Also known as: TSB, Training Stress Balance, Freshness
Form, also called freshness and often abbreviated TSB, is the gap between your Training Load (fitness) and your Fatigue. One number for how fresh or how tired you are today.
Form is the payoff number in the Training Load and Fatigue system. It takes the fitness you have built, subtracts the tiredness you are carrying, and estimates how much of that fitness you could actually put on the road today. Strongly negative Form means short-term fatigue is running ahead of what your long-term fitness has absorbed: training hard, not fresh. Positive Form means you are rested relative to your fitness, which is where you want to be walking into a race and not where you want to be mid-block.
Form is yesterday's Training Load minus yesterday's Fatigue. Both use the previous day's values, since today's training has not been absorbed into either number yet. Training Load moves slowly on its 42-day constant and Fatigue moves quickly on its 7-day one, so the gap between them opens whenever training load rises faster than your fitness adapts, and closes during easy weeks and tapers.
A convention popularized by Dr. Andrew Coggan reads Form between about +5 and +25 as fresh and race-ready, between about −10 and +5 as training normally, and below about −30 as a fatigue zone worth backing off from. These bands are widely used coaching heuristics rather than a single peer-reviewed threshold, and tolerance varies from runner to runner.
Form is the number a taper is built to move. Cutting volume before a race lets Fatigue fall faster than Training Load, which pushes Form positive and lets banked fitness show up on race day instead of hiding under tiredness. Away from race prep, Form that stays deeply negative across weeks, rather than through one planned hard block, is among the clearest load-based warnings of accumulating overreaching.
Negative Form is not automatically bad, and reading it that way is the usual misfire. During a build phase, moderately negative Form is what productive overload looks like, and recovery weeks are what resolve it. The real errors are letting it sit deep in the red for weeks with no plan to bring it back, and over-tapering into a Form so high that it reads as detraining rather than freshness.
A Form number in a spreadsheet is only as good as yesterday's stress-score entry. By itself it says nothing about whether today's plan should change.
Turning a Form reading into 'do this session today, not that one' is coaching judgment, not arithmetic.
Vertical computes Form after every synced run and feeds it straight into what it schedules next: pulling back before a race, pushing when you are fresh enough to take it.
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