Recovery: have we forgotten the brain?

When you have a performance to deliver, it’s not just your muscles and heart that are called upon, but also your nervous system. While the muscle’s ability to generate force is important, so is the coordinated recruitment of these muscles by the nervous system. For example, when you start strength training, it’s mainly nerve adaptations that are responsible for the first gains in strength. What’s more, during a time trial, the perception of effort and motivation, regulated by the brain, are strongly associated with performance. If the duration of this type of test is a few hours, we can see that muscle recruitment by the nervous system is affected (1).

Physical performance puts stress on the body, and strategies are often needed to speed up recovery. Those commonly used focus mainly on restoring muscle performance. In particular, protocols for replenishing our energy reserves (mainly glycogen) and repairing muscle micro-injuries are frequently used by health professionals and the general public. All this is important, but brain recovery strategies are much less well known and even less widely used. So we have to ask ourselves: have we forgotten the brain?

Current knowledge of brain recovery is far less developed than that of muscle recovery. As a result, no clear protocol has yet been established. However, a recent review of the literature on the subject has come up with some very pertinent recommendations. The overall message of this study is that two factors are essential for optimal brain recovery: carbohydrate intake (sugars) and, above all, sleep.

Carbohydrate intake
During endurance events lasting several hours, the concentration of serotonin, a hormone affecting the perception of effort, mood and motivation, is disturbed. Taking glucose and branched-chain amino acids (BCAAs) helps restore serotonin levels after this type of effort (3). Similarly, after 4 weeks of training in rats, brain glycogen stores are increased from baseline levels (2). This underlines the fact that the human brain’s energy reserves could recover and adapt to training in a similar way to muscles. In short, it seems that the strategies used to replenish muscle energy reserves are beneficial to the brain.

Sleep
Sleep deprivation impairs brain function, resulting in poor performance on cognitive and motor tasks, as well as affecting mood and motivation (3). These factors are all crucial to optimal sports performance. In fact, the brain’s glycogen reserves are replenished mainly during the night. Thus, during episodes of sleep deprivation, the state of these reserves is affected. This results in reduced use of the latter, and hence negatively affected cognitive performance (5). What’s more, sleep is the time when the brain eliminates neurotoxic waste (6). In short, sleep deprivation has a negative impact on the brain. From a sports performance perspective, during periods of high training load, the percentage of time spent in deep sleep increases (4), reflecting the increased need for recovery.

In concrete terms, the following recommendations are useful for optimizing sleep: sleep in a cool, dark environment, avoid the use of electronic devices before bedtime, avoid caffeine consumption during the second half of the day and maintain a regular sleep schedule (3).

In conclusion, recuperative sleep and adequate carbohydrate intake are 2 key elements in brain recovery. However, as this field of research is still in its infancy, current recommendations will certainly be improved in the years to come. It will be all the more interesting to verify the usefulness of these strategies in extreme environments (heat or altitude) where central nervous system fatigue is exacerbated.

Written by Mathieu Lanoue, Kinesiologist.

References:
1. Lepers, R., Maffiuletti, N. A., Rochette, L., Brugniaux, J., & Millet, G. Y. (2002). Neuromuscular fatigue during a long-duration cycling exercise. Journal of Applied Physiology, 92(4), 1487-1493.
2. Matsui, T., Ishikawa, T., Ito, H., Okamoto, M., Inoue, K., Lee, M. C., … & Soya, H. (2012). Brain glycogen supercompensation following exhaustive exercise. The Journal of physiology, 590(3), 607-616.
3. Rattray, B., Argus, C., Martin, K., Northey, J., & Driller, M. (2015). Is it time to turn our attention toward central mechanisms for post-exertional recovery strategies and performance? Frontiers in physiology, 6, 79.
4. Taylor, S. R., Rogers, G. G., & Driver, H. S. (1997). Effects of training volume on sleep, psychological, and selected physiological profiles of elite female swimmers. Medicine and science in sports and exercise, 29(5), 688-693.
5. Thomas, M., Sing, H., Belenky, G., Holcomb, H., Mayberg, H., Dannals, R., … & Welsh, A. (2000). Neural basis of alertness and cognitive performance impairments during sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity. Journal of sleep research, 9(4), 335-352.
6. Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., … & Takano, T. (2013). Sleep drives metabolite clearance from the adult brain. science, 342(6156), 373-377.