Initial experience of balance assessment introduces ‘first trial’ effects on emotional state and postural control

Abstract Background Anxiety and arousal have been shown to influence balance control and, therefore, have the potential to confound balance assessment. It has been suggested that the ‘first-trial’ effect, where performance on the first trial of a balance task differs from subsequent trials, may be a result of participants being more anxious during their first experience of having their balance assessed. However, this remains speculative since limited work has simultaneously examined emotional state and balance control during repeated assessment of the same balance task. Research question Determine how emotional state and standing balance control change over the course of repeated assessment. Methods Seventy-five healthy young adults completed five 120-s quiet standing trials. Psychological state was probed at each trial using self-report measures that assessed confidence, anxiety, and attention focus. Sympathetic arousal was estimated from electrodermal activity (EDA) and balance control was assessed from centre of pressure (COP) measures derived from forceplate data. Repeated measures ANOVAs were conducted to determine how each of these estimates changed with repeated testing. Results There were significant changes in emotional state with repeated testing; self-report and autonomic measures indicated that participants were most anxious and physiologically aroused during the first trial. This emotional response diminished with repeated testing, although the greatest changes occurred from the first and second trial. Despite these changes in emotional state, only some COP outcomes significantly changed. Individuals leaned further forward during only the first trial and demonstrated higher frequency and velocity mediolateral COP oscillations during the first two trials. Significance When balance is assessed for the first time in an unfamiliar laboratory setting, there is a transient emotional response which appears sufficient to influence balance control. It is critical to control for these confounds when designing experiments or interventions involving balance assessment.