From a step test to lactate thresholds
Record the test
One row per stage, the lactate taken in the last 30 s. The resting sample is the row with intensity 0.
| intensity | lactate | heart_rate | rpe |
|---|---|---|---|
| 0 | 0.93 | 96 | 6 |
| 50 | 0.98 | 114 | 7 |
| 75 | 1.23 | 134 | 8 |
| … | … | … | … |
| 191 | 8.64 | 198 | 19 |
- recording_sheet()
- A printable sheet, a web form and a CSV template with these columns.
- read_recording()
- Reads the .xlsx of the form: stages, recovery, the athlete.
- demo_data
- The test above;
lactate_testshas 16 more, four sports.
A last stage not completed
Enter its time-weighted intensity: the last completed stage plus the increment × seconds done / seconds of a stage. Or leave it out with max_intensity.
Make tests comparable
Same diet and training in the 24 to 48 h before, same time of day, stages of 3 min or more, two or three stages below the first rise, the same sampling site, sample type and analyzer every time.
Sources and the strength of each point: the Best practices article.
Sports and units
| sport | Intensity | Also shown |
|---|---|---|
| cycling | W | per kg with a body mass |
| running | km/h | pace, min/km |
| swimming | m/s | pace, min/100 m |
| rowing | W | 500 m split |
Estimate every threshold
results <- lactate_threshold( demo_data, intensity, lactate, heart_rate, rpe_column = rpe, sport = "cycling" )
| Method | What it finds |
|---|---|
| Log-log | Where two lines through log lactate and log intensity cross |
| OBLA 2.0–4.0 | A fixed lactate, 2 to 4 mmol/L |
| Bsln+ 0.5–1.5 | 0.5 to 1.5 mmol/L above the resting value |
| Dmax family | The point furthest below a line to the last stage |
| LTP1, LTP2 | The turn points of three straight segments |
| LTratio, IAT | The lowest lactate / intensity; 1.5 mmol/L above it |
| Keul, Simon | Running only: where the curve rises 1.26 or 1 mmol/L per km/h |
| Stegmann | A tangent from recovery to the curve |
Useful arguments
- method
- Some methods only, e.g.
c("Dmax", "LTP") - fit
- The curve: polynomial (3rd or 4th degree) or B-spline
- sport
- cycling, rowing (W), running (km/h), swimming (m/s)
- ci = TRUE
- Bootstrap confidence intervals
- recovery
- Recovery samples and
stage_duration, for Stegmann - sample
- blood, plasma, sweat or interstitial fluid
- .by
- Many tests in one call, e.g.
.by = "athlete"
Fine-tune the methods
- fixed
- OBLA targets, mmol/L; default 2 to 4
- baseline_plus
- Bsln+ rises, mmol/L; default 0.5, 1, 1.5
- iat_rise
- The IAT rise above LTratio; default 1.5
- dmax_anchor
- Where the Dmax lines start and end
- ltp_breakpoints
- 1 for a test that stopped before LTP2
- max_intensity
- Leave out stages above it
Look, then check
autoplot(results) # every method autoplot(results, method = "ModDmax") # one method
One method: the curve, its line, and the threshold at 140 W.
- lactate_checks()
- A checklist of what is easy to miss: missing rest, a lactate dip, a final plateau
- lactate_diagnostics()
- Residuals, influential stages, how far each threshold moves without one stage
- lactate_fit_quality()
- Which curve predicts the stages best
Leave one stage out: red, the threshold rises without that stage; blue, it falls; dark, it rests on it.
