By Carl Valle
The central nervous system (CNS) is a popular topic in the sports training community, but I have not seen any wise information about how to confidently measure it. CNS fatigue is like gravity—we all believe in it even though we cannot see it. As the saying goes, if it’s not measured it’s not managed. In this article I dive into the good stuff, cutting through the fluffy science and avoid rehashing the information anyone can read on Wikipedia.
CNS fatigue is a very hard topic to cover because the science is scarce as is the ability to evaluate it. To say that I’ve spent half my life exploring CNS fatigue is not an overstatement. I’ve invested a fortune testing athletes and trying to make sense of the research as it never seems to reveal what I need. If you are a coach, sports medicine pro, or athlete, this will be a resource you’ll read a few times over.
Is CNS Fatigue a Buzzword?
SimpliFaster has shared an extensive number of CNS articles, covering such topics as the roles of dopamine and serotonin in fatigue, transcranial direct stimulation in sport, and how the microbiome affects the neurotransmitters of speed and power athletes. We’ve also had some great interviews with experts on the brain and continue to publish information about motor learning. If you were to search around online, you’d find everyone is discussing the CNS, but few are moving the needle on managing it.
About every month, I fall for the clickbait—you know the great article promotions on Facebook and similar sites where the authors promise they’ve decoded CNS fatigue and want to share their secrets? I’m not a sucker, but I keep trying to put an honest effort into reviewing any material on the subject. Although mentioning CNS fatigue or any topic about the brain is a cool discussion point, I frankly have not seen practical takeaways when coaches or sport scientists present material about the brain and specifically central fatigue.
This article is much different than the typical review of CNS in sport. I cover the science and link research to defend my views, and I share a construct in how to use practical applied methods in coaching. My approach isn’t groundbreaking, but it works:
- Understand adaptation and fatigue
- Know what to measure exactly
- Prepare to make adjustments
It’s not rocket science, but it does take a lot of manual work to ensure that athletes don’t get stale or burn out. I’ve pushed athletes beyond what their genetics told them they could reach, and the results were erratic. When you play with fire you can get burned, but you can also put on a good show when you pull it off.
The Sport Science on Central Fatigue
The past is important to learn from. It forms an awareness baseline and forces a comparison of the innovation or the lack of evolution with the subject matter of central fatigue. Coaches and athletes have known for years that overtraining affects the nervous system.
The 1904 Olympic champion Archie Hahn warned in his book, How to Sprint: The Theory of Sprint Racing, about how “nervous overwork” creates a staleness effect on athletes. On page 228 of his book, Hahn shares his observations for overtraining the nervous system and points out that loss of sleep, mood changes like indifference, and cognitive interference such as lack of concentration can occur. Unfortunately many of the fatigue countering techniques used elixirs of brandy and strychnine to ward off exhaustion during many forms of racing, especially in equine sports.
But most of the discoveries don’t come from sport; the older brother war is the muse to finding out how a human body overcomes stress. We can trace the back and forth influences of sport and military to ancient Greece, but it wasn’t until the early 1900s when sport science and military war science converged. While the Germans get a lot of attention for their use of methyl-amphetamines during the war and get fingered for early doping in 1936 Olympic Games in Berlin, the Americans invented Benzedrine (amphetamine).
Coaches later came to understand that athletes could get amped-up and then crash without foreign substances in their systems; our bodies create a substantial quantity of performance-enhancing chemicals. The scientists in the first half of the century made a lot of discoveries about how the brain handled stress and what could be done to override battle fatigue.
The 1970s and 1980s saw a resurgence in trying to understand the direct relationships of central fatigue with track and field, specifically the sprint events. Hill and Francis, from East Germany and Canada, were addressing the central fatigue effect while earlier influences including Winter and Mach handled their athletes with such care they only needed to focus on general fatigue symptoms.
It wasn’t until the 1990s that sport science started digging deeper into what makes the brain tick and sometimes not tock. The pioneering and ingenious work of Dr. Romain Meeusen asked and answered some very tough questions. The questions he and his colleagues could not answer are why coaches are invaluable.
In the three key publications, Dr. Meeusen paved the road for us with his brilliant thought leadership about overtraining and CNS, central fatigue (the serotonin hypothesis and beyond), and fatigue (is it all neurochemistry?). Each decade from 1997 to 2017 had small but valuable steps forward in understanding the complex biology of fatigue and the brain in sport. The milestones of these three decades were:
- the age of substrate
- the age of neurochemical balance
- the age of the microbiome and the brain
Central fatigue is not a segregated experience or response, it’s an interplay between multiple factors and inputs. CNS drain is not just related to neurotransmitters and it’s not totally central. Inflammation and emotional variables also influence how the entire human body processes training and lifestyle challenges. The latest evidence-based position still shows that other causes may be at work. Dr. Meeusen and his colleagues end their latest gem with the following:
“In general, we can conclude that brain neurochemistry is clearly involved in the complex regulation of fatigue, but many other mediators also play a role.”
As you can see, distilling a complex event like CNS fatigue to a few chemicals or even a few systems of the body is not complete. General fatigue or all forms of stress response outside the central aspects, including the local or peripheral, all matter and interfere with regeneration.
Fatigue Symptoms Coaches Can Observe
Coaches are most likely to catch mood and performance changes in their athletes. Sure, self-monitoring helps foster communication, but coaches are very intuitive and trust their guts—almost to a fault. No one should scoff at these observations, but they shouldn’t worship them or haphazardly treat them as fact. New technologies like facial coding detect fatigue and mood changes with an almost frightening accuracy, but the science in practical application lags far behind.Facial coding detects fatigue & mood with frightening accuracy but practical apps lag far behind. Click To Tweet
Coaches easily see body language and other non-verbal communication because they are at distances far away enough to allow them to view the big picture. For a different vantage point, coaches can zoom in by talking to their athletes. This is when verbal and facial expressions really point to their state of mind. Finally, historical data and record keeping are valuable for detecting central fatigue since the zone between overreaching and overtraining is very cloudy. We must view training as an early detection system. Athletes are born with talents, but even the most gifted need sufficient training to either improve or win at the highest levels.
I look at four primary checkpoints to provide clues of an athlete’s central or general fatigue:
Concentration and Alertness. The athlete’s ability to concentrate and be alert during training is one clue. A sharp athlete is usually a fresh athlete. Tired athletes are not elastic and move without that clean, effortless look we strive for.
Mood Change. A change in mood usually includes an increase in both impatience and irritability. Some explosive and ballistic athletes are divas and rebels to begin with, and things can get really toxic when the blessed are pushed hard in training.
Willingness to Train and Motivation. A drop in either the willingness to train or motivation that accompanies long periods of training or competition is another sign. A loss in wanting to put the work in, even with training addicts, is a timeless clue something is going wrong.
Happiness. Nothing beats laughing and smiling as a metric of growth. As Dr. Viru stated years ago, a happy and improving athlete is a great biomarker for monitoring.
A simple way to view fatigue is to look at the response to loading and the ability to generate output easily with magnitudes that are appropriate for the training session. Subjective feedback in any form, provided it’s consistent and comparable, along with quantified training or testing is the backbone of observing fatigue in all forms.
Central fatigue is mostly subjective for the athlete. But the best coaching eyes pick up decays in neuromuscular power coupled with a lack of crisp movement efficiency in training or competition. A training session’s warm-up period is the best time to determine an athlete’s readiness, but at the end of the day, competition is the truth serum.
CNS Readiness and Willpower
Willingness to train and the deep internal core of motivation are not easy to measure. Readiness and willingness are not interchangeable terms, as athletes are more complex than the cerebellum status we tend to focus on. We don’t hear enough about willpower. In my experience, the difference between winners and losers often comes down to who wants it more. A person’s drive is not easily measured, but it certainly can be felt when spending time with those who have it. CNS readiness is willpower, and willpower is a part of readiness—it can amplify readiness or silence a fresh and prepared athlete.
Daily competitive fire can burn out an athlete. Those who listen and follow a process won’t let themselves grind down to an injury or to a halt. I can fairly argue that readiness to train may mean readiness to train differently or to rest. While willpower and readiness are similar, the key difference is motivation and recovery. It’s easy for someone to wake up and want to get better, but if the athlete’s body does not agree the coach and athlete must figure out the path that makes sense in the long run.
To alternate preparedness and readiness periods, we must know when to ride an athlete’s drive for greatness and when to pull back so they can recharge. We all know this, but it’s easier said than done. This is the primary reason coaches, including myself, struggle to juggle the differences between the person’s psychological willpower and profile and their readiness. What fuels an athlete may change and vary throughout a career, although many athletes stay fairly consistent through their lives.
The Diagnostic Inventory of Psychological Competitive Ability (DIPCA) attempts to profile injury rates and other patterns of success and failure. Other profiles and screens are available, but research has not shown a definitive method for teasing out the spirit of athletes and non-athletes. A true screen may never happen, but sometimes a screen will catch very important information that helps everyone involved learn what drives winners to succeed.
While not perfect, it’s important to rate the values and desires of athletes informally as well as in a structured format. After creating a well-rounded profile, it’s easy to compare the response accuracy of actions with what the athlete said. Talking about excellence is great in an office, but things tend to change days later on the field or in the weight room. In addition to the baseline profile, it’s also good to consider childhood screens as the apple sometimes doesn’t fall far from the tree. Tapping into the past as well as looking at a person’s genetics are areas that will certainly grow. Simple screens provide a good start.
Don’t Chase or Monitor Fatigue–Manage Power and Recovery
Fatigue is not bad nor a guarantee of future success or adaptation, so don’t be scared of it and certainly don’t depend on it. I’ve had a few All-Americans who I felt I babied until the end of their season or career, and I learned fatigue isn’t always a sign of biological growth. Conversely, I’ve had a few athletes who I tried to train out of a technical problem that resulted in overtraining that could have ruined them. Luckily we tried rest as a last resort, and the athlete was able to come back in full form as if I planned it.
Because fatigue is a variable in injury, it has paralyzed many coaches and sports teams with fear, and that’s creating a generation of fragile and unprepared athletes. If we didn’t have all of the current physiological instrumentation and biochemical testing, would we be as frightened of overtraining today? In a meeting of the minds at the BSMPG a few years ago, sport scientist Dr. Mujika was adamant that he never saw a true case of overtraining syndrome.
He might be right, but without a comprehensive report of how he defines the state of an athlete and possible mechanisms at play, no scientist can repeat his observation. It’s plausible that he and other researchers haven’t seen this with speed and power events because their focus is on endurance sport. It’s not that overtraining doesn’t exist in endurance sport, it’s likely that most programs are not truly dealing with overtraining.Any form of fatigue is part of the solution to a problem, not one of the causes. Click To Tweet
Any form of fatigue, even if it’s central, must be seen as a part of the solution to a problem and not one of the causes. Without some fatigue, it’s likely that improvements will not occur over the long term. Also “prevent defense” (reactionary approaches to training with physiological monitoring) seldom prepares athletes for a long season or effective career development. By focusing on the training and knowing which recoveries occur at different rates, managing power is a positive and effective strategy. Growth, or even selective maintenance, is much better than trying to escape the CNS fatigue boogeyman.
The focus on managing power instead of monitoring fatigue is something I’ve mentioned multiple times. And although monitoring prevents or at least reduces our mistakes, it’s just as dangerous not to take risks. Measure training loads and compare to subjective inputs and outputs and then look for ways to get better and fight fatigue. Don’t surrender and retreat to an eventual loss later on.
How to Capture Valid Measures of the Brain and Body
CNS fatigue is a lousy term. Modern recovery science uses overload, overreaching, and overtraining to define the relative severity of fatigue. Sometimes a clinical diagnosis is easy to reach such as a vitamin or mineral deficiency. An orthopedic diagnosis of a broken bone can be made without much time and effort. CNS fatigue is not a binary diagnosis, like a mononucleosis test. It’s an interpretation of all readily available knowledge, including a lot of athlete history and training information.
The cost of adaptation is a very selfish process, meaning the body (specifically the brain) finds ways to cope with disturbances from outside elements and internal factors, even if it means sacrificing the health of other systems of the body. Tracking just barbell data, countermovement force-time curves, and subjective questionnaires is not a foolproof way to reduce overtraining mistakes.
Plenty of assessments exist, but athletes don’t often adopt research profiles and questionnaires because these methods lack engagement and a human touch. When the same questions are asked by a professional, the process is remarkably different. It’s better to polarize the process by making sure every moment counts with a person. Let technology do the monkey work while people do the human work. A one-hour chat without a smartphone can unlock a lot of information and is the first step to measuring central fatigue.Measuring the brain in isolation will not solve modern sport’s problems. Click To Tweet
Next comes what many coaches want to start with–measuring the brain and trying to create proxy information about fatigue from training. I could go into Omegawave readings, break down how pupillography (measuring the reactions of the pupil) is growing, and talk more about how HRV can indirectly measure central fatigue if used with other data. But even if an athlete is ready centrally, an injury that is too small to influence the readings may be enough to hamper the athlete’s training. Measuring the brain in isolation isn’t going to solve modern sport’s problems.
The truth is that all measures including EEG and fMRI are not the answer unless we combine them with loss of power and symptoms that are clinical, so to speak. Reaction time is a good test, but in today’s world how many kids or adults would find a reaction time test fun or motivational? We need creative solutions to make the old tried and true interesting in a modern world. Even if we could measure CNS fatigue conveniently, interventions outside of rest and time will not salvage a bad training program or insane competitive schedules like the ones the MLB, NBA, NHL, and the Champion’s league have.
Monitoring is about finding the most actionable measures that are both valid and convenient in a rhythm that is sustainable to best reduce known errors in sports training. Measuring CNS status will make a difference, but psychomotor tests are not easy to administer and are extremely limited. Omega potential is not a litmus test to CNS readiness, but it does have the most promise based on my experience and what I gleaned from the limited research. Still, to rely on one measure, even if it’s non-invasive and reliable, requires more supportive data and an interpretation of an athlete’s training and experience.
The take-home here is that coaches and support staff need to triangulate chronic CNS overload with multiple inputs and outputs as well as additional impairments that tend to tag along, like joint overuse syndromes.
Coaches and athletes can use proxy information, including subjective and objective tests and training data, to confidently screen out what is likely not the cause and deduce that CNS exhaustion is the culprit. Strategic rest and deloading will likely be the intervention of choice. But just like training, unloading work from a state of fatigue demands a similar combination of art and science as building or developing athletes.
How to Load the CNS Smarter
If I had to rename one article, it would be my piece on velocity bands because most people thought it was about overspeed cords. It was actually about primary solutions to managing fatigue and knowing how a program worked or failed. My other suggestions on autoregulation and training readiness and the Raptor Test round out information for the weight room. Other areas like plyometrics are more complicated. Regardless, using a contact grid with simple measures of distance or height is a good start for jumps.
The cream of the articles just mentioned is frequently testing and seeing the trends in changes in speed and power. Talking about neurochemistry without measuring the loads and the responses to loads is armchair quarterbacking. My one piece of timeless advice is to know the demands of the load to near compulsive levels before trying to measure central fatigue. Being cognizant of what an athlete can do absolutely makes managing their training far easier to facilitate than trying to act as a recovery physiologist after high-intensity work.
I created the list below with blood and tears. Before I had a grasp on measuring load and physiological responses, I centrally overtrained athletes. I learned some of the most painful wisdom when we came up short at the end of the season. While some of these athletes hit personal bests, they likely did so due to the adrenaline of championship competition and forced rest by tapering work that should have been better earlier.
- Make sure you contrast and compare all-time best performances with training scores while interpreting the time course of when the measures were achieved.
- Focus on simple and direct measures that are reflective and nearly predictive of performance, such as field tests and workouts that are like time trials.
- Monitor and benchmark the true cost of eliciting great or poor training and competitive results. Keep track of the athlete status acutely and chronically.
- Trust your instincts about how athletes are responding to all factors involved with success, as issues outside the competitive arena usually interfere with growth and recovery.
- When in doubt, call or video conference both a coach and sport scientist to look at the training’s cause and effect on the human being.
It’s just as straightforward to administer these actions. Create a weekly self-rating checklist that reflects what you feel or know off the top of your head. We often ask athletes to fill out questionnaires to elicit more information about how they feel. You should do the same by reflecting on the training.
Put the five points above into a super short checklist with only a phrase response. It’s the best coaching log I know. For me, each point listed has either a horror story or a cautionary tale attached to it that shows how my training was littered with mistakes anyone could relate to. Start checking in with your own feelings as often as you’re checking your athlete’s needs.
Loading the CNS is about exposing the body to extreme levels of output, all near maximal level. Tolerance to stress is not like the beer-drinking analogy we see in some sport science articles; ethanol processing is not the same as elite sports training. Adaptability and resilience are more than time and rest. They’re about knowing how to sequence training better than just throttling workloads up or down.
Prepare Athletes with a CNS Management Blueprint
Don’t copy my outline, make your own by looking at my framework and deciding what you agree with and what you may do better. Blind faith is rarely a good idea. I’ve learned that each of us needs to come up with our own process or system. Copying other people’s cookbooks or training systems is a recipe for disaster. If you should get anything out of this article, it’s how to move forward away from casual discussions to something more tangible. Talk is cheap. Without actually trying to measure and manage the CNS, we’re playing the intellectual high horse game and not contributing to solving problems that matter.