Beyond the Numbers: Special Training Intensities, Part 2 (Threshold to Sprint)
Threshold, sub-threshold, Critical Power, VO2max and the anaerobic top end: the named training intensities at the hard end and what each one trains.
Part 1 covered the easy end: Fatmax, MAF, Zone 2, Tempo and Sweet Spot. Part 2 runs from threshold to the top. A zone number tells you how hard, a name tells you why.
Threshold and its tangle of names (LT2, FTP, MLSS, OBLA)
Where it sits: Zone 4, ~91–105% of FTP, the effort you can hold for about an hour.
What it is: the most important and most over-named landmark in endurance training. The labels point at the same place:
- LT2 / anaerobic threshold: where blood lactate starts climbing steeply.
- FTP (functional threshold power): the cycling shorthand for ~1-hour power.
- MLSS (maximal lactate steady state): the highest intensity you can hold without lactate drifting up. The gold standard, measured individually.
- OBLA (4 mmol/L): a fixed population-average proxy for the same thing.
They differ in how they are measured, not in what they chase. Full vocabulary in LT1, LT2 and LTHR explained.
Why train it: threshold is the best predictor of endurance performance and the most trainable. Set it with the FTP / power-zone calculator or LTHR zones.
Sub-threshold: the Norwegian "double threshold"
Where it sits: just below LT2, between high tempo and threshold.
What it is: controlled efforts kept under true threshold, often capped at 2–4 mmol/L lactate, sometimes twice in a day.
Why train it: a large volume of near-threshold work without the fatigue of going over the edge. Full detail in the Norwegian double-threshold method.
Critical Power / Critical Speed: your sustainable ceiling
Where it sits: very close to LT2/MLSS, derived differently.
What it is: Critical Power (Critical Speed for runners) fits several maximal efforts of different durations to a curve. It gives the highest intensity you can sustain aerobically, plus your finite anaerobic reserve (W′).
Why train it: a more individual threshold than a single 20-minute test, and often a better match for MLSS. Model yours on the Critical Power page.
VO2max: maximal aerobic power
Where it sits: Zone 5, ~106–120% of FTP, ~95–100% of max heart rate, sustainable for minutes.
What it is: the intensity that stresses maximal oxygen uptake, trained in hard 3–5 minute repetitions.
Why train it: to lift the ceiling of the aerobic system. Potent but costly, so small doses. This is the hard slice of polarized training.
Anaerobic capacity and neuromuscular power: the top end
Where it sits: Zone 6 (anaerobic capacity, ~121–150% of FTP) and Zone 7 (neuromuscular/sprint, maximal).
What it is: efforts of seconds to a couple of minutes, far above what the aerobic system supplies. Anaerobic capacity is tolerance for high-lactate efforts. Neuromuscular power is raw sprint force.
Why train it: surges, finishes, sprint power and running economy. Heart rate is useless this high, so govern these by power, pace or feel. Daniels' Repetition pace is the running version, which is why pace zones have intentional gaps up here.
Where they sit on the band
From threshold up:
- Sub-threshold (Norwegian): just under the line
- Threshold ≈ LT2 ≈ FTP ≈ MLSS ≈ Critical Power: the ~1-hour ceiling (Zone 4)
- VO₂max: maximal aerobic power, minutes long (Zone 5)
- Anaerobic capacity: seconds to ~2 min (Zone 6)
- Neuromuscular / sprint: all-out, seconds (Zone 7)
These cluster and overlap. Set your bands with the power, heart-rate or pace calculators, then aim each hard session at the right one.
Sources
- Allen & Coggan, threshold-family definitions (LT2, FTP)
- Mader, OBLA; MLSS research
- The Norwegian distance-running double-threshold method
- Monod & Scherrer and later two-parameter models, Critical Power
- Seiler, VO₂max and intensity distribution