Effects of attentional focus on movement coordination complexity.

Attentional focus affects performance and learning of motor tasks. An external attentional focus (on the effects of movement) can lead to more efficient and effective movements compared to an internal focus (on body movement itself). According to the "constrained action hypothesis", an external focus facilitates fast and reflexive movement control while an internal focus leads to disruption of automatic coordination processes. Such disruption should be apparent in the complexity of movement. In this study, multiscale entropy measures were used to investigate if the external focus is related to superior coordination complexity compared to internal focus. Twenty participants were divided in two groups that balanced over an unstable platform in fourteen trials over two days, either with internal or external focus of attention instructions, followed by seven retention trials on the third day. Multiscale entropy measures were used to quantify complexity of motions of the platform, the participant, and the composite of participant and platform motions. Results were contrary to expectations. For the external focus group, despite better overall performance, multiscale entropy values of participant and composite motions were lower in some scales compared to the internal focus group, especially in the first and last days. This may be consistent with previous findings that predictability increases during learning of a balance task. Results also indicate the need to identify the correct physiological interpretation of single or multiscale entropy measures. Further investigation is needed to establish if entropy differences are causally related to performance and learning advantages of the external focus.