Symptoms of attention deficit/hyperactivity disorder (ADHD) among adults are common. A survey of ∼20,000 US adults with no childhood diagnosis of ADHD found that 6.2% reported symptoms of hyperactivity and/or inattention to an extent that they screened positive for ADHD. Those who screened positive for adult ADHD reported more missed workdays, traffic citations, and accidents compared with those who did not screen positive for adult ADHD (1).
Acute aerobic-type exercise results in psychological changes that may benefit adults with elevated ADHD symptoms. Behavioral data from healthy adults show that cognitive performance can be enhanced after 20 min or more of moderate-intensity aerobic exercise (6). One preliminary study has been conducted investigating the effects of a single bout of exercise on attention among adults with ADHD (12). Low- to moderate-intensity treadmill exercise of 35 min had no significant effect on working memory or task-switching performance but was associated with better performance on the Stroop test among 10 adults diagnosed with ADHD. A clear interpretation of these findings is impossible because of design limitations, including the absence of a no-exercise control condition and differences in stimulant medication use among the participants.
The regulation of attention involves complex brain processes. Individuals with ADHD show abnormalities in the prefrontal cortex and its connections to striatal, parietal, and cerebellar circuits (25,39). An acute dose of a stimulant medication that increases dopamine and/or norepinephrine activates these attention-related circuits and improves cognitive control (10,38). Acute exercise plausibly could act in the same way as stimulant medications. In rats, acute exercise increases dopamine in the striatum and norepinephrine in the frontal cortex (8,15,29). In humans, moderate-intensity acute exercise increases prefrontal oxygenation (36).
The purpose of the experiment summarized here was to determine whether an acute bout of moderate-intensity cycling exercise would increase sustained attention, reduce leg hyperactivity, and improve mood and motivation to complete mental work in stimulant-free young adult men with above-average ADHD symptoms. It was hypothesized that after exercise, compared with a no-exercise control condition in which little change was expected, (i) performance on sustained attention tasks would improve, (ii) motivation to complete the tasks would be increased, (iii) lower leg movements (i.e., hyperactivity) during the cognitive tests would be reduced, (iv) related mood states would be improved (e.g., confusion and fatigue would be reduced), and (v) the mood changes would mimic those reported after amphetamine consumption in adults with ADHD.
Participants were recruited using listservs, flyers, and verbal announcements in academic classes. To qualify, participants had to be male, should be 18–34 yr old, were not currently taking CNS acting medication, had no contraindications to exercise, and should screen positive for adult ADHD. Only males were recruited because ADHD prevalence is 1.6 times higher in men than in women, and we lacked the resources to conduct a study with adequate statistical power for detecting possible sex-related differences in the outcomes (17). Smokers were excluded as were those indicating a current mental disorder other than ADHD. Participants received two $25 gas cards for their time. An a priori statistical power analysis indicated that 32 participants provided statistical power of 0.80 for the hypothesized treatment–time interactions. This analysis assumed an alpha error of 0.05, a correlation of r = 0.90 between repeated measures across time (7), and an evidence-based standardized effect size of 0.30. Because no previous studies of acute exercise effects on behavioral and psychological outcomes with adults with ADHD had been published, the estimated effect size was conservative and based on results from a meta-analysis focused on the influence of acute exercise on cognition in healthy, young adults (6).
Potential participants were directed to complete an online screening questionnaire administered via Qualmetrics. One questionnaire was used to obtain demographic and health-related background information and to screen out participants using psychoactive medication. A total of 247 individuals completed the screening questionnaire; 46 men met the study inclusion criteria and 32 agreed to participate. The Physical Activity Readiness Questionnaire was used to determine contraindications to maximal exercise. The Godin Leisure-Time Exercise Questionnaire was used to estimate leisure-time physical activity (14).
The Adult ADHD Self-Report Scale V1.1 (ASRS V1.1) was used to identify participants who had elevated symptoms of inattention or hyperactivity consistent with ADHD. The ASRS V1.1 is a six-item questionnaire that asks about the frequency of feelings or conduct for the past 6 months. A total score of ≥4 was used because it indicates that a person’s symptom may be consistent with adult ADHD (19). The sensitivity, specificity, and total classification accuracy of the ASRS total score was found to be 69.7%, 99.5%, and 97.9%, respectively, in a study of 154 adults with ADHD (19). Adult ADHD predicted from the total ARSR score was associated with a 4%–5% reduction in work performance and increased sickness absence in a longitudinal study of more than 6900 manufacturing workers (18).
The continuous performance task (CPT) measures sustained attention. During the CPT, 12 different letters were presented in Times New Roman (font size 60) (A, C, E, H, K, N, P, Q, S, U, X, and Z) individually for 200 ms with an interstimulus interval of 800 ms. Participants responded to a target letter (X) only when preceded by a cue (A). The CPT was ∼16 min in duration with a total of 179 correct responses and 930 total stimuli (37).
The more difficult Bakan vigilance (dual) task also assessed sustained attention. Random individual numbers (1–9) were presented for 1000 ms. The primary objective was to identify any series of three consecutive odd numbers that were different (e.g., 5, 1, 9 or 7, 3, 1) by pressing a button with their right thumb. The secondary objective was to identify any presentation of the number “6” and respond by pressing a different button. The ∼16 min Bakan vigilance task presented a total of 960 stimuli with 8 primary targets and 96 secondary targets.
A simple reaction time task assessed psychomotor speed. A warning stimulus (fixation cross) was followed by the response stimulus (red circle). Participants responded as fast as they could to the red circle by pressing a button on the response pad with their preferred hand. There were three practice trials, followed by five test trials. The interval separating the warning stimulus and the response stimulus varied and ranged from 500 to 1000 ms.
Motivation to perform the cognitive tasks
A 10-cm visual analog scale was used to assess motivation to perform the cognitive tasks. Participants indicated their level of motivation to complete mental work using a sliding ruler on a line on a computer. The verbal anchors ranged from 0 indicating “no motivation” to 100 indicating “highest motivation imaginable.”
Hyperactivity/lower leg activity counts
The ActiGraph GTX3 accelerometer was used to measure lower leg movements during the cognitive tests as an index of hyperactivity. The participants were told that the accelerometers were being used to measure leg movement during the exercise; the true purpose was to measure leg movement during the cognitive tasks. A sampling rate of 100 Hz was used. Participants wore one accelerometer on each ankle during testing. Data were downloaded in 1-s epochs. Useable activity count data from all participants were obtained from 880 s during the CPT and 947 s during the Bakan. Total activity counts from each test were divided by time and expressed as counts per minute.
The well-validated 30-item Profile of Mood States—Brief Form (POMS-BF) was used to assess the intensity of six different “right now” mood states: tension, anger, depression, confusion, vigor, and fatigue. Responses for each item (five per mood) scale the intensity of the mood as follows: 0 = not at all, 1 = a little, 2 = moderately, 3 = quite a bit, and 4 = extremely (27). The original 550-item Addiction Research Center Inventory (ARCI) was developed to assess the psychological effects of drugs. The ARCI-49 is composed of 49 yes–no questions that measure mood responses induced by psychoactive drugs. The focus here was on the 11-item amphetamine scale. These items increase the most in response to the experimental administration of D-amphetamine (2,3). Item content is as follows: Q24, I feel as if I would be more popular with people today; Q25, I feel a very pleasant emptiness; Q26, My thoughts come more easily than usual; Q27, I feel less discouraged than usual; Q29, I feel more excited than dreamy; Q30, Answering these questions was very easy today; Q31, My memory seems sharper to me than usual; Q32, I feel as if I could write for hours; Q33, I feel very patient; Q34, Some parts of my body are tingling; and Q35, I have a weird feeling. Mood was assessed before and after each round of cognitive testing for a total of five assessments (baseline 1, baseline 2, post 1, post 2, and post 3).
The experiment was a within-participants crossover design with one 20-min treatment (cycle ergometry at 65% V˙O2peak) and one 20-min nonexercise comparison (seated rest control). The exercise duration and intensity used in this study was based on previous research in healthy adults and children with ADHD showing positive psychological changes after moderate-intensity cycling of 20 to 30 min (6,28,34). The order of treatment was blocked randomized in blocks of two. All testing was approved by the University of Georgia Institutional Review Board.
Baseline day (day 1)
After signing the informed consent, the participant then performed practice trials of the cognitive tests after first being provided with instructions. The duration for the practice tests was ∼20 min. Performance on the practice trials was checked to determine whether participants understood the instructions. If performance was below a criterion based on a previous study (26), the participant completed another round of practice to ensure the instructions were understood.
After completion of the practice trials, the participant then performed a graded maximal exercise test on a cycle ergometer that included measures of power, O2, CO2, HR, RPE, and leg muscle pain as previously described (31).
Experimental days (days 2 and 3)
After participants arrived at the laboratory, they confirmed no caffeine within 6 h of testing, no exercise the day of the visit, and a normal prior night’s sleep (within 1 h of typical sleep duration). Accelerometers were placed on each ankle. Participants then completed the first trial of mood questionnaires followed by the first trial of cognitive tests. After completing the cognitive tests, participants then completed another set of the mood questionnaires. Participants were then allocated to one of two 20-min conditions. For the exercise condition, participants warmed up at 50 W for 2 min, after which resistance was increased. The level of resistance was designed to elicit 65% of a participant’s V˙O2peak (13). For the no-exercise condition, participants sat quietly on the cycle ergometer for 20 min. Immediately after the 20-min condition, the outcomes were measured twice (post 1 and post 2). Each assessment of mood and cognitive performance lasted ∼45 min. The time between each assessment was less than 5 min. The timing of the procedures is summarized in Table 1.
IBM SPSS Statistics (Version 22.0) was used for all data analyses. For the cognitive data, each data file was scored using Cedrus Data Viewer 2.0 (Cedrus Corp., 2007) and then imported into SPSS. Self-report data were scored and entered into SPSS. Because of technological problems, there was a loss of left leg activity data (∼16%). All data were examined for normality, homoscedasticity, and outliers. The primary analyses used all cases with nonnormal variables log transformed.
Condition (2: exercise vs rest control) × time (3: baseline, post 1, and post 2) repeated-measures ANOVA and ANCOVA were used to test the hypotheses, which predicted significant condition–time interactions for the cognitive performance, hyperactivity, motivation, and mood measures. V˙O2peak, ventilatory threshold, and self-reported physical activity were used individually as covariates. Using these covariates did not significantly influence the results. Also, motivation scores were weakly and insignificantly related to all the cognitive performance outcomes. Accordingly, only the ANOVA results are presented. Adjustments for sphericity, when needed, were made using the Huynh–Feldt epsilon. Simple effects analysis was used to decompose significant interactions using the Bonferroni correction to adjust the degrees of freedom.
Participant characteristics are presented in Table 2. Two participants in the sample reported having been diagnosed with ADHD. Descriptive statistics for leg activity counts during the cognitive tests, performance on the cognitive tests, mood, and motivation to complete mental work are provided in Tables 3–5.
As illustrated in Figure 1A, there was a significant condition–time interaction for motivation to complete mental work, F(2, 116) = 3.726, P = 0.027, partial eta2 = 0.060. Motivation to complete mental work was significantly higher at post 1 than at post 2 (P = 0.024) in the exercise condition. In the rest condition, motivation to complete mental work did not significantly change overtime. Motivation to complete mental work was significantly higher in the exercise condition than that in the rest condition at post 1 (P = 0.001) and post 2 (P = 0.044).
There were no significant time–condition interactions for (i) the simple reaction time (P = 0.153, partial eta2 = 0.029); (ii) the CPT: percentage correct (P = 0.880, partial eta2 = 0.002), false alarm errors (P = 0.374, partial eta2 = 0.018), reaction time (P = 0.974, partial eta2 < 0.001), or omission errors (P = 0.788, partial eta2 = 0.001); (iii) the primary Bakan task: percentage correct (P = 0.370, partial eta2 = 0.004), false alarm errors (P = 0.882, partial eta2 < 0.001 ), reaction time (P = 0.282, partial eta2 = 0.028), or omission errors (P = 0.827, partial eta2 = 0.004); (iv) or the secondary Bakan task: percentage correct (P = 0.381, partial eta2 = 0.002), false alarm errors (P = 0.762, partial eta2 = 0.005), reaction time (P = 0.874, partial eta2 = 0.001), and omission errors (P = 0.640, partial eta2 = 0.004).
Statistically insignificant condition–time interactions were found during the CPT for right (P = 0.324, partial eta2 = 0.029) and left leg hyperactivity (P = 0.474, partial eta2 = 0.046). During the Bakan test, condition–time interactions for right leg hyperactivity (P = 0.638, partial eta2 = 0.004) and left leg hyperactivity (P = 0.937, partial eta2 = 0.016) were insignificant. The activity counts for the right and left legs were combined and summed for those participants with complete data (n = 23). The condition–time interactions for summed activity during the CPT (P = 0.094, partial eta2 = 0.052) and Bakan tasks were insignificant (P = 0.844, partial eta2 = 0.004).
As illustrated in Figure 1B, the condition–time interaction for vigor was statistically significant, F(3.224, 199.90) = 12.630, P < 0.001, partial eta2 = 0.169. After exercise, vigor scores were significantly higher at post 1 than all other time points besides baseline 1 (P < 0.001) and returned to immediate pretreatment levels (baseline 2) by post 2 (P = 0.092). For the rest condition, vigor scores were significantly reduced after the first administration of vigilance tests (P < 0.001) and thereafter remained significantly lower than baseline 1 (P < 0.001).Vigor scores at post 1 and post 2 were significantly higher for exercise compared with those for rest (P < 0.05).
The condition–time interaction for fatigue was statistically significant, F(4, 248) = 2.616, P = 0.036, partial eta2 = 0.040. During the exercise condition, fatigue scores were significantly higher only at post 3 compared with scores at baseline 1 (P < 0.001). During the rest condition, fatigue scores were significantly higher at post 2 and post 3 compared with scores at baseline 1 (P < 0.001). Fatigue scores were significantly lower for the exercise condition at post 2 (P = 0.035).
The condition–time interaction for confusion was statistically significant, F(3.420, 212.014) = 3.396, P = 0.015, partial eta2 = 0.052. In the exercise condition, confusion scores did not differ compared with scores at baseline 1 (P > 0.05). During rest, confusion scores were significantly increased after the first administration of the vigilance tests (P = 0.005) and remained elevated (P < 0.05). Confusion scores were significantly lower at post 1 and post 2 (P < 0.05) in the exercise condition compared with those in the rest condition.
The condition–time interaction for depression was statistically significant, F(2.646, 164.052) = 3.299, P = 0.027, partial eta2 = 0.051. In the exercise condition, depression scores at post 1 were significantly lower compared with scores at baseline 1 (P = 0.001), and depression scores returned to baseline 1 values at post 2. In the rest condition, depression scores did not significantly change over time (P > 0.05). Depression scores were significantly lower at post 1 (P = 0.005) in the exercise condition compared with those in the rest condition.
The condition–time interactions for tension (P = 0.183, partial eta2 = 0.018) and anger (P = 0.217, partial eta2 = 0.020) were insignificant.
The condition–time interaction for the amphetamine scale scores was statistically significant, F(3.799, 235.535) = 7.525, P < 0.001, partial eta2 = 0.108. During the exercise condition, amphetamine scores were significantly higher at post 1 compared with the scores at all other time points (P < 0.001), with scores returning to baseline 1 values at post 2. During the rest condition, amphetamine scores were highest at baseline 1 compared with the scores at all other time points (P <0.006) except for post 1 (P = 0.843). Amphetamine scores were significantly higher for exercise at post 1 (P < 0.001) and post 2 (P = 0.003) compared with those for rest.
The primary findings were that, when compared with a no-exercise control condition, 20 min of moderate-intensity cycling exercise enhanced motivation for mental work, increased feelings of energy, and reduced feelings of confusion, fatigue, and depression, but this had no effect on cognitive performance or hyperactivity.
Acute exercise had the largest effect on increasing feelings of vigor. The finding is consistent with results from other studies with fatigued or normal adults showing increases in feelings of vigor after an acute bout of exercise (24). Although it is plausible that exercise-induced feeling of energy might provoke hyperactivity among those at increased risk for ADHD, increased vigor scores after the exercise condition were not accompanied by significantly higher leg hyperactivity levels compared with the scores after the rest condition. Responses for vigor were similar to responses on the ARCI amphetamine scale. The administration of the stimulant methylphenidate reliably produces feelings of increased alertness and energy (23). The increase in vigor scores reported after exercise could possibly be due to a mechanism similar to that of prescription stimulants. Brain imaging studies have revealed increases in dopamine after an acute administration of methylphenidate (41). Directly measured increases in dopamine have been reported after acute exercise in animals (15,29), although no change was found in 12 healthy humans without ADHD using positron emission tomography (43). In rodents, the influence of acute exercise bouts on behaviors consistent with human ADHD has been studied within an animal model of ADHD, such as the spontaneously hypertensive rat model. Chronic exercise studies using the spontaneously hypertensive rat model show promising results, including relevant brain adaptations, such as changes in tyrosine hydrolase—the rate-limiting enzyme in dopamine synthesis, accompanied by behavioral changes thought to reflect improved attention and reduced impulsivity (20,21,35).
Immediately after exercise, the increased feelings of confusion and fatigue induced by the attention tasks were attenuated. This resulted in significantly lower confusion and fatigue scores when compared with the rest condition. This finding is potentially interesting because it suggests that 20 min of moderate-intensity exercise may delay the confusion and fatiguing effects of cognitive tests requiring sustained attention in adults reporting ADHD symptoms. One previous study investigated the effects of 60 min of moderate-intensity exercise on mental fatigue and cognitive performance in healthy college students (31). Results from this study did not show an attenuating effect of exercise on increased feelings of mental fatigue induced by 40 min of cognitive testing. Adults at increased risk for ADHD may respond to exercise and cognitive testing with a pattern that differs from adults who are not at risk for ADHD.
Motivation to complete mental work was significantly higher after the exercise condition when compared with the seated rest condition. This finding is unique because motivation to complete mental work has rarely been measured in studies examining the cognitive effects of acute exercise, although increasing evidence points to abnormal motivation being an integral part of ADHD. Twenty minutes of moderate-intensity exercise resulted in significant increases in motivation to complete the cognitive tasks. Previous studies have shown that individuals with ADHD have reduced dopamine D2/D3 receptor availability in the nucleus accumbens, a striatal area thought to be involved with motivation (42). The significant improvements in mood after the exercise condition were not accompanied by significantly better performance on the attention tasks compared with the rest condition. One reason for the null findings in regard to the attention tasks may be the exercise stimulus used. The exercise duration and intensity used in this study was based on previous research in healthy adults and children with ADHD showing positive psychological changes after moderate-intensity cycling of 20 to 30 min (5,6,28,34). Adults with ADHD, or those with elevated ADHD symptoms, may require a different type or “dose” of exercise than the one used in the current study to realize improvements in attention. Another reason the acute exercise bout did not have an effect on cognitive performance may have been the cognitive tests used. The CPT and the Bakan vigilance task require sustained attention to perform well. It may have been useful to have administered a task requiring even greater inhibitory control (e.g., Stroop test, switch test, or go/no-go task) in addition to the sustained attention tasks used here. It is also plausible that the methods used in this study would have been sufficient to produce a significant effect had adults diagnosed with ADHD been studied.
To our knowledge, only one previous study has examined the effects of acute exercise on an index of hyperactivity (40). The results revealed that motor impersistence (i.e., the measure of hyperactivity used) in children with ADHD was improved after maximal exercise but not after submaximal (65%–75% V˙O2peak) or seated rest. These previous findings are consistent with the idea that the absence of significant differences in hyperactivity after exercise in the present study may have been due to the inadequate exercise intensity or the participants not being required to have an ADHD diagnosis.
The primary findings of the current study were that after 20 min of moderate-intensity exercise, men characterized by elevated ADHD symptoms reported improvements in mood and increased motivation to complete mental work. The improvements in mood were transient, lasting approximately 45 min. The effects of immediate release stimulants have been found to last approximately 3 h, and individuals taking these drugs often require repeated administration across the day to best manage their ADHD symptoms (30). It is possible that repeated bouts of acute exercise could be used in a similar manner to improve ADHD symptoms, although such an approach would be impractical for many. One previous study investigated the effects of the administration of amphetamine on changes in mood in low and high sensation seekers using similar measures to those in the current study. Results from that study showed increases in feelings of vigor and scores on the ARCI amphetamine scale that were similar to those in the current study, but these effects did not occur until 50–110 min after drug administration (16). The effects of acute moderate exercise may not last as long as the effects of stimulant medications based on findings from the current study, but the effects of acute exercise could be more immediate, meaning individuals who exercise could benefit sooner than those who chose to use a stimulant medication. Thus, an individual seeking quick symptom relief might decide to achieve it with exercise. For example, if an individual who required multiple daily medication doses forgot to take a dose and the medication was not immediately accessible, then exercise might be a useful adjunct for immediate ADHD symptom management. Whether medication dose could be lowered among regularly physically active ADHD medication users awaits future research.
The participants in this study had lower-than-average levels of self-reported physical activity compared with previous studies of college men and lower cardiorespiratory fitness levels, on average, when compared with large studies of men of the same age category performing cycle ergometry (22). No previous studies have measured cardiorespiratory fitness in adult men with ADHD. Groups with mental disorders, such as depression, are often characterized by low physical activity and cardiorespiratory fitness (4). One participant in the present study was characterized by perceived exertion, HR, and respiratory quotient responses indicative of an inadequate peak exercise test, but the others showed typical responses indicative of peak exercise test performance.
The current study is not without limitations. One limitation is the inability to generalize the results to adults diagnosed with ADHD. Participants included in the current study were screened positive for ADHD based on responses to the ASRS-V1.1 and were not required to have an ADHD diagnosis.
The extent to which the results were confounded by unmeasured comorbid conditions is unknown and a potential limitation. ADHD has significant comorbidity with mood, anxiety, and substance use disorders (17). No information about substance abuse was obtained. Baseline anxiety and depression scores were low, suggesting that the present participants were free from mood and anxiety disorders. Acute exercise does not cause anxiety attacks in those with mental disorders, including panic disorder (33), and can improve anxiety symptoms (32). The low baseline anxiety scores here may have attenuated the typical anxiety reduction reported after acute exercise (9).
The cognitive tests used in this study assessed the ability to sustain attention but may have been insensitive to change with acute exercise in the group studied and more sensitive among those diagnosed with ADHD. More difficult or engaging tasks, or those emphasizing other psychological outcomes, may have yielded different results. There is the possibility that moderate-intensity exercise could have a positive effect on cognitive performance, but the tests used in the current study may have inadequately emphasized processes most influenced by the exercise stimulus (e.g., inhibitory control). Others have suggested that using multiple assessments (i.e., cognitive batteries) could assist in obtaining a better overall perspective of the effects of acute exercise on cognitive performance (11).
Another limitation of the current study was that hyperactivity was measured only in the lower limbs. Acute exercise may have reduced fidgeting in other body locations that were unmeasured such as the arms or head.
The sample was not randomly selected from a defined population; thus, the results from the present sample may not generalize to most young men with elevated ADHD symptoms. For example, it is uncertain if young men with elevated ADHD symptoms truly are characterized by low fitness as suggested by the present results. If they are not, and the present findings are affected by small sample bias, then if fitness level moderates the outcomes measured here, the present results would not generalize to most young men with elevated ADHD symptoms. Negative mood changes during exercise might also be more common among those with low aerobic fitness, but mood states during the exercise bouts were not measured in the current study.
The “take home” message from this investigation is that in young men reporting elevated symptoms of ADHD, a 20-min bout of moderate-intensity cycle exercise performed in a laboratory environment transiently enhances motivation for cognitive tasks, increases feelings of energy, and reduces feelings of confusion, fatigue, and depression. Future work is needed to learn if other cycling exercise stimuli, such as brief high-intensity bouts or outdoor riding on mountain trails that require greater attention, influence behavioral measures of attention or hyperactivity.
This research study was not supported by external funding.
The authors report no conflicts of interest. The results of this study do not constitute endorsement by the American College of Sports Medicine.
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