Form: what fitness minus fatigue means
The gap between two trends
Form, or training stress balance (TSB), compares longer-term and shorter-term training load. In this example it is fitness minus fatigue: if the two numbers are 60 and 80, form is −20.
A recent increase in load tends to push the faster fatigue line above the slower fitness line. After load drops, the faster line usually falls sooner. Change the block below to see this happen.
See the gap change
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.
The gap between two trends
Form, or training stress balance (TSB), compares longer-term and shorter-term training load. In this example it is fitness minus fatigue: if the two numbers are 60 and 80, form is −20.
A recent increase in load tends to push the faster fatigue line above the slower fitness line. After load drops, the faster line usually falls sooner. Change the block below to see this happen.
Negative and positive values
A negative value means recent load is above the longer-term trend in this model. A positive value means it is below. Neither is a diagnosis: negative form can occur during a planned training block, and positive form can follow time away from training.
The same value can arise from very different training histories. Look at both component lines and the workouts behind them.
Is positive form race readiness?
Not on its own. A reduction in load can raise form even when an athlete has been ill or has missed weeks of training. The calculation does not know how well you slept, whether you are healthy, or what the event requires.
Use it as one piece of context alongside recent training, performance and how you feel. Avoid a universal target or claiming the number predicts an individual result.
Why platforms may disagree
Some products report form using previous-day fitness and fatigue, while others use same-day values or different time constants. The interactive example explicitly uses same-day values.
Missing workouts, starting values and different load scores also change the result. Check definitions and timing before comparing numbers.
Follow a block and a recovery period
Select a training block and move the day control through it. The acute line generally rises faster, making form more negative. When the daily load is reduced, the acute line can fall faster and form can rise.
The longer-term line also changes. Form is the difference between both values, not an independent measurement layered on top of them.
The same form, different histories
Fitness 60 minus fatigue 80 and fitness 30 minus fatigue 50 both produce −20. Those are different recent training histories despite the identical form value.
Read the component values and the actual sessions together. A single difference cannot preserve the details of the two numbers that created it.
Planning with the chart
A taper is a deliberate change in training before an event, not merely a target number on a graph. The event, recent training and individual response matter.
Use the chart to visualise what a proposed reduction does to the model, and use observations from training and recovery to decide whether the plan makes sense.