Does endurance training negatively affect the brain?

Endurance athletes may suffer from impaired cognitive abilities due to over-training, according to a new study. But how true are those claims?

Tom Otton, Endurance Athlete. courtsey: Honza Zak photography. (to go with Melanie Swan story)
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The UAE's race season is well under way, with the likes of the 42-­kilometre Abu Dhabi and Dubai Marathons, the 300km Al Marmoom Ultra Marathon and three-discipline Ironman 70.3 in Dubai drawing ever closer on the calendar. Each year, these events continue to grow, attracting a throng of participants from novices to elite athletes, taking to the UAE's terrains in some of the most gruelling human challenges. 

Not only are these long-­distance feats tough physically, but they are mentally demanding, too, and ­recent research has suggested some interesting side effects of people undertaking endurance training.

The study, led by ­economist Bastien Blain at University College London and supported by a team of medical researchers, analysed 37 male athletes with an average age of 35, as they went about a cycling regime where training increased by 40 per cent over a three-week period. This kind of spike is usually spread over several weeks or even months, but for the purposes of the research, it was done in order to induce a mild state of “over-training”. The results suggest cognitive functions could be impaired from excessive training.

The mental fatigue from over-training could, proffers the research published in Current Biology, reduce activity in a portion of the brain – the lateral prefrontal region – responsible for making decisions, such as stopping when the body is in pain. Athletes in the study were found to be more impulsive, less able to make serious decisions in areas such as finance, and opted for short-term gains or immediate rewards.

Last year, Dubai resident Marcus Smith ran 30 marathons in 30 days for the Dubai Fitness Challenge. As an endurance athlete and founder of InnerFight, whose company's motto is "show no weakness", he knows a thing or two about training hard. "We all know that when we are under huge cognitive fatigue, our ­decision-making process is affected to our detriment and we make poor choices," he says. It is something that happens daily, when someone chooses to eat fast food after a long day at the office, for example, or when a business decision is sub-optimal because of stress, he explains.

It is, however, important to keep things in perspective, says Smith, adding that any form of physical training needs to be calculated systematically with measurable goals to ensure maximal benefit. "In training, endurance athletes are essentially managing their tolerance and response to stress, and by this we mean not only the stress of the physical training itself, but stress of life in things such as jobs, home lives, nutrition and sleep." These are all factors in mental and physical performance.

Smith is no stranger to the effects of this kind of cognitive strain. When he undertook the gruelling desert race Marathon Des Sables, a 250km self-­supported, three-stage ultra-­marathon in Morocco's Sahara Desert, he was kept awake for about 60 hours, resulting in hallucinations and mental confusion. But, he says, there are simple ways to spot whether or not you're over-training, including not getting the desired results in spite of the required effort, feeling tired on waking and suffering from a lack of motivation.

Marcus Smith competing in the Marathon Des Sables ultra marathon in 2015. Courtesy Marcus Smith
Marcus Smith completed the 250km Marathon Des Sables in 2015. Courtesy Marcus Smith

Tom Otton, founder of Create Media, ran the ultra-marathon in Morocco alongside Smith. He says he’s not surprised by the findings from this new research, as the military has been assessing soldiers’ ability to make complex decisions under fatigue for decades. “Excessive or increased training loads, which is different to the physical condition of ‘over-­training’ [leading to] chronic fatigue or ­burnout, certainly does affect cognitive ability, as well as physical ability,” he explains. “I’ve found that when I’m pushing my limits physically, the mind goes into survival mode, therefore higher levels of cognition become increasingly difficult. Athletes get what we refer to as ‘brain fog’.”

Dr Arthur Williams, head of medicine at the Diversified Integrated Sports Clinics in Dubai, has been a doctor for more than 25 years and worked extensively with sports teams and athletes. He disagrees with the study's findings and believes, in his experience, endurance athletes in all types of sport tend to be mentally very strong with a high drive and focus, showing superior physical and mental skills than the average person.

It's happened to me in races, when I have failed to follow through on a nutrition plan [leading up to the race] that would have led to better results on race day, just because my brain told me I was fine and didn't need to eat.

With a wealth of science and data available today to guide the way people train, he says there are fewer reasons to reach the state of fatigue identified by the study. Yet, when training programmes are increased too rapidly, it is inevitable that bodies and brains will suffer, he adds. Symptoms of this include muscle fatigue, chronic injuries, slow recovery from minor injuries, repeat injuries, time off from participating and reduced performance.

“In some instances, athletes show a change in sleeping pattern, repeat incidence of respiratory infections, gastrointestinal symptoms, bone stress injuries and changes in their emotional and mental health,” he explains. “Impaired thinking or decision-­making and cognitive function in the long-term are possible, but I have rarely seen it in practice.” The key, he says, is to slowly increase training load to condition the body in preparation for events and allow time for recovery.

Stuart Caunt, a triathlete from Dubai, says while most training programmes suggest that increasing training goals by more than 10 per cent per week is likely to lead to issues, when it comes to ­decision-making, the physical demands an athlete endures takes a toll. "I would definitely agree that decision-making can be compromised as the body becomes fatigued," says the British national, who completed his first half Ironman in 2009 and has continued to do multi-stage cycling races ever since.

Stuart Caunt competing in last year's Wines to Whales - a multi-stage cycling race in the UK. Courtesy Stuart Caunt
Stuart Caunt competing in last year's Wines to Whales - a multi-stage cycling race in the UK. Courtesy Stuart Caunt

“It’s happened to me in races, when I have failed to follow through on a nutrition plan [leading up to the race] that would have led to better results on race day, just because my brain told me I was fine and didn’t need to eat.” He does assert, however, that the research should in no way deter people from participating in sport. Done with correct guidance, he says the benefits are unquestionable to both physical and mental health. 

Dr Williams agrees. He says the research could scare people away from exercise, if taken out of context. "From my practice and clinical experience, endurance training per se does not have any negative effect on your mental state," he says. "They adapt over time to their training demands and in the professional era, athletes know how to manage their programmes to prevent over-training."   

Researchers say the findings may not only be relevant to athletes, but also decisions-makers such as politicians or those in the judicial or economic fields, as mental fatigue from stressful intellectual work could equate to the same strain experienced during physical exertion. The project’s next phase will continue to explore possible treatments or strategies to help prevent any such neural fatigue.

From my practice and clinical experience, endurance training per se does not have any negative effect on your mental state.

Smith says while the findings in the study are straightforward, it has the potential to be detrimental. “Sadly, many people will read it and feel like endurance sports are high risk for our health and longevity, but then again so is working 12 hours a day in a sedentary office job and pulling ‘all-nighters’, but somehow, the corporate world thinks this is OK.

“In all honesty, I believe that if you changed ‘athlete’ in this study for ‘business executive’, you would have the same findings. Think about it: that financial investor who is playing around with your life’s savings may be doing so with cognitive fatigue caused by ­excessive work, stress from his family life and poor nutrition – and he is now in charge of ­investing money you have worked hard for. Are you comfortable with that? Me neither.”