There’s compelling research indicating that high carbohydrate diets enhance exercise capacity in endurance athletes.
On the other hand, acute exercise studies have shown that performing endurance based exercise under low carbohydrate availably (train low) can enhance the endurance adaptation.
This is typically achieved by training and recovering in the absence of carbohydrates.
A major drawback of train low is the lower quality training sessions – ultimately, carbs are vital for peak performance. But does carbohydrate intake need to be sacrificed to enhance adaptation?
So, why low carb for selected training sessions?
A key adaptive outcome from endurance exercise is the increase in mitochondrial content within the muscle. Low levels of muscle glycogen signals an enzyme called AMPK to make more mitochondria.
Therefore, the more mitochondria an endurance athlete has the greater capacity to ‘spare’ glycogen and keep the tanks topped up for latter parts of races.
However, when you apply this training and nutrition protocol to elite athletes over a longer period of time, does it have a performance impact?
Elite athletes are highly metabolically adapted and are less susceptible to exercise-induced stress compared to untrained individuals. Therefore training status and context is important here.
Based on a recent meta-analysis by Gejl and Nybo (2021), it doesn’t appear that periodised carbohydrate restriction improves performance outcomes in well-adapted endurance athletes.
It’s worth noting that many ‘train low’ studies consist of training bouts ~2 hours, where elite endurance athletes with 20-30hr training weeks will unlikely generate the necessary stress-response to gain benefits.
From experience, many endurance athletes fail to meet the fuelling demands of very big training weeks, and therefore don’t consume enough carbohydrate and may unintentionally train with lower levels of muscle glycogen.
Therefore, athletes may unknowingly ‘train low’ and benefit from heightened adaptation despite keeping carbohydrate intake higher (but not high enough for peak performance).
Ultimately, when specific ‘train low’ strategies are given to them, they don’t work due to previous exposure.
But for those who with moderate to low work–loads with constantly high carbohydrate intakes…this may have some utility in your plan.
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