60, 90 or 120 g of Carbohydrates per Hour: Opt for Personalized Dosing
The debate on the optimal carbohydrate intake during endurance exercise is far from settled, but recent data confirm that a systematic "high‑carb" strategy (≥ 90 g·h⁻¹) is not the best approach for all athletes.
In the article "Carbohydrate Intake in Ultra‑Endurance: What Dosage—60, 90, 120g…?!" I highlighted that an intake of 60 g·h⁻¹ can enable athletes to perform better than with 90–120 g·h⁻¹ strategies, thanks to improved metabolic flexibility (the ability to optimize fat and carbohydrate oxidation during exercise).
Link to the article
Carbohydrate Intake in Ultra-Endurance: Which Dosage: 60, 90, 120g...?
·Currently, sports nutrition companies associate ultra-endurance athletes' performances with the amount of carbohydrates consumed during the event. A few years ago, the goal was to consume 90 g/h, but more recently, higher doses of over 120 g/h have been promoted.
Improving Metabolic Flexibility with "Train Low, Race High"
Metabolic flexibility can be enhanced by using the nutritional strategy Train Low, Race High, which involves periodizing carbohydrate intake before, during, and after training. This approach offers two main benefits:
Stimulating cellular signaling pathways involved in endurance adaptations (mitochondrial biogenesis, glucose transporters, oxidative enzymes).
Increasing fat oxidation (FATox) during exercise, thereby sparing glycogen and delaying fatigue.
The "Glycogen Threshold": A Trigger for Adaptations
Research has identified a muscle glycogen threshold between 100 and 300 mmol·kg⁻¹ (dry weight). When an athlete performs specific sessions with glycogen reserves in this lower range—i.e., with restricted but sufficient carbohydrate intake to remain within the threshold—it triggers a cascade of beneficial cellular adaptations for endurance.
Important: Carbohydrate restriction applies only to the targeted session; it is then essential to restore glycogen stores during recovery to support subsequent training quality and to avoid the development of Relative Energy Deficiency in Sport (RED‑S).
Impact on Fat Oxidation
A recent meta‑analysis (Mora‑Fernandez et al., 2025) confirms that low‑carbohydrate protocols significantly increase FATox and the maximal fat oxidation rate (MFO). We will revisit these concepts later.
However, before diving deeper, I wish to present a recent scientific study that challenges the HighCarb approach as a universal solution. I will then illustrate its practical implications with examples from my work with athletes.