The Brain, Not Our Body, Limits Our Endurance Performance
Wanting to stop
“There is still 20 km of running to go, almost half a marathon.
I want to stop. I really do.”
My inner dialogue is becoming more desperate. It’s my first 100km ultra-marathon and I’ve been moving for more than 10 hours.
I physically cannot move for much longer, there is nothing left in the tank.
The Classical Model
The classical model of fatigue, originally put forward by A.V. Hill in the 1920s, contends that during extreme, aerobic exercise, lactic acid accumulates and impairs the muscles of the skeleton.
This build-up of lactic acid in the body causes us to terminate exercise — stopping is involuntary.
The model suggests:
- An inability to anticipate, or take the necessary actions to avoid catastrophic metabolic failure
- The body is unable to maintain homeostasis — the internal, and relatively constant, steady state, of living things — during extreme aerobic exercise
- A lack of oxygen to the muscles leads to skeletal muscle ‘anaerobiosis’ (the absence of air), causing the accumulation of lactic acid in the skeletal muscles, resulting in muscle fatigue
The following youtube video provides a good example of the body appearing to fail during the physical trauma of the now legendary finish at the 1997 Ironman world championships.
Endurance is in the mind
Humans have an incredible wealth of psychological resources to deal with physical challenges, but frequently we are unable to access them.
“I can see the finish, off in the distance.
The sounds of the finish line, the cheers and the announcements, drift over the warm evening air.
I talk to myself, I tell my legs to keep moving.”
To fully understand endurance and our limits, interdisciplinary models are required, taking direction from biology, genetics, biomechanics, psychology, neuroscience, and physiology.
The Central Governor Model
Most modern sports professionals now accept that the mental state of the athlete, and cognitive strategies of the human brain, impact endurance performance.
Tim Noakes, a leading researcher in endurance was one of the first, and most vocal, to reject the widely-held, classical view that exercise performance is limited by chemical factors in the muscles — a response to a failure of the heart.
Noakes’ view is that the classical, or peripheral, fatigue model requires a re-think. The existing model does not adequately explain (despite all available muscles having already been recruited and fatigued) the ability of athletes to increase pace near the end of competition.
Instead, he suggests a central governor within the brain that actively regulates the recruitment of appropriate numbers of muscle fibers to ensure exercise is completed safely.
According to the Central Governor Model (CGM) control systems, managing the number of motor units activated, ensure homeostasis is maintained, irrespective of either exercise intensity or duration. The perception of fatigue is generated by the brain to ensure increasing discomfort causes exercise to cease in advance of homeostasis failure.
During a race, a subconscious element of the athlete’s brain sets the pace, to ensure the athlete makes it to the finish line, whilst retaining physiological homeostasis, and maintain a degree of physiological reserve.
The pacing strategy of an athlete is the outcome of a comparison between the actual sensations of fatigue, or rating of perceived exertion (RPE), and the expected level of fatigue.
The perceived exertion, set early on during exercise, as part of a feedforward control mechanism, provides the link between the athlete’s physiology (impacted by exercise) and the subsequent behaviours to maintain homeostasis.
In this model, the rating of perceived exertion predicts the duration of exercise to exhaustion.
More recently, Samuel Marcora has suggested the Psychobiological Model, to challenge the existing classical model, that the length of aerobic exercise is limited by muscular fatigue.
He also argues:
There is no need for a central governor to deter the conscious brain through increased perceived exertion, and a subconscious element that controls maximal neural recruitment of locomotor muscles.
Instead, his proposed model integrates both psychology and physiology by suggesting exhaustion and disengagement from exercise are a result of:
- An athletes perception of effort exceeding the maximum effort they are prepared to exert.
- Mental fatigue, rather than cardiovascular, or muscular mechanisms, increasing the perception of effort. This results in a reduction in pace, set by the athlete, during endurance performance.
The Psychobiological Model, argues that exhaustion, which limits the ability to sustain aerobic exercise, is created by the conscious decision to terminate endurance task performance.
Research reports that mental fatigue in advance of endurance activities, increases the perception of effort, and this leads to early disengagement from physically challenging tasks.
I have a beer and a burger inside me, and I stand up to stop my legs from seizing,
Surprisingly, though its only 30 minutes since I ran through the finish line, I probably could run a little further, if I had to.”
What does this mean for endurance?
The Central Governor Model and the Psychobiological Model both attempt to explain endurance performance by combining, and understanding psychological and physiological factors.
Whether endurance is performance is limited consciously or unconsciously, there is no doubt that the mind has a large degree of control over the body, but that it may be difficult to override.
Research suggests that appropriate mental training may reduce mental fatigue and thereby limit the rate of perceived exertion, and benefit endurance performance.
Performance improvements have been found in response to the use of imagery, self-talk, and goal-setting.
Whether we consciously, or unconsciously decide to stop, or ease up, during distance training and competition, it is both a battle of mind and body.
A final, and important, logical conclusion of the Psychobiological Model is that training whilst mentally fatigued may positively impact race day performance. A long run at the end of an exhausting day in the office, or lectures, may benefit both the psychology and the physiology of the individual.
Marcora, S. M. (2008). Do we really need a central governor to explain brain regulation of exercise performance? European Journal of Applied Physiology,104(5), 929–931.
Mccormick, A., Meijen, C., & Marcora, S. (2015). Psychological Determinants of Whole-Body Endurance Performance. Sports Medicine, 45(7), 997–1015.
Noakes, T. D. (2007). The Central Governor Model of Exercise Regulation Applied to the Marathon. Sports Medicine, 37(4), 374–377.
Noakes, T. D, St Clair Gibson, A. (2004) Logical limitations to the “catastrophe” models of fatigue during exercise in humans. British Journal of Sports Medicine, 38(5), 648–649.