Lactate testing
Evidence: moderate
How blood lactate is measured, in the lab and by finger-prick during sessions. Useful for competitive runners; for most, race-pace and feel set zones well enough.
Lactate testing measures the concentration of lactate in the blood during exercise to locate the lactate thresholds that anchor training intensity. A small blood sample, usually from a finger or earlobe, is analysed at a series of running speeds, and the way lactate rises with intensity defines the thresholds. It is the most direct way to set individualised threshold paces, and it underpins methods such as double-threshold training.
The lab test
A graded test takes blood at the end of each stage of increasing speed, building a lactate-versus-intensity curve. From that curve several thresholds can be defined, and this is where the apparent precision frays. The first threshold (LT1) is the first rise above baseline; the second (LT2) approximates the highest intensity sustainable in a steady state. But there are many competing definitions of the second threshold: a fixed 4 mmol/L (OBLA), a fixed rise above baseline, the Dmax and modified-Dmax curve methods, and individual-anaerobic-threshold methods, and they do not all agree on the same runner (Faude et al. 2009). The genuine gold-standard criterion is the maximal lactate steady state, found by several constant-pace runs on separate days to find the fastest pace at which lactate stops rising, which is accurate but too costly and time-consuming for routine use.
This is why a “threshold pace” from one protocol or lab need not match another’s, and why the lactate threshold is best understood as a region rather than a single line.
Finger-prick testing during sessions
Portable analysers let runners and coaches measure lactate on the track from a finger-prick drop of blood, which is how the Norwegian double-threshold method controls intensity in real time. They are reasonably good, with caveats. The better devices, such as the Lactate Pro and Lactate Plus, are reliable and accurate against laboratory analysers, with a typical error around 0.4 to 0.5 mmol/L; others, such as the Lactate Scout, are noticeably less so, with roughly double that error (Tanner et al. 2010). Much of the real-world error comes not from the device but from the sampling: squeezing or “milking” the finger contaminates the sample, and sweat on the skin can distort the reading, so technique matters as much as the analyser.
A directional measure, not an absolute one
Even done well, lactate testing is a directional guide, not a precise readout. Part of that is what the test actually measures: blood lactate sampled at the fingertip reflects the balance of production and clearance across the whole body at that moment, read off a stepwise protocol with a portable analyser, not a clean reading of what a specific muscle is doing. The thresholds are then inferred from a handful of points on a curve, by one of several disagreeing definitions.
The curve itself also moves from day to day. Blood lactate at a given pace is sensitive to many things besides fitness:
- Carbohydrate and glycogen state. A low-carbohydrate or glycogen-depleted morning shifts the whole curve, so pre-test diet should be standardised.
- Heat and humidity. Warm conditions raise lactate at a given pace.
- Prior fatigue and rest. A tired runner, or one who trained hard the day before, reads differently from a fresh one.
- Caffeine, hydration and even the sampling site and technique, all of which nudge the number.
The practical consequence is to treat a threshold pace or heart rate as a moving region to revisit, not a fixed line to obey, and to act on the trend across several samples and several tests rather than any single mmol/L value, the same discipline that applies to wearable metrics.
When it is worth it
For most runners, perceived effort and pace from a recent race set training zones well enough, and lactate testing adds precision they will not use. It earns its place for competitive runners doing controlled threshold work, where holding intensity precisely below the second threshold is the point, and for anyone whose estimated thresholds from a watch look implausible, since watch lactate-threshold pace estimates are unreliable.