Lactate Threshold Running Guide
Garmin auto-LT says 4:25/km at 165 bpm. Your last honest 30-minute test averaged 4:35/km at 171. Training off the wrong number turns tempo into VO2 work. Lactate threshold (LT) is the highest intensity you can sustain while clearing lactate roughly as fast as you produce it — roughly 30–60 minutes hard for trained runners.
Field Test Before Watch Faith
30-min TT: full warm-up, then 30 min hardest sustainable effort; LTHR ≈ average HR of the last 20 minutes; LT pace ≈ average pace of the full 30. Prefer this when watch LT and recent tempo disagree. Zones from LTHR usually beat 220−age — see LTHR vs Max HR and the HR Zones Calculator.
Worked Scenario: Last-20 HR 168
Athlete finishes a controlled 30-min test: last-20 HR 168 bpm, full-30 pace 4:20/km. Tempo sessions target ~4:20–4:25/km on cool flats, or hold near 168 bpm when heat rises. Friel-style Zone 2 ≈ 85–89% of 168 → ~143–150 bpm. Cross-check race fitness with the Race Predictor and continuous sessions in the Tempo Run Guide.
Do not update every training zone from one hot, hilly auto-LT detection, and never copy bike LT HR into running. Sandbagging or blasting the field test both warp LTHR — the effort must be honestly sustainable, not a disguised 5K.
Train Around LT Without Burying It
- Continuous tempo: 20–40 min near LT
- Cruise intervals: 3–5 × 8–10 min at LT, short jog recoveries
- Keep most other mileage easy so LT sessions stay sharp
Pace leads on cool flats; HR catches cost when the same pace becomes reckless. Retest every 6–8 weeks in a build.
Pace and HR Together
On cool flats, LT pace is the primary target. In heat or on tired legs, the same pace can overshoot physiology — hold near LTHR instead and accept slower splits. Enter the field-test LTHR into your watch so Zone 2 and tempo alerts stop fighting each other mid-week.
Decision Rule
If watch LT pace is more than a few seconds/km faster (or several bpm lower) than a recent controlled field test or race-effort tempo, train from the field test until you retest. If they agree within a small band, use pace on cool days and HR as the governor in heat.