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What is Metabolic Flexibility in Cycling?


Metabolic flexibility in cycling refers to the body’s ability to efficiently switch between fat and carbohydrate metabolism based on exercise intensity, energy demands, and nutritional status.


A metabolically flexible cyclist can oxidize fat efficiently at low to moderate intensities and switch to carbohydrate use when high power outputs are required, optimizing fuel utilization and delaying fatigue.


Metabolic flexibility can be defined as:


“The capacity of the body to adapt fuel oxidation to fuel availability.”


In an endurance sports like cycling, this can be simplified to:


  • At lower to moderate intensities, relying more on fat oxidation.

  • At higher intensities, transitioning to carbohydrate (CHO) oxidation.

  • Efficiently transitioning between these states as needed.


So what is a good metabolic flexibility for a cyclist?


In general elite endurance athletes shows a superior capacity for switching between fuel sources (FAT and CHO), and have higher fat oxidation rates compared to less trained athletes. At a given percentage of their VO2max, they simply have a higher fat oxidation rate.


Thus, as a consequence of a relatively higher FatMax they spare glycogen by relying more on fat, and in the end have more stored CHO available, when it's needed for high intensity efforts.


So, metabolic flexibility tightly linked to 'durability', a topic covered on a previous blog post, as a higher carbohydrate availability late in a long ride or a long races, is a critical parameter for producing high intensity power outputs when in a fatigued state!


The table below summarizes how metabolic flexibility impacts cycling performance.



The next question that arises is, 'How to improve metabolic flexibility in training? '. Well, there are several things you can consider in your training, but one thing is for sure, there are no quick fix or short cuts. You need to put in the hours over a longer period of time to allow for training adaptations to take place.


Below is an overview of some important aspects of training that can help to improve your metabolic flexibility.



The overall goal with these metabolic training strategies is to:


  • Boost fat oxidation capacity

  • Improve fuel-switching capacity

  • Spare glycogen during long or high-intensity rides

  • Enhance durability


To implement these strategies there are a few things to consider and be aware of.


  • Fasted rides can be very demanding for the body, as fuel is limited. So don't overdo it - neither too long session and too often. Keep intensity low, and don't do it before key sessions like demanding endurance rides or high intensity workouts, as you need to come in fuelled for the hard sessions.

  • To do proper FatMax training you need to know your 'FatMax training zone'. Typically it will be somewhere in the endurance training zone (zone 2), but if it's in the upper, middle or lower part of zone 2 is very individual and dependent on training status. So preferably you need a test (lab test or INSCYD Test) to determine it.


  • Carbohydrate periodization is key as it will help the body to efficiently burn both fat and carbohydrates. So for longer endurance rides at low to moderate intensity, where you want to boost fat oxidation, it's favorable to reduce carbohydrate availability. On the other hand, a high carbohydrate availablity is needed for high intensity sessions, where carbohydrate is the main energy source for generating high power outputs. So fuel the high intensity sessions hard!


The table below summarizes how to implement nutritional strategies to improve metabolic flexibility.



To sum up, metabolic flexibility is of major importance for cycling performance, and a cyclists ability to burn fat at low to moderate intensities and efficiently switch to carbohydrate oxidation when intensity gets high is a key aspect closely related to durability (fatigue resistance)!



References:

  • Coyle EF, Coggan AR, Hopper MK & Walters TJ. Determinants of endurance in well-trained cyclists. J Appl Physiol (1985). 1988 Jun;64(6):2622-30.

  • Maunder E, Seiler S, Mildenhall M, Kilding A & Plews D. (2021). The Importance of ‘Durability’ in the Physiological Profiling of Endurance Athletes. Sports Medicine. 51. 1-10. 10.1007/s40279-021-01459-0.

  • Seiler S & Tønnessen E. (2009). Intervals, Thresholds, and Long Slow Distance: the Role of Intensity and Duration in Endurance Training. SPORTSCIENCE · sportsci.org. 13. 32-53.

  • Stellingwerff T, Morton J.P. & Burke L.M.. A Framework for Periodized Nutrition for Athletics. International Journal of Sport Nutrition and Exercise Metabolism, 2019, 29, 141-151.

  • Van Proeyen K, Szlufcik K, Nielens H, Ramaekers M & Hespel P. Beneficial metabolic adaptations due to endurance exercise training in the fasted state. J Appl Physiol (1985). 2011 Jan;110(1):236-45.







 
 
 
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