FTP, Threshold, and Why Your Zones Are Probably Wrong

The Threshold Terminology Mess

Every endurance coach, physiology textbook, and training app uses a different word for roughly the same thing. FTP. Lactate threshold. Anaerobic threshold. LT1. LT2. Critical power. MLSS. Maximum metabolic steady state. If you have ever tried to figure out which one to use as the basis for your training zones, you have probably given up and just accepted whatever number your Garmin or Zwift spat out.

That is a mistake, and it is not your fault. The field is genuinely confused. Terms that were coined in lab settings got borrowed by coaches, compressed into product UI, and layered on top of each other until the original meanings were almost unrecognizable. Most athletes are training to numbers that are a loose approximation of a concept that is itself a simplification of the actual physiology.

Here is what each term actually means.

Term	What it measures	How it is assessed	Practical significance
LT1 (first lactate threshold)	Intensity at which blood lactate first rises above resting	Lab blood sampling during graded test	Defines the top of true "easy" — zone 2 ceiling
LT2 (second lactate threshold)	Intensity at which lactate accumulation starts to outpace clearance	Lab blood sampling during graded test	The physiological basis for "threshold" training
MLSS / MMSS	Maximum intensity you can sustain without lactate rising continuously	Lab protocol, usually 30-min at fixed intensities	Often used interchangeably with LT2, slightly below FTP
Anaerobic threshold (AT)	Older term, originally meant to describe the same inflection as LT2	Field or lab estimate	Widely misused; sometimes means LT2, sometimes something else entirely
FTP (functional threshold power)	Highest average power you can sustain for ~60 minutes	20-min or ramp test in field	A field proxy for LT2/MLSS — practical, not physiological
Critical power (CP)	Mathematical model of the power-duration relationship	Derived from multiple time-trial efforts	More theoretically precise than FTP; higher than MLSS in most athletes
LTHR (lactate threshold heart rate)	Heart rate corresponding to LT2 / functional threshold	30-min field test or Garmin auto-detect	The HR-based equivalent of FTP for zone anchoring

The crucial thing to understand: LT2, MLSS, and FTP are not interchangeable, but they are close neighbors. LT2 and MLSS sit slightly below FTP in most athletes, because one-hour power requires a small contribution from anaerobic systems. Critical power sits slightly above FTP in most athletes. For zone calculation purposes, the distinction matters less than you think — the real problem is that most athletes are not accurately measuring any of them.

That is where the zone errors live.

Why Default Zones Are Wrong for Almost Everyone

Every power zone system and every heart-rate zone system is built on a threshold anchor — a number that represents your individual ceiling of sustainable intensity. Multiply or divide that anchor by fixed percentages, and you get zones 1 through 5, 6, or 7, depending on whose system you are using.

The problem is twofold. First, the anchors are wrong. Second, even if the anchor were right, the fixed percentages do not fit every physiology.

Where Coggan power zones came from

The Coggan zone system — the one Garmin, TrainingPeaks, and most cycling apps use — was developed for trained cyclists and calibrated against the physiology of trained cyclists. The percentages (55%, 75%, 90%, 105%, 120% of FTP) were reasonable averages for that population. If you are a different kind of athlete — a runner who also cycles, a masters athlete, a time-trialist versus a criterium racer, someone with unusual lactate dynamics — the percentages do not automatically apply to you.

Where %LTHR zones came from

The Joe Friel %LTHR zones for running and cycling were similarly derived from observations of trained endurance athletes in field conditions. The numbers — say, zone 2 at 85-89% of LTHR, zone 3 at 90-93% — represent population averages, not universal physiology. Some athletes have a very compressed LT1-to-LT2 range and will be doing legitimate threshold work at 88% of LTHR. Others have a wide range and zone 3 at 90% feels like easy aerobic work.

The three most common wrong-zone patterns

Pattern 1: FTP set too high. You tested at peak form — rested, motivated, ideal conditions — and everything since has been based on that number. Now zone 4 intervals feel like zone 5, you are grinding through threshold sessions, and your "easy" runs are actually moderate. All your zone statistics are shifted upward. If you suspect this, use the FTP estimator to cross-check your test value against your recent ride data before assuming your training is right.

Pattern 2: FTP set too low. You estimated rather than tested, or tested fatigued. Zone 2 feels genuinely easy — because it actually is zone 1 for your physiology. Your aerobic base work is not providing the right stimulus, and you wonder why training seems ineffective.

Pattern 3: Using cycling zones for running without adjustment. Threshold heart rate in running is typically higher than in cycling for the same athlete — more muscle mass engaged, different postural demands. Your cycling LTHR is not your running LTHR. Using one for both is guaranteed to misplace your running zones.

How to Find Your FTP Accurately (Cycling)

The 20-minute FTP test is the most widely used field protocol in cycling. It is also frequently misapplied.

The protocol: After a proper warm-up (20+ minutes with some high-intensity priming efforts), ride as hard as you can sustain for exactly 20 minutes. Take 95% of your average power for those 20 minutes. That is your estimated FTP.

The 95% multiplier is not a law of physiology. It is an approximation that works reasonably well for athletes who can pace a 20-minute effort accurately. Athletes who go out too hard and fade underestimate FTP. Athletes who conserve and sprint the last two minutes overestimate it. Athletes who are very good at anaerobic efforts produce a 20-minute number that skews higher than their actual 60-minute sustainable power, making the 95% correction insufficient. The FTP testing guide for cyclists covers each protocol in detail — but the main takeaway is that pacing is the variable most people get wrong.

Alternative protocols

The 8-minute test. Two maximal 8-minute efforts, 10 minutes recovery between, with FTP estimated at 90% of the average of both. Better for athletes who struggle to pace 20 minutes, but sensitive to pacing errors and anaerobic capacity.

The ramp test. Start easy, increase power by a fixed increment every minute (typically 20W), ride until failure. FTP is estimated at 75% of the final one-minute power. Ramp tests are repeatable and emotionally easier, but tend to overestimate FTP in athletes with high anaerobic capacity and underestimate it in very efficient diesels. Zwift and Wahoo have made the ramp test ubiquitous; that does not mean it is the most accurate protocol for every athlete.

Real-world validation

Your best validation tool is actual training performance. If you can sustain zone 4 intervals (91-105% of FTP) for 10-15 minutes at a time and feel genuinely maximal at the end, your FTP is in the right neighborhood. If zone 4 feels like a sprint in the first interval, your FTP is set too low. If you cannot hold zone 4 for 8 minutes, it is set too high.

Seasonal drift matters. FTP in February after a training break is not FTP in June after 16 weeks of structured build work. Testing once and riding that number for a full year is a common mistake. Quick cross-check with your recent data here if you have not tested recently.

A reasonable testing cadence: every 6-8 weeks during an active training block. At the transition between base and build phases. After any training break longer than 3-4 weeks. More on timing in the periodization section below.

How to Find Your Running Threshold Accurately

Running threshold is its own thing, even for the same athlete at the same fitness level. The physiology is different. The testing is different. And almost every running zone error traces back to borrowing a cycling number without adjustment.

The 30-minute LTHR field test

The gold-standard field protocol for running threshold heart rate is a 30-minute time trial at maximum sustainable effort, with the average heart rate over the final 20 minutes taken as your LTHR. This aligns with Garmin's lactate threshold detection methodology and produces a number you can use to anchor HR-based running zones.

Run this on a flat surface, no wind, when fully rested. Calibrate your HR zones afterward, not from memory of last year's test.

Why running LTHR is higher than cycling LTHR

For the same athlete at comparable fitness, running threshold heart rate is typically 8-12 bpm higher than cycling threshold heart rate. The mechanism is straightforward: running engages more total muscle mass and involves significant eccentric load that cycling does not. More muscle mass working = more cardiovascular demand at the same metabolic output = higher heart rate.

This means: if you set your running zones from your cycling LTHR, every zone is shifted too low. You will "be in zone 4" for runs that are actually your zone 3, and you will think you are running high-intensity sessions when you are actually doing moderate work. The training stress is miscategorized, and so are your Garmin zone statistics.

Critical velocity and running power threshold

Critical velocity — the running analog of critical power — is the highest speed you can sustain without continuous fatigue accumulation. It is slightly faster than your threshold pace and can be estimated from race performances using the power-duration model.

Running power threshold is available through Garmin's running dynamics and gives you a watts-based anchor for running zones, analogous to FTP in cycling. It is particularly useful for athletes who train across both sports and want a single power-based framework. One important note: running power watts are not comparable to cycling power watts. The numbers are in the same units but measure different things against different baselines. See the cycling vs. running power comparison for the full breakdown.

Sport-specific zone setup

The practical implication: set up your zones separately for cycling and running. Garmin supports this natively — the HR zone setup guide covers how to configure sport-specific zones. Alternatively, use the heart rate zone calculator to anchor zones from your test-derived LTHR for each sport independently.

Validating That Your Zones Actually Work

Testing gives you a starting number. Reality tells you whether that number is right.

The most useful validation is the subjective feel at threshold intensity. True threshold — zone 4 in most systems — should feel like a pace or power you could sustain for 30-45 minutes, but not much longer, and only by giving it genuine effort. Not a sprint. Not comfortable. A sustained hard effort that takes focus and control.

If zone 4 feels like you could hold it for two hours, it is not your zone 4. If zone 4 feels like a 2-minute maximal effort, it is above your threshold.

The 30-minute sustainability test

A practical check: pick a power or pace that should represent the top of your zone 4 (around 100% FTP or threshold pace). Hold it for 30 minutes. If you complete it comfortably and could have done another 10-15 minutes, your threshold is set too low. If you are struggling at 20 minutes and collapse at 25, it is set too high. The right threshold number should be right at the edge of sustainable — you finish, but barely, and you know you could not have held it another 15 minutes.

Validating against race data

Actual races are your cleanest validation. Average power or pace in a 40km time trial, a 10km running race, or a one-hour criterium gives you real-world evidence of what you can actually sustain. If your FTP is 250W but your average power in a rested one-hour effort was 220W, your FTP is too high. If your FTP is 250W and your one-hour race average was 260W, it needs to go up.

When to retest

Every 6-8 weeks during an active training block
At the base-to-build transition
After any break longer than 3 weeks (retesting will almost certainly show FTP declined)
After a major race block (FTP may be temporarily suppressed by accumulated fatigue — wait 10-14 days post-peak before retesting)
Seasonally if you have an off-season, before starting the next training year

Periodizing Around Threshold Progression

Your threshold is not a fixed property. It moves with training, and understanding how it moves across a training block determines how aggressively to chase it.

Threshold is a lagging indicator of aerobic fitness. You build the aerobic engine first — mitochondria, capillaries, cardiac stroke volume — and threshold catches up as those adaptations compound. This is why impatient athletes who skip base phase and jump to threshold intervals find that their FTP does not improve the way they expected: the infrastructure that would support a higher FTP is not yet built.

Base phase: slow FTP rise from volume

During a well-executed base phase, FTP typically rises slowly — 2-5% over 8-12 weeks — even without specific threshold work. The mechanism is improved fat oxidation, more efficient lactate clearance at submaximal intensities, and cardiac adaptations. You are not training FTP directly; you are building the foundation it sits on.

The base phase of periodized training is the correct time to establish an accurate FTP baseline. Test at the start of base, then again at the start of build, and you will have a clean before/after comparison that tells you how much the base work produced.

Build phase: faster FTP rise from targeted threshold work

Build phase is where FTP moves most aggressively. Threshold intervals (2x20 minutes at FTP, 4x10 minutes at 95-105% FTP) and over-under work (alternating just below and just above threshold) are the primary tools. When stacked on a solid aerobic base, these workouts can produce 5-10% FTP gains over 6-10 weeks. See how Garmin structured workouts support threshold training for the practical setup.

A well-managed build phase produces consistent "Productive" or "Peaking" training status on Garmin, alongside a measurable FTP increase that you can validate with the FTP estimator between formal tests.

Peak and taper: FTP holds or slightly drops — this is normal

Here is a misconception that causes real panic. During a well-executed taper, FTP often appears to drop slightly. Accumulated fatigue from the build block is suppressing performance. The fitness is still there; it is masked by fatigue. Race day, when fatigue clears, athletes frequently post their best-ever normalized power or pace at threshold effort.

Do not retest FTP during or immediately after taper. The number will mislead you. Wait 10-14 days post-race before testing again in the recovery phase.

Common Threshold Errors Across Cycling and Running

These are the mistakes that make test results unreliable, zones inaccurate, and training cycles frustrating.

Testing fatigued. The most common. You do a threshold test in week 3 of a hard build block, mid-overreach, and wonder why your FTP seems lower than last time. It is — not because your fitness dropped, but because fatigue is suppressing the expression of your fitness. Always test rested: 2-3 days of very easy training before any threshold test.

Testing in heat. Cardiovascular drift in heat means your HR is higher and your sustainable power is lower at any given intensity. Heat-adjusted FTP is not your actual FTP. Test in a controlled environment, or on an indoor trainer, and acknowledge that outdoor summer numbers will always be lower.

Testing after alcohol or poor sleep. Either suppresses performance by 5-10% in most athletes. Not enough to cause catastrophic deviation, but enough to make a test invalid if precision matters.

Using a too-short test. The 5-minute "FTP" estimates that some apps produce from very short hard efforts are almost useless. At 5 minutes, you are primarily measuring aerobic power capacity and anaerobic capacity together, not sustainable threshold power. The test is too short to separate them.

Assuming both sports have the same threshold. Even the most experienced triathletes sometimes forget that cycling and running threshold are not the same number in the same units. Cross-sport zone calibration is one of the most common sources of miscategorized training stress.

Ignoring cadence in cycling. A 250W effort at 70 rpm produces different physiological stress than 250W at 95 rpm. Threshold zone training at uncharacteristically low cadence can feel harder than the power suggests. When establishing FTP, match the cadence you plan to train at.

Integration with Training Load and Zone Distribution

This is where threshold accuracy has the largest downstream impact.

Every zone is anchored to threshold. If your FTP is wrong, all of your power zones are wrong by the same percentage. If your LTHR is wrong, all of your HR zones are wrong. A 10% FTP error does not affect just zone 4 — it shifts every zone 10%, from zone 1 through zone 6.

The practical consequence: your zone distribution data in Garmin becomes unreliable. If FTP is set 10% too high, sessions you think are zone 2 base work are actually zone 1 recovery. Sessions you think are zone 4 threshold work are actually zone 3 tempo — the "gray zone" that is too easy for meaningful high-intensity adaptation but too hard to function as recovery. You cannot read your training distribution accurately, so you cannot make good decisions about intensity balance.

Training load calculations are affected too. Garmin's training load is derived from heart rate and/or power compared to your threshold values. A misanchored threshold distorts training load numbers, load ratios, and ultimately the "Productive" vs. "Unproductive" training status calls. You can end up with a Garmin that consistently shows "Productive" while you are actually doing unproductive gray-zone training, because the underlying zones are miscalibrated.

This is why accurate threshold — for cycling power, running HR, and running power separately — is the first thing to get right before reading any other Garmin metric. Everything downstream of it depends on it.

Zone 2 training in particular is almost impossible to calibrate correctly without an accurate LT1 estimate. Most zone 2 cutoffs are defined relative to threshold (typically around 75% of FTP or 83-85% of LTHR). If threshold is wrong, zone 2 is wrong. See the zone 2 training guide with Garmin for how this plays out in practice.

When Continuous Data-Driven Calibration Helps

Manual retesting every 6-8 weeks gives you discrete snapshots of your threshold. Between tests, your threshold is drifting — usually upward during a build block, sometimes downward after illness or time off — and your zones are slowly going stale.

A coach watching your data continuously would notice this drift before you do. They would see that your power in threshold sessions is consistently sitting 8-12W above your prescribed zone 4 ceiling. They would see that your RPE notes say sessions feel easy. They would adjust your zones without waiting for a formal retest.

This is the specific thing Gneta does with your Garmin data stream. Rather than waiting for you to schedule a test, the system detects threshold drift from the pattern of your actual workouts — the sustained power you hold in hard efforts, the heart rate responses to structured sessions, the performance condition scores. When the evidence suggests your zones have moved, it surfaces that insight and can adjust your zone anchors accordingly.

This is not a replacement for rigorous testing when precision matters — before a key build block or an important race target, test properly. But between tests, continuous calibration means your daily training zones stay closer to reality than a number you set three months ago and have not revisited.

For most self-coached athletes, the combination works best: a formal test at the block transitions, and data-driven drift detection in between. You can explore how Gneta reads your power and threshold metrics and see how it compares to manually-managed platforms like TrainingPeaks.

Getting This Right

The threshold terminology mess is real, but it resolves into a simple practical hierarchy.

First: Understand that LT2, MLSS, and FTP are close neighbors, not the same thing, and for practical zone work the distinction matters less than test accuracy.

Second: Test sport-specifically. Cycling FTP and running LTHR are different numbers for the same athlete, and both require their own tests and their own zone calculations.

Third: Validate your zones against reality — the feel test, the 30-minute sustainability check, actual race data. Numbers from a test are a starting point, not a verdict.

Fourth: Retest on a schedule aligned to your training phases, not once a year when you happen to think of it.

Fifth: Read your Garmin zone data knowing that everything in it depends on the accuracy of your threshold anchor. Get that right first, and the zone distribution, training load, and training status metrics become reliable. Get it wrong, and all of that data is drifting on an inaccurate foundation.

The FTP estimator tool can get you a quick calibration check from recent power data. The HR zone calculator anchors your heart-rate zones from a proper LTHR field test. Between those tools, the testing protocols above, and sport-specific calibration, you have everything you need to stop training to default numbers that probably do not apply to you.

Accurate zones are not a detail. They are the foundation of every training decision you make.

If you want an AI coach that keeps your threshold calibration current from continuous data rather than waiting for you to schedule a test, see how Gneta works or explore plans and pricing.

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