Comment on: Unexpected dual task benefit on cycling in Parkinson Disease and healthy adults: A Neuro-Behavioural Model

In the present study, both healthy older adults (HOA) and participants with Parkinson Disease (PD) completed a baseline cycling task for two minutes at a self-selected comfortable rate against minimal resistance. Participants then completed a total of 12 cognitive tasks, progressing in hypothesised difficulty, while simultaneously cycling. The authors’ aimed to test the assumption that more difficult secondary tasks lead to greater dual task effects.
Firstly, caution is urged when interpreting the cycling speed data during the baseline condition (48.6 ± 12.8 and 53.9 ± 15.7 RPM for PD participants and HOA participants respectively). During self-paced exercise, perceived exertion is fundamental to self-regulated exercise intensity (1). Furthermore, attentional focus is known to impact on this relationship. Thus, when participants were asked to cycle at a “comfortable” rate, it is likely that their attention is directed inwardly toward physical sensations of effort, a focus which typically increases effort perceptions (2,3). In such conditions, it is likely that cycling speed will be reduced to maintain a “comfortable” feeling. It is likely, therefore, that baseline cycling speed represents a lowered cycling intensity for participants in this study. As baseline performance is fundamental to subsequent data analysis within this study, interpretation of the findings should be treated with caution.
The relative increase in cycling speed during the simple cognitive tasks also demands consideration. A general finding in the attentional focus literature is that when distractive thoughts are engaged by participants, performance tends to be reduced when compared with a task-relevant focus (4,5). This is in line with the dual task paradigm, and suggests a sharing of cognitive resources between cognitive and motor tasks. Some distractive tasks have, however, been shown to improve performance. Specifically, these tasks have included rhythmically repeating a word (6), or phrase (7) during task performance. We have previously suggested (8) that these rhythmical phrases may unintentionally stimulate a focus on cadence (i.e. RPM) rather than distract from the activity and, as a result, improve endurance performance. It is interesting to compare these foci with simpler cognitive tasks in the present study, specifically articulation speed, which required participants to say “Pa” as many times as possible within a 10 seconds period. It is noteworthy in the healthy older adults that articulation speed resulted in the greatest increase in cycling speed (26.3 ± 42.5%) relative to baseline. Thus, the articulation speed task may have been facilitative to performance due to its compatibility with the cycling task. This is in line with the authors’ conclusion that “pairing cycling with simple, fast-paced tasks may be an effective way to increase the intensity of exercise” (p. 10).
Accepting that baseline performance may under represent true self-selected speed, and that processing speed tasks may have facilitated cycling speed, performance on the main dependent variable, cycling speed, shows a progressive decrease thereafter as cognitive tasks increase in difficulty. This is consistent with traditional predictions of the dual task effect. Furthermore, if all performance measures are considered as dependent variables (i.e. cycling speed, response time/number, and accuracy) then a more complete analysis is possible. Thus, processing speed tasks, which resulted in an increased cycling intensity (relative to baseline), show a slight decrease in response time/number relative to single task performance. Similarly, Digit Symbol, which the authors interpret as a significant dual effect benefit in response time, results in a cost in cycling speed for the PD group (48.8 ± 12.9 rpm) compared with easier (i.e. Stroop Color Word; 52.2 ± 13.6 rpm) and more difficult (i.e. 1-Back; 51.1 ± 12.2 rpm) cognitive tasks. Finally, the dual effect cost noted for response accuracy in the 2-Back task is offset by relative increases in both cycling speed (+3.8% and +14.7% respectively) and response time (+5.8% and + 18.4% respectively) for PD and HOA groups. This pattern is evident throughout the results and reinforces the suggestion of Smith and colleagues (9), paraphrased within this article, that dual task performance involves switching attention between tasks. Thus, when performance improvements are seen in one task, they are typically offset by decrements in the other, the classic effect of the dual task paradigm and consistent with Kahneman’s (10) original account of dual task performance.
In conclusion, we commend the authors’ on an interesting study, with a novel methodology for investigating the dual task effect during self-paced endurance exercise. However, we propose an interpretation within which the findings support traditional accounts of the dual task paradigm. Finally, we recommend future studies employing self-paced endurance exercise tasks should account for potential performance decrements arising from an attentional focus which stimulates a focus on internal bodily sensations during baseline.
References
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