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

Endurance athletes have long relied on heart rate monitors and power meters to guide their training intensity.

But what if these tools have been leading runners astray all along?

In a fascinating conversation with Anar Vikmaa, founder of TimeWare, a revolutionary truth emerges about how we measure training zones.

The key to unlocking true zone 2 training might not be in your wrist-worn device at all—it’s in how you breathe.

The Problem With Zone 2 Training

Most athletes think they’re training in zone 2 when they’re actually in zone 3. This seemingly small mistake has massive consequences for adaptation and progress.

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

Vikmaa explains that in lab settings, researchers can see exactly what happens at this transition point. Below VT1 (the first ventilatory threshold), fat oxidation is maximized while carbohydrate consumption remains quite low.

Cross that threshold even slightly, and everything flips. The body stops adapting to improve fat oxidation and instead focuses on consuming carbohydrates more efficiently.

Understanding VT1: Your True Zone 2 Ceiling

VT1, or the first ventilatory threshold, marks the upper limit of zone 2. It’s also known as the aerobic threshold.

At this point, fat oxidation reaches its maximum capacity. As intensity increases beyond VT1, the body can no longer service energy requirements with fat alone, and carbohydrates begin making up the difference.

VT1 or the top of zone 2 that demarcates this sort of zone 2 that everybody talks about is the moment at which fat starts to decline because we can no longer service the energy requirement of the work at hand with fat oxidation and carbs start to make up the difference.

This transition is highly individual. Elite cyclists competing at the World Tour level might have their VT1 occurring at workloads above 90% of most people’s VO2 max.

Critically, VT1 doesn’t correlate with VO2 max. Two people with identical VO2 max values can have dramatically different VT1 points.

Why Heart Rate Fails as a Zone 2 Marker

Heart rate became dominant in endurance training primarily because it was available. When Polar released the first wearable chest strap between 1978 and 1980, research and patent applications exploded.

But availability doesn’t equal accuracy.

Heart rate maps primarily to oxygen consumption, not to the carbohydrate and CO2 production that define zone 2. Multiple confounders distort the heart rate signal during training:

• Temperature: Heat causes heart rate to rise independent of metabolic output
• Hydration status: Dehydration elevates heart rate without changing intensity
• Elevation: Altitude affects heart rate differently than sea level
• Life stress: Mental stress impacts heart rate readings
• Caffeine consumption: Stimulants alter heart rate responses
• Sleep quality: Poor recovery affects cardiovascular metrics
• Fatigue state: Accumulated training stress distorts readings

Vikmaa describes what happens in lab testing repeatedly: during proper zone 2 intervals, the body tends to settle in metabolically. Ventilation stabilizes or even decreases slightly. Lactate comes down. Fat oxidation may actually rise over time.

Meanwhile, heart rate drifts upward 15-20 beats, signaling the exact opposite of what’s actually happening physiologically.

The Cardiac Drift Phenomenon

During long runs or rides, heart rate climbs because of cardiac drift—the heart pumps more blood to capillaries for cooling, responds to slight dehydration, or simply reflects cardiovascular fatigue that’s independent of metabolic output.

At the same time, power output or pace typically drops due to muscular fatigue. This creates a confusing picture: two primary metrics moving in opposite directions while the actual physiological state remains consistent.

You have the two primary sources we have on our watches. One of them is going high when it’s not correlating with what’s actually happening. The other one is either staying the same or going down independent of the actual workload.

The Power and Pace Problem

Power meters revolutionized cycling training in the early 2000s. They provided objective external workload data that wasn’t available before.

But power and pace share a fundamental limitation: they need to be coupled with physiological state to be meaningful.

250 watts for an elite cyclist might represent easy zone 2 recovery. For a sedentary adult new to cycling, that same 250 watts could be a VO2 max interval.

FTP (Functional Threshold Power) and percentage-based training zones attempt to individualize these metrics. However, research now shows a 40-60% non-responder rate when using these approaches.

That means nearly half of athletes doing prescribed training fail to improve their fitness despite doing the work.

The reason? These systems lack true physiological individualization. They miss where each person’s actual VT1 and VT2 thresholds occur.

Lactate Monitoring: Promising But Problematic

Lactate measurements offer more direct metabolic insight than heart rate. Lactate threshold testing has been the gold standard in lab environments for decades.

But lactate has its own confounders. As a fuel source rather than a waste product, lactate can accumulate without necessarily indicating intensity level.

Vikmaa shares an anecdote about ultra-runner Killian Jornet showing a lactate reading of 12 many hours into the UTMB race—a physiological impossibility if lactate directly indicated intensity.

Lactate is actually something is an extremely powerful fuel and so it can just hang around no problem and it can pool. Give it enough time under enough load and it’ll just start to accumulate without it actually meaning anything.

Additionally, lactate production at the muscle level is 10-20 times greater than what appears in blood measurements. Continuous lactate monitors measuring interstitial fluid or sweat add another layer of dilution and time delay.

Response time also differs between athletes. Elite athletes with highly efficient lactate consumption might need 15-20 minute steady-state stages to present LT1 in testing. Less trained individuals might only need five minutes.

Ventilation: The Missing Link

Ventilation offers something heart rate and power cannot: a direct window into metabolic state that’s free from most confounding variables.

Everything going into and out of working muscles must pass through the lungs. Oxygen consumption and CO2 production at the muscular level map directly to ventilation volume.

This creates an incompressible signal. Air cannot be compressed or stored, so ventilation volume directly reflects metabolic demand in real-time.

How Ventilation Responds to Intensity

Unlike heart rate, which rises consistently from rest to maximum, ventilation responds nonlinearly to intensity changes.

At low intensities below VT1, ventilation remains quite stable. Fat oxidation consumes more oxygen than it produces in CO2, so the breathing response is minimal.

Cross into zone 3 above VT1, and carbohydrate metabolism produces more CO2 than oxygen consumed. The body is extremely sensitive to CO2 and must evacuate it quickly to maintain blood pH balance.

This triggers a sharp increase in ventilation—the first ventilatory threshold. Continue increasing intensity past VT2, and ventilation becomes extremely unstable, rising dramatically.

You get this sort of nonlinear response with ventilation where it’s quite stable then it starts to gradually rise until it’s just like going through the roof.

Measuring Ventilation in the Real World

TimeWare’s Vita Pro measures chest cavity expansion and contraction through the breathing cycle. The amplitude of this signal provides relative volume exchange per breath.

Combined with breathing rate (breaths per minute), this yields minute ventilation—the total volume of air exchanged each minute.

This approach captures breathing independent of whether someone breathes rapidly with shallow breaths or slowly with deep breaths. When breathing rate is constrained (like runners who entrain breathing to cadence), tidal volume adjusts to match ventilation demand.

The system benchmarks each individual’s ventilation response during threshold testing. As someone moves through intensities from low to high, inflection points in ventilation reveal their unique VT1 and VT2.

The Training Transformation

When athletes discover their true VT1, training transforms. Many realize they’ve been chronically overshooting zone 2, spending most “easy” runs in zone 3.

This is especially common in relatively fit individuals with high VO2 max but low VT1 relative to that ceiling. Running below VT1 feels easy for them, so they naturally drift faster—but they lose the fat oxidation adaptation that builds aerobic base.

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, race times improve, durability improve.

For less fit individuals, the revelation can be even more stark. Someone with a VO2 max below 50 ml/kg/min may find their VT1 is so low they cannot run at all while staying below it.

This creates a vicious cycle. They try to run, constantly exceed VT1, improve only carbohydrate metabolism (which has limited adaptation potential), plateau quickly, and wonder why training isn’t working.

The solution? Walking, incline treadmill work, hiking, or rucking. These activities allow intensity to stay below VT1 while still providing training stimulus.

Building Mitochondrial Density

Zone 2 training fundamentally improves the body’s ability to use fat as fuel. This requires building mitochondrial density and capacity within muscle tissue.

More mitochondria means more sites for fat oxidation. This pushes out the point where carbohydrate metabolism must take over, raising the ceiling for sustainable intensity.

That mitochondrial foundation then enables higher VO2 max development. More mitochondria means more oxygen consumption capacity, which raises the performance ceiling.

But this adaptation only occurs when training consistently below VT1. Train above it, and the body adapts to carbohydrate metabolism instead—a much more limited lever for improvement.

The Durability Factor

Durability describes how well muscles maintain workload at the same physiological state. How quickly does pace drop for the same internal effort? How long can intensity be sustained before fatigue forces a slowdown?

VT1 training is key for developing durability. In lab testing, researchers assess VT1 when fresh, then put subjects through a two-hour protocol at 90% of VT1 output. They measure VT1 again and calculate the performance drop-off.

Athletes with strong aerobic bases show minimal durability decline. Those lacking zone 2 foundation fade dramatically.

VT1 is what wins races. By the time they get to the final hill, there’s only one left. The difference is in the durability.

Zone 2 work improves durability through multiple mechanisms:

• Preserves carbohydrates: Better fat oxidation means glycogen lasts longer during races
• Maintains high output: When others deplete glycogen, well-trained athletes still have fuel available
• Trains fatigue resistance: Muscles adapt to sustaining work right at the VT1 limit

Using Ventilation in Practice

The first step with ventilation-based training is establishing individual VT1 and VT2 through threshold testing. This typically involves a ramp protocol, steadily increasing intensity from very low to maximum over 20-30 minutes.

The test reveals ventilation values at both thresholds, along with corresponding heart rate, pace, and power. These become personalized training zones.

For zone 2 training, the goal is simple: stay below VT1 ventilation. For hard intervals, go above VT2.

The test also reveals where improvement opportunity exists. VT1 occurring at a low percentage of VO2 max suggests untapped aerobic base development. VT1 already high relative to VO2 max indicates the ceiling needs raising through higher intensity work.

Real-Time Pacing Freedom

During workouts, ventilation allows athletes to pace purely by physiological state. Heart rate can drift upward—that’s now a pure signal about hydration, fueling, or recovery needs, not pacing.

Power or pace can drop—that reveals durability limits, not a need to slow down arbitrarily.

Athletes training in hot, humid conditions report this as particularly transformative. In Singapore’s 105°F heat and 80% humidity, heart rate skyrockets even at low intensity. Power drops significantly.

With ventilation monitoring, these athletes maintain confidence they’re getting quality training despite deteriorating traditional metrics. The proof comes in improved consistency, better durability, and faster race times.

The Technology Challenge

If ventilation is so valuable, why didn’t it become mainstream alongside heart rate in the 1980s?

The answer is technical difficulty. Capturing breathing signals accurately outside a laboratory proved extremely challenging at consumer price points.

Lab equipment for decades has measured breathing for sleep studies and metabolic testing, but those systems are cumbersome and expensive—not suitable for outdoor running or cycling.

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

Current generation devices still face some limitations. Very tight clothing or heavy backpacks pressing directly on sensors can introduce noise. The signal works reliably in most running and cycling scenarios, but certain configurations require design refinement.

TimeWare is developing next-generation designs to address these edge cases, making ventilation monitoring universally accessible across all training conditions and equipment configurations.

Breathing Efficiency and Performance

The breathing muscles—primarily the diaphragm and intercostals—function like any other muscles in the body. They have endurance capacity, strength characteristics, and coordination patterns that can be trained.

At high intensities, breathing muscles consume approximately 15% of total oxygen uptake. Making breathing more efficient reduces this metabolic cost, freeing oxygen for working muscles.

Generally, efficiency means breathing at lower rates with higher tidal volume (deeper breaths). This pattern typically reduces the oxygen cost of breathing itself.

Sports with high breathing entrainment face unique challenges. Cross-country skiers and rowers have breathing rate limited by movement cadence. If that cadence caps breathing rate, the only way to increase ventilation is through higher tidal volume.

For these athletes, breathing muscle training becomes particularly valuable. Increasing the volume achievable per breath when rate is constrained can significantly improve performance.

The Future of Intensity Monitoring

TimeWare is developing machine learning models that automatically detect VT1 and VT2 during regular workouts, without requiring formal testing.

The system trains on labeled data where thresholds are known from testing, then learns how breathing metrics respond relative to those thresholds. Applied to regular training, it can dynamically identify threshold crossings.

This addresses a key limitation of static testing: thresholds captured on one day may not perfectly represent daily fluctuations. Heart rate varies with stress and recovery. Ventilation at VT1 may shift slightly as fitness improves. Altitude changes everything.

Dynamic threshold detection allows the system to automatically adjust for these natural variations, providing more accurate intensity guidance without constant retesting.

There is this kind of ebbing and flowing that is quite natural for any given athlete on any given day within a workout. Fixing it to a test that you took four weeks ago is a good start but it’s quite limiting.

Rethinking Training Fundamentals

Ventilation monitoring forces a fundamental rethink of endurance training principles. For thirty years, athletes have relied on proxy metrics that provide directional guidance at best.

Heart rate tells us something about cardiovascular stress but confounds metabolic state with thermoregulation, hydration, and nervous system activation.

Power and pace measure external work but say nothing about internal cost or adaptive response.

Generic formulas and percentage-based zones ignore individual physiology, leading to massive non-responder rates in training programs.

Ventilation offers what endurance athletes have lacked: a real-time window into actual metabolic state. Not a proxy, not a correlation, but the actual physiological phenomenon that defines training zones.

For athletes who’ve struggled to improve despite consistent training, for those who’ve felt chronically fatigued, for runners who plateau inexplicably—the answer may be simpler than expected.

They’ve been training in the wrong zones all along.