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Scanning Sports Medicine

Latest Clinical Research Published by ACSM

Kiningham, Robert B. MD, FACSM

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Current Sports Medicine Reports: 9/10 2017 - Volume 16 - Issue 5 - p 301-302
doi: 10.1249/JSR.0000000000000411
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Athletes Intending to Use Sports Supplements Are More Likely to Respond to a Placebo

Sports supplements are a big business, despite the fact that most do not contain any ingredients proven to be ergogenic. Their popularity can be at least partially attributed to the fact that placebos have been shown to improve athletic performance. Hurst and colleagues (1) tested the hypothesis that placebos can have both positive and negative effects on performance depending on the athlete’s beliefs regarding the supplement. In addition, they investigated if previous use or intention to use supplements indicates a belief in the efficacy of supplements and thereby identifies athletes who are more likely to respond to a placebo.

All subjects were asked about their previous and current use of supplements, as well their intention to use supplements in the future. Teams, mostly soccer, rugby, and field hockey, were then randomized to one of three groups. All groups performed five 20-m sprints with 30 s of recovery between sprints, followed by a 20-min recovery period. During the recovery period, the “positive belief” group was given a placebo capsule described as a “potent supplement that improves both endurance and repeat sprint performance.” The “negative belief” group also was given a placebo capsule, but the capsule was described as a “potent supplement that improves endurance but has a negative impact on sprint speed.” The control group was not given a capsule and did not receive instructions. All groups then repeated the five 20-m sprint set. Performance was measured by the average sprint time for each of the five sprint sets and the fastest sprint time within each set.

Suggesting that a placebo supplement would have a negative effect resulted in worsening sprint performance, while a suggested beneficial placebo supplement had no effect on performance. Only the “negative-belief” group had a significant change in sprint performance during the second sprint set, with a worsening of performance compared to baseline and compared with the “positive-belief” group and the control group. Among the categorical variables, only the “intention to use supplements” (yes, no, maybe) was significantly related to sprint performance during the second experimental sprint set. Past use of supplements, current use of supplements, and frequency of supplement use were not significantly related to sprint performance. Within the positive belief group, those athletes who indicated that they planned on taking supplements in the future had improved performance in the second experimental set compared with athletes who did not plan on taking supplements or were undecided. These findings suggest that athletes who intend on taking supplements have a belief in their positive effects, and therefore are more likely to improve their performance in response to a placebo ergogenic aid. The fact that intention to use supplements was more of an influence on placebo response than previous and current use of supplements suggests that some athletes who have taken, or are currently taking, supplements do not believe them to enhance performance, and thus are less responsive to a placebo effect.

Bottom Line: Overall, the “negative” placebo had a greater impact on sprint performance than the “positive” placebo. However, athletes who intend to use supplements in the future improved sprint performance after taking a suggested performance-enhancing supplement. The impact of a placebo is related to the athlete’s belief in the efficacy of the placebo, which is influenced by both the information they are given about the placebo and their previous experience with supplements.

Cardiometabolic Correlates of Physical Activity and Sedentary Patterns in U.S. Youth

The World Health Organization recommends that children and adolescents engage in at least 60 min of moderate to vigorous physical activity a day. This level of physical activity has been shown to have a positive effect on cardiovascular disease (CVD) risk factors. Historically, child physical activity has been comprised of free play and movement spread throughout the day. Currently, however, physical activity in children is becoming more concentrated in discrete time blocks, with long periods of physical inactivity. It is not known if the pattern of physical activity within a day or week makes a difference in its impact on health in children. In addition, current physical activity guidelines in children are based primarily on self-reported data, which is notorious for recall and social desirability bias. This study used accelerometer data to see if total physical activity and patterns of physical activity were related to CVD risk factors in children.

Jenkins and colleagues (2) at the University of North Carolina used data from the National Health and Nutrition Examination Survey (NHANES) to create latent classes using accelerometer data. Latent class analysis (LCA) is a measurement model in which individuals are classified into mutually exclusive groups (or “latent classes”) based on their pattern of responses on categorical variables. Latent classes were established for average counts per minute, percent of time spent doing moderate or vigorous physical activity (MVPA), and waking time spent sedentary. The NHANES data was then examined to see if these latent classes were related to CVD risk factors.

Data for a total of 3984 children ages 6 to 17 yr from the years 2003 to 2004 and 2005 to 2006 were analyzed. Average age was 11.5 yr. Sedentary behaviors comprised 50.4% of the waking day on average, while 5.3% of the day was spent in MVPA. Separate regression analyses were done relating the average counts per minute, percent of time doing MVPA, or percent of time sedentary, with CVD risk factors as the dependent variables. Regression analyses also were done relating latent classifications derived from accelerometer data to CVD risk factors. Age, sex, race/ethnicity, and socioeconomic status were included as covariates.

Youth in the most active latent classes for both average counts per minute and MVPA had lower systolic blood pressure, waist circumference, glucose, and insulin, and higher HDL cholesterol compared to the least active latent classes. These associations were attenuated but remained significant for most CV risk factors even after controlling for mean physical activity. High sedentary behavior was only significantly related to waist circumference after controlling for mean physical activity.

Bottom Line: This study used accelerometer data to confirm the association of physical activity with decreased CV risk factors in children that had been previously established using self-reported data of physical activity. The data suggested that consistent physical activity was more beneficial than sporadic physical activity, even if the total amount of activity was the same. However, the data were far from definitive. More research needs to be done to understand the interactions between physical activity consistency and intensity and the impact on the health benefits of exercise in children.

The author declares no conflict of interest and does not have any financial disclosures.


1. Hurst P, Foad A, Coleman D, Beedie C. Athletes intending to use sports supplements are more likely to respond to a placebo. Med. Sci. Sports Exerc. 2017; 49:1877–83.
2. Jenkins GP, Evenson KR, Herring AH, et al. Cardiometabolic correlates of physical activity and sedentary patterns in US youth. Med. Sci. Sports Exerc. 2017; 49:1826–33.
Copyright © 2017 by the American College of Sports Medicine