Lactate step test: protocol, stage duration and termination criteria
A lactate step test records measurements while the load increases in stages. Starting load, stage increment, duration and sampling affect the result and must be documented. The protocol has to suit the question being asked and the person’s capacity for exercise.
What the test measures and what it does not
The step test shows how the blood lactate concentration responds to increasing load. As long as production and clearance are in balance, the value stays low. Beyond an individual transition range, it rises disproportionately. Thresholds are derived from this curve, and training zones from the thresholds.
The test does not measure performance capacity as a whole. It says nothing about strength, technique, race tactics or risk of injury. Nor is it a medical examination. A sports medicine assessment before exercise tests is a separate matter.
Stage duration: three or five minutes
Stage duration affects the lactate response and therefore the calculated thresholds2. Shorter and longer stages are not readily comparable. Shorter stages tend to shift the calculated thresholds towards higher values1. But the extent and direction depend on the specific test.
In practice, three- and five-minute stages are both used. Which duration fits depends on the question, the person and the method. A justified change is possible. But you have to take it into account when comparing over time.
The same applies to whether there is a short break between stages for blood sampling. This is also part of the protocol: it must stay the same and belongs in the report.
Stage duration is part of the documented test protocol. Changes need a professional justification.
Starting load and load increment
The starting load should be well below the expected transition range. Only then is the flat part of the curve captured at all. If the test starts too high, the lower points are missing. Several analysis methods build their construction on precisely these points. Geometric models are particularly sensitive to this. Modified D-Max therefore only starts the secant at the stage before the first clear rise in lactate and so depends less on the first measurement point than D-Max.
The load increment determines how finely the test resolves. Large increments make the test shorter. In exchange, the transition range can disappear between two stages, and the analysis method then interpolates into a gap. In practice, increments of 20 to 40 watts are common on a cycle ergometer, and 1 to 2 km/h per stage on a treadmill. Which increment fits depends on performance level and sport. There is no universally valid standard for this.
How many valid stages are needed depends on the model. Besides the number, what counts is how the measurement points are distributed and which load ranges they cover. A fixed minimum number does not guarantee a reliable threshold.
Sampling and typical sources of error
Sampling, contamination and sampling time can distort measurements. When carrying out the test, follow the validated procedure and the device manufacturer’s instructions.
The resting value is particularly important because several analysis models derive their reference point from it. It is taken before the warm-up. A value after an intensive warm-up is not automatically raised. But it describes a different state and is therefore no longer suitable as the reference point for the models based on the resting value.
The measuring device also matters for comparability. Different systems can deviate systematically5. If the device changes in the middle of a series of tests, this must be documented. That is not a detail.
- Resting value before the warm-up, not after
- Sampling according to a validated procedure and the manufacturer’s instructions
- Always take the sample at the same point within the stage
- Note the device, test strip batch and protocol in the report
- Record time of day, prior exercise and nutritional status
Termination criteria
Normally the test ends when the person is subjectively exhausted or can no longer fully complete the next stage. In addition, there are termination criteria that are not a matter of judgement: notable symptoms, circulatory signs, abnormalities in the accompanying ECG when the test is carried out by sports medicine, or an explicit request from the person being tested4.
For the analysis, it matters whether the last stage was complete. An aborted stage is not a valid measurement point in the same sense as a complete one. A sound analysis records the actual stage duration instead of assuming the planned one.
Post-exercise measurements: why recovery values make the difference
Many protocols end with the last exercise value. This omits information that some analysis methods strictly require: the course of lactate elimination after the end of exercise. The tangent method according to Stegmann, Kindermann and Schnabel starts exactly there and simply cannot be calculated without post-exercise measurements3.
If a method needs post-exercise values, follow its measurement times and conditions. Software cannot replace missing recovery values later either.
What was not recorded in the protocol cannot be calculated later by any software. At this one point, a decision about the protocol is final.
What belongs in the report
So that you can compare later, the raw values and the measurement conditions should be kept alongside thresholds and zones.
- Protocol: starting load, stage increment, stage duration, breaks
- Type of ergometry and device; for a treadmill, the incline
- Resting value and time of sampling
- Analysis model used, including its source
- Reason for termination and whether the last stage was complete
- Recovery values with time intervals, if recorded
Frequently asked questions
How long does a lactate step test take?
The pure exercise time results from the number of stages and the stage duration. It is usually between 20 and 40 minutes. On top of that come preparation, resting value sampling, warm-up and post-exercise measurements. In practice, 60 to 90 minutes is realistic for the appointment.
Three or five minutes per stage: which is better?
The right duration depends on the protocol and the question being asked. For comparisons over time it should stay the same as far as possible. If you change it, document this and take it into account in the interpretation.
Does the resting value have to be taken before the warm-up?
If a method requires true resting lactate as a reference, the baseline value must be taken under the resting conditions intended for this. The value can change after the warm-up. It is then not automatically raised, but it must not be treated as a resting value without being labelled.
What is the minimum number of stages a test needs?
This differs from model to model. What matters is having enough measurement points in the relevant load range and a plausible curve. There is no general minimum number for all methods.
Why keep measuring lactate after the test?
Because some analysis methods need the recovery curve. The Stegmann tangent method determines the individual anaerobic threshold via a point on the elimination curve. Without post-exercise values, it cannot be calculated. These values cannot be added afterwards.
Sources
- 1
Bentley DJ, Newell J, Bishop D. Incremental exercise test design and analysis: implications for performance diagnostics in endurance athletes. Sports Medicine. 2007;37(7):575–586.
- 2
Stockhausen W, Grathwohl D, Bürklin C, Spranz P, Keul J. Stage duration and increase of work load in incremental testing on a cycle ergometer. European Journal of Applied Physiology and Occupational Physiology. 1997;76(4):295–301.
Original researchDOI 10.1007/s004210050251PubMed 9349642
- 3
Stegmann H, Kindermann W, Schnabel A. Lactate kinetics and individual anaerobic threshold. International Journal of Sports Medicine. 1981;2(3):160–165.
Original researchDOI 10.1055/s-2008-1034604PubMed 7333753
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Fletcher GF, Ades PA, Kligfield P, Arena R, Balady GJ, Bittner VA, et al. Exercise standards for testing and training: a scientific statement from the American Heart Association. Circulation. 2013;128(8):873–934.
Position statementDOI 10.1161/CIR.0b013e31829b5b44PubMed 23877260
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Tanner RK, Fuller KL, Ross ML. Evaluation of three portable blood lactate analysers: Lactate Pro, Lactate Scout and Lactate Plus. European Journal of Applied Physiology. 2010;109(3):551–559.
Original researchDOI 10.1007/s00421-010-1379-9PubMed 20145946
Specialist information on the methods of performance diagnostics. No medical advice and no substitute for a sports medicine assessment before exercise tests.
Further reading
Protocol, raw values and model together.
Plenea records stage values, protocol details and the analysis model together in the report. This keeps it traceable later under which conditions you are comparing.