Gritmo looks at training through five capabilities that show up in real performance: Sprint Power, Sustainable Power, Hard-Effort Capacity, Durability, and Repeated-Effort Capability. They describe what a rider can do—not five isolated systems inside the body.
Not every useful ride needs to claim one of those capabilities as its outcome. Development workouts have a clear primary target. Foundation rides build broad aerobic support. Recovery protects continuity. Assessments collect evidence. A long endurance ride can matter without pretending that one session raised CP or proved better Durability.
Once the purpose is clear, Gritmo resolves the workout for the rider and follows the whole session as one changing state. The plan is a hypothesis. The execution is evidence. Improvement still has to appear across comparable efforts over time.
01
Five capabilities—and a foundation beneath them
A development workout needs one honest answer to the question: what are we trying to improve? Gritmo uses five capabilities so that a session does not quietly promise to develop everything at once.
Foundation work is different. It creates useful exposure that may support several capabilities over time, but it does not count as proof that a specific capability improved. Endurance is a real training method and long-ride performance is real; Gritmo simply does not reduce them to a sixth universal physiology score.
Definitions
Training targetTraining target
The rider quality or adaptation that training is intended to develop.
A Training target describes what should improve; a Workout method describes how.
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Workout method
The session structure or intensity used to pursue a Training target.
Sweet Spot, Threshold, and Microbursts are methods—not rider adaptations.
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Durability
Ability to preserve performance after accumulated fatigue.
Without relevant late-Ride evidence, Durability is unknown—not weak.
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Repeatability
Ability to reproduce hard efforts.
A large W′ does not automatically imply strong Repeatability.
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What it means
A development workout names one primary capability. A foundation ride can be valuable without being forced into a capability outcome.
| Capability | The question | Useful evidence |
|---|---|---|
| Sprint Power | How much very-short power can the rider produce? | Observed short efforts |
| Sustainable Power | How much power can the rider hold while fresh? | CP and sustained power evidence |
| Hard-Effort Capacity | What can the rider do during hard work above CP? | W′ and the severe-duration power curve |
| Durability | How much performance remains after prior work? | Fresh versus loaded performance |
| Repeated-Effort Capability | How well can hard efforts be reproduced after incomplete recovery? | Retention, falloff, and repeat count |
What this does not mean
The five capabilities are not five separate energy systems, and foundation is not filler. They are a clean way to describe intent without claiming more than the evidence supports.
02
Meaning comes before mathematics
The rider model does not decide what a workout means. A short hard repetition, a sustained severe interval, and a repeated-attack set can have the same modeled W′ cost while serving different purposes.
Gritmo first declares the role of the session. For development work, it names one primary capability and at most one secondary capability. A versioned protocol explains why the method may support that intent and what must not change. A template lays out the blocks. Only then does the resolver calculate the rider-specific watts and durations.
Definitions
Training targetTraining target
The rider quality or adaptation that training is intended to develop.
A Training target describes what should improve; a Workout method describes how.
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Workout method
The session structure or intensity used to pursue a Training target.
Sweet Spot, Threshold, and Microbursts are methods—not rider adaptations.
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What it means
Decide the role. Name the capability when the role is development. Choose a protocol for that purpose. Then make its structure fit the rider.
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Workout role
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Capability target
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Protocol hypothesis
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Template structure
What this does not mean
Using W′ in a calculation does not make Hard-Effort Capacity an outcome. Repeating intervals does not make Repeatability an outcome. Feasibility tells us whether the rider can execute the plan—not what the plan develops.
03
A target does not describe the whole cost
A target at 140% of CP tells us how far the requested power sits above one boundary. It does not tell us how much work the rider can perform there. W′ adds that missing capacity dimension.
For steady work above CP, Gritmo can express the interval as joules above CP and as a fraction of the rider’s modeled W′. That fraction is an above-CP execution cost—not the total training dose and not a promise of a particular adaptation.
Definitions
Critical power (CP)Critical power (CP)
The boundary above which fatigue cannot stabilize and modeled W′ begins to drain.
CP is not exactly FTP, 60-minute power, or a promise of indefinitely sustainable power.
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Above-CP work capacity (W′)
The finite amount of modeled work a rider can perform above CP.
W′ is not a literal tank, a single substrate store, or a purely anaerobic reserve.
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What it means
A target describes what the trainer requests. Modeled above-CP cost estimates how deeply that power and duration draw on this rider’s W′.
Modeled above-CP cost
(Target power − CP) × durationDivide that work by W′ to express the interval relative to the rider’s modeled above-CP work capacity.
| Rider A | Rider B | |
|---|---|---|
| CP | 300 W | 300 W |
| W′ | 12 kJ | 24 kJ |
| Interval | 420 W · 60 s | 420 W · 60 s |
| Modeled cost | 60% of W′ | 30% of W′ |
What this does not mean
A W′ fraction is not a physiological dose and does not choose the workout outcome. It is one modeled execution cost inside a larger prescription.
04
Every repetition inherits a state
A workout cannot be understood by calculating each repetition as if the rider were fresh. Work above CP reduces modeled W′ balance. Recovery below CP can restore part of it. Sub-CP riding accumulates Aerobic Load without spending W′. Every block changes the context in which the next one begins.
Gritmo therefore resolves the workout in chronological order—from the warm-up through every work, recovery, preload, and cooldown block. The modeled state can include W′ balance, Aerobic Load, Recovery Strain, accumulated work, and whether the workout started fresh or from an explicit carry-in.
Definitions
Modeled W′ balanceModeled W′ balance
An estimate of how much above-CP work capacity remains as work and recovery unfold.
W′ balance is calculated from the rider model and power trace. It is not a direct measurement of remaining physiology.
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Gritmo principle
Gritmo treats a workout as a state trajectory—not a list of isolated targets.
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Starting state
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Work
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Recovery
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Next starting state
| Moment | Above-CP work | Modeled W′ balance |
|---|---|---|
| Repetition 1 starts | — | 20 kJ · 100% |
| Repetition 1 ends | 3 kJ | 17 kJ · 85% |
| Recovery ends · Repetition 2 starts | — | 18.4 kJ · 92% |
| Repetition 2 ends | 3 kJ | 15.4 kJ · 77% |
What it means
The target can be identical while the demand is not. The next effort inherits the work and recovery that came before it.
What this does not mean
The state is a working model, not a live measurement of every process inside the rider. W′ balance is one part of the state, not the complete physiology of fatigue.
05
Recovery is part of the prescription
Recovery changes what the next repetition asks of the rider. Both recovery power and recovery duration matter: easier or longer recovery generally allows more W′ to be reconstituted, while harder or shorter recovery leaves the next effort starting deeper in the modeled deficit.
The direction is well supported. The exact rate is not universal. Recovery kinetics differ between riders and can slow after repeated severe work, so Gritmo treats W′ balance as an estimate rather than a countdown clock inside the body.
Definitions
RepeatabilityRepeatability
Ability to reproduce hard efforts.
A large W′ does not automatically imply strong Repeatability.
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What it means
Recovery is not empty time. It changes the modeled starting state of the next effort and therefore changes the execution context of the set.
What this does not mean
A four-minute timer does not prove full recovery, and incomplete recovery does not automatically make a workout a Repeatability protocol. The intent and evidence plan must say that explicitly.
06
One plan is resolved, frozen, and executed
A recommendation is still an idea. Before preview, Gritmo resolves the selected protocol and template against a frozen snapshot of the rider model and a declared starting state. The simulator checks the complete trajectory and either produces a safe, executable prescription or explains why it cannot.
That resolved prescription contains the exact commands the trainer will receive. Preview, Start, the live workout, and the saved result all use the same frozen plan. Starting the workout does not regenerate watts, quietly change the structure, or reinterpret the protocol.
Gritmo principle
The workout you preview is the workout the runner executes and the workout the result keeps.
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Resolve
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Simulate
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Freeze prescription
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Execute and preserve
What it means
Resolve once. Simulate once. Freeze the commands. Preserve the same plan when the ride is compared with what happened.
What this does not mean
A frozen prescription is not a guarantee that the rider will respond as modeled. It guarantees the identity of the plan, so observed differences remain interpretable.
07
The workout is a hypothesis
A planned trajectory is what the rider model expects from the requested power trace. The completed workout is new evidence. Gritmo should preserve both and compare them rather than quietly replacing the plan with the result.
Power completion, late-repetition falloff, pauses, cadence, heart rate when usable, and perceived exertion can all change how the session should be read. W′ trajectory alone cannot prove that the intended stimulus occurred, and a failed interval does not identify one physiological cause.
Definitions
ObservedObserved
A value directly supported by recorded or rider-provided evidence.
Observed efforts remain points; Gritmo does not connect sparse points and call the result observed.
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Modeled
An estimate produced by applying a defined relationship to the available evidence.
A modeled value is useful when its evidence, scope, and limits remain visible.
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Evidence
Observed information that supports or changes the rider model.
Evidence may come from rides, power bests, files, connected providers, or values entered by the rider.
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What it means
The plan makes a testable prediction. The ride adds evidence. Gritmo keeps them separate so the difference remains useful.
Execution assessment
Did the rider execute the frozen commands, and where did execution change?
Acute response evidence
How did the rider respond during this session, using the signals that are actually available?
Rider-model evidence
Is this execution compatible with the model, or is there a model-mismatch candidate worth reviewing?
Longitudinal outcome evidence
Across comparable sessions, is the targeted capability changing over time?
What this does not mean
One completed session cannot prove that a capability improved, an adaptation occurred, or a protocol was validated.
08
Progress one lever at a time
More power is not the only way to progress a workout. Depending on its purpose, progression may add a repetition, extend work duration, shorten recovery, change the next starting state, or preserve a race-specific target while changing the set around it.
The protocol declares which parts are invariant and which adjustments are allowed. Changing power, duration, repetition count, and recovery at once can hide the size and cause of the increase in demand. Where possible, Gritmo changes one meaningful lever and uses repeated comparable execution to decide what comes next.
What it means
Make one meaningful change, observe the response, and keep the reason for success or failure interpretable.
Repeatability
Keep the hard effort specific and adjust only the recovery or starting-state lever declared by the protocol.
Sustained power
Build stable accumulated work before allowing unnecessary above-CP cost.
09
Useful without pretending to know everything
Research supports CP as a meaningful intensity-domain boundary, W′ as a way to express modeled work above it, and recovery power and duration as relevant to W′ reconstitution. It also shows substantial variation between riders.
The evidence does not show that one W′ percentage uniquely produces one adaptation, that a modeled balance is an exact measure of remaining physiology, or that W′-based intervals normalize every rider’s acute response. Gritmo’s exact recovery functions, progression rules, and preset above-CP costs remain product models to test—not physiological truths.
That distinction is deliberate. The model should be specific enough to make a useful prediction and humble enough to show where that prediction can still be wrong.
What it means
CP and W′ help Gritmo reason about hard work. Repeated comparable observations—not one ride—show when the rider model or protocol calibration should change.
Why we cite it: a synthesis of CP as the boundary between exercise domains where physiological responses can and cannot stabilize.
Why we cite it: foundational experimental work for estimating W′ expenditure above CP and reconstitution below it during intermittent cycling.
Why we cite it: recovery followed fast and slow phases and varied materially between the ten trained cyclists studied.
Chorley et al., 2023
A dynamic model of the bi-exponential reconstitution and expenditure of W′ in trained cyclists
Why we cite it: controlled evidence that recovery power and duration both affect modeled W′ reconstitution, while individual calibration still matters.
Gritmo does not need to pretend that every workout has one known biological destination. It needs a clear intent, an honest hypothesis, a prescription that fits the rider, and enough observed evidence to learn when the model was wrong. This Note will change when the implementation, the evidence, or our understanding gives us a reason to change it.
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