AnT

Definition

AnT — the Anaerobic Threshold — is the intensity above which lactate production outpaces lactate clearance. Below AnT, a well-trained runner can hold the effort for an hour or more. Above it, fatigue compounds quickly.

Across training systems the same boundary goes by several names: VT2 (second ventilatory threshold), MLSS (maximal lactate steady state), FTP (functional threshold power — cycling), Critical Speed, or T-pace in Daniels' terminology. They point at the same physiology from different angles.

Why it matters to runners

AnT defines the upper edge of what your aerobic system can sustain. Threshold workouts — runs at or slightly below AnT — are the most efficient way to push this edge higher, which in turn makes every pace below threshold feel easier.

But AnT work is only productive when the aerobic base beneath it is deep enough to hold the load. Prescribe threshold work to an athlete with Aerobic Deficiency Syndrome and you stack intensity on an unready system; the result is fatigue without adaptation, and often injury. This is why Your Pacer watches the ratio between AeT and AnT before any threshold work enters the plan.

When threshold work is appropriate, it comes in small, precise doses: 2–3 intervals of 8–12 minutes at T-pace, or a single 20-minute continuous piece. Longer sessions are not better. The benefit comes from repeat exposure at the right intensity.

How it's measured

Several converging methods:

• 30-minute time trial (Johnston): your average heart rate during a hard, steady 30-minute effort approximates AnT heart rate.
• Race result → VDOT (Daniels): a recent 5K–10K race gives VDOT, and VDOT tables give corresponding T-pace. This is the most reliable pace anchor once you have a race in.
• Lab test: blood lactate ramp or ventilatory gas analysis — most precise.
• 20-minute TT × 0.95 (Coggan): a cycling convention that works approximately for running power metrics.

When heart rate and pace from different methods disagree, the most productive thing to do is verify with a drift test during a steady run near the disputed HR. See the HR Drift Test page.

AeT / AnT ratio

The relationship between your two thresholds tells more than either one alone. A ratio of 0.90 or higher indicates a well-developed aerobic system that can safely support threshold work. A ratio below 0.90 is the signature of Aerobic Deficiency Syndrome — the base needs building before the ceiling gets raised.

Related terms

• AeT (Aerobic Threshold) — the lower boundary of aerobic-dominant metabolism.
• ADS (Aerobic Deficiency Syndrome) — when the gap between AeT and AnT is too wide.
• HR Drift Test — used to verify AeT and, less directly, AnT.

Further reading

• Daniels, Daniels' Running Formula — VDOT tables and T-pace prescriptions.
• Johnston & House — published writing on anaerobic threshold work (mountain-athlete coaching literature).
• Pfitzinger & Douglas, Advanced Marathoning — LT runs and medium-long runs built around threshold intensity.