REPEATS · SCIENCE & METHOD

Critical Power and W′: useful for rowing, with limits worth showing.

Critical Power gives Rowing Intervals a principled way to describe the relationship between power and tolerable duration. W′ adds a finite work-above-CP term. Together they can support interval forecasting, but neither parameter is a magic threshold and recovery between repetitions is less certain than the basic model.

IN ONE MINUTE

A compact model of how sustainable power changes with duration.

Critical Power: the asymptote of the two-parameter power-duration model and a useful marker near the heavy-to-severe exercise boundary.

W′: the model's finite work capacity above CP, expressed as work rather than a second power threshold.

Rowing Peak's rule: use the model to forecast and compare, while keeping test quality, machine provenance and uncertainty visible.

THE MODEL

Power and duration are linked.

For high-intensity exercise, higher power can be sustained for less time. The classic two-parameter Critical Power model represents that relationship with CP and W′. Above CP, the model predicts tolerable duration from how quickly the finite W′ term is expended.

Exercise-physiology reviews support CP as a meaningful fatigue-related boundary, but modern reviews also warn against the old shorthand that CP is a power you can sustain indefinitely. In practice, the model is an approximation whose estimates depend on testing protocol, data range and model choice.

Poole et al., Critical Power as a fatigue threshold Burnley & Jones, power-duration physiology and fatigue Dotan, critical review of Critical Power

ROWING EVIDENCE

Critical Power has been studied on the rowing ergometer.

Research in trained rowers has tested Critical Power directly rather than simply borrowing a cycling model. A study of trained male rowers found that a modified three-minute all-out rowing test could estimate CP and W′ against values established from multiple constant-work tests, with test-retest work included in the design.

More recent work in well-trained male and female rowers has reported a strong relationship between CP and rowing performance, while a 2025 systematic review of rowing-ergometer performance testing also identified CP as a promising correlate of 2,000 m performance, albeit from a smaller evidence base than VO₂max and peak power.

Cheng et al., Critical Power in trained rowers Critical Power and rowing performance Systematic review of rowing-ergometer performance testing

THE TWO-PARAMETER FORM

Simple enough to use. Not simple enough to use carelessly.

In the common two-parameter representation, target power for a maximal effort of duration t can be expressed as CP plus W′ divided by time. That makes the model useful for comparing efforts of different durations and estimating how demanding work above CP should be.

POWER-DURATION MODELP(t) = CP + W′ / tCP is power. W′ is work. The quality of both estimates depends on the efforts used to fit the model.

WHY TEST SELECTION MATTERS

A clean equation can still give a poor athlete model.

Critical Power estimates can move when the predictive efforts change. The broader power-duration literature therefore recommends using appropriately spaced maximal efforts rather than assuming any convenient pair of results defines a stable physiological truth.

There is also active scientific debate about the hyperbolic model outside the durations where it tends to fit best. Rowing Peak therefore treats CP and W′ as versioned model estimates from qualifying evidence, not permanent athlete attributes.

Bishop et al., dependence on predictive-test duration Drake et al., power-law vs Critical Power modelling

RECOVERY BETWEEN REPEATS

W′ recovery is useful context, not settled rowing arithmetic.

Models of W′ reconstitution have been developed mainly from cycling and related intermittent-exercise research. Reviews conclude that recovery modelling is potentially useful for interval prescription, while also noting that the individual determinants and kinetics of W′ reconstitution are not fully resolved.

That distinction matters for Rowing Intervals. The product can use recovery evidence to make the set forecast more informative, but it should not present an estimated W′ recovery curve as a directly measured physiological quantity.

Chorley & Lamb, CP, W′ and reconstitution review Skiba et al., modelling W′ expenditure and reconstitution

HOW ROWING INTERVALS USES IT

The model supports the recommendation. It does not replace the completed set.

Qualify maximal evidence

Use efforts that are suitable for the power-duration model rather than every hard-looking workout.

Keep machines separate

Power evidence remains scoped to the machine and measurement system that produced it.

Version the model

CP and W′ estimates are tied to their underlying evidence so later changes remain explainable.

Forecast the set

Use the model to estimate a demanding, repeatable target for the requested work and recovery structure.

Observe execution

Compare repetition power, pace, rate and decay with the prepared target rather than collapsing the set into one mean.

Show uncertainty

When the evidence or recovery model is weak, Rowing Peak should say so instead of manufacturing precision.

PUT THE MODEL TO WORK

Prepare a set around your own evidence.

Connect or upload your rowing history. Intervals will use a pacing forecast only when the evidence supports one.

Prepare an interval session