Exercise reduces the symptoms of attention-deficit/hyperactivity disorder and improves social behaviour, motor skills, strength and neuropsychological parameters
Abstract
This review summarises research studies on the impact and beneficial effects of different types of exercise on childhood attention-deficit/hyperactivity disorder (ADHD) and provides recommendations for the scientific and therapeutic communities.
Conclusion
Although the design and the exercise interventions featured in these studies varied considerably, all showed that exercise reduced the symptoms of ADHD and led to improvements in social behaviour, motor skills, strength and neuropsychological parameters.
Graphical Abstract
Key notes
- This literature review summarises the effects of exercise on symptoms related to attention-deficit/hyperactivity disorder (ADHD).
- It looks at the effects of various types of exercise on physiological, psychological and neurological parameters, as well as the cardinal and behavioural symptoms associated with ADHD.
- We conclude that all types of exercise employed in the studies reduced the symptoms of ADHD without causing undesirable side effects.
Introduction
With a worldwide prevalence of 5.3% 1, attention-deficit/hyperactivity disorder (ADHD) is diagnosed in 2–6% of preschool children 2 and 6–13% of adolescents 3, being more common in boys (7.9%) than girls (1.8%) 4. The typical characteristics of this disorder include inattention, hyperactivity and impulsiveness 5. The associated limitations in cognitive, psychosocial and emotional competence impair mental well-being, disturb familial and academic environments, cause psychological strain and result in a low health-related quality of life 4. Both environmental and genetic factors appear to be involved in the aetiology of ADHD 6.
Pharmaceutical treatment of ADHD-related symptoms is commonly based on administration of methylphenidate, atomoxetine and amphetamines. Methylphenidate, a psychostimulant, reduces reuptake of dopamine, thereby enhancing the free level of this neurotransmitter in the pre-frontal cortex. Atomoxetine selectively inhibits reuptake of norepinephrine and amphetamines influences the dopamine system in such a way as to improve resistance to fatigue and elevate mood. The major drawbacks of such drug treatment include the relatively high cost, the dose-dependent efficiency, the unknown long-term side effects and the fact that the medication only addresses symptoms, not the cause.
Other approaches applied in treating children with ADHD include psychotherapy 7, psychoeducation 7, neurofeedback 8, multimodal interventions 9 and numerous forms of physical exercise 10. The types of exercise used in this context to date include combined postural, respiratory and meditation training by yoga 11, games designed to improve cooperation 12, guided walks 13-15, submaximal 16 and maximal 17 cycling, athletic training such as aerobic exercise 18 and skipping rope 19 and different ball games, e.g. basketball and soccer 18. Because of the wide variety of methods (with diverse types of exercises of differing intensity, duration and frequency, differing numbers of boys and girls of various ages, including various types and doses of medication) involved in such studies a comparison is difficult.
In this brief literature review concerning treatment of children with ADHD using exercise, we attempt to (i) summarise available and relevant data, (ii) document the effectiveness of the varying types of exercise, (iii) discuss the physiological, psychological and neurological benefits, along with changes in the typical behavioural symptoms of ADHD and (iv) provide practical recommendations for the scientific and therapeutic communities.
Methods
During the period of December 2012 to January 2013, we performed computerised literature searches in PubMed, MEDLINE and SportDiscus using the following mesh terms: ‘ADHD’, ‘attention-deficit/hyperactivity disorder’, ‘exercise’ along with the keywords ‘physical activity’, ‘training’, ‘movement’, ‘child’, ‘youth’, ‘adolescent’ and ‘boy’. In addition, we searched the literature manually for additional articles about therapy of ADHD.
Inclusion and exclusion criteria
The inclusion and exclusion criteria are summarised in Table 1.
| Inclusion criteria | Exclusion criteria |
|---|---|
| Peer reviewed | Unpublished data |
| Participants' < 14 years of age | Animal studies |
| Participants diagnosed with ADHD, both, boys and girls | Studies focusing on comorbidities |
| Studies involving any kind of physical activity or exercise with children with ADHD | Retrospective interviews Case scenarios and reports |
| A minimum of 2 training sessions per week, 5 such sessions in all, with a minimal duration of 5 days | Letters of opinion; Reviews |
| Written in English or with English abstract | ADHD as a subgroup of children with mental problems |
| Assessment of the effects of the activity on the symptoms of ADHD (inattention, hyperactivity, impulsivity), as well as other physiological, neurological, cognitive function and/or psychological parameters before, during and/or after the intervention. | All types intervention not related to endurance type of exercise (such as eurhythmy, sensomotoric training) |
| All types of trial or intervention (group and individual intervention) | |
| Publication not older than 10 years |
We included any type of study – blinded or not, randomised or not, group or individual intervention, with both boys and/or girls as subjects – of more than 5 days in duration. Investigations in which children with ADHD were treated as a subgroup of children with mental problems were excluded. We included all outcomes for children participating in an exercise-based intervention.
The flow diagram in Figure 1 illustrates our search strategy and the subsequent steps of exclusion based on these pre-defined criteria.
Results
All data regarding background characteristics of the participants, characteristics of the exercise interventions employed, overview of the protocols and major findings of the studies, methodological approaches and primary outcomes as well as an overview of the studies excluded and the specific reasons for exclusion are presented in Tables 2, 3 and S1–S3.
| Reference | N, sex | Mean or range of age [years] | Type of ADHD | Medication |
|---|---|---|---|---|
| Haffner et al. 11 | 19 (13 ♂, 7 ♀) | 8–11 | 8 medicated | |
| Taylor/Kuo 15 | 17 (15 ♂, 2 ♀) | 7–12 | 6 ADD | 56% used medication daily |
| 10 ADHD (all types) | 19% only on weekdays | |||
| 56% without comorbidities | 31% not at all | |||
| No medication on the day of intervention. | ||||
| Gapin/Etnier 13 | 18 ♂ | 8–12 | 5 hyperactive impulsive | Stimulants, 15 daily and 3 only on weekdays |
| 10.6 ± 1.5 | 2 inattentive | |||
| 8 combined type | ||||
| 2 not reported | ||||
| 45% with and | ||||
| 55% without comorbidities | ||||
| Kang et al. 19 | Control group (education) (n = 13, ♂) | 8.6 ± 1.2 | Both groups were taking 10–40 mg methylphenidate/day | |
| Intervention group (exercise) (n = 15, ♂) | 8.4 ± 0.9 | |||
| Verret et al. 18 | Intervention group (exercise): (10, 9 ♂, 1 ♀) | 9.1 ± 1.1 | Hyperactive impulsive | 30% medicated |
| Control group (no exercise): (11, 10 ♂, 1 ♀) | 13.8 ± 1.7 | All medicated |
- ♂ = boys; ♀ = girls; ADD = Attention Deficit Disorder; ADHD = Attention-Deficit/Hyperactivity Disorder.
- The values presented are ranges or means ± SD.
| Reference | Intensity | Type | Duration of each session | Frequency of sessions | Length of the intervention |
|---|---|---|---|---|---|
| Haffner et al. 11 | Low-moderate | Yoga (postural, respiratory and meditation training) in comparison to active games | 1 h | 2×/week | 8 weeks |
| Taylor/Kuo 15 | Low-moderate | Guided walking in an urban park, downtown or residential area | 20 min | 1×/day | 30 day |
| Gapin/Etnier 13 | Moderate | Walks | 1×/day | 5 day | |
| Kang et al. 19 | Moderate-high | Athletic (aerobic exercise, goal-directed exercise, skipping rope) vs. self-control training (education) | 90 min | 2×/week | 6 weeks |
| Verret et al. 18 | Moderate-high (77% of maximal heart rate) | Aerobic training of muscular and motor skills (basketball, soccer, exercise stations, tag and ball games) | 45 min | 3×/week | 10 weeks |
Description of the methodology
In all of the studies included, the subjects were selected and diagnosed professionally by a paediatrician. The participants in the investigation by Kang et al. 19 were divided randomly into groups; whereas those studied in the study by Haffner et al. 11 were assigned randomly employing a cross-over design. Taylor and Kuo 15 conducted individual guided walks (for a period of 30 days) as single-blind controlled trials, with each subject acting as his/her own control.
Number, age, gender and medication of the participants
The background characteristics of the participants involved in the studies analysed are summarised in Table 2.
Two of these studies 18, 19 included a control group, while in another case the participants served as their own controls 15. The investigation of yoga training versus active games involved a cross-over design 11. Only Gapin and Eitner 13 provided information about their control group in their examination of the effects of walking. In all cases, all subjects were seven to 13.8 years old. Only Taylor and Kuo 15 and Verret et al. 18 included both boys and girls. The degree and type of medication varied widely.
The type, intensity, duration and frequency of exercise and length of the intervention
As documented in Table 3, the nature of the exercise intervention employed in these studies on children with ADHD varied widely.
Effects of exercise on the characteristic symptoms of ADHD
Yoga training attenuated the characteristic symptoms of ADHD significantly, especially in combination with unspecified medication 11. In this cross-over intervention, therapeutic efficiency was higher when active games were performed prior to yoga training rather than vice versa. With medicated participants (methylphenidate), athletic training, including aerobic and goal-directed exercise and skipping rope, ameliorated symptoms to a greater degree than training of self-control, although both groups showed improvement 19. Following aerobic muscular exercise and training of motor skills, the medicated group was less impulsive and demonstrated fewer attentional and cognitive problems 18.
Effects of exercise on social behaviour
Walking at moderate intensity attenuated inhibition in boys 13, while athletic training, especially in combination with unspecified medication, enhanced social skills and cooperativeness 19. Verret et al. 18 observed less anxiety depression and fewer social problems after an intervention involving aerobic training of muscular and motor skills.
Effects of exercise on strength and motor skills
Aerobic training of muscular and motor skills led to better locomotion and motor skills, as well as greater muscular capacity 18.
Effects of exercise on neuropsychological measures
Guided walks improved concentration and walks in the park were considered more enjoyable than those in a residential or downtown area 15. These authors note that the effect of such walks in the park on concentration was roughly equal to the maximal effect of two doses of typical ADHD medications. Memory and processing speed were enhanced after 5 days of walking 13. These investigators attributed the improved performance on the Tower of London planning task to more rapid execution times. They associated physical activity with improved executive function and concluded that moderate-to-vigorous physical activity (MVPA) is a predictor of significantly improved planning.
Athletic training improved speed of processing, as well as indicators of intelligence 19. Moreover, in this case the intervention group exhibited enhanced attention, especially visual attention, and speed of processing. The level of information processing was improved by moderate-to-high-intensity aerobic training of muscular and motor skills 18.
Discussion
The major findings of this highly focused review of published reports on the effects of exercise on symptoms of ADHD are the following: First, the study designs (number, age, gender and medication of participants) and exercise modalities (type, intensity, duration and frequency of exercise and length of the intervention) employed varied significantly. Secondly, the characteristic symptoms of ADHD were attenuated by all of the exercise interventions, and measures of social behaviour, motor skills, strength and neuropsychological measures were improved. Furthermore, no side effects were reported.
Because we only analysed interventions lasting one to 10 weeks here, we can draw no conclusions concerning the effects of longer programs. We refrained from analysing interventions involving only one session each week, since we believe that this is insufficient to induce any sustainable response. Unfortunately, some of the investigations considered here did not include a control group and in most cases mean values and standard deviations were not presented, so that effect sizes could not be calculated. Because of the small sample sizes, lack of control groups and varying nature of exercise, no general conclusions about the effectiveness of exercise for treatment of ADHD can be drawn.
In addition, since with the onset of puberty, hormones that influence strength and strength-related skills (motor skills) are released, we did not analyse studies involving children older than 13 and can therefore not say anything about adolescents. Moreover, potential differences between boys and girls are difficult to evaluate on the basis of the interventions included here. Such sex differences may be important, since ADHD is four times as common among men (7.9%) than women (1.8%) 4, which also explains why most investigations focus on boys. Only three of our studies also involved girls 11, 15, 18 and none took hormonal development into consideration.
It should also be noted that the participants we analysed were taking different types (stimulants such as methylphenidate or amphetamine or non-stimulants like atomoxetine) and doses of medication. Although Haffner et al. 11 and Kang et al. 19 did observe that exercise was more efficient in attenuating symptoms in medicated participants, the correlation between exercise and ADHD medication obviously requires further examination.
The only other review on the impact of physical activity and exercise on children with ADHD currently available [Gapin et al. 10] also concludes that exercise exerts positive impacts on behavioural symptoms and cognitive performance. These authors state that additional professional physiological, psychological and neurological research in this area is required. However, they do not critically analyse the characteristics of the participants, nature of exercise or various parameters measured, methodological differences that all complicate arriving at general conclusions.
In the five reports considered here, characteristic symptoms were assessed with five different tests, social behaviour with four, fitness and motor skills with six different approaches and neuropsychological impact with three. Neurophysiological parameters 16, the startle eye blink response (ASER) [Tantillo et al. 14] and quality of sleep [Tantillo et al. 14] were all examined in one study each. Nonetheless, as summarised in Tables 2, 3 and S1, regardless of the nature of the exercise or outcome examined, exercise exerted beneficial effects in all cases.
Of special interest in this context is the demonstration by Haffner et al. 11 that active games followed by yoga training resulted in greater improvement in symptoms than when the order of these interventions was reversed.
A key question involves the impact of intensity, frequency and duration of exercise on gene expression and/or protein synthesis. Wigal et al. 16 observed that children with ADHD of the combined type exhibit smaller increases in serum levels of catecholamines in response to acute exercise than do healthy, aged-matched controls. These authors therefore proposed that ADHD is associated with a catecholamine dysfunction involving the hypothalamic–pituitary axis that results in elevated cerebral levels of dopamine following a single session of exercise 10. At present, we cannot conclude which type of exercise is most beneficial for the characteristic symptoms of ADHD. Potentially, both the amount and regularity of training and the duration of the intervention may play crucial roles, perhaps by altering gene expression and/or protein synthesis.
The number of studies included in this literature review is relatively small. However, as a result of our systematic use of inclusion and exclusion criteria, these studies all involved interventions lasting longer than 5 days. Including shorter interventions would have potentially resulted in misinterpretation of the effects of exercise on symptoms related to ADHD. We are aware that the nature and length of the interventions analysed here are heterogeneous, but they all attenuated symptoms related to ADHD, even though we cannot conclude which type is most effective. Most of the studies were on boys, so we cannot draw conclusions concerning girls. In all cases the intensity of exercise was from low to moderate, so the influence of high-intensity exercise interventions remains to be explored. Finally, the variety of diagnostic tools employed renders direct comparisons between these investigations difficult.
Considerations for future research and therapeutic strategies
Our present analysis reveals that various types of either moderate- and/or high-intensity exercise improve psycho-social and physiological parameters related to ADHD in children, with no undesirable side effects being reported. Unfortunately, it is not yet known which type of exercise is most beneficial. With interventions of 1–10 weeks involving at least two sessions of moderate exercise each week, yoga, walking and ball and activity games all appear to attenuate the characteristic symptoms of ADHD.
From a practical point of view, high-intensity physical activity may represent an interesting alternative to pharmaceutical treatment of ADHD for the following reasons: First, high-intensity exercise is less time consuming than submaximal exercise and is thereby of increasing interest to other groups of individuals with a particular focus on health 20-23. Secondly, the natural movements of children are characterised by spontaneous, short-term high-intensity activity, with repetitive bouts of sprints interspersed with short periods of recovery 24. Moreover, pre-pubertal children maintain performance without substantial fatigue to a greater extent than adults 24. Furthermore, repetitive movement at a velocity close to or even higher than the maximal aerobic speed, separated by short periods of recovery, improves endurance in children 25-28. Although continuous aerobic activity has been more extensively characterised and is a more established mode of training, high-intensity intermittent training may enhance both aerobic and anaerobic performance in children even more effectively.
Conclusion
The present review summarises the impact of exercise interventions (1–10 weeks in duration with at least two sessions each week) on parameters related to ADHD in 7- to 13-year-old children. We may conclude that all different types of exercise (here yoga, active games with and without the involvement of balls, walking and athletic training) attenuate the characteristic symptoms of ADHD and improve social behaviour, motor skills, strength and neuropsychological parameters without any undesirable side effects. Available reports do not reveal which type, intensity, duration and frequency of exercise is most effective in this respect and future research focusing on this question with randomised and controlled long-term interventions is warranted.
Acknowledgements
The authors have no conflicts of interest directly related to this article to declare. No external funding was required or provided.
