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 on the importance (or lack thereof) of muscle glycogen, 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.

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Meet the Myth-Busters

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.
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• Just 10 g glucose per hour eliminated hypoglycaemia and extended time-to-exhaustion by 22 % on both diets.​​

My Athletica 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

1. Intensity Ceiling: How far into the red zone can a fat-adapted athlete go before small-pool glucose becomes rate-limiting?
2. Sodium & Neuro-drive: Preliminary data hint that strategic salt boosts central motor recruitment—watch this space.
3. 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.
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Let’s keep feeding it with better questions—and fewer sugary distractions.

See you on the climb,

Paul Laursen, PhD

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