Incorporating methods and findings from neuroscience to better understand placebo and nocebo effects in sport

A narrative review of the placebo effect: historical roots, current applications, and emerging insights

PURPOSE

Placebo is a term to define physiologically inactive compounds used in treatment that causes physical and emotional changes. The placebo effect, driven by expectation and conditioning, plays a significant role in various conditions like pain, depression, and Parkinson's disease, while the nocebo effect can hinder treatment outcomes. Understanding mechanisms such as neuromodulation and genetics has gained importance in modern medicine. This review aims to explore the clinical relevance of placebo responses, particularly in neuropsychiatric disorders, and their potential in personalized medicine. By integrating placebo research into healthcare, it highlights opportunities to enhance treatment efficacy, improve patient well-being, and reduce reliance on pharmacological interventions.

METHODS

A comprehensive literature search was conducted in PubMed, Scopus, and Google Scholar databases. Recent studies were reviewed to evaluate placebo effects, and the variability of the placebo response in neuropsychiatric disorders was summarized.

RESULTS

Placebo effects significantly impact treatment outcomes across various conditions, including Parkinson's disease, depression, pain syndromes, and epilepsy. The mechanisms involve neurobiological and psychological factors, with evidence suggesting that placebo interventions can modulate neurotransmitter activity and improve patient well-being.

CONCLUSION

Integrating placebo research into clinical practice may enhance treatment outcomes, reduce drug dependency, and support personalized medicine by tailoring interventions to individual placebo responsiveness. Understanding placebo and nocebo mechanisms can optimize therapeutic strategies while minimizing unnecessary pharmacological treatments.

"I am open to self-belief": A study examining the impact of open-label effects on postexercise affect and postintervention exercise behaviour

The contribution of placebo effects can be measured by manipulating psychological factors, such as positive expectations for exercise outcomes, without the need for traditional placebos (such as inert substances). While placebo effects are well known, research has revealed intriguing findings suggesting that placebos can have beneficial effects even when studies are performed without deception. Open-label placebo (OLP) interventions (prescribed honestly), which harness the power of belief, may represent another effective method for enhancing the benefits of exercise effects. This study compared the efficacy of a conventional placebo intervention, an OLP intervention, and a control group among 89 individuals. Participants' levels of affective response after exercise and exercise behaviour were assessed during the intervention period (4 weeks) and at follow-up (4 weeks). The results revealed similar levels of improvement in all outcomes across the three conditions. Both the conventional placebo and OLP intervention groups exhibited greater enhancements in postexercise enjoyment. OLP interventions demonstrated distinct advantages in terms of remembered affect and expectation fulfilment. Nonetheless, neither intervention directly stimulated postintervention exercise behaviour. Future studies should continue to explore the impact of OLP interventions on adherence to exercise behaviour.

Does ischemic preconditioning enhance sports performance more than placebo or no intervention? A systematic review with meta-analysis

BACKGROUND

Ischemic preconditioning (IPC) is purported to have beneficial effects on athletic performance, although findings are inconsistent, with some studies reporting placebo effects. The majority of studies have investigated IPC alongside a placebo condition, but without a control condition that was devoid of experimental manipulation, thereby limiting accurate determination of the IPC effects. Therefore, the aims of this study were to assess the impact of the IPC intervention, compared to both placebo and no intervention, on exercise capacity and athletic performance.

METHODS

A systematic search of PubMed, Embase, SPORTDiscus, Cochrane Library, and Latin American and Caribbean Health Sciences Literature (LILACS) covering records from their inception until July 2023 was conducted. To qualify for inclusion, studies had to apply IPC as an acute intervention, comparing it with placebo and/or control conditions. Outcomes of interest were performance (force, number of repetitions, power, time to exhaustion, and time trial performance), physiological measurements (maximum oxygen consumption, and heart rate), or perceptual measurements (RPE). For each outcome measure, we conducted 3 independent meta-analyses (IPC vs. placebo, IPC vs. control, placebo vs. control) using an inverse-variance random-effects model. The between-treatment effects were quantified by the standardized mean difference (SMD), accompanied by their respective 95% confidence intervals. Additionally, we employed the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to assess the level of certainty in the evidence.

RESULTS

Seventy-nine studies were included in the quantitative analysis. Overall, IPC demonstrates a comparable effect to the placebo condition (using a low-pressure tourniquet), irrespective of the subjects' training level (all outcomes presenting p > 0.05), except for the outcome of time to exhaustion, which exhibits a small magnitude effect (SMD = 0.37; p = 0.002). Additionally, the placebo exhibited effects notably greater than the control condition (outcome: number of repetitions; SMD = 0.45; p = 0.03), suggesting a potential influence of participants' cognitive perception on the outcomes. However, the evidence is of moderate to low certainty, regardless of the comparison or outcome.

CONCLUSION

IPC has significant effects compared to the control intervention, but it did not surpass the placebo condition. Its administration might be influenced by the cognitive perception of the receiving subject, and the efficacy of IPC as an ergogenic strategy for enhancing exercise capacity and athletic performance remains questionable.

Transcranial direct current stimulation (tDCS) and cycling performance on the 3-minute aerobic test (3mAT): placebo and nocebo effects

Transcranial direct current stimulation (tDCS) has been used extensively but research on its efficacy within the sport and exercise science realm has been inconsistent. There may be placebo and nocebo effects present with its use. Our objective was to determine if subjects can be influenced to believe that tDCS will improve cycling performance. Subjects were separated into a belief group (B; 5 women, 6 men) and a disbelief group (DB; 9 women, 3 men). The B group was told that the stimulation would improve performance on a subsequent cycling test. In the DB group, subjects were told that it was not effective and would hinder performance. The cycling test was a 3-minute aerobic test (3mAT) where subjects maintained the highest power output possible for three minutes, after completing a full 20 min warmup. During the warmup, they were given either no stimulation (control) or 2 mA bilateral stimulation over the M1 region. There was a very slight increase in maximal minute power for the B group (0.22%) and a small decrease for the DB group (-1.00%); however, these differences were not significant. No significant differences were found for any of the cycling variables. In conclustion, tDCS was unable to improve performance on the 3mAT. These findings, in conjunction with others, suggest that the acute effect of tDCS is still questionable when aiming to enhance endurance performance.

Caffeine Placebo Effect in Sport and Exercise: A Systematic Review

The objective of this review article is to systematically identify the caffeine placebo effect in sport and exercise activities. We selected randomized controlled trial studies to better understand the impact of caffeine and its placebo effect on sports performance. We extracted a set of articles that refer strictly to the topics of caffeine and its placebo effect in sport and exercise, considering the databases integrated to the Core Collection Web of Science and Scopus, as well as the registration of the documents in PubMed®, a system with a selection process aligned with the guidelines for the PRISMA methodology, establishing the eligibility criteria of the articles with the PICOS tool, to which a systematic review is applied. Finally, the results show that caffeine improves anaerobic capacity and endurance, while placebo perceived as caffeine can also increase performance by reducing pain and improving concentration. This finding underscores the influence of expectations and placebo on physical performance, suggesting that managing these expectations may be an effective strategy for improving athletic performance.

Preserving the placebo effect after disclosure: A new perspective on non-deceptive placebos

The present study explores whether a particular style of placebo disclosure could serve as a tool to foster a renewed trust in one's own inherent resources and elicit a meaningful placebo effect. In a motor performance task, two placebo groups received inert transcutaneous electrical nerve stimulation (TENS) in each of four sessions along with information on its force-enhancing properties. Before the final session, one of the placebo groups was informed about the placebo, which was portrayed as a means to unleash an inherent potential. Along with force, we systematically monitored task-specific self-efficacy to test whether this variable would be differentially modulated in the two placebo groups. Compared to two control groups, placebo groups showed higher force and self-efficacy in the last session. No differences in self-efficacy were observed in the placebo groups even after revealing the placebo procedure, suggesting that the disclosure was effective in 'safeguarding' individuals' self-efficacy. These findings may have important implications, paving the way for the use of placebos that not only are ethically permissible but also support individuals' self-efficacy.

Placebo and Nocebo Effects on Sports and Exercise Performance: A Systematic Literature Review Update

Sports performance could be affected by placebo and nocebo effects. The last literature review on placebo and nocebo effects on sports and exercise performance was published in 2019. In the past five years, several new studies have been published. This review aimed to update the previous synthesis and evaluate the results of new studies focusing on placebo or nocebo interventions in sports and exercise by determining the form and magnitude of their effect. Hence, we searched for empirical studies published from 2019 until the end of May 2024 indexed in PubMed, Medline, Web of Science, EBSCO, and Google Scholar databases. The search yielded 20 eligible studies with control or baseline-control conditions, focusing on nutritional, mechanical, and other mixed ergogenic aids. They yielded small to large placebo effects (Cohen's d) for nutritional (d = 0.86), mechanical (d = 0.38), cream and gel (d = 0.05), and open-label placebo (d = 0.16) interventions. The pooled effect size for placebo effects was moderate to large (d = 0.67), larger than in the earlier review, suggesting that placebo effects can improve motor performance even more than previously reported. However, based on five measures from three studies, the nocebo effects were almost twice as large (d = 1.20). Accordingly, the current findings support and expand the last review in the field by yielding additional support for placebo and nocebo effects in sports and exercise.

Expectations Come True: The Placebo Effect of Exercise on Affective Responses

Objective: This study investigated the placebo and nocebo effects of habitual and induced expectations. Methods: In Study 1, 95 participants (Mage = 19.65 ± 2.21 years, MBMI = 21.94 ± 2.55) were grouped according to habitual expectations (positive, neutral, or negative) and completed a 30-min moderate-intensity aerobic exercise, and their affective response, rating of perceived exertion (RPE), and heart rate variability (HRV) were measured before, during, and after the exercise. In Study 2, the participants from Study 1 were grouped according to induced expectations (control, positive, or negative) and completed a 30-min moderate-intensity aerobic exercise. Affective response, RPE, and HRV were measured before, during, and after exercise. Results: In Study 1, positive habitual expectations increased affective response during and after exercise [F(2, 92) = 2.959, p = .057, ηp2 = .060], and negative habitual expectations increased RPE during exercise [F(2, 92) = 5.174, p = .007, ηp2 = .101]. In Study 2, positive induced expectation increased affective response during [F(2, 86) = 5.492, p = .006, ηp2 = .113] and after exercise [F(2, 86) = 6.096, p = .003, ηp2 = .124] and was not affected by habitual expectation. Conclusion: The affective response during and after exercise is influenced by habitual and induced expectations. Positive expectations enhance affective benefits, while negative expectations reduce affective benefits.

Light-Weight Wearable Gyroscopic Actuators Can Modulate Balance Performance and Gait Characteristics: A Proof-of-Concept Study

Falling is a major cause of morbidity, and is often caused by a decrease in postural stability. A key component of postural stability is whole-body centroidal angular momentum, which can be influenced by control moment gyroscopes. In this proof-of-concept study, we explore the influence of our wearable robotic gyroscopic actuator "GyroPack" on the balance performance and gait characteristics of non-impaired individuals (seven female/eight male, 30 ± 7 years, 68.8 ± 8.4 kg). Participants performed a series of balance and walking tasks with and without wearing the GyroPack. The device displayed various control modes, which were hypothesised to positively, negatively, or neutrally impact postural control. When configured as a damper, the GyroPack increased mediolateral standing time and walking distance, on a balance beam, and decreased trunk angular velocity variability, while walking on a treadmill. When configured as a negative damper, both peak trunk angular rate and trunk angular velocity variability increased during treadmill walking. This exploratory study shows that gyroscopic actuators can influence balance and gait kinematics. Our results mirror the findings of our earlier studies; though, with more than 50% mass reduction of the device, practical and clinical applicability now appears within reach.

Placebo and nocebo effects and mechanisms associated with pharmacological interventions: an umbrella review

OBJECTIVES

This review aimed to summarise the existing knowledge about placebo and nocebo effects associated with pharmacological interventions and their mechanisms.

DESIGN

Umbrella review, adopting the Assessment of Multiple Systematic Reviews 2 tool for critical appraisal.

DATA SOURCES

MEDLINE/PubMed, Scopus, Web of Science, PsycINFO, Cochrane Central Register of Controlled Trial were searched in September 2022, without any time restriction, for systematic reviews, narrative reviews, original articles. Results were summarised through narrative synthesis, tables, 95% CI.

OUTCOME MEASURES

Mechanisms underlying placebo/nocebo effects and/or their effect sizes.

RESULTS

The databases search identified 372 studies, for a total of 158 312 participants, comprising 41 systematic reviews, 312 narrative reviews and 19 original articles. Seventy-three per cent of the examined systematic reviews were of high quality.Our findings revealed that mechanisms underlying placebo and/or nocebo effects have been characterised, at least in part, for: pain, non-noxious somatic sensation, Parkinson's disease, migraine, sleep disorders, intellectual disability, depression, anxiety, dementia, addiction, gynaecological disorders, attention-deficit hyperactivity disorder, immune and endocrine systems, cardiovascular and respiratory systems, gastrointestinal disorders, skin diseases, influenza and related vaccines, oncology, obesity, physical and cognitive performance. Their magnitude ranged from 0.08 to 2.01 (95% CI 0.37 to 0.89) for placebo effects and from 0.32 to 0.90 (95% CI 0.24 to 1.00) for nocebo effects.

CONCLUSIONS

This study provides a valuable tool for clinicians and researchers, identifying both results ready for clinical practice and gaps to address in the near future.

FUNDING

Università Cattolica del Sacro Cuore, Milan, Italy with the 'Finanziamento Ponte 2022' grant.

PROSPERO REGISTRATION NUMBER

CRD42023392281.

Impact of Verbal Suggestions on Finger Flexor Activation and Strength in Healthy Individuals

BACKGROUND Words uttered by other people can have an enormous influence on how we perceive our surroundings, what we expect, what we experience, and how we behave. This study aimed to evaluate the effect of verbal reinforcement on the placebo effect in the context of finger flexor muscle activation measured with surface electromyography (sEMG) and hand grip strength measured with a hand dynamometer in healthy subjects. MATERIAL AND METHODS Eighty-eight individuals aged 22.64±5.2 years took part in the study. For each person, paper tape was applied (placebo). The participants were randomly assigned to 1 of the 3 groups: positive information group (P) - "the tape increases hand muscle strength", negative information group (N) - "the tape decreases hand muscle strength", and control group (C) - "the effect of the tape on hand muscle strength is unknown." The activation of muscles was assessed using surface electromyography (sEMG) while measuring the strength of wrist and finger flexors with a hand dynamometer. Each participant was examined twice - prior to and immediately after taping and providing verbal reinforcement. RESULTS Only group N manifested a decrease in muscle strength, from 39.7N to 37.6N (P=0.003). Group C displayed an increase in muscle strength from 34.3N to 36.4N (P=0.035). None of the groups demonstrated statistically significant changes in bioelectrical activity of the muscles. At no stage of examination were the differences between the groups significant. CONCLUSIONS Negative verbal information combined with the placebo intervention resulted in a significant decrease in the strength of finger flexors.

Are there placebo or nocebo effects in balancing performance?

Placebo and nocebo effects could influence the perceived, actual, or both postural stabilities. Therefore, this experiment examined whether postural stability is susceptible to placebo and nocebo effects. Driven by expectations, these cognitions could influence the motor stability of people in physical rehabilitation and those with motion instability. We randomly assigned 78 participants to a placebo, nocebo, or control group. Then, we applied a sham sports cream with positive, negative, or neutral instructions about its impact on balance. Next, we tested postural stability with a modified version of the Modified Clinical Test of Sensory Interaction in Balance, including standard, proprioceptive, visual, and vestibular tests before and after the intervention. Further, we measured expected and perceived performance with visual analog scales and assessed trait anxiety, change in state anxiety, optimism, holistic thinking, persistence, and cooperation with questionnaires. The intervention did not affect actual test performances; similarly, trait and state variables and expectations did not have an impact. Furthermore, the experimental manipulation and trait and state variables did not significantly affect perceived performance. However, the association between expectation and perceived performance was strong (ϱ = 0.627, p < 0.001). These findings suggest that postural stability is not susceptible to placebo and nocebo influences. Still, there is a dissociation between objective and subjective performance, showing that expectations impact perceived but not actual performance, which could fuel motivation in rehabilitation settings.

The Effectiveness of a CrossFit Training Program for Improving Physical Fitness of Young Judokas: A Pilot Study

The aim of this pilot study was to examine the effectiveness of a CrossFit-based training program to enhance the general and sport-specific physical fitness of 10−12-year-old judokas. The study was conducted between September 2021 and February 2022. The pedagogical research experiment was designed to be one complete, annual macrocycle (September−June). The current study presents mid-point data. Twenty male participants (3 years average sports experience; age = 11 ± 0.64 years) were randomly assigned to one of two groups: CrossFit-based training (experimental, n = 10) and traditional training (control, n = 10). Baseline testing was conducted by the researcher and included tests for motor skills and general physical fitness domains including Sweden wall pull-ups and leg raises, push-ups, long jump, squats, burpees, shuttle run, and forward rolls. Judo-specific tests included O Soto Gari and O Goshi throws. CrossFit-based training was implemented twice per week for 15−20 min in the experimental group after usual training. The control group completed traditional methods of physical fitness training for judokas with the same training load regarding time. Experimental group participants significantly improved on leg raises (p < 0.01), push-ups (p < 0.05), and shuttle run (p < 0.001); the control group improved their shuttle run (p < 0.001). Only the experimental group improved on the O Soto Gari (p < 0.01) and O Goshi throws (p < 0.05). Results showed that the use of CrossFit-based trainings had a positive effect on 10−12-year-old judokas’ speed-strength abilities, speed-strength endurance, and muscular strength.

Mechanistic evidence and exercise interventions: Causal claims, extrapolation, and implementation

RATIONALE

Exercise interventions and policies are widely prescribed in both sport and healthcare. Research investigating exercise interventions and policies is generally conducted using an Evidence-Based framework, placing an emphasis on evidence gathered from randomised controlled trials (RCTs).

AIMS AND OBJECTIVES

To explore the idea that, in addition to the assessment of evidence from RCTs when investigating exercise interventions, mechanistic studies ought to also be assessed and considered.

METHODS

This article assesses the rationale supporting the use of RCTs as evidence for exercise interventions, and the use of evidence of mechanisms in establishing efficacy, determining external validity, and tailoring interventions.

RESULTS AND CONCLUSIONS

The article argues that evidence from mechanistic studies ought to be considered alongside evidence from RCTs because: as RCTs investigating exercise interventions tend to be of low quality, mechanistic studies ought to be used to reinforce the evidence base; further, evidence from mechanistic studies is highly useful for both questions of extrapolation and implementation. This article argues for this on theoretical grounds, and also draws on a number of case studies.

Benchmarking occupational exoskeletons: An evidence mapping systematic review

OBJECTIVES

To provide an overview of protocols assessing the effect of occupational exoskeletons on users and to formulate recommendations towards a literature-based assessment framework to benchmark the effect of occupational exoskeletons on the user.

METHODS

PubMed (MEDLINE), Web of Science database and Scopus were searched (March 2, 2021). Studies were included if they investigated the effect of one or more occupational exoskeletons on the user.

RESULTS

In total, 139 eligible studies were identified, encompassing 33, 25 and 18 unique back, shoulder and other exoskeletons, respectively. Device validation was most frequently conducted using controlled tasks while collecting muscle activity and biomechanical data. As the exoskeleton concept matures, tasks became more applied and the experimental design more representative. With that change towards realistic testing environments came a trade-off with experimental control, and user experience data became more valuable.

DISCUSSION

This evidence mapping systematic review reveals that the assessment of occupational exoskeletons is a dynamic process, and provides literature-based assessment recommendations. The homogeneity and repeatability of future exoskeleton assessment experiments will increase following these recommendations. The current review recognises the value of variability in evaluation protocols in order to obtain an overall overview of the effect of exoskeletons on the users, but the presented framework strives to facilitate benchmarking the effect of occupational exoskeletons on the users across this variety of assessment protocols.

Nocebo effects on motor performance: A systematic literature review

Directionally opposite to placebo effects are the nocebo effects that negatively impact people's thoughts, feelings, and actions. An important but scarcely studied aspect of everyday functioning is motor performance, in which nocebo effects might impair athletic skills and the much-needed purposeful daily movements and motor actions. The aim of this literature review is to unveil the nocebo effects on motor performance. Searched databases were PubMed, PsycINFO, and SPORTDiscus. Twenty-one articles, reporting 23 studies, met the eligibility criteria for inclusion in the current review. All reports exhibited "some" risk of bias. Of the 23 studies, 14 found a nocebo effect on motor performance, equivocal results emerged from two studies, and negative findings were reported in seven studies. Most (10/12) studies using a between-subjects design have reported a nocebo effect. The mean effect size was 0.60, suggesting a medium-to-large effect of nocebo intervention on motor performance. Based on this review, we conclude that nocebo effects do influence motor performance and can be evoked with negative verbal information. This effect may be more robust than the placebo effect but also depends on the type of motor performance, on the examined sample, and on the nocebo agent. Hence, nocebo effects should be recognized and controlled in empirical research on motor performance, and they should be prevented or extinguished in practical and therapeutic settings. More extensive examination of the nocebo effect on motor performance is warranted, especially using between-subjects research design and a "no agent" control condition.

Placebo Effect of Caffeine on Substrate Oxidation during Exercise

By using deceptive experiments in which participants are informed that they received caffeine when, in fact, they received an inert substance (i.e., placebo), several investigations have demonstrated that exercise performance can be enhanced to a similar degree as a known caffeine dose. This 'placebo effect' phenomenon may be part of the mechanisms explaining caffeine's ergogenicity in exercise. However, there is no study that has established whether the placebo effect of caffeine is also present for other benefits obtained with acute caffeine intake, such as enhanced fat oxidation during exercise. Therefore, the aim of this investigation was to investigate the placebo effect of caffeine on fat oxidation during exercise. Twelve young men participated in a deceptive double-blind cross-over experiment. Each participant completed three identical trials consisting of a step incremental exercise test from 30 to 80% of V.O_2max. In the two first trials, participants ingested either 3 mg/kg of cellulose (placebo) or 3 mg/kg of caffeine (received caffeine) in a randomized order. In the third trial, participants were informed that they had received 3 mg/kg of caffeine, but a placebo was provided (informed caffeine). Fat oxidation rates were derived from stoichiometric equations. In received caffeine, participants increased their rate of fat oxidation over the values obtained with the placebo at 30%, 40%, 50%, and 60% of V.O_2max (all p < 0.050). In informed caffeine, participants increased their rate of fat oxidation at 30%, 40%, 50% 60%, and 70% of V.O_2max (all p < 0.050) over the placebo, while there were no differences between received versus informed caffeine. In comparison to placebo (0.32 ± 0.15 g/min), the rate of maximal fat oxidation was higher in received caffeine (0.44 ± 0.22 g/min, p = 0.045) and in informed caffeine (0.41 ± 0.20 g/min, p = 0.026) with no differences between received versus informed caffeine. However, the intensity at which maximal fat oxidation rate was obtained (i.e., Fat_max) was similar in placebo, received caffeine, and informed caffeine trials (42.5 ± 4.5, 44.2 ± 9.0, and 41.7 ± 10.5% of V.O_2max, respectively, p = 0.539). In conclusion, the expectancy of having received caffeine produced similar effects on fat oxidation rate during exercise than actually receiving caffeine. Therefore, the placebo effect of caffeine is also present for the benefits of acute caffeine intake on substrate oxidation during exercise and it may be used to enhance fat oxidation during exercise in participants while reducing any risks to health that this substance may have.

Understanding placebo and nocebo effects in the context of sport: A psychological perspective

Research over the past 15 years on the placebo effect has substantiated its contribution to the efficacy of established treatments for a range of clinical conditions and identified its underlying mechanisms. There is also evidence that placebo effects contribute to the performance benefits of many ergogenic aids, and that performance can worsen when dummy treatments are associated with expectations of a harmful outcome (i.e. nocebo effect). Unfortunately, the bulk of sport research involving placebos and nocebos continues to be hampered by outdated definitions and conceptualizations of placebo effects and their mechanisms. This has implications not only for research but also application, as nearly 50% of athletes report experiencing a beneficial placebo effect, and a similar proportion of coaches report providing placebos to their athletes. The objective of this paper is to attempt to stimulate research by presenting updated definitions of placebo and nocebo effects in the context of sport, describing their major mechanisms and, highlighting the importance of the psychosocial context on placebo effects in the sport setting.