The Standard Model: Why We Use Zones
Most training is built on Output Zones—calculated as a percentage of your FTP or Max Heart Rate (mine is 203 bpm). We use them because they provide a repeatable, objective language for intensity:
• Zones 1-2: Aerobic foundation and recovery.
• Zone 3: Tempo and steady-state work.
• Zone 4-5+: Threshold and VO2 Max “top-end” speed.
They are designed to ensure specificity and measurability. But zones only measure what you are doing—they don’t measure what it’s costing you.
For decades, endurance training has been an exercise in accounting. We balance the columns of power, heart rate, and lactate, expecting a predictable “profit” in performance.
• Power zones guide the workload.
• Heart rate zones reflect cardiovascular demand.
• Lactate thresholds anchor metabolic intensity.
These frameworks are the bedrock of modern coaching. I still rely on them. But increasingly, I find myself questioning why some training blocks lead to massive breakthroughs while others—despite “perfect” numbers—result in a “fragile” kind of fitness.
I’m beginning to suspect that while we are measuring Output, we are failing to measure Integrated Strain.
The Morning the Data Lied
Last week, my data was shouting “Go!” from the rooftops. My HRV (Heart Rate Variability) was trending at an all-time high, my Resting Heart Ratewas a rock-solid athletic baseline, and my Garmin Body Battery was pinned at 100%.
On paper, I was a physiological specimen ready for a personal best. But I woke up with a scratchy, sore throat and a heavy, “foggy” sensation in my limbs.
If I followed the data, I’d be doing 4×10 minute intervals at Threshold. If I followed my biology, I’d be back in bed. This is the Subtle Friction that athletes ignore. The sensors saw the “battery,” but they didn’t see the Immune Activation or the Central Nervous System (CNS) fatigue starting to boil over.
Output vs. Cost: The “Strain Zone” Theory
Every ride has a “Cost of Production.” Usually, that cost is predictable. But when you are under-recovered or fighting a sub-clinical bug, the cost shifts.
I’m currently exploring a framework of Strain Zones—measuring how the body “pays” for the power it produces. Each metric captures a specific signal, but none measure global readiness:
• Power: External mechanical work.
• Heart Rate: Cardiovascular demand and autonomic activity.
• Lactate: Substrate flux (fuel burning), not systemic fatigue.
As physiologists like George Brooks have shown, lactate is a fuel, not a waste product. Two athletes can produce identical lactate levels under very different internal conditions. Even within the same athlete, lactate can remain low during sessions that feel unusually demanding due to sleep disruption, heat, or accumulated stress.
The Subtle Yellow Flags
We all know the “Red Flag” days where Zone 2 feels like Zone 4. Those are easy. The real danger lies in the Compensatory Zone—the subtle friction athletes usually ignore:
• The “Focus” Shift: You hit your target power, but it requires a “smidge” more mental effort to keep the pedals turning.
• The Breathing Drift: You’re in your Z2 range, but you find yourself taking deep, “resetting” breaths every few minutes.
• The HR Creep: Even with a high ceiling (my max HR is 203), I notice when my steady-state heart rate is 5 beats higher than the “standard” cost for that wattage.
On a training log, this looks like a “Success.” In reality, you are likely in a Non-Adaptive state. You are doing the work, but you aren’t building the engine—you’re just wearing down the parts.
Why Identical Workouts Don’t Produce Identical Outcomes
Training adaptation is governed by signaling pathways like AMPK and PGC-1α. These pathways are sensitive to your global physiological state.
• The Psychobiological Model (Marcora): Suggests performance is regulated by the perception of effort. Cognitive fatigue—from work, family, or stress—impairs performance even when physiological capacity is unchanged.
• Central Regulation (Noakes): Proposes that the brain modulates motor output to maintain homeostasis, integrating signals from every system to prevent catastrophic failure.
A session performed in a well-recovered state stimulates mitochondrial growth. The exact same session performed under cumulative, subtle fatigue may primarily add stress without any meaningful benefit.
The “Push or Pivot” Protocol: When Data and Biology Clash
It’s easy to train when everything is green. The elite skill is knowing how to handle the “Grey Area.” Before you clip in, run through this 3-step audit.
1. The “Quiet Mind” Test
Sit for two minutes before kitting up. Forget the recovery scores. If you didn’t have a computer telling you that you were recovered, how would you rank your energy on a scale of 1–10? If your “gut” score is 3+ points lower than your “Data” score, the data is missing something.
2. The 15-Minute Warm-Up Audit
The first 15 minutes are your “Internal Strain” window. Pay attention to your Heart Rate.
• High & Spiky: Your sympathetic nervous system is red-lining (Stress/Illness).
• Stubbornly Low: Your parasympathetic system is “throttling” you (Overreaching).
• The Feel: If you have to concentrate to keep Zone 2 power steady, you are in the Compensatory Zone.
3. The Decision Matrix
Final Thoughts
We are the first generation of athletes to have a laboratory on our handlebars. It is a gift, but it’s also a trap.
Integrating these subjective “strain” signals with our objective “output” metrics is the key to closing the gap between being “fit on paper” and being “fast on the road.” The next time your HRV is “Green” but your throat is scratchy, remember: The map is not the territory.
Build a durable engine. Listen to the friction.
What if the problem isn’t your fitness — but how we define zones?
Most models measure output. Few measure cost.
I’m building a more holistic system that integrates physiology, perception, and recovery bandwidth.
If that conversation interests you, subscribe. This is a work in progress — and it’s getting sharper.
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