Understanding metabolic flexibility for performance

By Paul Cadman, pro sports coach and manager, sports nutritionist and endurance athlete

Picture this. You’re racing side by side with another athlete with 10km’s to go in your ‘A’ endurance race of the season, when suddenly you feel significant fatigue start to set in. Your engine is quickly running out of gas and you’re slowing rapidly in a desperate attempt to preserve your dwindling fuel supplies, meanwhile the other athlete is pulling ahead and further away from you with every stride they take.

Paul Cadman Kayaking

While there are many reasons this could be happening, one of the more likely is that the person you're racing has greater metabolic flexibility and therefore has been able to mix their fuel sources more effectively, ensuring their gas tank had plenty in reserve for when they needed it most.

What is metabolic flexibility?

In an athletic sense, metabolic flexibility refers to someone's ability to effectively utilize both glycogen and fat as fuel at varying levels of exercise intensity and whichever fuel is more available at the time. When thinking about metabolic flexibility it's important to note that you're never using just glycogen or fat at a point in time. It's a combination of the two. In simple terms, having a flexible metabolism means a human skeletal muscle can easily access and utilize both fuels. This in itself is one of the keys to staying healthy and achieving athletic success.

Having the metabolic machinery to mix the sources of energy supply based on the demands of the body and events is an important factor for success. Through optimal metabolic flexibility, it's possible to increase your fat-burning capacity when working at higher intensities. This is important especially in endurance sports as it allows you to preserve your glycogen supply for those periods of output when it becomes the predominant source of fuel for energy expenditure. Think back to the example of the athlete above.

To be metabolically flexible means that an organism can change its rate of fuel oxidation, both fatty acid oxidation and glucose oxidation, in response to changes in its nutritional status. On the other hand, the inability to adjust fuel oxidation can lead to metabolic inflexibility, which over time, can lead to insulin resistance or fat storage.

Fat and glycogen as fuel

Fact - most of us have upwards of 60,000 calories of fuel stored as fatty acids and at most, approximately 2,000 calories of glycogen.

This gives an indication of the almost infinite supply of fuel we have as stored body fat and the very limited supply of glycogen. One of the other key benefits revolves around the reduced need to provide fuel. The reason for this being we can only process a certain amount during energy metabolism. As a guide, most people can tolerate up to approximately 100g of glycogen an hour, much more than this, and the chances of suffering gastric distress increase significantly.

Strategies you can introduce to help improve metabolic flexibility:

  • Ensuring your diet is rich in unprocessed foods including ample volume of healthy fats and protein
  • Introducing some days of intermittent fasting
  • Increasing mitochondrial density and supporting mitochondrial function by varying the intensity of your exercise and supplementing with MitoQ
  • Complete some of your shorter easy morning training sessions in a "fasted" state

Benefits of optimal metabolic flexibility include:

  • Better overall health
  • Improved athletic performance
  • Stronger immune system
  • Better sleep
  • Consistent blood glucose levels and support the improvement of insulin sensitivity
  • Easier weight management and optimized lean body mass

In summary metabolic flexibility is the ability to effectively utilize both glycogen and fat as fuel at varying levels of exercise intensity. You are never using just glycogen or fat at a point in time, it's a combination of the two. Not only will an optimized metabolism help you maintain better overall health, but it will also get you to the finish line faster.

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