Fitness: what chronic training load shows
A longer view of training
Fitness, often called chronic training load (CTL), is a weighted average of daily training load. In the familiar TrainingPeaks model the default time constant is 42 days, so recent days have more influence while older days fade gradually.
It is a history of recorded load, not a direct test of your fitness. Change the block below and watch the solid line respond.
Watch longer-term load build
Start with three weeks at 50 load a day. Change the following block, then move through the timeline.
Illustration starts both trends at 50. Daily updates use 1/42 and 1/7; form is same-day fitness minus fatigue. Platforms may use different timing and settings. These curves describe the model, not your body.
A longer view of training
Fitness, often called chronic training load (CTL), is a weighted average of daily training load. In the familiar TrainingPeaks model the default time constant is 42 days, so recent days have more influence while older days fade gradually.
It is a history of recorded load, not a direct test of your fitness. Change the block below and watch the solid line respond.
Why the line moves slowly
The example updates today’s value by adding one forty-second of the difference between today’s load and yesterday’s value. A single hard day changes it a little; a sustained change moves it further.
A 42-day time constant is not a 42-day cutoff: older training still contributes with decreasing weight. Different products and settings can use different constants.
What a higher number means
A higher value means more recorded load according to the chosen model. It does not establish that you are faster, healthier or ready to race. The same total can come from different workouts, and adaptation differs between people.
Compare it with actual performance, the training you did and how you feel rather than chasing a number.
Missing history matters
An unrecorded workout contributes no load to the model. A new account, changed device or missing activities can make the line look artificially low.
The initial value, scoring method and threshold settings also affect the curve. Check those before comparing it across platforms or athletes.
A day-by-day example
Start at 50 load per day and add a block of 100 per day. On the first day, the example rises by (100 − 50) ÷ 42, or about 1.2. Continued days at 100 keep moving the line upward, with the increase getting smaller as the line approaches that load.
Select the day control to follow the change. The 42-day setting controls the rate of smoothing; it is not a promise that adaptation takes 42 days.
Why lower load can be useful
A recovery period or taper may lower the longer-term load line. That is a consequence of the arithmetic, not proof that the decision was wrong or that performance has necessarily fallen.
A training plan also needs space for recovery, specific preparation and life outside training. Judge the line in that context.
Compare with evidence outside the chart
A stable or rising load can be compared with repeatable sessions, power or pace at a given effort, and how workouts feel. Each observation has its own noise and conditions.
A performance change cannot be attributed to a single line without considering the training, environment and other circumstances.