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PLACEBO EFFECTS OF CAFFEINE ON ANAEROBIC PERFORMANCE IN MODERATELY TRAINED ADULTS

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Serbian Journal of Sports Sciences ISSN 1820-6301

Original article

Original article

Original article

Original article

2010, 4(3): 99-106

ID 177993484 Received: 03 May 2010

UDC 796.015.574:615.039 Accepted: 06 July 2010

PLACEBO EFFECTS OF C

PLACEBO EFFECTS OF C

PLACEBO EFFECTS OF C

PLACEBO EFFECTS OF CAFFEINE ON ANAEROBIC

AFFEINE ON ANAEROBIC

AFFEINE ON ANAEROBIC PERFORMANCE

AFFEINE ON ANAEROBIC

PERFORMANCE

PERFORMANCE

PERFORMANCE

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IN

IN

IN MODERATELY

MODERATELY

MODERATELY

MODERATELY TRAINED ADULTS

TRAINED ADULTS

TRAINED ADULTS

TRAINED ADULTS

Michael J. Duncan

Department of Biomolecular and Sports Sciences, Coventry University, UK. Abstract

Abstract Abstract

Abstract This study examined the placebo effect of caffeine on anaerobic exercise in 12 moderately trained male athletes during a Wingate test. A double disassociation protocol was employed consisting of four conditions: Told caffeine/given caffeine (CC, 5 mg·kg-1), told caffeine/given placebo (CP), told placebo/given placebo (PP), told placebo/given caffeine (PC) performed in a randomised order. Repeated measures ANOVA was used to examine differences in peak power output, mean power output, RPE, fatigue index, peak heart rate and peak blood lactate across conditions. Results indicated significant differences in peak power output (PPO), mean power output (MPO) and rating of perceived exertion (RPE) across conditions (all p = 0.001). PPO, MPO and RPE were all significantly higher in the CC condition compared to other conditions. These values were significantly lower in the PP condition compared to all other conditions. Values for the CP and PC conditions were lower than for CC but higher than PP. Mean ± SD for PPO (W) were 763.6 ± 78.1, 725.2 ± 59.3, 665.7 ± 62.9 and 714.6 ± 59.2 for CC, CP, PP and PC respectively. Mean ± SD for MPO (W) were 529.4 ± 72.8, 506.9 ± 74.9, 475.9 ± 83.5 and 491.3 ± 77.6 for CC, CP, PP and PC respectively. There were no differences in peak heart rate, fatigue index or peak blood lactate concentration across experimental conditions (all p > 0.05). In conclusion, anaerobic exercise performance was enhanced when participants were told they had caffeine and received it but negatively influenced when they were told they had received a placebo and actually did.

Key words: Key words: Key words:

Key words: Wingate test, ergogenic, beliefs, power output

INTRODUCTION

INTRODUCTION

INTRODUCTION

INTRODUCTION

A range of studies have documented placebo effects, or a favourable outcome arising from the belief that one has received a beneficial treatment [10]. Although placebo effects influence physiological and psychological variables [17], only recently has it been examined in sport and exercise, with findings suggesting it improves aerobically based performance [6, 10]. Clark et al. [10] reported a 3.8% increase in mean power in a 4km time trial when cyclists were deceived to believe they had received a carbohydrate solution. Likewise, Beedie et al. [7] reported 1.4% lower, and 1.3% and 3.1% greater power, in cyclists during a 10km time trial, when they believed they had ingested 0 mg·kg-1, 4.5 mg·kg-1 and 9 mg·kg-1 of caffeine respectively. Further research by Foad et al. [19] incorporated a double disassociation design to examine placebo effects of caffeine on 40 km time trial performance in cyclists. This design is recommended as the most effective means to assess substance effects, expectancy effects and any interaction between them [29]. In the absence of caffeine, belief did not significantly enhance performance, nor was there a significant nocebo effect [19]. Additionally, a recent review concluded that this area is still developing and further research is required to elucidate the nature of the placebo effect in sports performance [5].

Given the use of nutritional supplements in recreational and competitive sports, examining placebo effects is important in determining the effect of a substance compared to the expectation that a substance will benefit performance. This has implications for athlete preparation as if there is a placebo effect of caffeine, coaches may simply need to instil beliefs that a substance will enhance performance rather than provide active nutritional manipulation. Furthermore, there is a need to examine placebo effects in sport generally [5], few studies having examined placebo effects in high intensity exercise performance (i.e., anaerobically based exercise) specifically. This has been highlighted as a future research need [16].

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Duncan.: Placebo effects of caffeine on anaerobic performance in adults Serb J Sports Sci 4(3): 99-106

Duncan et al. [16] found that when participants believed they had ingested caffeine they reported lower rating of perceived exertion (RPE) and completed significantly more repetitions of leg extension to failure at 60% of 1 repetition-maximum (1RM) compared to when they believed they had ingested a placebo. However, participants had not actually ingested an active substance, making it difficult to determine the impact of the placebo vs. caffeine.

In respect of the ergogenic effect of caffeine, research has demonstrated that it enhances aerobic exercise performance [12, 21] and reduces RPE during submaximal, aerobically based exercise [15].

More recently, studies on caffeine consumption have examined its impact on resistance exercise and anaerobic performance. Astorino et al. [4] reported a non-significant, 11% and 12% increase in total weight lifted and in repetitions completed at 60% of 1RM to failure during the bench press and leg press after caffeine consumption compared to placebo. Similarly, Green et al. [22] reported that caffeine consumption resulted in a greater number of repetitions and a higher peak heart rate (PHR) during leg press to failure at 10RM: As a result, these authors concluded that caffeine has an ergogenic effect during short-term anaerobic performance without alterations in RPE. Likewise, Woolf et al. [31] reported that caffeine consumption (5 mg·kg-1) resulted in significantly greater peak power but not mean power attained during the Wingate test and greater weight lifted during chest press performance in male athletes. However, no differences were found for RPE, PHR and plasma lactate between caffeine and placebo conditions. Conversely, research by Greer et al. [23] reported that ingestion of caffeine (6 mg·kg-1) had no effect on performance of the first 2 and a negative effect on the final 2 of four repeated Wingate tests. Other authors have also reported that caffeine does not significantly enhance Wingate test performance [8]. Consequently, Davis and Green [13] recently reported that data on the impact of caffeine on anaerobic power, particularly Wingate test performance, are equivocal and further studies are needed on this topic.

Furthermore, research examining anaerobic performance has not considered whether the expectancy of the effect of caffeine causes any improvement in performance rather than the caffeine itself. The aim of this study was to examine placebo effects of caffeine on Wingate test performance exercise in a sample of moderately trained males in order to test the hypothesis that there will be positive placebo effects of caffeine on Wingate test performance

MATHERIALS AND METHO

MATHERIALS AND METHO

MATHERIALS AND METHO

MATHERIALS AND METHODS

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UBJECTSUBJECTSUBJECTSUBJECTS

Following institutional ethics approval and informed consent, 12 males (mean ± SD = 23.5 ± 3.5 years, 75.3 ± 12.2 kg, 177 ± 0.7 cm; years participating in competitive sport = 8.3 ± 2.5 years) volunteered to participate. All participants were free of any musculoskeletal pain or disorders and competed in team games (rugby union, football) at university level. They were currently participating in > 12 hours week programmed strength and endurance activities and had prior experience in the test protocols employed within the study. The participants had completed at least 6 Wingate tests within 12 months prior to participating in the study as part of regular athlete monitoring. The most recent of these occurred 2-3 weeks prior to participation in the experimental trials and was used to re-familiarise participants with the testing mode to be used within the study.

All participants refrained from vigorous exercise for 24h prior to testing and completed 24h diet and exercise recalls before each trial and were required to follow the same diet on the day preceding each trial. They were provided with a list of dietary substances containing caffeine and were asked to refrain from caffeine intake in the 48h prior to each trial. This was verified via a participant food diary including caffeine consumption questionnaire [28] completed for the 48h period prior to each testing session.

Habitual caffeine consumption was assessed via questionnaire [28] as was general health. Similar to prior research on this topic, in order to ensure familiarity with the effects of caffeine and to control for individual differences in reactivity to caffeine from caffeine habituation, only moderate caffeine users (ingesting approximately 250 mg·day-1) were included in the study.

Prior to participation, participants were informed that the aim of the study was to assess the effect of caffeine ingestion on short term, high-intensity exercise performance. In accordance with prior research [19] and the guidelines of the APA [1], participants were also informed that they could receive either caffeine or placebo in any one trial. Participants were not informed of the true purpose of the study or that they would be deceived in the informed caffeine/received placebo and informed no treatment/received caffeine conditions.

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EASUREMENTS EASUREMENTS AND EASUREMENTS EASUREMENTS AND AND AND

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ROCEDUREROCEDUREROCEDUREROCEDURE

The aim of the study was to use a 2 (drug: caffeine/no caffeine) X 2 (belief: caffeine/no caffeine) within subjects, repeated measures design to quantify the placebo and pharmacological effects of caffeine on short-term, high-intensity anaerobic performance. This approach, also termed a balanced placebo or double disassociation design, required the participants to be deceived about the substance they had ingested in both the told caffeine/given placebo (i.e., placebo) and told treatment/given caffeine (i.e., antiplacebo) conditions. A comprehensive debrief, in accordance with the guidelines of the American Psychological Association [1] was also completed immediately after data collection. The study was completed on a single blind basis.

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All testing took place between 9.00am and 12.00pm and at the same time for each participant to avoid circadian variation. The participants completed four trials in a randomised order separated by at least 72h. The experimental conditions were as follows:

1. Told Caffeine/Given Caffeine (CC) – participants were told they would receive caffeine and actually did. 2. Told Caffeine/Given Placebo (CP) – told they would receive caffeine but actually did not.

3. Told Placebo/Given Caffeine (PC) – told they would not receive caffeine but actually did receive it. 4. Told Placebo/Given Placebo (PP) – told they would not receive caffeine and did not.

This protocol was chosen as it is more appropriate to test the placebo effect alone [27] and has been identified as essential in examining placebo effects on sport performance [19].

In regard to caffeine/placebo administration, participants ingested 5 mg·kg-1 caffeine diluted in 250ml of artificially sweetened water or a placebo where 5 mg·kg-1 of dextrose diluted in 250ml of artificially sweetened water drink was consumed. Solutions were administered in opaque 750ml water bottles and were consumed 60 min before each exercise trial as plasma caffeine concentration is maximal 1 hour after ingestion of caffeine [21].

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ELIEF ELIEF ELIEF ELIEF

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ANIPULATIONANIPULATIONANIPULATIONANIPULATION

Before the performance trials, and with the aim of catalyzing or reinforcing beliefs about caffeine, participants were provided with literature reviewing the published research on caffeine and high intensity exercise performance and detailing anecdotal evidence relating to caffeine use among elite team games performers in line with procedures used in previous studies [16, 19].

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XERCISE XERCISE XERCISE XERCISE

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ROTOCOL AND ROTOCOL AND ROTOCOL AND ROTOCOL AND

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ERFORMANCE ERFORMANCE ERFORMANCE ERFORMANCE

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EASURESEASURESEASURESEASURES

Before the exercise tests, the participants completed a 10-min warm up consisting of both dynamic and static stretches. The exercise test consisted of a 30 second Wingate Anaerobic Test (WANT) completed on a Monark Peak bike (Ergomedic 894E, Vansbro, Sweden). The cycle ergometer was calibrated on each morning of testing and prior to any testing being conducted. Participants cycled with no resistance until they reached their perceived maximum speed. At this time, the predetermined load (7.5% body mass) was dropped and the test continued at maximal effort for 30 seconds. The peak power output (PPO), mean power output (MPO), and fatigue index (FI) were calculated during the WANT using Monark’s anaerobic testing software (version 1.0). No verbal encouragement was provided during the trials. Peak power was defined as the highest power output achieved during any 5 second interval and mean power was defined as the average power over the 30 second test.

During each test, peak heart rate (PHR) was assessed using heart rate telemetry (Polar Electro Oy, Kempele, Finland) and on completion of each test rating of perceived exertion (RPE) was determined using the Borg 6-20 RPE scale [9]. This is in accordance with protocols used to assess RPE following Wingate testing and nutritional manipulation including caffeine ingestion [31, 32]. Peak blood lactate (PBla) was also determined 2 minutes after each test using a capillary blood sample from the earlobe (Lactate Pro, Arkray Inc, Japan).

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TATISTICAL TATISTICAL TATISTICAL TATISTICAL

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NALYSISNALYSISNALYSISNALYSIS

Any differences in PPO, MPO, PHR, FI, RPE and PBla were assessed using a series of 4 ways repeated measures Analysis of Variance (ANOVA). Post hoc analysis using Bonferroni adjustment were performed where any significant interactions and main effects were found. Partial η2 was also calculated as a measure of effect size. This was used as Partial η2 has been identified as a more appropriate measure of effect size for repeated-measures designs as it enables the researcher to determine how much variance is explained by the independent variable of interest alone [11, 25, 26, 30]. Data are expressed as Means ± SD. A p value of 0.05 was used to establish statistical significance and the Statistical Package for Social Sciences (SPSS, Inc, Chicago, Ill) Version 15.0 was used for all analyses.

RESULTS

RESULTS

RESULTS

RESULTS

Results indicate PPO was significantly different across trials (F3, 33 = 21.42 p = 0.0001, η2 = 0.661). Bonferroni post hoc multiple comparisons indicate PPO was significantly higher for CC vs. CP (Mean Diff = 38.4 W, p = 0.032), PP (Mean Diff = 97.9 W, p = 0.001) and PC (Mean Diff = 49.1 W, p = 0.02). PPO values for CP were significantly higher than for PP (Mean Diff = 59.4 W, p = 0.003) but not PC (Mean Diff = 10.6 W, p = 0.1). Likewise, PPO for PC was significantly higher than PP (Mean Diff = 48.8 W, p = 0.009). Mean ± S.D. of PPO values across conditions are presented in Figure 1.

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Duncan.: Placebo effects of caffeine on anaerobic performance in adults Serb J Sports Sci 4(3): 99-106 0 100 200 300 400 500 600 700 800 900 CC CP PP PC P P O

Figure 1. Mean ± S.D. of PPO (Watts) across conditions.

* = significantly higher than CP (p = 0.03), PP (p = 0.001), PC (p = 0.02) † = significantly higher than PP (CP, p = 0.003), (PC, p = 0.009)

Scores for MPO across trials revealed a somewhat similar pattern to PPO (F3, 33 = 8.44, P=0.0001, η2 = 0.434). Scores for CC were significantly higher than CP (Mean Diff = 22.4 W, p = 0.024), PP (Mean Diff = 53.4 W, p = 0.017) and PC (Mean Diff = 38.9 W, p = 0.036). There were no significant differences in MPO values for CP vs. PP (Mean Diff = 30.9 W, p = 0.07), for PC vs. PP (Mean Diff = 15.6 W, p = 0.518) or CP vs. PC (Mean Diff = 15.3 W, p = 1.0) conditions. Mean ± SD of MPO values across conditions are presented in Figure 2. 0 100 200 300 400 500 600 700 CC CP PP PC M P O

Figure 2. Mean ± S.D. of MPO (Watts) across conditions

* = significantly higher than CP (p = 0.024), PP (p = 0.017), PC (p = 0.036)

*

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Rating of perceived exertion was also significantly different (F3, 33 = 19.9 p = 0.001, η2 = 0.644). RPE scores were lower for CC vs. CP (Mean Diff = -1.08, p = 0.02), PP (Mean Diff = -2.1, p = 0.0001) and PC (Mean Diff = -1.0, p = 0.024). There was also significantly lower RPE for CP (Mean Diff = -1.0, p = 0.04) and PC (Mean Diff = - 1.08, p = 0.004) compared to PP. There were no differences in RPE for PC vs. CP (Mean Diff = 0.083, p = 1.0). Mean ± SD of RPE scores across conditions are presented in Table 1.

Table 1. Mean ± SD of PPO, MPO, Fatigue Index, RPE, Peak BLa and PHR across conditions

CC CP PP PC

Mean ± SD Mean ± SD Mean ± SD Mean ± SD PPO (Watts) (F3, 33 = 21.42 P=0.0001) 763.6±78.1 725.2±59.3 665.7±62.9 714.6±59.2 PPO (Watts/kg) (F3, 33 = 8.44, P=0.0001) 10.3±1.9 9.8±1.7 9.0±1.4 9.7±1.7 MPO (Watts) (F3, 33 = 8.44, P=0.0001) 529.4±72.8 506.9±74.9 475.9±83.5 491.3±77.6 MPO (Watts/kg) (F3, 33 = 2.7 P = 0.8) 7.1±1.2 6.8±1.0 6.4±1.0 6.6±1.1 Fatigue Index (%) (F3, 33 = 2.7 P = 0.8) 40.4±6.4 45.5±5.6 37.1±8.3 37.8±7.1 RPE (F3, 33 = 19.9 P=0.001) 16.5±1.1 17.6±1.0 18.6±0.7 17.5±0.8

Peak BLa (mmol) (F3, 33 = 2.1 P = 0.116) 13.3±1.5 12.6±1.3 12.6±1.6 12.9±1.3

PHR (Bpm) (F3, 33 = 1.16 P = 3.36) 190.0±3.7 188.0±5.1 188.0±5.6 189.0±4.8

There were no significant differences in FI (F3, 33 = 2.7 P = 0.8, η2 = 0.174), PBla (F3, 33 = 2.1 p = 0.116, Partial η2 =0.162) or PHR (F3, 33 = 1.16 p = 3.36, η2= 0.096) across conditions. Mean ± SD of PBla, PHR across conditions are presented in Table 1 alongside data for PPO, MPO and RPE. Intraclass correlation coefficients were also calculated for PPO, MPO and RPE across days (i.e., across conditions) as a means to help describe the size of the change in performance that was expected. These were R = 0.88 for PPO, 0.87 for MPO and 0.81 for RPE.

DISCUSSION

DISCUSSION

DISCUSSION

DISCUSSION

Collectively, this study demonstrates a significant placebo effect to be associated with presumed caffeine consumption on short-term, high intensity exercise. In CC, PPO and MPO were significantly higher (See Figures 1 and 2 respectively) and values for RPE were significantly lower compared to the other conditions. This finding would generally support the ergogenic effect of caffeine on performance [13, 15]. They would more specifically support double blind studies that have reported caffeine to be ergogenic in short term high intensity exercise such as bench press repetitions to failure [4]. These results partially support prior findings of Woolf et al. [31] who reported significantly higher PPO, but not MPO, following caffeine ingestion but are contrary to previous research that reported no significant effect of caffeine on Wingate test performance [8, 23].

In terms of potential mechanisms by which caffeine and placebo could have enhanced performance, caffeine may enhance short-term, high intensity performance by delaying fatigue by increasing lipolysis and sparing muscle glycogen [3]. Another suggestion is that caffeine may stimulate the central nervous system by acting as an adenosine antagonist which increases neuron excitability, synaptic transmission and muscular contraction [3]. However, further scrutiny of this issue is required to verify whether caffeine enhances short term high intensity exercise via adenosine antagonism. Whereas, the placebo effect has been purported to influence performance via expectancy-driven changes in pain sensation, fatigue resistance and anxiety [5]. In the context of the present study, in the told CC and PP conditions, the cues that participants may have picked up would serve to confirm what they have been told by the researchers and subsequently worked to change performance in a positive or negative fashion. However, in the CP and PC conditions, participants may have actively searched for cues that they had ingested an active substance with any received conflicting with the information given by the researchers thus creating dissonance between what they have been told and the physiological cues detected. This may, in part, explain why no performance differences were found between these two conditions. At present, this is speculative and further research is required to substantiate these claims.

A potentially negative effect on performance was also observed in PP where PPO and MPO were significantly lower and RPE was significantly higher in comparison to the other conditions. These results also seemingly support the research that has suggested that caffeine suppresses RPE during submaximal exercise [15]. Doherty and Smith [15] proposed that caffeine dampens the perceptual response during exercise, which leads to a greater capacity to tolerate the discomfort associated with fatigue during exercise leading to lower values for RPE at the same exercise intensity with caffeine ingestion compared to placebo.

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Duncan.: Placebo effects of caffeine on anaerobic performance in adults Serb J Sports Sci 4(3): 99-106

studies have predominantly been based on submaximial, typically constant load exercise, the demands of which are much different from those experienced during and following the Wingate test. Secondly, Doherty and Smith [15] reported that RPE values are significantly greater when obtained during exercise than at the end of exhaustive exercise. They also reported that there are no differences in RPE following ingestion of caffeine or a placebo following all out exercise and suggest that effort sense and fatigue following high intensity aerobic exercise are similar. RPE was not different between trials in the present study (PC vs CP), but there were higher PPO and MPO in CP compared to PC (See Table 1). This is important to consider as when performance improves, more work is completed and it would be expected that RPE would also increase. When RPE does not increase but more work is completed it could be argued that this is evidence of a positive effect.

The RPE results in the present study are different to those reported previously [15, 31]. In respect to the study by Woolf et al. [31], this is somewhat surprising as RPE was assessed post exercise in both studies. There are, however, some possible explanations for this incongruence. Firstly, although the participants employed in the present study were moderately trained, their level of competition was not high. Therefore, training status may have influenced RPE responses post exercise following caffeine and placebo ingestion. Mean values for PPO and MPO in the present study suggest that the participants were placed anywhere between the 35th and 75th percentiles for healthy individuals but are lower than the published norm values for team sport athletes [24] and lower than the values reported following caffeine ingestion in other studies [23]. It may be that the effect of caffeine on RPE following high-intensity exercise differs with training status. This may be one area researchers could consider in future research. Furthermore, although the participants in the present study had performed the Wingate test on a number of occasions prior to taking part in the research study, Davis and Green [13] have suggested that, when examining the effect of caffeine ingestion on Wingate performance, subjects participating in regular sprints, particularly cyclists, might be better adapted to perform this test. Future research might therefore benefit from examining placebo effects of caffeine on Wingate test performance in trained cyclists. Finally, in the present study, RPE values were lower in the CC condition compared to other conditions. It may be that the belief that caffeine ingestion coupled with the presence of caffeine mediated symptoms resulted in lower RPE values post exercise in comparison to other studies that have examined the effect of caffeine ingestion on RPE [e.g. 31] but have not manipulated beliefs at the same time. As no prior studies have examined this issue, this suggestion is speculative and merits further scrutiny.

The results of the present study also support prior research by Beedie et al. [7] that reported a similar impact of caffeine in a 10 km cycling time trial. In this way it appears any possible placebo effects of caffeine on performance are similar across aerobic or anaerobically based exercise tasks. The data for PPO and RPE do seem to indicate some interaction between pharmacology and the belief that the performance for CP and PC were significantly higher for PPO (See Figure 1) and significantly lower for RPE in comparison to PP. This adds support to conclusions made in a recent review paper on the placebo effect on sports performance [5]. In this instance as participants produced greater power for CP than PP, a placebo effect could be inferred. Furthermore, there were no significant differences in PHR or PBLa across conditions, indicating that the physiological strain was similar across trials. In regard to values for PBLa, this response does not fit previously published effects of caffeine on anaerobic exercise generally and Wingate performance specifically [2, 31]. It is also interesting to note that although there were no significant differences among the four trials, mean values for PBla were higher during the caffeine trials compared to the placebo trials. This indicates that there was no more anaerobic metabolism between conditions and, therefore, differences in performance may be more a result of psychological, rather than physiological factors.

However, the lower values recorded for PP may be more a result of negative or nocebo effects on performance. Nocebo effects on performance have been reported in prior studies [16]. These support the findings of the present study. In the present case, once participants had been informed they were receiving a placebo and, after consumption, their active search for symptoms of caffeine ingestion confirmed that placebo had been administered, it may have led to low a priori expectations of performance corresponding to lower PPO, MPO and higher RPE compared to other conditions. In debriefing sessions following the completion of all the experimental conditions, 7 out of the 12 (58%) participants correctly identified the CC condition and 3 (25%) correctly identified the PP condition. In these cases, the participants’ active search for caffeine mediated symptoms will have confirmed what they had been told they were receiving and may have acted to amplify the interaction between the physiological effect of caffeine and the expectancy of the effect of ingestion of caffeine, resulting in increased or decreased performance in the CC and PP conditions respectively. Recent research by Duncan et al. [16] employing a leg extension exercise to failure has also suggested that it may be nocebo effects rather than true placebo effects that account for the changes in performance seen as a result of manipulating expectancy beliefs in the exercise setting. However, their study and those of others [6, 7] did not involve participants ingesting an active substance. Instead, they were simply led to believe they had ingested an active substance.

Although the double disassociation protocol has been recommended [5], only two prior studies, Foad et al. [19] and McClung and Collins [29] employed this experimental design prior to the present study. When

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a person receives an active substance they are more able (consciously or unconsciously) to respond to cues that might suggest its presence [19]. In some cases participants may actually search for these cues as confirmation of what they have been told they have consumed by the researcher. When using the double disassociation design, this may allow for comparisons of subjective perceptions in experimental conditions. Thus, participants may be in a position to make a comparison between conditions when an active substance is administered compared to a placebo.

One other explanation for the findings discussed above may be the issue of expectancy. In the current design, also used by others [19], participants were informed that they definitely had or definitely had not received caffeine prior to each trial. Prior research investigating placebo effects has tended to use a design (within-subjects, double blind) where participants were unsure whether they had consumed caffeine or placebo [e.g., 16]. This is problematic if using the placebo to examine the impact of caffeine on performance, as research suggests that simply administering a placebo can enhance exercise performance [7]. Therefore, any improvement due to caffeine ingestion may be masked if compared to a placebo instead of a control condition. Inclusion of a control condition (where no substance is consumed) or use of the double disassociation design has been recommended [5] as the most appropriate way to determine the placebo effect of a substance on performance. However, research has suggested that a degree of uncertainty might be required to elicit a placebo effect [14, 18]. It might therefore be that, as other authors have suggested [16, 19], the placebo effect and its impact on sports performance is more an artefact of a laboratory-based research setting where participants are given a 50% expectation of a treatment effect as compared to real world settings where the athlete has a complete expectation based on any nutritional substances consumed.

There are a number of further limitations of the current research and the placebo effect may not be the only explanation for the results obtained in this study. Low a priori expectations of performance or differing motivational climates fostered by each condition may be the factors. If a performer had low expectations, any differences in performance in the PP condition compared to the other conditions may have been magnified. There might also have been intraindividual differences in the response to caffeine ingestion which could have influenced the results as variations in genotype may alter caffeine metabolism and the magnitude of performance in response to caffeine ingestion [3]. Personality characteristics may also predispose an individual to respond to a placebo [20]. It may therefore be prudent for future studies to examine these issues. Furthermore, performance in the Wingate test has been shown to have a significant aerobic contribution [13]. Use of alternative measures of anaerobic power may need to be considered in future studies.

CONCLUSION AND

CONCLUSION AND

CONCLUSION AND

CONCLUSION AND PRACTICAL APPLICATIO

PRACTICAL APPLICATIO

PRACTICAL APPLICATION

PRACTICAL APPLICATIO

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Despite this, the results of the current study indicate that when participants are told they will consume caffeine and then do, there appears to be an augmentation of PPO, MPO and RPE compared to conditions where participants are told they will consume caffeine and consume a placebo or vice versa. Likewise, when participants are told they will consume a placebo and actually do, performance in the Wingate anaerobic test is comparatively worse. Results suggest that placebo mechanisms of caffeine may play a part in performance. However, although the placebo effect has been highlighted as a factor in sports performance, the results of this study agree with assertions by Foad et al. [19] that the belief-expectancy relationship is not necessarily constant in all settings and may be more complex and unpredictable than previously suggested.

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EFERENCESEFERENCESEFERENCESEFERENCES

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Science in Sports and Exercise, 40, 158-165.

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Research, 22, 1645-1653.

Address for correspondence: Michael J. Duncan, PhD,

Department of Biomolecular and Sports Sciences, James Starkey Building, Coventry University, Coventry, CV1 5FB, UK.

Tel.: 024 76888613 Fax.: 024 7688 8609 E

EE

Figure

Figure 1. Mean ± S.D. of PPO (Watts) across conditions.

References

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