ECHO Coaching · Endurance Education
Why "Aerobic vs. Anaerobic" Has Been Lying to You
A smarter way to understand your engine — and what to do about it.
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You've been told for years that you're either an "aerobic athlete" or an "anaerobic athlete." Built for endurance, or built for power. One or the other.
It's a clean story. It's also wrong.
Every athlete uses both systems, all the time. The real question isn't which one are you — it's:
That single question changes everything about how we train you.
Does any of this sound like you?
1. You can hit huge numbers in intervals — but the second you try to hold them for race distance, you fall apart.
2. You feel "fine" at race pace for the first hour, then watch your power or pace bleed away while your heart rate climbs.
3. Your easy days feel hard. Your hard days feel impossible. Nothing feels truly easy anymore.
4. You've trained consistently for years, your fitness "tests" keep improving — and your race results have plateaued.
If any of those land, you're not broken. You're not undertrained. You're just being measured by the wrong question.
The better question: ASRC
We call it Aerobic Sustainability Relative to Capacity — or ASRC.
It's a ratio. We take your highest sustainable output (Critical Power on the bike, Critical Speed on the run) and compare it to your absolute ceiling (pVO₂max — the power or pace at maximum oxygen uptake).
ASRC = Sustainable Ceiling ÷ Absolute Ceiling
How much of your top floor can you actually live in?
That single percentage tells us more about how to train you than any "type" label ever could. It tells us where the weak link is, where the next gain is hiding, and what kind of work will get you there.
The four ASRC tiers
Very Low ASRC — under 78%
Big top-end, small sustainable window. You sprint well and fade fast. Priority: aerobic expansion. Build the floor before sharpening the ceiling.
Low ASRC — 78 to 83%
Decent base, weak link is sitting right at threshold. Priority: threshold consolidation. Lift the sustainable line up toward the ceiling.
Moderate ASRC — 83 to 87%
Balanced engine. Priority: hybrid work. Sharpen the ceiling and protect the floor at the same time.
High ASRC — above 87%
You sustain almost everything you've got. The floor is up — now the ceiling is the limiter. Priority: raise the ceiling, then re-consolidate.
Why this matters for you
The old "aerobic vs. anaerobic" label gave you a personality. ASRC gives you a direction.
It tells us where to push, what to build, and — just as importantly — what not to do this block. A Very Low ASRC athlete pounding more VO₂max intervals is digging the same hole deeper. A High ASRC athlete grinding endless Z2 is leaving meters on the table.
Once we know where you sit, the block writes itself.
"Your tier isn't a verdict. It's a starting point. Athletes move across the spectrum every season — that's the whole job."
Tiers are not destinations
An athlete who sits at 76% in October can be at 84% by race day. The whole curve shifts — LT1, OGC, and Critical Power all move together when training is matched to the limiter.
That's the work. Identify the gap, close it, then re-test against the ceiling and decide what's next.
See where you sit
We built an interactive tool that shows all four ASRC profiles side-by-side. Toggle the curves, watch how the landmarks shift across the spectrum, and read the coaching priorities for each tier.
Explore the full ASRC framework →
Want to know your ASRC tier — and what to actually do about it?
That's what ECHO Coaching does. We map your physiology, identify the limiter, and build the block that moves you forward — instead of running you in circles.
Coaching that meets you where your physiology actually is —
not where a label says it should be.
ECHO Coaching · AngelaNaethCoaching.com