The use of power poses—standing in a “powerful” position with broad posture, hands on hips, shoulders high and pushed back—was unsuccessful in attempts to boost subjects’ confidence in a study by University of Pennsylvania researchers Coren Apicella, assistant professor in the psychology department in the School of Arts & Sciences and Kristopher Smith, a fourth-year psychology PhD student.

Dr. Apicella and Mr. Smith attempted to replicate the original power pose study by Dana Carney, Amy Cuddy and Andy Yap, which appeared in 2010 in the journal Psychological Science. The initial study reported increases in feelings of power, risk taking and testosterone and a decrease in cortisol. The Penn researchers found no support for any of the original effects, what’s called embodied cognition, results they published recently in Hormones and Behavior.

The pair started working on this study in 2014, with the aim of putting the power pose concept into a relevant ecological context grounded in evolutionary theory. Because hormones change in a competitive context, the researchers wanted to study contest winners and losers for hormonal changes.

They studied nearly 250 college-age males from the Philadelphia region. Participants provided a saliva sample to offer a baseline measure for testosterone and cortisol levels, then took part in rounds of tug-o-war. One person was declared the strong man, the other the weak man. Then the participants would perform a high, low or neutral power pose based on random placement into one of three groups.

High power poses enable a body to take up more space (i.e., the Wonder Woman stance); low power poses constrict the area a body occupies (i.e., hunching over). While posing, study subjects viewed faces on a computer screen, the same images used in the original study, then 15 minutes later, the researchers took a second saliva sample to measure the same hormones again.

“We didn’t find any support for this idea of embodied cognition,” Dr. Apicella said. She added, “We did find that if anything — and we’re skeptical of these results, because we’d want to replicate them — that, if you’re a loser and you take a winner or high power pose, your testosterone decreases.”

In other words, Mr. Smith said, “people might not be able to ‘fake it until they make it,’ and in fact it might be detrimental.”

Dr. Apicella said the results should cause researchers to proceed with caution on this topic.

“Even if power poses were found to work in the short term,” she said, “we don’t know if they could backfire in the long term.”