March 7, 2017
W.C. Ian Janes, Brandon B.G. Snow, Caisie E. Watkins,
Elecia A.L. Noseworthy, Jonathan C. Reid, David G. Behm
INSTITUTION: School of Human Kinetics and Recreation Memorial University of Newfoundland
Much of the static stretching (SS) literature reports performance impairments with prolonged SS. However, the Canadian Society for Exercise Physiology (CSEP)(Behm et al. 2016a) position stand illustrated that the SS-induced impairments are not consistent as their SS data revealed 119 significant performance reductions, 145 non-significant findings and 6 significant improvements following SS. They speculated that some of these inconsistent findings might be due participants’ knowledge or bias. Placebo effects (Hrobjartsson et al. 2011) and researcher bias (Rosenthal 1963a; 1963b; Rosenthal et al. 1963). can affect outcomes based on the expectations of individuals performing a task or treatment (Beedie and Foad 2009). To reduce the likelihood of bias, the CSEP position stand recommended that researchers should use naïve participants and researchers who are blind to treatment conditions. Since many research participants are kinesiology, physical education students, or informed (knowledgeable) athletes or fitness enthusiasts, they might have some knowledge of the literature, and their performance could be subconsciously influenced by expectations. Hence, the objective of this study was to examine the effect of stretching knowledge or deception on subsequent force output following SS. Two groups of male participants who were either aware (BIASED: 14) or unaware (DECEPTION: 14) of the SS literature participated. Unaware participants were misinformed (deceived) that SS increases force production. Testing involved maximal voluntary isometric contractions (MVIC) of the quadriceps and hamstrings pre-, post-, and 5 min after stretching (three 30s passive static hamstring stretches to the point of discomfort with 30s rest intervals) or control (no stretching).
While the DECEPTION group displayed impaired knee flexion force (p=0.04: 3.6% and 10.4%) following hamstrings SS, there was no significant impairment with the BIASED (-1.1% and +0.9%) group. Whereas BIASED participants exhibited an overall decrease (p<0.05: 1.8% and 4.2%) in knee extension MVIC, DECEPTION participants showed (p=0.005: 8.8% and 5.1%) force increases. So, the impairments associated with prolonged hamstrings SS seemed to have a greater effect than possible placebo effects with the knee flexion (hamstrings) force production with the DECEPTION group. However, the lack of prior SS of the quadriceps may have permitted the positive placebo effects (increased knee extension force) to emerge. Thus, while deception resulted in enhanced quadriceps muscle force output, there was no knowledge or deception advantage when stretching the hamstrings. Coaches, athletes and fitness enthusiasts should be aware of the scientific findings that show that a complete warm-up with moderate durations of SS (<60 s for each muscle group) will not substantially affect force or power output (Behm et al. 2016). This knowledge should ensure that negative expectations will not psychologically influence the performance after stretching.
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This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend citing any information in this article, please consult the original article and cite that source. This summary has been reviewed by the CSEP Knowledge Translation Committee.
Janes WCI, Snow BBG, Watkins CE, Noseworthy EAL, Reid JC, Behm DG. Effect of participants’ static stretching knowledge or deception on the responses to prolonged stretching. Applied Physiology Nutrition and Metabolism 2016 DOI: 10.1139/apnm-2016-0241