Challenging Beliefs
Small Pool, Big Engine
The Catalyst —My 36-Hour Fasted Climb
A few weeks ago I finished recording a podcast with Prof. Tim Noakes and Dr. Phil Maffetone—two mentors whose work underpins much of my own coaching.
Inspired (and a little rattled) by their latest thinking, I tested my own beliefs in the subsequent days:
Fed vs. 36 hours fasted (black coffee + water).
90-min climb up Mt Revelstoke.
Result: Personal-best power with –13 % Athletica Workout Reserve.
One ride doesn’t rewrite physiology textbooks, but it demolished the story I’d told myself for two decades: you must start hard efforts with bulging muscle-glycogen stores.
“Only n = 1, but I needed to prove it to myself first.” – Me, mid-bonk epiphany
Meet the Myth-Busters
We are always challenging beliefs because we want more out of our patients, out of our athletes.” – Phil Maffetone
“I realised I’d had it wrong for 33 years.” – Tim Noakes
In our conversation Tim laid out the bombshell that will headline his forthcoming 100-page review: muscle glycogen is a glucose sink, not the limiting fuel we thought. What really governs endurance performance is the small glucose pool—blood glucose topped up by liver glycogen. When that pool crashes (hypoglycaemia), the brain throws the red flag long before muscles “empty the tank.”
The New Model in Plain English
The key regulator? Insulin. High pre-exercise insulin locks fat in the garage; low insulin unlocks fat and lets you cruise on virtually unlimited fuel.
Fresh Data to Back It Up
A randomized crossover trial led by Prins et al. (2025) put competitive triathletes on either a high-carb (380 g·d⁻¹) or very-low-carb (40 g·d⁻¹) diet for six weeks. During a severe time-to-exhaustion test (70 % VO₂max):
Performance was identical across diets.
Just 10 g glucose per hour eliminated hypoglycaemia and extended time-to-exhaustion by 22 % on both diets.
My Data From Fueled and Fasted Ride
Snapshot: In the fasted state I rode faster and stronger while working at a lower heart-rate cost and showing tighter aerobic stability. The –13 % mWR confirms the PB-level effort (it naturally compares the prior ride against it in real time).
Practical Take-Aways for Athletes & Coaches
Note: medical conditions, ultra-long events and very hot climates demand extra nuance—test in training.
Why This Matters Beyond the Finish Line
Low-insulin, fat-adapted athletes often report:
Stable moods & sharper cognition (Noakes: “much more emotionally stable”).
Healthier body composition—less “invisible” visceral fat despite stable body weight.
Freedom from the gut turmoil that plagues high-gel fueling strategies.
Open Questions & Next Experiments
Intensity Ceiling: How far into the red zone can a fat-adapted athlete go before small-pool glucose becomes rate-limiting?
Sodium & Neuro-drive: Preliminary data hint that strategic salt boosts central motor recruitment—watch this space.
Real-world Performances: Case studies (e.g., Dan Plews’ sub-8 Ironman on ~1 gel·h⁻¹) suggest theory scales to elite outcomes. Let’s gather more files.
Want to Put Your Own Physiology to the Test?
We’re recruiting everyday athletes for the FIELD study—a real-world look at how fueling strategies affect performance and recovery inside Athletica.
🔗 Join or learn more → athletica.ai/field-study
Help us turn n = 1 stories into evidence-based coaching insights—and snag some personalised analytics along the way!
Watch, Listen, Share
Podcast – Full conversation with Noakes & Maffetone (YouTube link).
Charts – Athletica session analysis available to all via free trial.
Discussion – Drop your experiments or counter-arguments in the Forum comments.
“The most important body part for athletes is their brain.” – Phil Maffetone
Let’s keep feeding it with better questions—and fewer sugary distractions.
See you on the climb,
Paul “Coaching Prof” Laursen
Disclosure: This newsletter is for education; it is not medical advice. N = 1 anecdotes are powerful catalysts but poor substitutes for individualized care. Consult qualified professionals before drastic dietary change.