ANC Knowledge Hub · Physiological Profiling
Physiological Profiling: Why "Aerobic vs. Anaerobic" Misleads You
A smarter way to understand your engine, and what to do about it.
Every athlete uses both systems, all the time. The real question is how close your sustainable output sits to your absolute ceiling.
The old storyAerobic athlete or anaerobic athlete?
For years you have been told you are either built for endurance or built for power. It is a clean story, and it is wrong. That one question about sustainable output against ceiling changes how we train you.
Sign 1
You hit huge numbers in intervals, then fall apart when you try to hold them for race distance.
Sign 2
You feel fine at race pace for the first hour, then watch power or pace bleed away while heart rate climbs.
Sign 3
Easy days feel hard, hard days feel impossible, and nothing feels truly easy anymore.
Sign 4
Years of steady training, rising test numbers, and race results that have plateaued.
If any of those land, you are not broken and you are not undertrained. You are being measured by the wrong question.
The better questionASRC: Aerobic Sustainability Relative to Capacity
ASRC is a ratio. We take your highest sustainable output, Critical Power on the bike or Critical Speed on the run, and compare it with your absolute ceiling, pVO2max, the power or pace at maximum oxygen uptake.
That one percentage tells us more about how to train you than any type label. It shows where the weak link is, where the next gain is hiding and what work will get you there.
The four tiersWhere you sit, and what we do about it
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%
A decent base, with the weak link sitting right at threshold.
Priority: Threshold consolidation. Lift the sustainable line toward the ceiling.
Moderate ASRC · 83 to 87%
A balanced engine.
Priority: Hybrid work. Sharpen the ceiling and protect the floor together.
High ASRC · Above 87%
You sustain almost everything you have. The floor is up, so the ceiling is the limiter.
Priority: Raise the ceiling, then consolidate again.
All four profiles side by side
The ASRC framework, from our physiological profiles page
Why it mattersA direction, not a personality
The old label gave you a personality. ASRC gives you a direction. It tells us where to push, what to build and what not to do this block. A Very Low ASRC athlete pounding more VO2max intervals digs the same hole deeper. A High ASRC athlete grinding endless zone 2 leaves meters on the table. Once we know where you sit, the block follows.
Easy, moderate and hard
Katy Walmsley, measured time in zone
Three athletes, three block orders
Blocks in order, from each athlete’s TrainingPeaks season
Tiers are not destinationsAthletes move across the spectrum
Your tier is not a verdict. It is a starting point.
An athlete at 76% in October can be at 84% by race day. The whole curve shifts: LT1, OGC and Critical Power move together when training is matched to the limiter. That is the work. Find the gap, close it, retest against the ceiling and decide what comes next.
A full build, start to finish
Katy Walmsley, fitness, fatigue and form from her daily TrainingPeaks TSS
Keep reading
Want to know your ASRC tier?
Our team maps your physiology, finds the limiter and builds the block that moves you forward. Coaching that meets you where your physiology actually is.
Start your coaching inquiryOr see 1:1 Comprehensive CoachingWant this built into your training? See how Angela Naeth Coaching coaches triathletes, or book a free consult.