wbal.io — W′bal analysis for coaches and athletes

Everything you need to model anaerobic capacity

From file upload to individualised recovery rate fitting — built for sports scientists and coaches who need more than population-level models.

Upload .fit and .csv files

Drag and drop any Garmin, Wahoo, or CSV power file. Irregular sampling is handled automatically.

Critical power determination

Enter test results manually or upload files. The tool fits your personal P-t curve and gives you CP and W′ directly. Read the guide

Free

Interactive W′bal chart

Zoom and pan through the effort. W′bal and power plotted together with CP as a reference line.

Recovery rate calculator

Derive individualised A and B constants from a structured HIIT test. Multiple bouts, least-squares fit.

Original method

Compare efforts

Overlay multiple analyses on the same chart. Compare models, parameters, or different sessions.

Export results

Download the full W′bal time series as CSV or export the chart as PNG for reports.

Seven recovery models in one tool

Population models for reference. Individualised and biexponential models for precision — fitted directly from your athlete’s own test data.

Model	Formula	Constants	Type
Skiba	τ = 546·e^−0.01·DCP + 316	Fixed	Population
Bartram	τ = 2287·DCP^−0.688	Fixed	Population
Pugh (International)	τ = 789·DCP^−0.468	Fixed	Population
Pugh (National)	τ = 1883·DCP^−0.487	Fixed	Population
Pugh (Regional)	τ = 5184·DCP^−0.700	Fixed	Population
Individualised	τ = A·DCP^−B	Fitted from test	Individualised
Biexponential	τ = A1·e^−B1·DCP + A2·e^−B2·DCP	Fitted from test	Individualised

The individualised and biexponential models are the core of what makes wbal.io different. Rather than applying population constants to your athlete, you derive their own recovery rate from a structured HIIT test — then use those constants for all future analysis.

From file to insight in minutes

No installation. No setup. Works entirely in the browser.

Upload a power file

Drag and drop a .fit or .csv file from Garmin, Wahoo, or any head unit. The parser handles irregular sampling, missing power data, and encoding automatically.

Set your critical power parameters

Enter CP, W′, and optionally Pmax for the 3-parameter model. These come from standard CP testing protocols.

Choose a recovery model

Select from five models. For best accuracy, use the recovery rate calculator to fit individualised constants from a HIIT test session first.

Analyse and export

View the interactive W′bal and power charts. Compare multiple efforts or models. Export to CSV or PNG for reports and presentations.

Built for people who care about the details

If you’ve ever wondered whether a population-level τ is actually right for your athlete, this tool is for you.

Performance coaches

Understand W′ depletion and recovery across training and racing. Use athlete-specific models rather than population averages.

Sports scientists

Access individualised and biexponential recovery models not available in commercial software. Export full time series for further analysis.

Serious athletes

Go beyond what training platforms show you. Understand exactly where your W′ is going and how quickly it recovers.

Start free. Upgrade when you’re ready.

The free tier gives you enough to understand the tool. Pro unlocks the features that make it genuinely useful.

Free

£0

forever

CP determination (manual entry)
CSV file upload
2-parameter CP model
Skiba recovery model
CP & W′ determination
W′bal and power charts
.fit file upload
Individualised models
Recovery rate calculator
Export CSV and PNG

Get started

Common questions

What file types are supported?

CSV files are supported on all plans. .fit files from Garmin, Wahoo, and most other head units are supported on Pro.

Where do I get my CP and W′ values?

Use the built-in CP determination tool — it's free and works directly in the browser. Upload power files or enter test results manually from two or more maximal efforts at different durations, and it will fit your personal power-duration curve.

How do I determine CP and W′?

Go to the "Determine CP" tab in the app. You can enter test results manually (label, duration, mean power) or upload individual power files and trim them to the test window. The tool fits a 2-parameter model using ordinary least squares and shows you the residuals so you can judge the quality of the fit. A good fit has residuals under 5 W.

What is the recovery rate calculator and do I need it?

It derives your athlete's personalised recovery constants from a structured HIIT test — fitting the A and B parameters in the τ = A·DCP⁻ᴮ model to that specific individual. You don't need it to get started: the five published population models (Skiba, Bartram, three Pugh variants) work out of the box. But personalised constants give more accurate W′bal predictions, especially if your athlete's recovery rate is unusual.

Is my data stored on your servers?

Power files are sent to the server only to parse binary .fit data into a time/power series. All W′bal computation runs in your browser. We do not store your training files or results.

Can I cancel at any time?

Yes. Cancel from your account settings at any time. You keep access until the end of your billing period. No questions asked.

Do you offer academic or student discounts?

Yes. Get in touch via the contact page with your institutional email address and we'll sort a discounted rate.

What's the difference between the Pro and Institutional plans?

Pro is for individual athletes, coaches, or scientists. Institutional covers up to 20 seats under one subscription, with a shared team workspace and invoice billing — suitable for university labs, professional teams, or coaching businesses.

Know exactly how much W′ your athletes have left