Introduction

Sports nutrition research has often focused on the how consumption of substances may enhance muscular performance through tangible mechanisms, such as increasing muscle glycogen stores,[1] increasing muscle phosphocreatine stores,[2] increasing the speed of mitochondrial fat oxidation,[3] or increasing buffering capacity.[4] However, a growing body of evidence supports the critical role of mental beliefs, independent of measurable physical changes in muscle, on exercise performance.[5] Positive beliefs such as the belief that an ingested performance-enhancing substance may imbue benefits to exercise performance. This may occur regardless of whether said substance is actually exerting a peripheral effect or even whether the substance was truly ingested. Conversely, belief that one has ingested a substance with negative effects may negatively impact exercise performance.[6]

For example, Azevedo et al.[7] found that the belief that one had ingested a harmful substance (lactate) caused perception of effort to increase during a 30-min run, although there was no significant effect on the performance itself. In both sessions (Placebo and Nocebo), caffeine was used as a supplement, and subjects were deceived in regard to what they were consuming. The cited study[7] tested performance using 30-min run, likely because most evidence found on the ergogenic effects of caffeine is in long-term efforts.[8,9] However, some studies[10-12] have found positive effects from caffeine ingestion during short-duration and high-intensity efforts.

Caffeine’s measurable impacts on exercise are posited to come from its effects on the central nervous system, including its role as an adenosine receptor antagonist.[8] Whether it is ingested or not, belief in caffeine’s ergogenic properties is widespread and may contribute to enhanced performance. Conversely, the belief that lactate causes muscle fatigue could hamper performance if one were told that they had ingested it. With this in mind, we sought to test the impact of positive and negative beliefs regarding an ingested pre-exercise substance on a short duration exercise. We hypothesized that muscular endurance exercise performance and rating of perceived exertion (RPE) would differ from a control condition following ingestion of both placebo and nocebo substances.

Materials and Methods

Results

Our results showed that there was a significant difference in the performance of the participants according to the type of stimulus given (nocebo=control<placebo; P < 0.001; η² = 0.491) as can be seen in [Table 1]. In addition, we found significant differences in RPE (nocebo>control >placebo; P < 0.001; η² = 0.344) [Table 1]. Effect sizes for each comparison were as follows: Placebo versus nocebo = 1.17272, placebo versus control = 1.0476, and control versus nocebo = 0.000.

Table 1 Comparison of bench press repetitions completed and rating of perceived exertion after ingestion of a believed control, placebo, or nocebo. Data presented in Mean±SD (CI 95%)

We also performed a correlational study to verify the association between belief in the described effects and performance in the number of repetitions (we compared placebo and nocebo treatments). A moderate negative and significant correlation was found between performance in the number of repetitions [Figure 1, Spearman’s Rho −0.578; P = 0.024]. On the other hand, RPE showed no significant association between treatments (Spearman’s Rho 0.344; P = 0.209) [Table 3].

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Figure 1

Relationship between number of repetitions performed at 80% 1 rm bench press under placebo and nocebo conditions (n = 15).

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Table 2 Post hoc analyses using Durbin-Conover tests between conditions

Discussion

The Placebo/Nocebo effects observed in this study were quite large: Ingestion of Placebo resulted in 37% greater performance in repetitions and a significantly lower RPE when compared to Control. Ingestion of Nocebo resulted in no difference in the performance of repetitions compared to Control, but a higher RPE.

In regard to RPE, our results corroborate those obtained by Azevedo et al.[7] When imagining they were using an ergogenic supplement (caffeine), subjects perceived a lower level of effort, and they perceived the opposite when they thought that they were using something harmful (lactate). Unlike the aforementioned study, we found positive results in terms of performance in a number of repetitions when comparing placebo versus nocebo, while there was no difference between control and nocebo. The positive benefits to performance seen in the present study versus the no measureable impact on performance reported by Azevedo et al.[7] may be ascribed to differences in the exercise bout performed, including the shorter duration of the bout completed (single set to fatigue in ~30 s vs. 30 min run) and the lower volume of muscle mass exercised (bench press vs. running). This contrast leads us to speculate that briefer exercise stress focused on a smaller area of muscle mass may be more subject to measureable placebo/nocebo effects.

The moderately strong[15] Spearman correlation [Figure 1] indicated a negative relationship between repetitions performed under placebo versus nocebo. This allows us to speculate that one’s belief in the success of a placebo is equally detrimental to the performance of a nocebo. In other words, beliefs seem to be more ingrained in some individuals than others, modifying their behavior in the practice of exercises. There is some evidence[16] supporting this notion, though was not our primary objective to discuss the matter.

In conclusion, in this experiment, the belief in the ergogenic or ergolytic effects of a supplement affected both performance and perceived exertion. Furthermore, it seems that individuals who most strongly believe in positive effects will also believe in the negative.

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