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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Keywords:© 2016 American College of Sports Medicine
ACCELEROMETRY; ATTENTION; CONFUSION; FATIGUE; HYPERACTIVITY; VIGOR