Multi-Activity CP Calculator
Harvest maximal efforts you have already run — a race, a hard segment, a tempo — and fit Critical Power and W′ across all of them by least squares, rather than going out to perform a CP test. Three or more efforts are fitted to the two-parameter model P = CP + W′/t.
With more points than parameters the fit produces what two efforts cannot: a standard error on CP, so you see how precisely they pin it down. All three published models are shown whichever you pick, because they can disagree by real amounts. Efforts should come from a two-week window — the model assumes one athlete at one fitness level.
Type each effort yourself, or drop one .fit per effort and we read the measured power — the duration is typed either way, because the file has to be told what window to search.
Have exactly two efforts? Two points determine the curve exactly, so least squares has nothing to fit — use the Critical Power Calculator, which solves that case in closed form and can also read both efforts out of a single CP-test activity.
Your efforts
Three or more maximal efforts from separate runs, ideally within a two-week window. Enter each as a duration and an average power.
Advanced — environment adjustment (optional)
Corrects each effort to one target condition before fitting, so runs from different days are comparable. All-or-nothing: if any effort is incomplete, nothing is corrected.
Check my W′ against Stryd norms (optional)
The norms come from the SuperPower Calculator.
Nothing here is assumed. We never infer your pod from the file — guessing it wrong shifts the result a whole band.
Values are never sent to the server.
Result
All three fit the same curve — they differ only in which of your measurements is treated as the noisy one, so they can disagree by real amounts. Parity with the SuperPower Calculator (SPC) is linear.
Nothing fitted yet
Enter 3 or more maximal efforts above — typed, or one .fit per effort. There is a Load demo data button up there too, if you would rather see it work first.
About the three models
Critical power was described by Monod and Scherrer in 1965, and the three options below are later rearrangements of that one idea rather than rival physiologies. All three describe the same hyperbola; they differ only in which of your measurements is treated as the noisy one, which is a choice of error metric:
- linear — residuals in work (Moritani 1981). What the SuperPower Calculator computes, so this is the one to pick for parity with your own sheet. Squared residuals scale with t², so long efforts dominate the fit.
- 1/time — residuals in power (Whipp 1982). If you committed to a duration or ran a race, power is the quantity that actually varied.
- 2-hyp — residuals in time (Hill 1993). For hold-a-power-until-failure testing, where time is what varied. That needs a treadmill or ergometer, so it rarely fits efforts recorded outdoors.
Nothing ranks them, and the tool never picks one for you beyond its stated default. A model fitted to the wrong kind of data still returns a plausible-looking number — with a standard error that is too small — so the comparison table is always on screen.
References
- Monod & Scherrer (1965), The work capacity of a synergic muscular group — Ergonomics 8(3): 329–338. Where critical power comes from. It describes a single muscle group rather than a whole athlete, which is what the next entry extends.
- Moritani, Nagata, deVries & Muro (1981), Critical power as a measure of physical work capacity and anaerobic threshold — Ergonomics 24(5): 339–350. The work–time form, and the model this tool calls linear.
- Whipp, Huntsman, Storer, Lamarra & Wasserman (1982), A constant which determines the duration of tolerance to high-intensity work — Federation Proceedings 41(5):1591. The power–inverse-time form, 1/time. A one-page abstract with no DOI and no PubMed record, so it is cited here rather than linked.
- Hill (1993), The critical power concept: a review — Sports Medicine 16(4):237–254. The hyperbolic form, 2-hyp, and the best single entry point to the literature around all three.
- SuperPower Calculator (SPC) — documentation and the SPC workbook (opens a copy in your Drive), by Coach Steve Palladino — the source of this mode’s entry rules and of the W′ norms used by the optional RWC check. The basis of those standards is not published and the reference group is self-selected, so treat the bands as a prompt to look closer rather than a measurement.
- Critical Power and W′ Explained — High North — an independent explainer.