Threshold step test

LT2 Step Test

Log each interval of a stepped threshold run. The chart plots lactate, heart rate, and RPE against pace and marks an estimated LT2 pace and heart rate.

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What’s this for? What LT2 is, why it matters, and how to find it

LT2, the second lactate threshold, is the fastest pace you can hold before blood lactate stops leveling off and starts climbing steadily. Below it, your body clears lactate about as fast as it produces it. Above it, lactate and acidity build quickly and fatigue arrives within minutes rather than hours. For trained runners it sits close to the pace they could race for about an hour. You’ll also see it called the anaerobic threshold or simply “threshold,” and it’s closely related to maximal lactate steady state (MLSS).

For training

  • Sets the pace and heart rate for threshold and tempo work, so those sessions hit the intended intensity instead of drifting too hard.
  • Anchors your other training zones, which helps keep easy days easy.
  • Retesting every few months shows whether your aerobic fitness is improving, even without a race.

For racing

  • Gives you a ceiling for pacing longer races. Half marathon pace sits near or just under LT2, and marathon pace well below it.
  • Going over LT2 early in a long race is a common cause of a late fade.
  • Helps set realistic goal paces from your current fitness rather than a past result.

Three ways to estimate it

  • Blood lactateMost reliable

    Measures what LT2 is actually defined by, using finger or earlobe samples taken during a step test like the one below. It’s by far the most reliable option, though readings still need consistent conditions: a clean, sweat-free sample, similar fueling, and the same meter.

  • Heart rateModerate

    Heart rate rises fairly steadily with pace, so the bend at LT2 is often hard to see, and heat, fatigue, hydration, and caffeine all shift it. Most useful once you’ve anchored it to a lactate test.

  • RPELeast reliable

    LT2 often feels “comfortably hard,” where you can only speak in short phrases. Finding it with any real accuracy takes deep familiarity with your body, usually built over years and checked against lactate or race results.

Suggested protocolPace ladder 5:00 intervals, 90 s recovery, 10 s/mi faster each step
  1. Warm up. 15 min easy running.
  2. Recover 2–3 min. If you're measuring lactate, take a baseline reading now. That's rep 0.
  3. Run 5:00 intervals with 90 s recovery. Start 20–30 s per mile slower than your predicted threshold pace and run each interval 10 s per mile faster than the last.
  4. Record during each recovery. Lactate as soon as you stop, then average and final-minute heart rate and RPE for the interval.
  5. Confirm any spike. If lactate, heart rate, or RPE jumps sharply, repeat the same pace to confirm the reading.
  6. Go one step past. Once a second rep confirms the jump, run one more faster interval to get a reading past threshold, then stop.
  7. Cool down. 10–15 min easy.

Pace ladder

/mi

    Enter a pace to see the steps.

    Intervals

    Pace
    RPE

    Rep 0 · baseline lactateOptional. Taken after the warm-up and used as a reference line on the chart.

      Each interval needs a pace plus lactate, heart rate, or RPE, and at least one of those must be recorded on every interval. “Add interval” fills in the next step 10 s/mi faster; “Repeat pace” adds a confirmation rep. Mark an interval as an outlier to keep it on the chart but leave it out of the estimate. Completely blank intervals are ignored until you fill them in.

      HR from
      mmol/L
        How each method works
        Modified Dmax (default)
        Fits a cubic curve to lactate against speed. A straight line runs from the last pace before lactate first rose by 0.4 mmol/L or more to your fastest pace. LT2 is the point on the curve farthest below that line. After Bishop et al. (1998).
        Dmax
        Same curve, but the line runs from your slowest pace to your fastest. Its line is less steep, so it usually lands at a slower pace than Modified Dmax. After Cheng et al. (1992).
        Fixed lactate
        The pace where lactate first crosses the value you set, interpolated between intervals. 4.0 mmol/L is the classic OBLA marker, but individual LT2 values vary widely, so treat this as a reference.
        RPE and HR breakpoints
        Two straight lines are fitted to the metric against speed, testing every split point. LT2 is where the best-fitting pair meets. Needs readings at 4 or more paces. These are rougher than the lactate methods; heart rate deflections in particular don't show up reliably in everyone.

        Repeated paces are averaged before any fitting. LT2 heart rate, lactate, and RPE are read off your data at the estimated pace by interpolating between neighboring intervals. Outliers stay on the chart as hollow markers and are ignored everywhere else.