Cycling Training Load Calculator
Created by: Lucas Grant
Last updated:
Calculate CTL, ATL, and TSB from a week of cycling TSS values so you can judge whether your current training pattern is building fitness, accumulating fatigue, or moving toward fresher race form.
Cycling Training Load Calculator
CyclingUpdate CTL, ATL, and TSB from a week of TSS values so you can judge fitness, fatigue, and form more clearly.
What is a Cycling Training Load Calculator?
A cycling training load calculator turns daily TSS values into CTL, ATL, and TSB so you can see whether your current pattern is building fitness, accumulating fatigue, or moving toward fresher race form. For cyclists who already track ride stress, this is one of the clearest ways to step back from individual workouts and understand the shape of the week.
CTL is often described as fitness because it changes slowly and reflects the rolling effect of accumulated training. ATL is usually described as fatigue because it responds more quickly to recent stress. TSB is the balance between those two forces. In simple terms, it describes whether you are carrying a lot of short-term fatigue relative to the fitness you have built.
That does not mean the metrics are perfect. They do not know whether the week included travel, poor sleep, illness, heat, emotional stress, or technical terrain that made the same TSS cost more than usual. What they do very well is show training direction. When ATL rises sharply while CTL inches upward, you are in a load-building phase. When ATL falls and TSB rises, you are likely recovering or tapering.
This calculator focuses on the practical interpretation. It lets you enter a week of TSS values, updates CTL and ATL day by day, plots the trend, and explains what the final form state is likely to mean for training readiness. That makes the numbers more actionable than a simple dashboard screenshot with no context attached.
How CTL, ATL, and TSB Are Calculated
The calculator starts from a prior CTL and ATL value, then applies each day's TSS to update the two moving averages. CTL uses a longer time constant, which means it moves slowly and behaves like accumulated fitness. ATL uses a shorter time constant, which means it rises and falls faster and behaves like short-term fatigue.
After both values are updated, TSB is calculated as CTL minus ATL. A more negative number usually means you are carrying more fatigue. A more positive number usually means you are fresher. The exact number matters less than whether the direction matches the week you intended to build.
Core model
New CTL = Prior CTL + (Daily TSS - Prior CTL) x (1 / 42)
New ATL = Prior ATL + (Daily TSS - Prior ATL) x (1 / 7)
TSB = CTL - ATL
This is not a promise of performance. It is a clean way to visualize whether fatigue is being managed or merely ignored. Used well, the model helps riders avoid the trap of training hard every day without noticing that freshness has disappeared long before motivation catches up.
Example Scenarios
Example 1: Build-week fatigue accumulation
A week with two interval days, a long ride, and only one real easy day will often push ATL upward faster than CTL. That is not necessarily a problem. It becomes a problem when the rider expects to keep hitting the same quality without backing off soon enough.
Example 2: Recovery week reset
When TSS drops for several consecutive days, ATL usually falls faster than CTL. TSB improves, and the rider starts to feel fresher without instantly losing all of the underlying fitness. That is the pattern many cyclists want to see before an event or after a heavy block.
Example 3: Race-week form check
A rider heading into a target race often wants ATL to come down while CTL stays reasonably intact. The model can show whether that is happening. If freshness improves but CTL collapses because training fell off too far, the week may have become rest rather than taper.
Practical Applications
- Check whether a build week is carrying productive fatigue or tipping into unsustainable overload.
- See whether a recovery week is actually reducing ATL enough to restore freshness.
- Use daily TSS values to explain why form feels good or flat before races and hard sessions.
- Compare current readiness for racing, threshold work, or high-volume training based on the balance between fitness and fatigue.
- Plan tapers more rationally by watching ATL fall while CTL stays relatively stable.
- Spot when low freshness is not bad luck but a predictable outcome of the week's training pattern.
Tips for Using Training Load Metrics
Look for patterns, not single-day meaning. One morning with a negative TSB does not automatically mean you should cancel the workout. A repeating pattern of deep negative form, poor motivation, and low-quality execution is far more informative than one isolated number.
Also remember that these metrics are only as good as the TSS feeding them. If FTP is stale or rides are missing, the chart will still look precise while being directionally wrong. Keep the inputs honest and use the result as a coaching tool, not a substitute for judgment.
FAQ
What do CTL, ATL, and TSB mean for cyclists?
CTL represents longer-term fitness, ATL represents shorter-term fatigue, and TSB describes the balance between them. Together they help explain whether a rider is building fitness, carrying heavy fatigue, or arriving at a fresher point for racing or quality training. They are not perfect, but they are useful because they connect daily TSS to a bigger training narrative.
Why do CTL and ATL move at different speeds?
They intentionally respond on different time scales. ATL uses a shorter time constant, so it reacts quickly when you stack hard days and also falls quickly when you back off. CTL uses a longer time constant, so it changes more slowly and behaves like a broader view of accumulated fitness rather than day-to-day tiredness.
What does a negative TSB usually mean?
A negative TSB usually means fatigue is currently outrunning freshness. That is not automatically bad. Productive build phases often live with some negative form. The key question is whether it is controlled enough that you can still hit key sessions. Very negative values are a warning sign that the week may be asking more than you can absorb cleanly.
Can a very positive TSB be a problem?
Yes. A positive TSB usually means you are fresher, which is often useful before races or demanding tests, but a very positive number can also mean training load has fallen off too far. Freshness and readiness are not always the same thing. The score is most useful when interpreted alongside CTL, not on its own.
How should I use a weekly CTL/ATL/TSB view?
Use it to check whether the pattern of the week makes sense. A block with several hard days should show ATL rising faster than CTL. A taper or recovery week should show ATL dropping and TSB improving. The goal is not to chase exact numbers but to see whether the direction of the trend matches the purpose of the training week.
Are CTL, ATL, and TSB accurate predictors of race performance?
They are helpful indicators, not guarantees. Riders can perform well with different combinations of fitness and freshness depending on event type, psychology, sleep, travel, and heat. These metrics are strongest when they support good decision-making rather than pretending to predict the future with certainty.
Sources and References
- Coggan and Allen, Training and Racing with a Power Meter, for TSS-based training load concepts.
- TrainingPeaks education on CTL, ATL, TSB, and taper planning.
- British Cycling and USA Cycling coaching materials on fatigue management and load distribution.