Training Stress Balance (TSB)
TSB (Training Stress Balance), often just called "form", is the difference between your slowly built-up training load (fitness, CTL) and your recent load (fatigue, ATL). The number sums up how fresh or tired the load model thinks you are.
In Trimetra this is called freshness.
What is TSB?
Fitness builds slowly; fatigue comes and goes fast. TSB sets those two against each other: a positive balance goes with freshness (little recent load relative to your base), a negative balance with built-up training fatigue. Both are part of normal training — anyone who wants to improve spends a good share of the time on a slightly negative form.
The familiar pattern towards a race: first build load (form drops), then in the taper reduce volume so fatigue fades while fitness is largely kept — and form peaks positive right around race day.
How is TSB calculated and read?
TSB follows from your daily load scores (such as TSS): in the common models, fitness is a slow average that moves over roughly six weeks, fatigue is a faster average over about a week, and form is the difference between the two.
Read TSB as context, not as an order. Chronically positive form usually means you’re training too little to improve; deeply and lastingly negative form is a signal to take recovery seriously. And because the model only sees training load, sleep, HRV, niggles and how you feel are still needed to judge your real recovery.
How Trimetra personalises this
Trimetra calculates your form balance from sport-specific load scores on your own anchors and uses it in daily planning alongside recovery signals like sleep and HRV — form is one voice, never the only one. Towards a target date, the app tunes the taper where possible to how you actually responded in earlier tapers.
Frequently asked questions
Is a negative form (TSB) bad?
No — if you want to improve, you train with slightly negative form most of the time. It simply means you are building. Only deeply and persistently negative form is a signal to take recovery seriously.
What is a good TSB for a race?
Around race day you want your form to peak positive: in the taper, fatigue drains away while your fitness largely holds. The exact number is personal — how you responded to earlier tapers says more than a fixed target value.
What is the difference between form and fitness?
Fitness (CTL) is the load you build up slowly over weeks; form (TSB) is the difference between that fitness and your recent fatigue. So you can be fit and tired at the same time: high fitness, negative form.
Every term at a glance in the full glossary.
TSS, NP, IF, CTL, ATL and TSB are trademarks of Peaksware, LLC (TrainingPeaks). Trimetra is not affiliated with them; this page merely explains the term.