Neurophysiological Mechanisms of Placebo and Nocebo Effects in Sports - a Protocol Paper

This trial will examine temporal and spatial aspects of neurophysiological mechanisms behind nocebo and placebo effects before (expectation) and at exercise onset (perception) using high-density EEG. It will further investigate possible predictors of responsiveness and non-responsiveness to acute placebo and nocebo stimuli in the context of sports, notably interpretating psychological mechanisms (e.g. personality, beliefs, expectations) as well as temporal neurophysiological measures.

This study is designed as a randomized, controlled clinical trial (RCT) with data collection on two different occasions and four parallel groups: 1) positive-expectations, 2) negative-expectations, 3) control, and 4) natural history.

The first three groups will be addressed as intervention groups. On the first visit, participants' baseline data, specifically performance measures (all groups) and EEG data (all but natural history), as well as key characteristics will be collected. On the second visit, in the belief groups, participants will receive an in-person manipulation of beliefs and two placebo pills and will be informed that they are expected to positively (positive-expectations) or negatively (negative-expectations) affect their isometric strength and fatigue resistance measured using a Biodex System 4 Isokinetic Dynamometer in a 5x5sec test protocol with a minimum of 1 minute rest in between sets. In addition, after a resting period of three minutes, they will perform an isometric knee extension hold to failure at 60% MVC. The control group and the natural history group will receive no pills, with the control group receiving a neutral explanation of EEG data, its relevance and general information about isometric strength testing and the natural history group not receiving EEG at all, but serving as a control to the potential influence of experiencing an EEG set up on performance measures. The primary endpoints of this trial are placebo and nocebo induced changes in EEG signaling via Event Related Potentials (ERPs) during administration of reinforcements of beliefs through words as well as during expectancy and perception phases of physical performance.

The key question of this trial is whether participants exposed to placebo or nocebo stimuli will exhibit distinct neural activity pattern (temporal and spatial) in the context of sports performance. The second major question is, whether individual differences in character traits and states as well as motivation and beliefs can significantly predict the magnitude or likeliness of placebo and nocebo responses in participants' performance in an isometric strength and fatigue resistance task. In addition, EEG data to better understand the valence of and emotional response to words will be used to further investigate how semantics and our choice of words influence susceptibility to placebo and nocebo effects in other people. Several elements that were not adequately addressed in previous studies will be incorporated into this RCT:

(1) temporal and spatial aspects of neural correlates of placebo and nocebo effects in sports, (2) hard data (EEG) on how an individual reacts to semantic implications on performance and (3) correlation of subjective ratings of expectations of performance and data from neural processes associated with affective processing, emotional valence and motivation (LPP,LPC) and anticipation as well as motor preparation (CNV). To further understand the above point may result in a change on how athletes, coaches and therapists approach placebo and nocebo effects in the context of sports performance.

Inclusion criteria

• Healthy adult participants (18+)
• physically active (WHO, 2020)
• no medical history pf psychological disorders/mental health issues
• no acute or regular medication intake
• no severe injury to the lower limb within the last 6 months
• proficient in english
• normal or corrected eyesight