Endurance · 5 min read
Training zones are only as good as the boundaries they are drawn from. Blood lactate testing puts those boundaries where your physiology actually places them, rather than at a percentage of a number that was never measured.
By Chris Gkoufas, DVOTION Labs ·
Lactate is produced continuously during exercise and cleared continuously. At low intensities clearance keeps pace with production and blood lactate stays near resting values. As intensity rises, two points of interest appear.
The first — LT1 — is where blood lactate first rises meaningfully above baseline. It marks the ceiling of genuinely easy work, the intensity below which fatigue accumulates slowly enough that duration is limited by other things.
The second — LT2 — is the highest intensity at which production and clearance still balance. Above it lactate rises progressively and so does fatigue, which is why the time you can hold it is measured in tens of minutes rather than hours.
The measurement itself is a fingertip sample at the end of each stage of a graded protocol, analysed immediately. At DVOTION Labs that analysis is done on an Arkray Lactate Pro 2.
Zone systems built on percentages of maximum heart rate assume that everyone's thresholds fall at the same fraction of their maximum. They do not. Where LT1 and LT2 sit relative to maximum varies substantially between individuals and shifts with training status in the same individual.
The error this produces is not random. It is systematic for any given athlete, which means a runner whose first threshold sits unusually low will be prescribed easy runs that are too hard, every single week, for as long as they use the percentage.
The critique of intensity-prescription methods in the literature is broadly this: anchoring intensity to thresholds is defensible, anchoring it to percentages of a maximum is not, and the two produce genuinely different training for the same athlete.
Gas exchange identifies two thresholds as well, from breathing rather than blood. Broadly the ventilatory thresholds correspond to the lactate thresholds, and a protocol that records both gives two independent readings of the same underlying transitions.
When they agree, you can hold the zones with more confidence than either alone would justify. When they diverge, that is information rather than a problem — it can reflect the protocol, the athlete's training background, or where the measurement sits relative to a genuinely gradual transition.
This is why the two are worth doing in one protocol rather than separately. Two measurements of the same transition on the same day, in the same person, in the same session, is a stronger basis for a zone than either taken alone on a different day.
Two things are worth separating here. What trained endurance athletes actually do is well described: most volume at genuinely low intensity, a smaller proportion hard. Whether a polarised distribution beats a threshold-dominant one in a head-to-head trial is far less settled — an early meta-analysis favouring polarised rested on three studies, later and larger work is more equivocal, and several trials find no difference between the two. The case for keeping easy work genuinely easy does not depend on winning that argument.
That structure only works if the boundaries are right. A programme that is nominally polarised but whose easy zone sits above the athlete's first threshold is not polarised at all. It is a large volume of moderate work with some hard sessions on top. Whatever the label says, the athlete is not getting the low-intensity volume the plan assumes they are — which is the more useful point than which distribution wins in a trial.
So the zones do two jobs. They set a ceiling on easy that is low enough to leave the hard sessions recoverable, and they set a floor on hard that is high enough for those sessions to do something. Both boundaries are individual, and neither can be derived from a maximum.
Thresholds move with training, which is the point of training. Twelve to sixteen weeks between tests is long enough for a measurable change to have occurred and short enough that the zones have not drifted far from reality in the meantime.
Retesting sooner tends to measure day-to-day variation — sleep, glycogen status, recent training load and the ambient conditions all move a lactate curve somewhat, and a change smaller than that variation is not evidence of adaptation.
The other reason to retest is a change in what you are training for. Zones set for a marathon block are not the zones for a track season, and the relevant thresholds may have moved in different directions.
It is a lancet prick at the end of each stage, comparable to a blood glucose test. Most people find the protocol itself considerably harder than the sampling.
It appears widely and it is a population convention rather than an individual measurement. Some athletes reach their second threshold well below 4 mmol/L and some well above, so using the fixed value in place of an individually identified threshold reintroduces exactly the error that testing was meant to remove.
Yes, and it is a legitimate standalone test that gives you both lactate thresholds and the curve between them. What it does not give you is VO₂ max, measured maximum heart rate or substrate use, and it does not let the two threshold systems be compared against each other.
Nothing hard in the 48 hours before, and nothing at all the day before if you can manage it. A lactate curve measured on tired legs sits in a different place, and the zones drawn from it will be wrong for as long as you use them.
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