Poor mental health, mental disorders, mental stress, and low quality of life (QOL) are widespread in the general population. Epidemiological data indicate that during any 1-yr period, 65 million American adults (26.2%) suffer some form of mental disorder, especially anxiety disorders and depression (18). Similarly, 4 of the 10 leading causes of disability in the United States and other developed countries are mental disorders (29).
There is growing evidence in support of the positive relationship between regular physical activity with improved QOL and reduced anxiety and depression (1,4,5,12,35,39). For example, using the National Comorbidity Survey, Goodwin (12) showed that regular physical activity was associated with a significantly decreased risk of major depression and anxiety disorders, even after adjustment for sociodemographic characteristics. The influence of age, sex, body mass index (BMI), and other demographics and lifestyle on the relationship between physical activity and mental health is poorly understood. In addition, the influence of physical activity on other measures of psychopathology including hostility, obsessive–compulsive disorder, somatization, and psychoticism has seldom been measured.
Mental cognition declines with increase in age (36). Physical activity has been shown to delay the incidence of dementia and the onset of cognitive decline associated with aging (9,21,23,32,41). Little is known regarding the influence of regular physical activity on mental cognition within the general population, especially when controlling for the effects of age, sex, BMI, disease status, and other lifestyle factors (31).
The purpose of this study was to measure the influence of physical activity frequency on QOL, psychopathology, and mental cognition in a large heterogeneous group of community-dwelling adults while controlling for a variety of demographic and lifestyle confounders.
Study participants (N = 998, 60.4% women and 39.6% men, 18–85 yr, BMI = 16.7–52.7 kg·m−2) were recruited via mass advertising from the community. Subjects had to be noninstitutionalized, and women were excluded if pregnant or lactating. No other exclusion criteria were used, and both diseased and nondiseased subjects were admitted into the study, with monitoring of disease status and medication use. Subjects were paid a stipend for participation. Data from this 12-wk study on the effects of quercetin supplementation on inflammation and oxidative stress have previously been published (15,34). However, quercetin supplementation at two doses (500 and 1000 mg·d−1) had no influence on psychological and cognition measures, and the data from this study were reanalyzed to investigate the influence of exercise frequency on psychopathology and neurocognitive function measures. All psychological measures represent the average of the pre- and poststudy evaluations. Written informed consent was obtained from each subject, and the Appalachian State University Institutional Review Board approved all experimental procedures.
Two weeks before the start and end of the study, subjects provided demographics, lifestyle habit information, QOL, and perceived stress assessments using SurveyMonkey.com (Portland, OR). Subjects reported to the laboratory in an overnight-fasted condition at the beginning and end of the 12-wk period. Height and body mass were measured. Subjects without Internet access were mailed a printed version of the surveys, with instructions to complete all questions before the two laboratory sessions. Subjects completed the Brief Symptom Inventory (BSI) during a 15-min seated period. After measurement of height and body mass, subjects reported to the computer laboratory to complete the 30-min CNS Vital Signs (Morrisville, NC) test battery (20).
A categorical question from the National Health Interview Survey (US National Center for Health Statistics, 1999) was used to assess exercise frequency habits in the subjects’ daily lives. The question consisted of the following: “Outside of your normal work or daily responsibilities, how often do you engage in exercise that at least moderately increases your breathing and HR and makes you sweat for at least 20 min (such as brisk walking, cycling, swimming, jogging, aerobic dancing, stair climbing, rowing, basketball, racquetball, vigorous yard work (gardening), etc.)?” Response categories included seldom or never and less than one, one to two, three to four, or five or more times per week. Subjects were grouped into aerobic exercise frequency tertiles of one time or less, one to four times, or five or more times per week. Single-item measures of physical activity have been shown to perform as well as the Global Physical Activity Questionnaire in terms of reliability and concurrent validity (28).
Psychological assessment was performed using CNS Vital Signs, which is a computerized test battery that is composed of seven tests: verbal and visual memory, finger tapping, digit symbol coding, the Stroop test, a shifting attention test, and a continuous performance test. These seven tests are used to derive five domain scores representing memory, psychomotor speed, reaction time, complex attention, and cognitive flexibility. This test has been shown to be reliable and valid (13) for healthy and nonhealthy subjects age 8–90 yr. This battery has also been used in prior exercise intervention studies (26). Memory scores indicate how well subjects can remember and retrieve words or images. Psychomotor speed scores indicate how efficiently and automatically a subject can perform a cognitive task. Reaction time measures how fast the subject can react to increasingly complex sets of directions. Complex attention is a measure of how well the subject can maintain focus, whereas cognitive flexibility measures how well the subject can adapt to rapidly changing instructions. The Neurocognition Index is an average score derived from the domain scores and is an overall assessment of neurocognitive status. This score was used to investigate overall correlations between exercise frequency and neurocognitive function in the entire study population.
The BSI is a 53-item checklist scored on a five-point Likert scale from “not at all” to “very much” (8) and was used to assess psychological symptoms including nine primary symptom dimensions and three global indices. The nine primary symptom scales included somatization, obsessive–compulsive disorder, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism. The three global indices include the Global Severity Index (GSI), which measures overall psychological distress levels; the Positive Symptom Distress Index, which measures the intensity of symptoms; and the Positive Symptom Total (PST), which simply reports the total of self-reported symptoms. This test has been reported as valid and reliable (8).
The World Health Organization QOL questionnaire (40) was used to assess overall QOL in study participants. The questionnaire consisted of 26 questions with responses answered on a Likert scale.
Perceived stress assessment.
The Perceived Stress Scale (PSS) (6) was used to get a global measure of stress in subjects. This test consists of 10 questions that are answered on a Likert scale and are designed to assess sensitivity of stress in different life situations, as well as how “unpredictable, uncontrollable, and overloaded” subjects’ perceive their life situation. The scale is also designed to measure current levels of experienced stress (6).
A general linear model was used to examine the effect of fitness (or exercise frequency) on the performance of each cognition or mental health assessment. Backward selection in the GLMSELECT procedure in SAS (version 9.1.3; SAS Institute, Inc., Cary, NC) was used to identify confounding variables. The candidate confounders that the GLMSELECT procedure selected from were age, gender, BMI, marital status, education level, job status, smoking status, sleep habit, alcohol usage, and chronic disease condition. For each psychological assessment, the model with the smallest Akaike information corrected criterion was selected. A contrast to test linear trend was performed to study the effect of fitness (or exercise frequency) on the performance of cognition or mental health assessment after adjusting for confounders. The Benjamini–Hochberg method for false discovery rate correction in the MULTTEST procedure in SAS was used for multiple testing correction. Pairwise comparison was performed between the three fitness (or exercise frequency) levels using the Tukey–Kramer method. The normality and homoscedasticity of the residuals from each model were examined. Outliers with studentized residue >3 or <−3 were excluded. Statistical significance was set at P ≤ 0.05 (two-tailed).
Table 1 summarizes age, BMI, education, smoking habit, sleep, job classification, and alcohol intake data for males and females across exercise frequency tertiles. BMI, smoking habit, education level, blue-collar job classification, and the ratio of males to females but not age or the proportion sleeping 7–9 h per night differed significantly across exercise frequency tertiles. Eighty-one percent of subjects in the upper tertile of exercise frequency reported a history of regular exercise for 5 yr or more, whereas only 58% of the middle tertile had been engaging in that level of activity for 5 yr or more. Small differences in the proportion of males and females drinking less than two drinks per day were measured across exercise frequency tertiles. Thirty-seven percent of subjects reported past or current history for one or more chronic diseases: hypertension (19%), arthritis (16%), cancer (6%), cardiovascular disease (4%), and/or diabetes (4%). The percentage of subjects with chronic disease did not differ across tertiles of exercise frequency (chi-square = 0.711, P = 0.701).
Table 2 summarizes results from the neurocognitive function tests across the three exercise frequency tertiles, with adjustment for subject characteristics listed in Table 1. GLM analysis revealed that the total neurocognitive index score (mean of scores from the five domains) and scores from each of the five domains did not vary significantly across the exercise frequency tertiles.
P for trend values were significant across the three exercise frequency tertiles for all nine primary symptom scales and three global indices after adjustment for potential confounders as shown in Table 3 and Figure 1. Scores from the nine primary symptom scales between low– and high–exercise frequency tertiles differed from 5.9% to 8.8%. The GLM model rank ordered exercise frequency as number 1 among all potential factors for the GSI (Fig. 1) and the PST and second for the positive symptom distress (Table 3).
Scores for the PSS decreased across the three exercise frequency tertiles after adjustment for sleep, age, and smoking habit (P for trend < 0.001) (Fig. 2). QOL scores increased across the three exercise frequency tertiles after adjustment for sleep, BMI, chronic disease status, and smoking habit (Fig. 3). For both perceived stress and QOL, exercise frequency emerged as the most important variable in the GLM model.
Our results indicate that reported exercise frequency was not related to neurocognition but was significantly associated with several measures of psychopathology in a large heterogeneous group of community-dwelling adults. Similarly, perceived stress was significantly lower and QOL was significantly higher across tertiles of exercise frequency.
Increasing evidence indicates that mental cognition is enhanced transiently after acute moderate exercise (17,22,42). Acute exercise-induced improvement in cognition may translate into chronic enhancement if exercise training is habitual (42). However, evidence for the chronic benefits of exercise on mental cognition in middle-age populations is lacking, and our data are nonsupportive for this relationship. The linkage between exercise training and improved mental cognition is better established in elderly populations, especially those with impaired cognitive skills (3,16,19,24,33). Older adults who adopt a physically active lifestyle typically experience a delay in the onset of cognitive decline and a reduction in incidence and severity of symptoms in diseases such as Alzheimer disease (24,33). Limited human and animal studies suggest several pathways, including reduced inflammation, enhanced brain perfusion with blood through a buildup of extra brain capillaries, improved neural connections between brain regions, and an enhanced caffeine-like arousal (22,24,33). Among our subjects, age and education best predicted cognition scores, and this finding is in concert with other studies (7,10,38). Thus, exercise likely plays a significant role in neurocognitive function in diseased or elderly populations, but exercise frequency seems not to be a significant factor in predicting neurocognitive function in relatively young and healthy adults such as those who participated in the current study.
Although no relationship between exercise frequency and mental cognition was observed in the current study, there was a consistent but modest relationship with measures of psychopathology. Scores for the nine primary domains and the three global indices of the BSI were 7.5% greater when comparing low– and high–exercise frequency tertiles. Few exercise-related studies have used the BSI instrument, especially in healthy subjects. However, two of the domains in the BSI, depression and anxiety, have been measured using other instruments in many exercise training studies using both healthy and diseased subjects. Studies consistently support a reduced level of depression and anxiety in physically active subjects regardless of age or health status (27,31). Our study supports significantly lower psychopathology scores for all nine BSI domains across exercise frequency tertiles, even after adjustment for multiple factors. In two BSI composite indices (global severity and PST), exercise frequency was the number 1 ranked predictor in the GLM model after adjustment for potential confounders.
Both epidemiological and randomized controlled intervention studies support a strong positive relationship between physical activity and QOL (4), especially in special populations such as those with chronic disease (11) and depression (30) and the elderly (37). However, there are limited studies showing this relationship in healthy populations. Our data support that QOL scores are 10% higher when comparing low and high tertiles of exercise frequency after adjustment for lifestyle and demographic factors. GLM analysis indicated that exercise frequency was the most important factor in relation to QOL followed by sleep, BMI, chronic disease status, and smoking habit.
Few studies investigating the relationship between exercise frequency and perceived stress among healthy adults using the PSS have been done. Our study indicates a significant inverse relationship between exercise frequency and perceived stress, with a 30% difference between low and high tertiles. Exercise frequency was the number 1 ranked factor in the GLM analysis ahead of sleep, age, and smoking habit. This result is supported by Aldana et al. (2), who showed that working adults who participated in leisure time physical activity had nearly half the rate of perceived stress as nonexercisers. Similarly, other studies have confirmed a positive relationship between exercise and perceived stress studied within the context of job performance and health complaints (14,25).
A potential limitation to the current study design was the use of a single-item physical activity question to establish exercise frequency tertiles. This question did not provide data for calculating the average duration per exercise bout but did allow us to determine how frequently subjects engaged in aerobic bouts lasting 20 min or longer. There is increasing support, however, for the use of single-item physical activity questions in large population studies. Milton et al. (28) established that single-item measures perform as well as the Global Physical Activity Questionnaire in terms of reliability and concurrent validity. Similarly, epidemiological studies often rely on one validated question for assessing physical activity (National Center for Health Statistics, 1999).
In conclusion, nine BSI psychopathology domains, perceived stress, and QOL but not five neurocognitive function domains were modestly but significantly associated with aerobic exercise frequency in community-dwelling adults. These findings were strengthened by GLM adjustment across exercise frequency tertiles for age, gender, BMI, marital status, education level, job status, smoking status, sleep habit, alcohol usage, and chronic disease condition. These results support the independent mental health benefit of physical activity even after adjustment for demographic and lifestyle factors.
This research was supported by grants from Coca-Cola (Atlanta, GA) and Quercegen Pharmaceuticals (Sudbury, MA). All authors were involved in the design and conduct of this study, assisted in the writing of the article, and have seen and approved the submitted version.
No conflicts of interest were reported.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:©2012The American College of Sports Medicine
PERCEIVED STRESS; QUALITY OF LIFE; AEROBIC EXERCISE; NEUROCOGNITION