Cognitive functioning may be preserved or improved through exercise. Both acute and regular exercise have positive effects on cognition, particularly on measures of attention, executive functioning, and memory. Improving fitness may be especially beneficial to cognitive function in older adults and persons with chronic medical conditions. Future studies should identify the mechanisms for these benefits and seek to determine the clinical utility of routinely recommending exercise to promote better neurological outcomes.
Cognitive impairment is prevalent and associated with high personal and societal costs. An estimated 13 to 16 million Americans are believed to experience some level of cognitive dysfunction (1), and this dysfunction is associated with poorer quality of life (2), greater risk for disability (3), and increased mortality risk (4). Unfortunately, despite the success of stimulant mediations (5) and cholinesterase inhibitors (6), many cognitively impaired persons obtain insufficient benefit from pharmacological intervention for their symptoms.
Researchers have sought to identity other interventions with the potential to improve cognitive outcomes in those suffering from chronic medical conditions. Physical fitness has been associated with improved cognitive functioning in persons across the lifespan, including children (7), young adults (8), middle-aged adults (9), and older adults (10). Regular exercise supports brain health and is associated with a decreased risk for age-related dementia and cognitive decline (11). Given these findings, exercise interventions may ultimately prove to be an essential component in improving or maintaining cognition throughout the lifespan.
The goal of this paper is to briefly review and integrate the current literature on the relationship between exercise/physical activity and cognitive function, with a particular focus on older adults and persons with chronic medical conditions, such as cardiovascular disease (CVD) and obesity. These areas of emphasis were chosen as they have important societal implications for public health. For example, by 2030, the number of adults over the age of 65 years is expected to rise to 72 million (12). In regards to chronic medical conditions, an estimated 85.6 million adults in the United States have some form of CVD (13). Similarly, more than two-thirds of American adults are now overweight or obese (14). Each of these is associated with greater risk for cognitive impairment and, as highlighted below, may be alleviated through exercise.
ACUTE VERSUS CHRONIC EXERCISE AND COGNITIVE FUNCTIONING
Numerous studies suggest that acute exercise may produce immediate cognitive benefits. Exercising for as little as 30 min results in improved executive functioning (15,16), memory (17), and attention (18). A recent review also concluded that submaximal exercise performed for 60 min can also produce benefits in information processing (19). Consistent with such findings, a meta-analysis also found exercise resulted in improved executive functioning during, immediately after, and following a brief delay, though only small effect sizes were achieved (20). However, despite these encouraging effects, high-intensity exercise can actually suppress cognitive function under certain circumstances, particularly with excessive fatigue or dehydration (21,22).
In addition to these acute effects, there is growing evidence that regular physical activity and/or participating in an exercise intervention can produce lasting cognitive benefits for many individuals. A randomized controlled trial employing a 12-month cycling intervention structured as 1 h a day, three times per week, stabilized cognitive functioning in a group of healthy older adults (23). Similarly, Lieberman and colleagues (24) found improved reaction time in females following 10 weeks of the U.S. Army Basic Combat Training course. Regular exercise has also been found to be protective against cognitive decline and dementia in older cohorts (10, 25,26).
FITNESS AND COGNITIVE FUNCTIONING
Exercise produces many positive physiological changes with the potential to promote better neurocognitive outcomes, including improved memory, enhanced executive functioning, and positively influence cerebrovascular structures (27). A complete review is beyond the scope of the current work, but studies demonstrating the benefits of physical activity on structural and functional brain outcomes will be highlighted below.
Fitness is Associated with Enhanced Cerebrovascular Regulation
Increased cardiovascular fitness (CVF) leads to greater activity in the frontal and parietal lobes (28) and preservation and increase of both gray and white matter in the medial-temporal, parietal, and frontal brain regions (5, 28–31). Fitness is also positively related to increased cerebral blood flow (25) and greater volume of the hippocampus (32,33), amygdala, and other gyri important for cognitive function (9). Randomized controlled trials demonstrate increased CVF is related to improvement of hemodynamic functioning in brain regions responsible for response inhibition (34) and memory (35). Functional magnetic imaging (fMRI) demonstrates increased cerebral efficiency during a visual memory task (36) and increased connectivity between brain regions (37). Individuals enrolled in a high-intensity interval and resistance exercise training program exhibit increased cerebral oxygenation and cognitive functioning (38).
These and other studies strongly support the possibility that exercise may promote better neurocognitive outcomes. As previously highlighted, the beneficial effects of exercise may be most prominent in those persons at greater risk for cognitive decline, such as older adults or persons with chronic medical conditions. The areas of discussion (i.e., older adults, those with CVD, those with obesity) for this paper were chosen as they have important implications for public health and are likely to exhibit benefit from exercise.
Fitness and Cognitive Function in Older Adults
Though mental abilities such as vocabulary and general knowledge remain relatively preserved until late in life (39), others such as memory, executive functioning, and processing speed begin to diminish as early as middle age (39,40) and can lead to reduced function in everyday life (41).
Both intervention and observational studies show that exercise is associated with better cognitive outcomes in older adults, including better cognitive performance and protection against generalized cognitive decline (10,25,26). Exercise has also been shown to benefit specific cognitive domains, including executive function (42–45), attention (46,47), and memory (43) in older adults. Notably, a metaanalysis suggested that increased fitness can improve cognitive test performance by approximately 0.5 standard deviations, regardless of the cognitive domain, type of exercise, or participant characteristics (10).
Epidemiological studies also suggest physical activity and exercise protect against cognitive decline in healthy older adult populations (48–51). With regular exercise, older adults are at lower risk of developing vascular dementia (49–54). Conversely, older adults with lower levels of CVF at baseline show greater decline in global cognition and verbal and visual memory over time (55). However, results of a recent meta-analysis suggest that not all forms of exercise are equal, finding that some forms of exercise (e.g., resistance training, Tai-Chi) are beneficial for some facets of cognitive functioning (e.g., attention, processing speed) but not for others (e.g., memory) (56).
Observational studies have also established a positive relationship between exercise and cognition. Older adults who walked less than one quarter mile per day are significantly more likely to develop dementia (50). Likewise, older adults who are in the highest quartile of energy expenditure had a significantly lower risk of developing dementia than those in the lowest quartile (51). In a rigorous study, Larson and colleagues (57) followed a group of older adults for an average of 6 years assessing exercise frequency, cognition, and risk factors for dementia every 2 years. Results of the study indicate greater exercise is associated with reduced risk for development of dementia, including Alzheimer's disease.
Other studies demonstrate cognitive benefits of exercise in those individuals with established cognitive impairment. Individuals with mild cognitive impairment who participate in moderate to high levels of physical activity showed better memory at 6- and 18-month follow-ups (58–60). Similar results are seen following exercise in those with Alzheimer's disease (61–64).
Fitness and Cognitive Function in Cardiovascular Disease
Cardiovascular disease is an umbrella term used to describe the many conditions capable of disrupting blood flow through the body (65). Past work has established reduced cardiac function alters the amount of oxygen available to the brain (66) and is associated with numerous changes in the cerebrovasculature that can impact cognitive functioning (67). Two common forms of CVD, with known neurocognitive effects, are heart failure (HF) and cerebrovascular accident (CVA) (68,69).
Patients with HF exhibit impairment in multiple cognitive abilities, including attention, memory (70,71), learning (72), and executive functioning and processing speed (73, 74). Recent studies suggest that structured exercise might improve cognitive function in persons with HF. After participation in cardiac rehabilitation, HF patients show improvements in the domains of attention, executive functioning, and memory (2). Such gains are maintained at 9-month (75) and 12-month follow-ups (76).
The pattern of cognitive impairment after CVA is dependent on many factors, including size of occluded vessel, capacity for compensation, and location of the lesion (68). If the anterior cerebral artery becomes blocked, damage may occur in the frontal and temporal lobes with expected deficits in executive functioning and working memory (68). Blockage of the middle cerebral artery often results in damage to the hippocampus, temporal lobe, medial temporal area, parietal lobe, and parts of the occipital lobe. Impairments in memory, language, movement, and visual perception would be expected (68). Finally, damage to the posterior cerebral artery would likely damage the occipital lobe and lead to reduced visual perception (68). Research on the impact of exercise on cognitive functioning following CVA is limited. However, participation in exercise programs following CVA leads to improvements in global cognitive function (77), executive function, and memory (78).
Fitness and Cognitive Function in Obesity
In 2012, more than one-third of adults in the United States were obese (14), and projections suggest that 50% will be obese by 2030 (79). Obesity is now recognized as an independent risk factor for adverse neurological outcomes. Midlife obesity is associated with increased risk for Alzheimer's disease later in life (55). Obese individuals also exhibit cognitive deficits in memory (80,81), attention, and executive functioning (4,82,83). When CVF is increased, obesity decreases (84) as do related medical conditions. Reduced symptomatology is seen for conditions such as sleep apnea (85–88), hypertension (89–93), type 2 diabetes mellitus (94,95), and inflammation (92, 96–98). Reduction in these comorbid conditions is important as these conditions may contribute to cognitive dysfunction often seen in obesity (99–101).
Cognitive functioning is important in everyday life and can be particularly important for those suffering from chronic conditions that need to adhere to complex medical regimens. For example, after undergoing bariatric surgery, individuals often need to adhere to a sophisticated and often changing pattern of diet, medication management, and monitoring of conditions like blood pressure (74). Cognitive functioning often plays a role in the success of aftercare requirements for bariatric surgery patients (102), and cognitive deficits are associated with reduced weight loss after these procedures (103). A similar relationship between cognitive dysfunction and reduced treatment adherence is found in persons with conditions like CVD (104, 105), type 2 diabetes mellitus (106), Parkinson's disease (107), and HIV (108). Interventions to preserve or even improve cognitive function in high-risk patients may lead to better clinical outcomes. In the obese population, exercise is related to decreased weight, as well as reduction in symptoms associated with comorbid conditions (e.g., hypertension, type 2 diabetes, mellitus, etc.) and improved cognitive ability.
SUMMARY AND FUTURE DIRECTIONS
The rapidly growing literature demonstrates that exercise is beneficial for cognitive functioning in older adults and persons with chronic medical conditions. Recent research shows exercise is associated with both acute and persistent improvements in multiple cognitive domains. These gains in cognitive functioning are paralleled by positive changes in important structural areas of the brain responsible for cognitive ability, such as the hippocampus and prefrontal cortex. The benefits of exercise on cognition can be seen in many populations but are often most pronounced in those at greatest risk for cognitive decline. For instance, exercise is beneficial and protective for older adults, often improving executive functioning, attention, and memory. Similar to older adults, exercise is also advantageous to those with chronic medical conditions. Patients with CVD (e.g., HF, CVA) demonstrate improvements in global cognitive functioning, executive functioning, attention, and memory.
Such findings encourage additional research to identify the most acceptable and effective types of exercise programs. Many older adults are sedentary, and this population identifies numerous obstacles to participation in land-based exercise, such as time constraints, lack of motivation/determination, lack of familiarity with recreation facilities, fear of falling, poor physical health, and lack of knowledge about recommended type and intensity of activity (109–113).
There is also much to be learned about the underlying mechanisms for the neurocognitive benefits of exercise. Studies employing advanced neuroimaging (e.g., fMRI, magnetic resonance spectroscopy, arterial spin labeling, and biomarkers associated with both physical activity and neurological outcomes [e.g., brain derived neurotrophic factor, insulin growth factor-1]) would facilitate greater understanding of the physiological underpinnings for the neurocognitive benefits of physical activity and exercise. Similarly, work is also needed to better understand the relative contribution of aerobic versus resistance training exercises. Past work suggests that both provide cognitive benefits (114) and that the combination is effective in persons with a range of neurological conditions (115); however, their differential physiological effects raise the possibility that they make a unique contribution to neurological outcomes.
1Department of Psychological Sciences, Kent State University, Kent, Ohio
Conflicts of Interest and Source of Funding: None.