Beyond the Numbers: Special Training Intensities, Part 2 (Threshold to Sprint)

In Part 1 we mapped the named training intensities at the easy end: Fatmax, MAF, Zone 2, Tempo and Sweet Spot. Each is a destination on the intensity band, defined by the adaptation it targets rather than its position in a numbered system. This second part picks up where threshold begins and runs to the top, covering the hard, sharp, time-limited efforts. The same idea applies. These names tell you why you're doing the effort, where a zone number only tells you how hard.

Threshold: and its tangle of names (LT2, FTP, MLSS, OBLA)

Where it sits: the boundary between sustainable and unsustainable. Roughly Zone 4, ~91–105% of FTP, the effort you could hold for about an hour.

What it is: the single most important landmark in endurance training, and also the most over-named. The labels all point at (or near) 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. This is the gold-standard, individually measured version.
• OBLA (4 mmol/L): a fixed population-average proxy for the same thing.

They differ in how they're defined and measured, not in what they're chasing. We untangle the full vocabulary in LT1, LT2 and LTHR explained.

Why train it: threshold is the best predictor of endurance performance, and the most trainable. Raise it and every sub-threshold pace gets easier. Set it with the FTP / power-zone calculator or LTHR zones.

Sub-threshold: the Norwegian "double threshold"

Where it sits: just below LT2, a hair easier than full threshold, between high tempo and threshold.

What it is: the intensity behind the Norwegian "double threshold" method. These are controlled efforts kept deliberately under your true threshold (often capped by lactate around 2–4 mmol/L), sometimes done twice in a day.

Why train it: it lets you accumulate a large volume of quality, near-threshold work without the deep fatigue of going over the edge. The restraint is the point. Staying just under the line is what makes the high volume repeatable. Full detail in the Norwegian double-threshold method.

Critical Power / Critical Speed: your true sustainable ceiling

Where it sits: very close to LT2/MLSS, but derived differently. It typically lands just around threshold.

What it is: Critical Power (or Critical Speed for runners) comes from a handful of maximal efforts of different durations, fitted to a curve. The result is the highest intensity you can sustain aerobically, plus your finite "anaerobic battery" (W′) for efforts above it.

Why train it: it gives you a more individual, physiologically grounded threshold than a single 20-minute test, and it tracks MLSS more reliably for many athletes. 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 only for minutes.

What it is: the intensity that stresses your maximal oxygen uptake. You train it in hard 3–5 minute repetitions with recovery. It sits well above threshold and is genuinely hard.

Why train it: to lift the ceiling of your aerobic system. A bigger VO₂max raises the roof that threshold and everything below sit beneath. It's potent but costly, so use it in small, sharp doses. This is the "hard" slice of polarized training.

Anaerobic capacity and neuromuscular power: the top end

Where it sits: the very top. Zone 6 (anaerobic capacity, ~121–150% of FTP) and Zone 7 (neuromuscular/sprint, maximal).

What it is: efforts measured in seconds to a couple of minutes, far above what your aerobic system can supply. Anaerobic capacity is your tolerance for high-lactate efforts. Neuromuscular power is raw sprint force and coordination.

Why train it: anaerobic work sharpens repeatability for surges and finishes. Neuromuscular work builds sprint power, running economy and stride/pedal force. Heart rate is useless this high. These efforts are governed by power, pace or feel, not the number on your wrist. (Daniels' Repetition pace is the running expression of this end; see why pace zones have intentional gaps up here.)

Where they sit on the band

From the 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)

As at the easy end, these cluster and overlap rather than tiling neatly. They're targets you aim at for a specific adaptation, not a tidy partition of the range. Set your bands with the power, heart-rate or pace calculators, then aim your hard sessions at the right named intensity.

That completes the tour. Part 1 covers Fatmax through Sweet Spot; together they map the intensities that matter most between the lines of the numbered zones.

Sources

The threshold-family definitions (LT2, FTP, MLSS, OBLA) follow Allen & Coggan and the lactate-threshold literature (Mader on OBLA; MLSS research). The double-threshold approach reflects the Norwegian distance-running method. Critical Power follows Monod & Scherrer and later two-parameter models. VO₂max and intensity-distribution rationale draw on Seiler.