Effects of Desk-Bike Cycling on Phonological Working Memory (WM) Performance in Adolescents With ADHD.

Despite evidence that points to positive associations between physical activity, cognitive function (Hillman et al., 2008), academic performance (Castelli et al., 2007; Donnelly et al., 2016), and overall health (Butte et al., 2007) in school-aged youth, children’s opportunities to engage in physical activities during the school day have significantly decreased during the last two decades (Institute of Medicine, 2013). This trend has co-occurred with the increasing prevalence of sedentary behaviors in western society due to advances in technology and environmental changes (Ng and Popkin, 2012) and contributes to chronic health problems across the life span, such as obesity and cardiovascular diseases (Hillman et al., 2008). As a response to these negative developments, organizations have begun to promote physical activity in the classroom (National Association for Sport and Physical Education et al., 2008). In addition, there has been a gradual increase in studies investigating the impact of active teaching lessons or active workstations on health and cognition (see also Kibbe et al., 2011; Donnelly et al., 2016; for a review see Mavilidi et al., 2018; Ruiter et al., 2019).

Recently, it has been suggested that physical activity interventions are especially beneficial for those children characterized by lower cognitive control and self-regulatory behavior¹ (Drollette et al., 2014). That is, overall findings revealed that a single, acute bout of moderate-intensity aerobic exercise facilitates cognitive performance, with more extensive effects observed for the lower-performing group than the higher-performing group on a flanker task. Similarly, Mahar et al. (2006) reported that increasing physical activity opportunities in the classroom to improve on-task behavior were especially beneficial for children who demonstrated poor on-task behavior at baseline. One specific class of individuals with cognitive control impairments is children diagnosed with attention deficit hyperactivity disorder (ADHD). Attention deficit hyperactivity disorder is a psychological outcome that manifests itself during childhood and is characterized by developmentally inappropriate levels of inattention, impulsivity, and hyperactivity (Rapport et al., 2009). Contemporary leading theories have explained the mechanism underlying ADHD-related deficits as an imbalance in the catecholaminergic systems in the brain, leading to dysfunction of attentional circuits (Rapport et al., 2009). Specifically, it has been hypothesized that attentional impairments may be due to depleted levels of dopamine in the prefrontal cortex. The efficacy of psychostimulants in the treatment of ADHD supports this notion (Yu-Kai et al., 2012).

Pontifex et al. (2013) investigated the effect of a single bout of moderate-intensity aerobic exercise on children with and without ADHD using objective measures of attention and brain neurophysiology. Although both groups improved performance on the flanker task following exercise, acute exercise appeared to have an additional benefit for children with ADHD. The ADHD group exhibited an increase in a neuroelectric component (i.e., error-related negativity, ERN) that has been linked to the upregulation of processes involved in action monitoring. Importantly, these exercise-induced facilitations in action monitoring processes resulted in increased task performance following errors in the ADHD group only.

Apart from the reported benefits of physical activities, such as aerobic exercise, recent studies also suggest that self-initiated spontaneous motor activity seems to serve as a positive function for children with ADHD. Rapport et al. (2009) noticed that the relationship between increased rates of activity and ADHD is pervasive, as the disorder is associated with excessive gross motor activity and fidgeting from early childhood (Corkum et al., 1998; Rapport et al., 2009), in both children and adults (Teicher et al., 2012). Moreover, also during the performance of cognitively demanding tasks (i.e., WM, stop-signal, and choice tasks), increased levels of activities among children and adults diagnosed with ADHD have been reported (Rapport et al., 2009; Alderson et al., 2012; Hudec et al., 2014). Rapport et al. (2009) hypothesized that increased movement may serve as a compensatory function to augment chronic cortical under-arousal associated with ADHD (Dickstein et al., 2006). In other words, hyperactivity is a functional and secondary symptom reflective of unconscious efforts to increase arousal to meet cognitive WM demands. This model therefore predicts a positive relation between gross motor activity and cognitive performance for persons with ADHD. Indeed, this functional WM model was substantiated with recent findings showing that higher rates of spontaneous motor activity predicted significantly better phonological WM performance (Sarver et al., 2015) and better cognitive control performance (Hartanto et al., 2016) for children with ADHD. However, findings also showed that increasing set size demands within the context of a phonological WM task was not significantly related to an activity level as one should expect when adhering to the functional model (Rapport et al., 2009; Sarver et al., 2015).

With these recent findings, the widespread assumption that excess gross motor activity interferes with children’s ability to actively engage in learning-related activities that challenge executive functions, such as WM, and the subsequent recommendations or measures to target this hyperactivity in the classroom, should be reconsidered. Instead of decreasing the activity levels of children and adolescents diagnosed with ADHD, research should investigate how opportunities for physical activities, particularly, ones that are neither disruptive nor stigmatizing, can be used in academic settings to help children perform cognitively demanding tasks. One promising strategy for increasing physical activity in the classroom is through the use of active workstations, such as desk bikes (Torbeyns et al., 2014; Ruiter et al., 2017).

Given the role of physical activity on cognitive function and academic performance, the aim of the present study was to investigate whether an exercise that is concurrent and of light intensity (i.e., self-paced cycling on a desk bike) could increase cognitive control of adolescents diagnosed with ADHD. Most research in the acute exercise literature has found positive effects on cognitive control processes after at least 20 min of moderate exercise (e.g., Hillman et al., 2003) in adults. To our knowledge, very few studies have investigated the effectiveness of a seated concurrent light intensity physical activity for preadolescents or adolescents diagnosed with ADHD (Sarver et al., 2015; Ruiter et al., 2019). Therefore, in the present study, the effects of structured motor activity on a desk bike on phonological WM performance in adolescents diagnosed with ADHD were examined. Desk-bike cycling was used in the study given its feasibility (i.e., allows students to stay seated and is relatively quiet) and affordability to be used in a classroom setting. Based on findings in previous work in which higher rates of spontaneous motor activity predicted significantly better phonological WM performance for children with ADHD (Sarver et al., 2015), it was hypothesized that adolescents with ADHD would benefit from cycling on the desk bike (i.e., concurrent light-intensity activity) and consequently show higher WM performance during cycling than during seated-rest. Since cycling on a desk bike is considered a light intensity activity in this study, no hypothesis was formulated for effects after cycling. We also explored whether WM performance during cycling would be differentially affected by WM load. In addition, we explored the effects of desk-bike cycling on subjective measures of mental effort, enjoyment, and difficulty.

This study is the first one to examine whether physical activity in the form of stationary cycling can be used in the classroom to help adolescents diagnosed with ADHD perform cognitively demanding tasks. Based on literature pointing toward a positive association between motor activity and cognitive control for adolescents with ADHD (Drollette et al., 2014; Sarver et al., 2015; Hartanto et al., 2016), we hypothesized that exercise in form of cycling during a phonological WM task would result in increased WM performance. Yet, no statistically significance of cycling was found on total WM performance. The present study therefore fails to substantiate the assumption that facilitating physical activity helps adolescents with ADHD improve their WM performance. This result is in line with several previous studies failing to find a beneficial effect of active workstations on cognitive functioning (Bantoft et al., 2016; Torbeyns et al., 2017). It is important to note, however, that these earlier results have arrived with a different population, namely, adults or typically developing children and not children or adolescents diagnosed with ADHD.

As an additional exploratory analysis, we also looked at the effect of condition on WM task performance at low and high levels of the cognitive load instead of total WM performance. Data revealed that at low levels of load (i.e., set sizes 3 and 4), seated-rest and cycling resulted in comparable WM scores, whereas cycling resulted in better WM performance when set sizes increase (i.e., set sizes 5 and 6).

This result is in line with the study of Hartanto et al. (2016) who found that higher rates of spontaneous motor activity predicted significantly better performance on inhibitory control. In their study, participants’ movements were measured by affixing an actometer to their ankles that measured their level of activity while completing the flanker test. The accuracy of the participants with ADHD was significantly improved when they were moving. In other words, correct answers were associated with more motion than incorrect answers. This result suggests that accuracy in ADHD may be enhanced by more intense activities or that when a child with ADHD is using more cognitive resources they are more likely to be engaging in physical activity. One possible mechanism for a relationship between movement and cognitive performance is that children with ADHD use movement to self-regulate alertness. An optimal level of arousal is required for peak cognitive performance (Yerkes and Dodson, 1908). The results of the present investigation and the study of Hartanto et al. (2016) support Rapport et al.’s (2009) model that hyperactivity may serve to compensate for underarousal and acts to improve cognitive performance.

Another explanation for this result can be found in the fact that cycling on a desk bike is a very specific form of structured, continuous movement with the lower body. Possibly, this type of movement will prevent adolescents with ADHD from making more uncontrolled movements with the upper body (e.g., arm movements) that are unrelated to the task at hand and that negatively affect task performance, since they take away the attention necessary for well-performing a task under high WM load conditions (Engle, 2002). More specifically, cycling movements have the potential to channel the surplus of motor activity common to adolescents with ADHD, while keeping a focus on the challenging cognitive task at hand. As a result, performance under high WM load conditions will be increased, while no such performance gains are obtained in tasks under low WM conditions. This explanation resonates well with findings that continuous body movements, as opposed to discrete movements, increase performance on WM tasks under conditions of high cognitive load (Maes et al., 2015). More research is needed to shed light on how task difficulty moderates the potential compensatory effect of cycling on task performance, especially, in children with ADHD. These findings have important implications for the educational field or clinical practice. Desk bikes can be implemented in the classroom to help manage students’ hyperactivity symptoms and boost their performance in the classroom on cognitively demanding tasks, without interrupting, or distracting peers or teachers in the classroom.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Ethics Review Committee at the Department of Psychology, Education and Child Studies of Erasmus School of Social and Behavioral Sciences. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

MR, EG, SL, and FP conceived and planned the experiments. MR and EG carried out the experiments. MR, SL, JW, and FP contributed to the writing of the manuscript. SL and FP supervised the project. All authors provided critical feedback and helped shape the research, analysis, and manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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