This new phrase was coined in 2016 by James P. Morton, the head of nutrition for Team Sky, and a sports scientist Samuel G. Impey who co-authored a study called “Fuel for the work required: A practical approach to amalgamating train-low paradigms for endurance athletes”. Later, in December 2018, they published a landmark study called: “Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis” that discusses this approach more broadly.
Training low, competing high
Their approach builds on an already established field of research that studies training in carbohydrate (CHO) restricted conditions or, in other words, training when muscle glycogen, liver glycogen, and external carbs are limited. This includes training models such as the twice-per-day training, fasted training, post-exercise CHO restriction, and “sleep low, train low”. They summarize the observed benefits this way:
“Periodically completing endurance training sessions (e.g. 30-50 % of training sessions) with reduced CHO availability modulates the activation of acute cell signalling pathways (73 % of 11 studies), promotes training-induced oxidative adaptations of skeletal muscle (78 % of 9 studies) and, in some instances, improves exercise performance (although only 37 % of 11 studies demonstrated performance improvements).”
The new addition to this field of study is their glycogen threshold hypothesis. They propose that there are certain concentrations of muscle glycogen that facilitate the abovementioned benefits while allowing completion of required training workloads.
Based on the current research, the beneficial training adaptations associated with CHO restriction are most evident when absolute pre-exercise muscle glycogen concentrations are equal to or lower than 300 mmol/kg dry weight. The problem is that starting an exercise with less than 200 mmol/kg dry weight is likely to impair training intensity. And repeated training in CHO depleted state may increase susceptibility to illness.
Fuel for the work required
To deal with the possible negative effects of training low, the authors proposed the “fuel for the work required” model. In contrast to chronic periods of CHO restriction, they suggest that CHO availability should be manipulated day-to-day and meal-by-meal according to the intensity, duration, and specific training goals.
This new model makes a big shift in thinking about carbohydrates. The main goal shouldn’t be to super-compensate glycogen stores as it is currently common with carb-loading but to get just the right amount of carbs to maintain training intensity while also creating a consistent metabolic environment that best facilitates training adaptations. We will explore the benefits and drawbacks of this approach in more detail and show you how to implement this approach in the rest of the series.