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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 terrific summer of riding and are having fun with your hard-earned fitness because the days proceed to shorten. In this text, I would love to introduce a comparatively latest concept generally known as the ‘Glycogen Threshold’. I’ll briefly discuss the cellular mechanisms behind it, in addition to discussing how & why it’d 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 a giant ride or race is well-known by us all. With that in mind, the idea 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). The truth is, 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 extremely 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 whenever you run out of carbs may be miserable.

What happens during Carb Depletion?

There are just a few ways to intentionally cause carb depletion, but they may 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 to 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 styles of adaptations which increase fat utilization are commonly wanted by athletes & their coaches.

Note: It is crucial to indicate that key (HIIT) training sessions and competitions ought to 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 very 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 may 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) may be reached via a wide range 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 just won’t achieve adaptions for endurance training should you perform training with higher levels of muscle glycogen. Somewhat, this threshold suggests that enhanced adaptations related to low levels of muscle glycogen are especially distinguished once a specific amount 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 edge change for various athlete populations? More research can also 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 just 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 few times per week – make certain it’s for one in every of 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 are going to proceed exploring among the key cellular regulators that allow you to adapt & increase your fitness level. That’s all for this month. Stay secure, 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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