Author(s): HANSSEN, J., HURST, P., Institution: CANTERBURY CHRIST CHURCH UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2313

INTRODUCTION
Placebo and nocebo effects can substantially influence motor performance measures such as strength and fatigue resistance. However, the underlying neurophysiological mechanisms remain poorly understood. This study used a randomised controlled design with high-density electroencephalography (EEG) to characterise the temporal and spatial dynamics of cortical activity associated with placebo- and nocebo-induced modulation of motor performance.
METHODS
Fifty-six healthy participants were randomly assigned to one of four groups: placebo, nocebo, control, or natural history. At baseline, all participants underwent high-density EEG recordings during an isometric knee-extension task on an isokinetic dynamometer and completed validated questionnaires assessing expectancy, optimism, anxiety, and additional psychological measures. After 48–72 hours from baseline, participants in the experimental groups received one of three interventions: (1) a positive-expectation manipulation (placebo), (2) a negative-expectation manipulation (nocebo), or (3) neutral instructions (control). In the placebo and nocebo groups, an inert substance was described as either performance-enhancing or performance-impairing, respectively. Expectancy was further reinforced using EEG-guided presentations of positive, negative, or neutral adjectives matched to each condition. Baseline measurements were then repeated. Participants in the natural history group received no intervention and simply repeated baseline testing.
RESULTS
Collected Data is currently being analysed. Primary neurophysiological outcomes focus on the contingent negative variation (CNV), complemented by exploratory source localisation analysis. Behavioural outcomes include maximal and mean peak torque and force production during isometric leg extensions and time-to-failure at 60% of maximal voluntary contraction. Data are analysed with a 2 × 4 mixed-design ANOVA, with condition (baseline vs. test) as the within-subject factor and group (placebo, nocebo, control, natural history) as the between-subject factor. Questionnaire data are being analysed for potential correlations and regressions with objective measures. Significant interactions are followed by post hoc comparisons corrected for multiple testing. Statistical significance is set at p < 0.05.
DISCUSSION
This study will provide insight into when (temporal dynamics), where (cortical sources), and how placebo and nocebo effects influence motor performance. Improved understanding of these mechanisms has direct implications for sport and exercise contexts, informing ethical and evidence-based approaches to placebo and nocebo modulation in performance enhancement.
Preregistration Trial registration number: NCT06835777.