Zone 2 Training: Why All the Talk

Zone 2 training has become something close to a new religion in endurance sports. Andrew Huberman keeps bringing it up on his podcast. Peter Attia lists it as a cornerstone of longevity. After Iñigo San Millán coached Pogačar to the Tour de France title, the Zone 2 system he promotes has been cited everywhere.

Episode 41 of the Inside Exercise Podcast featured host Glenn McConnell interviewing Andrew Coggan. If you’ve spent any time in the power training world, the name should be familiar — he coined the concept of FTP (Functional Threshold Power), co-authored Training and Racing with Power with Hunter Allen (over 100,000 copies sold, translated into eight languages), won time trial championships across five states, and built a small wind tunnel in his basement to study aerodynamics. Power training is a system that measures output in watts — dominant in the cycling world, but conceptually equivalent to pace or heart rate management in running.

In this episode, he said a few things that I think deserve serious attention in the middle of all the Zone 2 noise.

How FTP Came About — and Why He Calls Them “Levels,” Not “Zones”

Coggan introduced the term FTP around 2002 on an online forum called wattage forum. He deliberately chose the word “functional” because he understood that true physiological thresholds don’t have precise tipping points — they’re fuzzy continuums. FTP was never a physiological measurement. It’s a practical anchor: the highest steady-state output you feel you can sustain for about an hour, giving coaches and athletes a shared reference point.

He named his system “seven training levels,” not “zones,” for equally deliberate reasons. Power output in outdoor cycling is inherently volatile — you coast through corners, surge over short climbs, accelerate out of bends. If your mindset is “stay inside a zone,” you end up managing a number instead of responding to the road. Train that way long enough and you become what Coggan calls a diesel engine: smooth at constant effort, useless when the race demands acceleration. “Levels” implies movement within a range. It’s not a box to lock yourself inside.

A Few Things About Zone 2 You May Have Accepted Too Quickly

Coggan has a clear position on why people say Zone 2 works: many of the popular explanations are based on misreading the underlying physiology. He’s not dismissing Zone 2 — but if you don’t understand the real mechanism, your training decisions rest on a shaky foundation.

You Don’t Need to “Train in a Fat-Burning State” to Improve Fat Metabolism

The most widely repeated Zone 2 argument goes like this: low-intensity exercise burns primarily fat, so if you want to get better at burning fat, train at that intensity and teach your body to do it.

Coggan’s point: an untrained person sitting at rest already gets almost all their muscle energy from fatty acid oxidation. Endurance training improves fat metabolism capacity, but the mechanism is an increase in mitochondrial number and quality — mitochondria being the cellular machinery that handles aerobic metabolism regardless of whether the fuel is fat or glucose. The signals that drive mitochondrial biogenesis are changes in the muscle’s energy state and calcium release from contracting fibers. Neither of those signals is “you are currently burning fat.”

This means that through high-intensity interval training, even when the primary fuel being used is carbohydrate, as long as the mitochondrial adaptation occurs, your capacity to oxidize fat during exercise will improve. “You must train in a fat-burning state to improve fat metabolism” doesn’t hold up mechanistically.

Elevated Lactate Doesn’t Switch Off Fat Burning

Another popular claim traces back to a 1960s research hypothesis: high-intensity exercise causes lactate to accumulate, lactate inhibits lipolysis, and so the body switches into carbohydrate-only mode.

The mechanism here is wrong.

During high-intensity exercise, circulation priorities shift — blood flow is redirected from adipose tissue toward working muscles. Fatty acids need albumin as a carrier to leave fat cells and enter the bloodstream, because they’re not water-soluble. With less blood reaching adipose tissue, albumin delivery drops, and fatty acids can’t get out. Blood-borne free fatty acid concentration falls as a result. That’s a physical blood-flow constraint, not a biochemical suppression by lactate.

In 1999, Trudeau and colleagues used microdialysis probes inserted directly into subcutaneous abdominal fat tissue in human subjects, infusing high-concentration lactate into one probe and saline into the other as a control, while measuring glycerol (a direct marker of lipolysis) throughout rest, moderate exercise, and recovery. Result: no difference between the two probes whatsoever. George Brooks’ laboratory’s lactate clamp experiments point the same direction — when blood lactate is artificially elevated under controlled pH conditions, lipolysis is not suppressed; if anything, it trends slightly higher.

Metabolic Reset After High Intensity Is Faster Than You Think

Zone 2 purists sometimes argue that if you include a sprint or a hard climb inside an aerobic session, the low-intensity work that follows “doesn’t count” — because the high-intensity effort has disrupted the hormonal environment and compromised whatever fat-burning benefit the easy portions would otherwise deliver. The practical extension of this belief: keep Zone 2 and hard efforts on separate days, never mix them in the same session.

Data from Coggan’s doctoral research addresses this directly: subjects alternated between time trial intensity for 15 minutes and easy recovery for 15 minutes. In the second half of each recovery block (the final 5 minutes), fatty acid and glycerol metabolism rates had already returned to levels identical to control conditions where no high-intensity effort had been performed at all.

The underlying reason is hormonal clearance rate. Epinephrine and norepinephrine spike significantly during high-intensity exercise and do affect metabolism — but their half-lives are extremely short, cleared within 1–2 minutes of the effort ending. Total metabolic reset window: roughly 10 minutes.

The implication is straightforward: as long as the recovery interval is genuinely easy and long enough, each low-intensity block is independently effective — regardless of what came before it. Outdoor riding rarely stays perfectly flat and steady. Accelerating through a traffic light or rolling over a bumpy climb doesn’t erase the low-intensity training that follows. “Hard efforts contaminate Zone 2 benefit” is a concern the data doesn’t support.

What Coggan Actually Thinks You Should Do

After dismantling those misconceptions, Coggan’s training advice is remarkably practical.

He says the core principles are straightforward: Specificity, Overload, Progression. Your training should match what your race demands, intensity must be sufficient to drive adaptation, and the stimulus must build over time. These hold regardless of which training trend is dominating the conversation.

His concrete example: a college student with six hours a week to train gets more out of spending part of that time at “sweet spot” — roughly 88–93% of FTP — than dedicating all of it to pure Zone 2. That intensity delivers a higher training stimulus in less time. For athletes with limited hours, it’s simply more efficient.

Zone 2 does have a place. For ultra-endurance athletes, high volumes of low-intensity aerobic work have clear justification — because the race is conducted at that intensity, and you need to practice there. But the justification is specificity: “my race demands this capacity.” Not “this is the only intensity that improves fat metabolism.”

He uses the Tokyo Olympic 5000m final as an example: the top three finishers trained in completely different ways — one emphasizing high volumes of easy running, one doing two-a-days with heavy intervals, one taking a mixed approach. All three finished within a meter of each other. What he means by “all roads lead to Rome” isn’t that every method is equally good — it’s that more paths to the goal exist than people assume, and you don’t need to lock yourself into one.

Coggan returns repeatedly to one principle: “The best predictor of performance is performance itself.” He’s skeptical of the belief that you need regular VO₂max or lactate threshold tests to track progress. His reference point is physiologist Ed Coyle’s tracking of Greg LeMond through the 1988 Tour de France season — VO₂max barely changed over the season, yet race performance improved significantly, correlating closely with a roughly 10% increase in mitochondrial enzyme activity in his muscles. The number you most need to track isn’t a lab value — it’s what you can actually do at your target intensity.

On the subject of social media training advice, his stance is clear: stay skeptical. Whoever’s saying it, ask what the evidence is and whether it applies to your situation. Decades of endurance research have already established many of the core principles. You don’t need to restart with a new zone system every two years.

And if you train for health and longevity, his advice is simple: find something you can sustain and genuinely enjoy. Over-rigid intensity control reliably leads to one outcome above all others — losing motivation.

Your body needs time to adapt. But first you have to keep showing up.