Attentional focus influences sample entropy in a balancing task

An external focus of attention has consistently been associated with improved balance (Wulf, 2013). Recent work has considered whether changes in postural control entropy, a measure of repeated movement patterns, could be a factor influencing this benefit. Rheaet al. (2019) reported that during quiet standing sample entropy when using an external focus was increased relative to baseline, whereas an internal focus did not differ from baseline. External and internal focus conditions did not differ from each other, but the authors speculated this difference may emerge with more complex balance tasks. The purpose of the present study was to determine if sample entropy and standard deviation of angular displacement differed when balancing on a stability platform while using an external, internal, or holistic focus. Young healthy adults (N = 36) completed three familiarization trials on the stability platform, followed by three trials each using an external focus (focus on keeping markers level), an internal focus (focus on keeping feet level), and a holistic focus (focus on feeling calm and stable). All trials lasted 20 s, and focus condition order was counterbalanced. Angular displacement of the platform was recorded at a frequency of 25 Hz, and sample entropy and standard deviation of angular displacement were calculated using a custom MATLAB code. Separate mixed ANOVAs for each dependent variable were used to assess differences due to focus and condition order, and Sidak post-hoc tests were used for pairwise comparisons. Results indicated an external focus led to higher sample entropy than a holistic focus (p = .001) and internal focus (p = .031). Standard deviation trended toward lower values with an external focus, but was influenced by a Focus x Order interaction. These results suggest that an external focus may promote more adaptive movement adjustments relative to a holistic focus and an internal focus.