The “Fuel for the work required” model is looking at sports nutrition from a new angle. What benefits can this approach produce? Why does it make sense to stop focusing on glycogen stores’ super-compensation and start periodising carbohydrate intake? Let’s take a closer look.

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As you know from the previous article, the benefits of this approach stem from periodically completing endurance training sessions in a carbohydrate-restricted state. Training this way seems to enhance molecular signalling pathways that result in adaptations favourable to endurance-type exercise.

This new model makes a big shift in thinking about carbohydrates. © Profimedia, Zuma Press – News

Increased mitochondrial biogenesis

There are 9 studies (78 % of all reviewed) showing that training in a state of low carbohydrate availability promotes training-induced oxidative adaptations of skeletal muscle such as increased maximal mitochondrial enzyme activities and mitochondrial content. This results in a higher capacity for oxidative metabolism. For example, four studies show that the “twice-a-day training” model produces notable improvements in just 3-10 weeks.

Improved fat burning and glycogen sparing

A major benefit that’s observed in all “train-low” models including the twice-a-day training, fasted training, and train-low sleep-low is a better use of fat for energy. Increased lipid oxidation allows cyclists to use a higher proportion of fatty acids at the same intensity. This, for example, has the potential to preserve precious glycogen stores for crucial attacks later in a race.

Improved performance

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. © Profimedia, AFP

Current research shows that the physiological changes translate into improved performance, although it was observed only in 37 % of 11 reviewed studies. The authors write:

“Using a sleep-low model, Marquet et al. (2016) observed that 1–3 weeks of sleep-low training in elite triathletes and cyclists improve cycling efficiency (3.1 %), 20 km cycling time-trial performance (3.2%) and 10 km running performance (2.9 %) compared with traditional train-high approaches.”

Also, in the “twice-a-day training” model Hansen et al. (1985) showed that the low-carb availability group improved time to exhaustion for knee extensor exercise more than the high-carb group. And Cochran et al. (2015) showed that the training-induced improvement in 250-kJ time trial performance was greater in the low-carb group.

Potential drawbacks

To deal with the possible negative effects of training low, the authors proposed the “fuel for the work required” model. © Profimedia, Actionplus

There are several recognized drawbacks of training in a low-carbohydrate availability state. The authors warn about three in particular.

  • Inability to maintain the same training load. When carb availability is low, protein synthesis may be impaired and the ability to complete sessions is compromised.
  • Higher risk of illness. Repetitive daily training with a reduction in carb availability may increase susceptibility to illness.
  • Loss of top-end performance. Studies show that 1-5 days of high-fat feeding reduces the expression and activity of the pyruvate dehydrogenase complex, ultimately impairing carbohydrate oxidation and high-intensity performance.

These issues are the reason for periodizing carbohydrate consumption, meal by meal, around planned training sessions, or in other words, “fuelling for the work required”. That’s the only way to maintain high-intensity performance, training load, and low risk of illness while enjoying the benefits of “training low”. The following two articles will be all about implementing the train-low strategies into an overall training schedule the right way.

Next up in A New Paradigm in Cycling Nutrition series

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