The Feeling of a Hard Sustainable Pace — and Why "Lactate Threshold" Is Not One Number

There is a pace you can hold for most of an hour and cannot hold for another minute, and you can feel it arrive without being told. That feeling is real, it is reproducible, and it is the most useful intensity cue most rowers have. The trouble starts when you try to put a number on it, because the number you are given depends heavily on which of several different measurements someone ran.

One name, several measurements

"Lactate threshold" is not one thing. Over the decades at least four distinct quantities have carried the label: the first ventilatory or lactate threshold, the second, the anaerobic threshold derived from oxygen deficit, and the maximal lactate steady state — the highest pace a rower can hold indefinitely without lactate accumulating further. They are found by different protocols, and the historical literature is largely a record of researchers disagreeing about which one they were measuring ([2] Poole).

The disagreement is not academic, because the methods do not return the same number. In thirty-eight well-trained rowers, Dwyer and colleagues compared critical power against two lactate-threshold methods built from the same incremental ergometer test. Agreement between the methods was moderate to strong (r² = 0.49–0.70), but the absolute power they assigned to the same physiological boundary was not the same: 311 watts at critical power, against 324 and 323 watts for the two threshold methods — a difference of about thirteen watts, significant at p < 0.001 ([1] Dwyer).

Thirteen watts is not a rounding error on an ergometer. It is several seconds over 2,000 metres, and it is the difference between two athletes being told they are at the same level when they are not.

What performance actually tracks

The same study asked a practical question — which of these predicts a 2,000-metre time — and the answer was closest to critical power. Its association with rowing performance was r² = −0.81, against −0.75 for both lactate-threshold methods, and adding work above critical power produced a model predicting 2,000-metre time at r² = 0.92 in men and 0.81 in women ([1] Dwyer).

Two cautions belong with that number, because the study's own conclusion is more measured than its title. The margin between 0.81 and 0.75 is small, and the authors describe all three methods as showing moderate-to-high correlations with performance — they report an association, not a verdict ([1] Dwyer). The result is also contested: the interchangeability of critical power and the second lactate threshold is disputed in a published comment on this exact paper, which argues that treating the two as the same quantity overstates what the data show ([10] Dotan).

So the honest position is that critical power is a strong predictor and may be a slightly stronger one, not that it has displaced the lactate threshold. Anyone telling you the threshold concept is finished is running ahead of the evidence.

What lactate actually is

The older story — muscle burns fuel, the waste product accumulates, and at some point there is too much of it — has not survived contact with the literature. Brooks' shuttle description put lactate in the middle of the transport system rather than at the end of it, produced from one tissue and consumed by another ([4] Brooks), and the position has been refined rather than overturned since: lactate is a fuel, a transport intermediate and a marker, and it moves in both directions ([5] Gladden).

The practical consequence is that a blood lactate reading measures a net quantity. It reflects what was produced and what was removed, at one moment, and neither of those is a direct measure of how hard the effort was.

That net behaviour has a specific consequence for thresholds, and it is measurable. Maciejewski and colleagues took seventeen trained rowers through a three-minute all-out test, estimated non-oxidative energy supply from the accumulated oxygen deficit, and tracked blood lactate through recovery. Non-oxidative supply correlated with the amount of lactate released from the working muscles (r = 0.58), with the muscle content of the lactate transporters MCT1 and MCT4 (r = 0.63), and with the removal rate constant (r = 0.55) ([3] Maciejewski).

Read that carefully: the same "anaerobic capacity" number is entangled with how well you move lactate, not just how fast you make it. Two rowers with identical threshold paces can be genuinely different underneath — one producing and clearing more, the other relying more heavily on the oxidative side for a given output. Your threshold is partly a clearance property, and clearance is trainable.

The part that is definitely not optional

None of this makes the oxidative system optional, and the rowing-specific measurements are blunt about it. In 2,000-metre race simulations, eight rowers produced an aerobic, phosphocreatine and glycolytic split of 84, 7 and 9 percent on the ergometer, and 87, 7 and 6 percent on the water ([6] de Campos Mello). Shortening the piece moves that: over 6:30, 5:10 and 4:00, anaerobic contribution climbed from 17.5 to 27.5 percent and mean power rose from 322 to 360 watts ([7] Higgins).

So roughly four-fifths of a 2,000-metre effort is oxidative in every measurement that has actually been taken. Whatever threshold number you are chasing, it sits inside a system that is overwhelmingly aerobic — and the work you are describing has to be produced by a stroke that repeats cleanly, since handle force peaks in the middle of the drive rather than at either end ([8] Ledergerber).

Reading your own threshold without a lab

You do not need a laboratory to find a usable number. You need a number you can reproduce, and that is a lower bar than it sounds.

Run a hard, even piece and find the pace you can just barely hold to completion — a 30-minute test is the most forgiving place to start because failure is gradual rather than abrupt. Write down the split. Repeat it three or four weeks later. The change in that number is the signal; the absolute value is not, for exactly the reasons above.

Two habits make this far more useful. Record the stroke rate alongside the split, because the same split at a different rate is a different effort — not a rounding difference, a different one. And repeat the test under the same conditions each time: same machine, same damper setting, same time of day, because a number you cannot reproduce is not a measurement.

If a club has a proper incremental test with gas exchange or blood sampling, take the number and record which method produced it. That single detail is what makes the result comparable next time.

Training the thing you can actually feel

The sensation of hard sustainable is trainable, and it responds to something more specific than "go harder".

Shorten the piece to the duration whose energy balance you want. That is the lever that actually moves the anaerobic contribution ([7] Higgins), and it is the one most often left unused — an hour of steady rowing at a moderate intensity changes the oxidative side, and nothing about it will move the other one.

Keep the rate honest. The force you produce is a mid-drive peak, not a catch or a finish ([8] Ledergerber), so an interval that starts fast and fades is not a hard-sustainable effort, however uncomfortable the first repetition felt.

Give the recovery enough room. Across nine studies and 176 elite athletes, high-intensity interval training raised VO₂max under specific recovery conditions: an interval rest of at least two minutes, and recovery-phase intensity at or below 40 percent ([9] Ma). Those are the conditions the effect was found under, not a general licence for any rest period — the same meta-analysis found no such advantage when recovery was shorter or more intense.

And expect the sensation to move before the number does. If you can hold the old threshold pace for longer than you used to, that is the adaptation, and it shows up on the erg weeks before any lab re-test would.

Limitations worth stating

The threshold you can feel is a perception, and perceptions are real but not instruments — they shift with heat, caffeine, sleep and how the session is ordered. The published dispute over critical power and the second lactate threshold is unresolved. And the strongest evidence in this article comes from groups of well-trained, mostly adult, mostly male rowers, which is not the same thing as the club squad on a Tuesday.

The honest position is narrower than the marketing: there is no single number that describes a hard sustainable pace, the methods that try disagree by about thirteen watts, and the disagreement between them is not yet settled. What is repeatable is the duration and rate you can hold. Write those down. Everything else is a label attached afterwards.