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How Low Carbohydrates Can Increase Aerobic Capability: The Glycogen Threshold

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We frequently discuss concepts just like the aerobic threshold, the anaerobic threshold, the lactate threshold, etc. But have you ever heard of the Glycogen Threshold?  To place it simply, low carbs availability in your muscles can function strong signals to extend your muscle’s aerobic capability.

Hello everyone, welcome to fall! I hope you had a fantastic summer of riding and are having fun with your hard-earned fitness because the days proceed to shorten. In this text, I would really like to introduce a comparatively latest concept often known as the ‘Glycogen Threshold’. I’ll briefly discuss the cellular mechanisms behind it, in addition to discussing how & why it would help your training.

The Role of Carbohydrates in Cell Signaling

As cyclists, we are likely to love our carbohydrates: pastries, pastas, and pizzas, oh my! And the principle of carb-loading before an enormous ride or race is well-known by us all. With that in mind, the speculation of deliberately training with reduced carbohydrate (CHO) availability is a heavily debated topic in sports nutrition.

Training in a fasted/carb-depleted state can significantly impact fat oxidation during steady-state cycling (Hulston, et al., 2010), in addition to stimulate mitochondrial biogenesis, e.g., the creation of more mitochondria, commonly known as “the powerhouses of the cell” (Bartlett, et al, 2013). Actually, I even have already elaborated on the concept of “training low”, or training with reduced carbohydrate availability previously.

Increasing mitochondrial biogenesis and fat oxidation is very wanted within the endurance community, since our bodies are only able to holding so many carbs. The sensation of hitting the wall/bonking on a ride while you run out of carbs might be miserable.

What happens during Carb Depletion?

There are just a few ways to intentionally cause carb depletion, but they might be summarized below:

  1. Two-a-day training – the primary training session of the day is followed by reduced CHO intake in order that the second training session is performed with reduced muscle glycogen.
  2. Fasted training – we’ve covered this topic previously, but the concept is to attend until after your training session to eat breakfast
  3. Sleep low, train low – like two-a-days, the concept here is to perform a night training session followed with reduced CHO intake overnight preceding a fasted training session within the morning

No matter how carbohydrate depletion is reached, the result is analogous: reduced muscle glycogen serves as a robust signal to our cells. Our cells reply to these low levels of carbohydrate by employing two vital cellular messengers, PGC-1α and AMPK, each of that are vital energy regulators in your cells. These messengers indicate that the cell is critically low on CHO and in response, the cell should be prepared to effectively utilize fats as a fuel source. These types of adaptations which increase fat utilization are commonly wanted by athletes & their coaches.

Note: It’s important to indicate that key (HIIT) training sessions and competitions must be performed with high carbohydrate availability!

The Glycogen Threshold

Researchers have proposed a ‘glycogen threshold’, where a critical absolute level of glycogen depletion during (or following) training is particularly potent for skeletal muscle adaptations – mainly for increases in mitochondrial biogenesis and increases in fat oxidation. To place it simply, low carbs availability in your muscles can function strong signals to extend your muscle’s aerobic capability.


It’s interesting to notice that glycogen levels might be depleted from a big selection of exercises, from short, high-intensity efforts, to longer, aerobic exercise.

This image shows that the proposed ‘glycogen threshold’ (the grey band) might be reached via a wide selection of coaching sessions – from 9 min of HIIT to 4 hours of endurance riding. Muscle glycogen concentration is displayed on the vertical axis, while exercise duration is displayed along the horizontal axis. Image taken from Impey, et al., 2018.

Future Studies

The existence of a glycogen threshold doesn’t mean that you simply won’t achieve adaptions for endurance training in case you perform training with higher levels of muscle glycogen. Reasonably, this threshold suggests that enhanced adaptations related to low levels of muscle glycogen are especially outstanding once a certain quantity of depletion has been reached. Nevertheless, further research is required to know exactly how low muscle glycogen concentration must be to optimize skeletal muscle adaptations – does the brink change for various athlete populations? More research can be needed to know the carbohydrate cost of essential training sessions – take into consideration workouts like 4×8, 5×5, etc. – in order that athletes ensure they’ve enough carbs to successfully complete those tough sessions. No person desires to be bonking during a tough workout!

How Can You Apply This?

In the true world, it is probably going that you simply might practice one (or several) of the methods mentioned previously to cut back your carbohydrate availability. I like to recommend trying out a fasted ride perhaps a couple of times per week – ensure it’s for one among your easier/aerobic rides and never a high-intensity ride/workout, or a Zwift race!

zwift
Try it on a Zwift race

Conclusion

In today’s article, we explored a bit more behind what makes fasted training, and low carbohydrate availability, such a potent stimulus. In my next couple of articles, we’ll proceed exploring among the key cellular regulators that show you how to adapt & increase your fitness level. That’s all for this month. Stay protected, ride fast, and I’ll see you next month!

References

Impey SG, Hearris MA, Hammond KM, Bartlett JD, Louis J, Close GL, Morton JP. Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Med. 2018 May;48(5):1031-1048. doi: 10.1007/s40279-018-0867-7. PMID: 29453741; PMCID: PMC5889771.

Bartlett, J. D., Louhelainen, J., Iqbal, Z., Cochran, A. J., Gibala, M. J., Gregson, W., … & Morton, J. P. (2013). Reduced carbohydrate availability enhances exercise-induced p53 signalling in human skeletal muscle: implications for mitochondrial biogenesis. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 304(6), R450-R458. https://pubmed.ncbi.nlm.nih.gov/20351596/

Hulston, C. J., Venables, M. C., Mann, C. H., Martin, C., Philp, A., Baar, K., & Jeukendrup, A. E. (2010). Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine and Science in Sports and Exercise, 42(11), 2046-2055. https://pubmed.ncbi.nlm.nih.gov/23364526/

 

 


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