you have more energy and power in the last hour of long rides?
All training metrics provide insights and have limitations. Chronic Training Load is useful for gauging the workload you’ve been sustaining through the past six weeks. In the early season it can be a good tool to evaluate your readiness for transitioning from generalized training to more event-specific training. Just be careful about putting too much importance on the absolute number. Care more about how CTL is trending and how it is changing in relation to changes in your training focus.
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