Most Athletes Think They’re Training Zone 2, But They’re Actually in Zone 3. Here’s Why That Kills Your Progress

Understanding training intensity has become the holy grail for endurance athletes.

Yet despite all the technology strapped to our wrists and chests, most runners and cyclists still can’t answer one fundamental question with confidence: Am I actually training in zone 2?

In a recent conversation, Anar Vikmaa, mechanical engineer and founder of TimeWear, explained why traditional metrics like heart rate and power have been leading athletes astray—and why ventilation measurement might finally solve the decades-old problem of accurate intensity tracking.

The implications for both performance and longevity are profound.

The Zone 2 Problem Nobody’s Talking About

Zone 2 training has exploded in popularity among older athletes and longevity enthusiasts. The promise is compelling: maximize fat oxidation, build aerobic base, and create the foundation for all other training.

But there’s a massive problem lurking beneath the surface.

A lot of people struggle with zone 2 is that they’re actually in zone 3 and then you’re sort of past this point of fat starting to drop.

Vikmaa explained that zone 2 represents an intensity where working muscles predominantly use fat as fuel, sustainable for hours. The upper limit is called VT1 (first ventilatory threshold), also known as the aerobic threshold.

Cross that threshold, even slightly, and everything changes.

In the lab you can see this super clearly. You can just see below VT1 fat max carbs are quite low. You make that transition and it doesn’t have to be a very big transition and then you just see it flip and then now the body is no longer adapting to improving the fat oxidation.

The body switches to improving carbohydrate consumption efficiency instead—a valuable adaptation, but extremely limited in scope.

Why Heart Rate Has Been Lying to You

Heart rate became the dominant training metric for one simple reason: it was available.

When Polar released the first wearable heart rate chest strap between 1978 and 1980, research publications and patent applications exploded. Breathing measurement research, which had been developing in parallel, essentially plateaued.

But availability doesn’t equal accuracy.

Heart rate primarily maps to oxygen consumption, Vikmaa explained. Zone 2, however, is fundamentally about carbohydrate metabolism, CO2 production, and lactate—not oxygen.

The confounders are extensive:

• Heat and humidity
• Elevation changes
• Fatigue state
• Life stress
• Dehydration
• Caffeine intake
• Sleep quality

Heart rate is acting independently. That might be because you are now needing to cool yourself, right? So your core temperature is rising a little bit. You’re pushing out more blood into the capillaries and the small blood vessels to cool. You might be getting a little bit dehydrated.

The phenomenon of cardiac drift demonstrates the problem perfectly. During long workouts, heart rate climbs 10-15 beats while metabolic workload remains stable—even decreasing slightly.

Athletes see rising heart rate and assume they should slow down. But the signal is telling them something completely different: perhaps they need better hydration, fueling, or sleep—not a slower pace.

The Power Meter Trap

Power meters revolutionized cycling in the early 2000s. The concept of FTP (Functional Threshold Power)—essentially your one-hour maximum effort—gave cyclists a stake in the ground.

But FTP and its percentage-based zones share the same fatal flaw as heart rate zones: they’re not physiological.

The individual response of what my FTP is or what my 65% of heart rate reserve means for me is very different than what it means physiologically than what it means for you or anyone else.

Research has proven this spectacularly. Randomized controlled trials with thousands of participants show that using power or heart rate based zones produces a 40-60% non-responder rate.

Read that again: 40-60% of people doing the prescribed work don’t improve their fitness.

Two athletes training at the same percentage of their FTP or max heart rate can be in completely different physiological zones, getting dramatically different training effects.

The Lactate Limitation

Continuous lactate monitors seemed promising when they started appearing. But lactate measurement has its own complications.

Lactate is actually a fuel source—half of a carbohydrate molecule that muscles can consume for energy. It’s not harmful; supplement companies are now creating lactate-based fueling products.

The measurement challenges are significant.

Muscle production of lactate is 10-20x higher than what appears in blood. Getting lactate from muscle to blood to interstitial fluid (where wearables measure) creates cascading gradients and time delays.

Kilian Jornet has this anecdote where he was at the UTMB with a lactate of like 12 or something like that. There’s no way you’re, you know, 13 hours into a race and you have a lactate of 12.

During ultra-endurance events, lactate can accumulate in the blood simply because it’s constantly being produced and partially consumed, floating around without indicating current intensity.

Elite athletes require 15-20 minute steady-state stages in lab testing just to get accurate lactate readings because their consumption efficiency is so high.

Why Ventilation Changes Everything

Ventilation measurement attacks the problem from a completely different angle.

Everything going into and out of working muscles must pass through the lungs. Oxygen consumption and CO2 production—the actual metabolic markers of intensity—create a direct, measurable relationship with breathing.

If you breathe in oxygen you’re breathing in oxygen because your muscles are demanding it. And if you’re breathing out CO2 you are breathing out CO2 because your muscles are producing it.

The body is extremely sensitive to CO2 accumulation. It must evacuate CO2 quickly to maintain blood pH balance. This creates a fast, responsive signal directly tied to carbohydrate metabolism.

When athletes transition from fat oxidation to carbohydrate oxidation at VT1, CO2 production increases relative to oxygen consumption. Ventilation must rise to meet the evacuation demand.

This physiological requirement creates measurable inflection points—VT1 and VT2—that appear in ventilation data with remarkable clarity.

The Stability Advantage

During steady-state exercise below VT1, something remarkable happens.

Heart rate drifts upward 15-20 beats due to heat, dehydration, and cardiovascular fatigue. Power or pace declines as muscles fatigue. But ventilation remains stable—even decreases slightly as metabolic efficiency improves.

Athletes training in hot, humid conditions report transformative experiences. In Singapore’s 80% humidity and 105°F temperatures, heart rate numbers from indoor lab tests become completely useless outdoors.

They say that they’ve transformed their training because the ventilation stays consistent. They allow heart rate to go up. They allow power to drop importantly because in those scenarios the power is going to drop even more.

This creates confidence to train at the correct physiological intensity regardless of external conditions, leading to more consistent training and better race results.

How TimeWear Vita Pro Measures Ventilation

TimeWear’s approach measures chest cavity expansion and contraction during breathing.

The device tracks two critical variables:

• Breathing rate (breaths per minute)
• Tidal volume (volume per breath, measured via circumference change)

Multiplying these together produces minute ventilation—the total volume of air exchanged per minute, which maps directly to metabolic workload.

This is crucial because breathing rate alone is insufficient. Many runners entrain their breathing to cadence—4 steps inhale, 4 steps exhale at easy pace; 3-3 at moderate; 2-2 at hard efforts.

When breathing rate is fixed, tidal volume automatically adjusts to meet ventilation demand.

If you decide to breathe at a 2-2, 3-2, 4-2 whatever, in order to match that demand the breathing mechanism will respond by the tidal volume will shift accordingly.

Try this yourself: after a long run, attempt to slow your breathing rate to pre-run levels while walking. It becomes extremely uncomfortable because the body still needs to evacuate CO2.

Establishing Your Personal Thresholds

The first step with TimeWear involves a threshold test—a ramp protocol from low to maximum intensity.

This test establishes individual VT1 and VT2 markers along with associated metrics: ventilation at each threshold, heart rate, pace, and power at those transition points.

These thresholds are highly individual and don’t correlate with VO2 max.

You can have two people with identical VO2 maxes with dramatically different VT1 or top of zone 2 transition points and that’s why it’s so important to measure where this point occurs physiologically.

World Tour cyclists might have VT1 occurring above 90% of most people’s VO2 max. Someone with relatively low fitness might struggle to run at all below their VT1, requiring walking, hiking, or incline treadmill work to stay in zone 2.

The test also reveals where improvement opportunities exist. Low VT1 as a percentage of VO2 max indicates massive potential for base building. High VT1 suggests the ceiling (VO2 max) is the limiting factor.

The Training Zone Transformation

Many athletes experience profound realizations when they discover their true VT1.

Fit individuals with high VO2 max but relatively low VT1 find it easy to override their threshold. Running faster than VT1 feels comfortable and doable, so they spend enormous training volume there.

They’re not getting the adaptation that VT1 and below gives which is that fat oxidation improvement that base building and when they make that realization of where VT1 actually is and they change their training around to actually target that zone appropriately then you start to see base building really start to happen.

The feedback is consistent: athletes who correctly identify and target VT1 report exploding through previous plateaus, improved durability, better race times, and more enjoyable training.

For lower-fitness individuals, the revelation cuts the other way. Running itself might push them above VT1, creating a negative feedback loop where they improve carbohydrate metabolism (limited adaptation potential) while neglecting aerobic base.

Walking, hiking, and incline treadmill work become legitimate training that systematically builds the foundation for future running at appropriate intensities.

The Durability Connection

Durability—the ability to maintain power or pace at the same physiological cost over time—increasingly determines race outcomes.

Laboratory protocols measure durability by assessing VT1 when fresh, running a two-hour protocol at 90% of VT1 output, then reassessing. The difference represents durability decline.

VT1 training is key for developing durability.

If you neglect the VT1 training then the muscles don’t adapt to improving that limit and then it maybe stagnates or sort of erodes a little bit and that can be the difference maker.

In cycling races with multiple climbs, the front group shrinks with each ascent. The riders remaining at the final climb share one characteristic: superior durability developed through proper base training.

They’ve preserved carbohydrates through efficient fat oxidation in early efforts, maintaining high oxidation rates of both fuels when others begin depleting and dropping off.

Breathing Rate and Perceived Effort

An intriguing phenomenon emerges during long, steady efforts.

Minute ventilation remains stable. Power might drop. Heart rate drifts upward. But breathing rate gradually increases while tidal volume decreases.

This occurs because breathing rate closely tracks perceived exertion.

As hours pass, effort perception increases even though metabolic workload hasn’t changed. The central nervous system increases breathing rate in response. This doesn’t affect minute ventilation because tidal volume compensates.

The breathing muscles themselves—the diaphragm and intercostals—fatigue like any other muscle. As they tire, the body defaults to easier but less efficient breathing patterns: higher rate, lower volume.

This suggests potential for respiratory muscle training to delay this response, potentially reducing perceived exertion during prolonged efforts.

The Technology Challenge

Vikmaa’s background in prosthetics and exosuits for military applications provided crucial insight: measuring metabolic output with precision was possible but required face masks and metabolic carts.

Making ventilation measurement practical for consumer use required technological breakthroughs.

It’s really only in the last few years where we’ve had certain sensing technologies that have come online and have kind of met economies of scale to enable these price points.

Current challenges involve form factor rather than fundamental measurement. Very tight clothing or heavy backpacks pressing on sensors can introduce artifact, though most running vests and packs don’t cause issues.

The company continues developing designs to handle even these edge cases.

Beyond Testing: Dynamic Threshold Detection

TimeWear is developing AI models that identify VT1 and VT2 dynamically during regular training—without formal testing.

The system trains on thousands of labeled threshold tests, learning how breathing metrics respond relative to VT1 and VT2. It then analyzes regular workouts to detect these transitions.

This addresses a fundamental limitation: formal tests provide only a snapshot. Thresholds naturally ebb and flow with training load, recovery, altitude changes, and adaptation.

Fixing it to a test that you took four weeks ago is a good start but it’s quite limiting when the reality is that there is this sort of natural ebbing and flowing that provides a lot of information.

Dynamic detection enables automatic adjustments for elevation, training fatigue, overreaching, and fitness improvements—making truly individualized training possible.

The Longevity Imperative

For Vikmaa, the fascination with endurance extends beyond performance.

If we think about just health, health span, longevity, it is the dominant factor. If you look at all other attributes or lifestyle choices, having good endurance meaning like high VO2 max, strong VT1 aerobic base, if you can solve that problem then your chances of having a longer health span and sort of reaping the fruits of life as long as possible is that much greater.

High aerobic capacity provides stronger protection against mortality than virtually any other measurable factor.

But building that capacity requires training at the correct intensities—something most athletes have been unable to do reliably despite decades of technological advancement.

Ventilation measurement finally provides the missing link: a systemic, responsive signal that remains anchored to actual metabolic workload regardless of environmental conditions, fatigue state, or individual physiology.

Heart rate can drift upward, revealing stress and adaptation needs. Power and pace can decline, showing durability limits. And through it all, ventilation maintains its connection to the fundamental question every endurance athlete needs answered:

What physiological zone am I actually in right now?

After decades of relying on proxies and accepting massive non-responder rates, athletes finally have access to ground truth.