The Brain’s Use of Energy and What it Means to Cyclists
The human brain is energy-intensive, consuming hundreds of calories every day. This energy is a finite resource stored in the body as glycogen. Mental energy is also limited, with only so much cognitive load available to face the stresses and complexities of a race. Can you train your brain to be more efficient?
For more information on mental efficiency and cognitive load, check out Ask a Cycling Coach Ep 264.
Glycogen Stores and Blood Glucose
The most important fuel that drives both muscles and brains is glucose, a sugar stored in your body as glycogen. At low intensities, the body can fuel itself by metabolizing fat, but as exercise intensity increases muscles rely more and more on glycogen. The glycogen stores that supply this work are primarily located in your muscles themselves, and improving the capacity to store and utilize this fuel is one of the most important results of training.
A separate supply of glycogen is also stored in the liver, and released into the bloodstream as glucose. Your brain and central nervous system rely on this supply, and consume as much as 60% of blood glucose when the body is at rest. Separating this glucose supply from the muscles allows your body to prioritize fueling the brain above all else, and even during hard exercise, blood sugar levels are maintained through this release of liver glycogen. When blood glucose levels do fall, serious consequences occur – weakness, shakiness, and chills associated with bonking. In this condition your muscles actually still contain glycogen and are capable of continuing to work, but the reduction of the brain’s energy supply is a non-negotiable limiting factor.
This means fatigue is in the brain as much as in the muscles, and keeping your brain fueled is of primary importance to performance. Research suggests that unlike muscular energy stores, liver glycogen storage unfortunately can’t be trained. What can be actively influenced is your liver’s release of this precious supply. Studies show ingesting 40-100g of sugar per hour during exercise can reduce or almost eliminate depletion of liver glycogen, prolonging endurance dramatically.
Key Takeaway: Your brain uses lots of energy and holds the keys to fatigue; keeping blood sugar supplies maintained during exercise is crucial.
The Brain’s use of Energy
While we are limited in directly improving the brain’s energy supply, it may be possible to influence its energy demand. Most of the brain’s calories are spent on maintenance, but complicated tasks activate more of the brain’s machinery and increase local glucose consumption by about 5%. While this might not seem like much, imagine increasing the intensity of an interval by 5%, or having 5% more to give in a final sprint. Marginal gains are meaningful in bike racing, and although this is not proven by research, reducing the brain’s energy demand by even a little might help you gain the upper hand.
Riding a bike becomes more uncomfortable as intensity increases. Hard efforts challenge your mental fortitude, with the desire to stop arising long before the muscles actually reach their limits. This is an example of how cycling challenges response inhibition, also known as impulse control. Suppressing the impulse to stop takes real effort, and this effort is taxing.
Studies of runners and cyclists using Stroop Tasks have shown that amatuer athletes experience significant decreases in performance after completing challenging cognitive tasks. Professional athletes in the same studies were better able to complete these tasks to begin with, and experienced no decline in athletic ability afterwards. This suggests that improved response inhibition is one hallmark of elite riders, and that reducing the cognitive load of racing and training might result in meaningful gains on race day.
Key Takeaway: High cognitive load can negatively affect performance.
System 1 and System 2 Thinking
Reducing cognitive load starts with deliberate practice. Nobel Prize-winning economist Daniel Kahneman describes two modes of thinking associated with practicing and learning complicated tasks. System 2 thinking is slow, deliberate, and self-aware, and requires concentration and effort. As you become more skilled at a task you utilize more System 1 thinking, which is fast and more intuitive. An example of this process is learning an instrument: initially, every note demands focus, but with practice the technique becomes automatic.
There are countless examples of this idea in racing and training. From learning to clip in, to riding efficiently in aero or learning to position yourself in the peloton, every skill in cycling benefits from focused repetition. The more you are able to internalize and automate your tasks on the bike, the more cognitive space you open up, and perhaps the less energy your brain demands.
Key Takeaway: Increasing your skill at a task decreases the cognitive load of that task.
Perfect Practice Makes Perfect
Thoughtlessly practicing something isn’t enough to cause improvement. Instead, practice perfection by starting slow and prioritizing good form in a low-stakes environment. For instance, if you want to be more efficient through corners in cyclocross, repeat turns at low speed and focus on each individual element of the act- your body’s position and distribution of weight, the angle of your bike below you, and the proper line through the corner. Find a safe place to practice, and do it over and over. The learning process itself is not glamorous, but the outcome makes the process worthwhile.
Good practice also requires intention and reflection. As you repeat the task, have a more-skilled friend watch you and offer a critique, or record yourself and compare it to a pro doing the same thing. Your ability to do something well does not come automatically, but by making intentional improvements to your technique you can internalize good skills. Create a deliberate feedback loop – carefully examine successful performances of others, apply what you learn to your own efforts, and seek external critique of your results.
Key Takeaway: Internalize the best version of a skill through deliberate, specific, form-first practice and critique.
Your brain’s energy supplies probably can’t be directly improved, but your brain’s use of this energy almost definitely can. This applies both to physical energy stores (glycogen) as well as to impulse control/ mental energy. By fueling your workout properly and developing the cognitive economy of type 1 thinking, you can be more efficient, more effective, and more intuitive athlete.
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References/ Further reading:
- Gonzalez, Javier & Fuchs, Cas & Smith, Fiona Elizabeth & Thelwall, Pete & Roy, Taylor & Stevenson, Emma & Trenell, Michael & Cermak, Naomi & Loon, Luc. (2015). Ingestion of Glucose or Sucrose Prevents Liver but not Muscle Glycogen Depletion During Prolonged Endurance-type Exercise in Trained Cyclists. American journal of physiology. Endocrinology and metabolism. 309. ajpendo.00376.2015. 10.1152/ajpendo.00376.2015.
- Gonzalez, Javier & Fuchs, Cas & Betts, James & Loon, Luc. (2016). Liver glycogen metabolism during and after prolonged endurance-type exercise. AJP Endocrinology and Metabolism. 311. 10.1152/ajpendo.00232.2016.
- Kahneman, Daniel. Thinking, Fast and Slow. New York: Farrar, Straus and Giroux, 2011.
- Martin K, Staiano W, Menaspà P, et al. Superior Inhibitory Control and Resistance to Mental Fatigue in Professional Road Cyclists. PLoS One. 2016;11(7):e0159907. Published 2016 Jul 21. doi:10.1371/journal.pone.0159907
- Pageaux B, Lepers R, Dietz KC, Marcora SM. Response inhibition impairs subsequent self-paced endurance performance. Eur J Appl Physiol. 2014;114(5):1095-1105. doi:10.1007/s00421-014-2838-5
- Raichle, Marcus E, and Debra A Gusnard. Appraising the brain’s energy budget. Proceedings of the National Academy of Sciences of the United States of America vol. 99,16 (2002): 10237-9. doi:10.1073/pnas.172399499
- Wasserman, David H. Four grams of glucose. American journal of physiology. Endocrinology and metabolism vol. 296,1 (2009): E11-21. doi:10.1152/ajpendo.90563.2008