Brain in Sport

Neural  plasticity  is  the  mechanism  by  which  the brain  encodes  experience  and  learns  new  skills, behaviors, and habits in daily life and on the athletic field. Brain cells called neurons form a communication network that serves as the foundation of information processing in the brain. The neural network  of  the  brain  holds  the  capacity  to  rearrange and strengthen communication efficiency. It is  through  this  process  of  rearrangement  (neural plasticity)  that  we  can  experience  changes  in  the way our minds think, feel, and act. This includes everything from changing your backswing in golf or tennis, to developing a new mental routine for shot  preparation,  or  restoring  function  following biomechanical  or  nervous  system  injury.  Thus, optimal performance, skill learning, and recovery are achieved when the capacity for neural plasticity is maximized. Research has shown that physical exercise  increases  the  brain’s  capacity  for  plasticity, reflected in part by changes in brain structure and function following exercise training in animal models  and  humans.  Since  aging  results  in  gradual  neurodegeneration,  or  loss  and  dysfunction of  brain  cells,  and  decreased  neuronal  plasticity, aged samples (e.g., 60–80 years) form a platform for  studying  methods  to  increase  brain  plasticity. This entry reviews research on exercise effects on mental  performance  and  the  brain  and  highlights results with aged samples.

Exercise’s Influence on Cognitive Performance

Since  the  1960s,  studies  have  shown  that  physically more active people perform better on tests of cognitive  performance  compared  with  physically less  active  peers.  The  first  studies  examined  performers’ ability to successfully complete dual tasks by primarily measuring simple response time, the speed to respond quickly and accurately to a flash of light, and discrimination time, the speed to press one key if stimulus A appears and another key if stimulus B appears. Over time, more complex cognitive  processes  have  been  examined,  such  as  the ability to switch between tasks, the ability to selectively pay attention and block out distractions, or the ability to inhibit automated responses or habits.  Importantly,  in  these  early  studies  the  physically  active  groups  were  comprised  primarily  of competitive athletes. This may present interpretive problems  due  to  the  possibility  of  self-selection, such  that  athletes  may  seek  and  continue  sports participation,  in  part,  because  of  their  natural superiority in cognitive processes that benefit sport performance,  such  as  fast  response  time  or  the ability to focus amidst distraction. Thus, the best understanding  of  the  effects  of  physical  activity and exercise on mental performance and the brain comes from studying samples that have been well-matched on all characteristics other than physical activity level.

Several reviews have now quantified the effects of physical exercise on mental performance across studies  in  meta-analyses.  Meta-analyses  attempt to aggregate results from many studies and group results  from  similar  variables  together  for  the purpose  of  identifying  and  comparing  replicable effects across studies at either the level of measurement (Does the effect replicate for a specific task?) or construct (Does the effect replicate across tasks that  are  all  theoretically  deemed  to  measure  the same  construct?).  For  example,  the  effect  size  of exercise training on simple response time could be calculated in different studies that included training  and  pre and  post-tests  of  simple  response time,  and  then  an  average  could  be  computed across studies to determine if exercise results in a consistent  improvement  independent  of  any  one study or laboratory.

Meta-analyses that have examined the question of how exercise training affects different domains of  mental  performance  have  demonstrated  that exercise has a small to moderate effect on a range of  cognitive  abilities  across  the  lifespan.  In  older adults,  consistent  benefits  have  been  shown  in speed  of  processing,  as  in  simple  response  time; visuospatial  and  selective  attention,  such  as  the ability  to  compare  line  drawings  or  to  selectively attend  to  stimuli  or  objects  in  the  environment without  distraction;  executive  function,  a  set  of abilities  related  to  inhibiting  unwanted  actions, multitasking, or juggling information in one’s mind such  as  mentally  carrying  out  long-division;  and declarative memory, which refers to the ability to remember previous events like the face and name of someone you met at a party last week. Across studies with older adults ages 55 to 80 years, several moderating variables have been identified that may result in greater effects of exercise on mental performance. In regard to exercise type, a combination  of  strength  and  aerobic  training  seems  to result in greater effects than either alone. In regard to  participant  characteristics,  women  seem  to benefit  more  than  men  and  participants  between ages  66  and  70  years  may  benefit  more  than younger  or  older  adults.  In  regard  to  duration, 30to 45-minute exercise sessions over 6 months have produced a larger benefit than shorter training  periods.  Since  many  of  these  studies  included previously sedentary participants, it does not take long for benefits to occur. Yet the question of how long benefits last and what type of exercise is optimal for maintenance of cognitive benefits is open for  future  research.  It  is  also  important  to  note that moderating variables such as these remain an active area of research in exercise neuroscience.

Exercise’s Influence on Human Brain Structure

Exercise  impacts  performance  in  part  through enhancement of structural properties of the brain. For  example,  aging  typically  results  in  shrinkage  of  brain  volume  in  the  frontal  and  temporal association  cortices.  This  can  be  measured  using in vivo brain imaging technology called magnetic resonance  imaging  (MRI).  However,  studies  have shown that greater physical activity (e.g., distance walked) or moderate aerobic exercise training over 6 months (walking at 60%–70% HR max) among older adults is associated with greater gray matter volume  in  the  frontal  and  temporal  cortices  and greater white matter volume in the frontal cortex. Gray matter refers to where neurons expend their energy for information processing and form their connections  with  communication  points  called synapses. White matter represents the part of neurons that transmit neuronal activity between different areas of the brain and is composed primarily of myelin,  which  insulates  the  transmission  “wires” (known  as  axons)  of  neurons  and  increases  the speed of neural communication.

Increases  in  gray  matter  from  exercise  could therefore be from increases in the number of connective branches a neuron forms to communicate with  other  neurons.  In  some  brain  regions  like the  hippocampus,  exercise  may  actually  accelerate normal generation of new neurons (neurogenesis).  In  contrast,  changes  in  white  matter  could result  from  increased  myelination  production  or repair  or  from  increases  in  the  number  of  axons that branch out from the neuron. Increases in the number and thickness of blood vessels could also contribute  to  increases  in  brain  volume  as  measured  in  humans;  blood  vessels  traverse  through gray and white matter and are not well identified on typical brain scans that have been used in most studies  to  date.  However,  there  is  evidence  that exercise  training  increases  cerebral  blood  flow  in the  hippocampus  in  humans,  which  is  consistent with  animal  studies.  One  reason  enhanced  blood flow  is  important  is  because  energy  for  neuronal processing,  and  therefore  information  processing, is  transmitted  to  brain  cells  through  increases  in blood  flow.  Therefore,  greater  resting  cerebral blood  flow  is  thought  to  predict  greater  responsiveness  to  the  energy  demands  of  information processing.

In  sum,  while  aging  results  in  gray  and  white matter  volume  decline  in  the  frontal  and  temporal  association  areas,  aerobic  exercise  has  been shown  to  attenuate  this  atrophy  through  mechanisms of neuroplasticity that increase the connective  branching  of  neurons,  volume  of  insulating myelination, density of synaptic connections, and through increased birth and survival of brain cells in the hippocampus. Future research will continue to examine the cellular and molecular mechanisms of  changes  in  human  brain  volume  after  exercise training.

Exercise’s Influence on Human Brain Function

Contrasted to brain structure, brain function refers to how well neurons and their support system can coordinate  activity  to  support  ongoing  thoughts, emotions, perceptions, and behaviors. Using MRI, the effects of exercise on brain function have been studied  by  either  examining  how  well  different parts of the brain respond to demand for information  processing,  which  we  call  task-evoked  functional  MRI  (fMRI),  or  by  examining  how  well different  regions  in  the  brain  activate  in  teams (functional networks) that we know support coordinated  mental  performance.  Some  studies  have also used more direct neuronal stimulation methods  like  transcranial  magnetic  stimulation  (TMS) to study the link between regular exercise and synaptic plasticity.

When examined with task-evoked fMRI, aging studies  have  examined  activation  during  executive  function  tasks.  Executive  function  tasks  are of interest because they are known to engage the prefrontal  cortices,  which  are  areas  of  the  brain that become dysfunctional with increasing age. In turn, studies have found that more aerobically fit older adults have more prefrontal brain activation during executive function performance. For example,  one  study  found  that  greater  aerobic  fitness was  associated  with  greater  prefrontal  activation during the Stroop task, which requires responding to the ink color of a word regardless of what the word  says.  Because  of  the  automaticity  of  reading, the Stroop task is cognitively demanding and it requires coordinated brain activity in prefrontal and visual cortex. Importantly, greater fitness was only associated with greater prefrontal activity and not visual cortex activity.

Similarly, a training study found that 6 months of  walking  training  in  sedentary  older  adults resulted in increased prefrontal cortex activity during  a  task  requiring  attentional  focus  and  inhibitory  control,  and  that  greater  prefrontal  activity was coupled with greater task performance. These studies support that aerobic exercise benefits mental  performance  in  part  through  enhancement  of prefrontal  cortex  function.  Recent  research  also supports  a  beneficial  effect  of  resistance  training on brain activation associated with inhibition and memory  processes  that  rely  on  areas  outside  the prefrontal  cortex,  suggesting  resistance  training may play a complementary role to aerobic training in supporting brain function across the lifespan.

Evidence also exists demonstrating that aerobic exercise  is  associated  with  greater  coordination of  brain  activity—in  regard  to  both  broad  brain networks and to synaptic plasticity in specific neuronal circuits. Brain networks are teams of physically distant regions that work in coordination and provide a system for the brain to carry out highly specific,  local  processes  that  feed  up  to  coordinated,  complex  processes;  neural  plasticity  is  the foundation for these functional networks to maintain  coordinated  teamwork.  In  one  study,  older adults  with  greater  aerobic  fitness  had  greater functional coactivation in a brain network known as  the  default  network,  whose  deterioration  has significant  implications  for  cognitive  aging,  risk for  dementia,  and  a  host  of  developmental  psychiatric  disorders.  Exercise  effects  were  strongest in the lateral and ventromedial prefrontal regions and  the  temporal  cortex,  including  the  hippocampus.  Importantly,  this  research  also  suggests that greater functional coordination in the default network  is  associated  with  some  of  the  cognitive benefits that are linked to aerobic fitness, suggesting this network may be an important component of how exercise improves cognition and decreases risk  for  dementia  in  late  life.  It  may  also  suggest that exercise would be beneficial for developmental  disorders  related  to  impaired  default  network function.

Finally,  there  is  evidence  that  greater  aerobic fitness  is  associated  with  greater  TMS-induced synaptic  plasticity.  The  basis  of  learning  is  the brain’s ability to form new neural connections or to  strengthen  existing  pathways  based  on  experience. One way to study this is to pair stimulation of a hand muscle with electromagnetic stimulation of  a  corresponding  region  of  motor  cortex.  The capacity for synaptic plasticity in this circuit can be measured by the increase in reactivity of the hand muscle  to  activation  of  the  motor  cortex  following paired training. One study showed that more active adults had greater synaptic plasticity in the specific  motor  circuit  studied.  Although  this  was a cross-sectional study, it presents complementary evidence  for  the  link  between  aerobic  fitness  and enhanced synaptic plasticity that may be a generalizable  mechanism  for  the  effect  of  exercise  on coordinated brain function and improved learning and performance.

Overall,  there  is  exciting  evidence  for  exercise’s  potential  to  attenuate  age-related  brain dysfunction,  and  these  results  have  implications for  improving  the  brain’s  capacity  to  learn  and respond adaptively to injury at any age. However, the mechanisms for how this happens are not fully understood and future research should be guided by the need to understand the cellular and molecular basis of these benefits.


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