RPE (0-10 scale) (mean [SD] 7.7 [1.2] vs 7.7 [1.4]), and blood lactate concentration (mean [SD] 10.2 [3.7] mmol.l -1 vs 9.8 [3.9] mmol.l -1 ) were not different between placebo and control trials, respectively. Using a 1.5% difference as a meaningful difference in performance, 17 75% of the subjects ran faster during the placebo trial, and 9% ran faster during the control trial. A direct comparison of performance during placebo and control trials suggested that the relatively slower subjects (control trial >1200 seconds) had a larger mean improvement in performance (mean [SD] 2:22 [1:02]) than the relatively faster subjects (control trial
effect. These data suggest that the placebo effect is more likely to be present during exercise that may need to be sustained for some moments and is more likely in individuals least likely to adequately monitor their physical response to exercise. The magnitude of effect supports the concept that something in excess of one-third of individuals will be responsive to the placebo effect. 1 The results can be understood in terms of the anticipatoryperceived exertion feedback model, recently proposed by Tucker and Noakes. 18 According to this model, the pattern of energy output during a task is defined by a template based on individual expectations regarding the appropriate effort distribution and experience with the task. In the presence of a placebo, some individuals may revise their pre-exercise template and start exercise at a higher intensity. In most individuals (eg, the patients during the 6-minute walk test and the more accomplished runners) feedback from homeostatic disturbances during exercise causes a reduction of an overly ambitious pace to a more appropriate pace. This concept is supported by recent work in our laboratory 19 that has shown that the relative growth of effort sense (ie, RPE) during exercise is remarkably stable despite differences in task duration and/or the blinded administration of a hypoxic gas mixture. Similar findings have been reported in relation to running distance 20 and during both hypoxia and hyperoxia. 21-23 Morgan 24 has demonstrated that less accomplished competitive runners do not adequately attend to the growth of fatigue during marathon running, preferring to dissociate from the sensations of running. This observation may explain the frequency of “hitting the wall” in less accomplished runners. It may also explain the persistence of a higher running pace in the less accomplished runners during the placebo trial, many of whom may not have raced enough to fully use their physiological capacity during competitions. Past experience with the criterion task may also affect the way energy is expended. Previous work from our laboratory 25 has demonstrated that performance often changes over the first several trials of a new task, primarily attributable to the subject being willing to begin at a faster pace. Given the failure to slow as much after the first laps of the 5 km (Part A) and the trend toward a faster start in the 6-minute walk (Part C), it seems reasonable to suggest that one of the ways in which the placebo works is to encourage a faster start. Similar results have been demonstrated with the clinical use of the 6-minute walk test, 26 where patients typically take 2 to 3 trials to achieve a stable performance. It likewise seems reasonable to suggest that experience with performing a task and the placebo effect would influence performance in the same way. The failure to observe a significant placebo effect during the high-intensity exercise bout can be attributed to both the protocol employed and the nature of the task. In the Wingate Test it is ordinary to allow the subject to increase the pedaling rate of the cycle ergometer prior to loading the flywheel. 16 However, this may spuriously elevate the measured power output during the first seconds of the test. Although this pre-load spinning is a normal way of conducting this test, Havenetidis 27 and Reiser 28 have discussed the limitations of this approach. Mendez-Villaneuva 29 has demonstrated in a repeated sprint protocol that losses in power output are attributable to an inherent loss of motor unit recruitment rather than to reductions of effort. Thus, both the nature of the experimental approach (peak power) and the way that power is reduced in sprint exercise (mean power), the Wingate Test would be somewhat resistant to demonstrating a placebo effect. In conclusion, the results of this study demonstrate that the placebo effect is of sufficient magnitude to justify the normal practice of including control groups for intervention studies involving exercise capacity as an outcome from exercise training 30 or pharmacologic interventions. 31 Although the specific results of this study (Part B) did not demonstrate an effect on sprint performance, the results of the other portions of the study suggest that the general practice of using a control group is well-justified. referenCeS 1. Beecher HK. The powerful placebo. J Am Med Assoc. 1955;159(17):1602-1606. 2. Turner JA, Deyo RA, Loeser JD, Von Korff M, Fordyce WE. The importance of placebo effects in pain treatment and research. JAMA. 1994;271(20):1609-1614. 3. Kirsch IPD, Sapirstein GPD. Listening to Prozac but hearing placebo: a metaanalysis of antidepressant medication. Prevention & Treatment. 1998;1(2). 4. Benson H, McCallie DP Jr. Angina pectoris and the placebo effect. N Engl J Med. 1979;300(25):1424-1429. 5. Hashish I, Harvey W, Harris M. Anti-inflammatory effects of ultrasound therapy: evidence for a major placebo effect. Br J Rheumatol. 1986;25(1):77-81. 6. Moseley JB, O’Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2002;347(2):81-88. 7. Preston RA, Materson BJ, Reda DJ, Williams DW. Placebo-associated blood pressure response and adverse effects in the treatment of hypertension: observations from a Department of Veterans Affairs cooperative study. Arch Intern Med. 2000;160(10):1449-1454. 8. Godfrey S, Silverman M. Demonstration by placebo response in asthma by means of exercise testing. J Psychosom Res. 1973;17(4):293-297. 9. Ariel G, Saville W. Anabolic steroids: the physiological effects of placebos. Med Sci Sports Exerc. 1972;4:124-126. 10. Clark VR, Hopkins WG, Hawley JA, Burke LM. Placebo effect of carbohydrate feedings during a 40-km cycling time trial. Med Sci Sports Exerc. 2000;32(9):1642- 1647. 11. Maganaris CN, Collins DJ, Sharp M. Expectancy effects and strength training: do steroids make a difference? Sport Psychologist. 2000;14:272-278. 12. Sonetti DA, Wetter TJ, Pegelow DF, Dempsey JA. Effects of respiratory muscle training versus placebo on endurance exercise performance. Respir Physiol. 2001;127(2-3):185-199. 13. Beedie CJ, Stuart EM, Coleman DA, Foad AJ. Placebo effects of caffeine on cycling performance. Med Sci Sports Exerc. 2006;38(12):2159-2164. 14. Beedie CJ, Coleman DA, Foad AJ. Positive and negative placebo effects resulting from the deceptive administration of an ergogenic aid. Int J Sport Nutr Exerc Metab. 2007;17(3):259-269. 15. Borg G. Borg’s Perceived Exertion and Pain Scales. Champaign, IL: Human Kinetics; 1998:104. 16. Maud PJ, Berning JM, Foster C, et al. Testing for anaerobic ability. In: Maud PJ, Foster C, eds. Physiological Assessment of Human Fitness. 2nd ed. Champaign, IL: Human Kinetics; 2006:77-92. 17. Hopkins WG, Schabort EJ, Hawley JA. Reliability of power in physical performance tests. Sports Med. 2001;31(3):211-234. 18. Tucker R, Noakes TD. The anticipatory regulation of performance: the physiological basis for pacing strategies and the development of the perceptionbased model for exercise and performance [published online ahead of print February 17, 2009]. Br J Sports Med. doi:10.1136/bjsm.2008.050799. 6 <strong>Gundersen</strong> <strong>Lutheran</strong> Medical Journal • Volume 6, Number 1, June 2009
- Page 1 and 2: Th e Gundersen Lu T h e r a n M e d
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