Can how you stand or sit affect your success?

New research shows posture has a bigger impact on body and mind than previously believed. Striking a powerful, expansive pose actually changes a person's hormones and behavior, just as if he or she had real power.

Merely practicing a "power pose" for a few minutes in private—such as standing tall and leaning slightly forward with hands at one's side, or leaning forward over a desk with hands planted firmly on its surface—led to higher levels of testosterone and lower levels of the stress hormone cortisol in study participants. These physiological changes are linked to better performance and more confident, assertive behavior, recent studies show.

Marketing executive Katy Keim used to step back from listeners during presentations or conversations, resting her weight on her back foot with her hands clasped in front of her, twirling her ring. She was often surprised when people asked if she was nervous, says Ms. Keim, chief marketing officer of San Francisco-based Lithium, a firm that builds online communities for clients' brands. After she began working with a coach to improve her skills and saw herself on video, she realized her posture "was slightly standoffish" and didn't look strong, she says.

Mike Sudal/The Wall Street Journal based on photo by Philibert Leow (6)

In addition to standing straighter, with her hands at her side, the 5-foot-1 executive began getting up from the table when speaking at meetings. "When I'm sitting at a table of men, I feel petite. Standing up is a dynamic change for me," she says, sending a message: "I want to command your attention. I want you to get off your BlackBerrys and smartphones and listen to what I have to say." During a three-hour meeting last week where she made a presentation, she says, she noticed no one picked up a smartphone.

Striking a powerful pose can reduce symptoms of stress, says Dana Carney, an assistant professor at the Haas School of Business at the University of California, Berkeley. Subjects in a recent study she headed were guided for five minutes into either high-power poses or low-power postures, slumping or leaning back with arms or ankles crossed. They then delivered a videotaped speech before critical evaluators dressed in white lab coats and holding clipboards. Those who had practiced a power pose before the speech showed lower cortisol and fewer outward signs of stress, such as anxious smiles or biting a lip.

Assuming an expansive body position can also increase testosterone, which tends to boost confidence and aggressive behavior, according to another study co-authored by Dr. Carney. Subjects who struck power poses for two minutes had higher testosterone levels later and were more likely to take a gamble when given the chance. Some 86% of high-power posers risked losing $2 they were given in return for a 50-50 chance of doubling it, compared with 60% of low-power posers who took the bet, according to the 2010 study, published in the journal Psychological Science.

Answers to the Quiz: 'Who's In Charge Here?' High-power: A, D, F Low-power: B, C, E A: Expansively taking up a large swath of desktop real estate conveys power and confidence. B: Crossing the arms and legs in a close-bodied posture expresses powerlessness, as if trying to take up as little space as possible. C: Touching the neck, face or hand is a symptom of stress, suggesting anxiety or a lack of control. D: Staking out a broad surface with the hands conveys a sense of control. E: Folding arms in front of the chest suggests defensiveness. F: Opening limbs expansively expresses power and dominance. Source: University of California, Berkeley, Haas School of Business

Power posing is also linked to improved performance. In another study published last year, led by Amy J.C. Cuddy, an associate professor of business administration at Harvard Business School, participants who struck power poses for several minutes before beginning a mock job interview received better reviews and were more likely to be chosen for hire—even though the evaluators had never seen them in the poses.

Other research links power posing before a college-entrance exam to improved scores, Dr. Carney says.

Researchers are studying why the effects of the power pose linger after a person returns to a normal, relaxed stance. One theory: It may prompt lingering changes in voice pitch or facial expression.

Most speakers aren't aware of the signals they send through body language, says Kelly Decker, president of Decker Communications, a San Francisco coaching, training and consulting firm. "We pick up habits, such as walking into a meeting and sitting down with our shoulders slumped, and we don't even think about it."

After seeing himself on video, Steven Murray of Houston learned to lean forward more. Jennifer Franco

Steven Murray says seeing himself on video last year when he was working with Decker coaches helped him realize that "you're broadcasting nonverbal information to listeners from the moment you step up to the podium." Mr. Murray, president of Direct Energy Residential, an energy company based in Houston, says he learned to adjust his posture, leaning slightly forward rather than standing straight upright in the authoritative stance he formerly used as a military officer. "Leaning forward really engages people" and helps get his message across, he says.

Hunching over a smartphone before a meeting or presentation may be self-defeating, because it forces the user into a low-power pose, according to a recent study led by Maarten Bos, then a postdoctoral research fellow at Harvard Business School. Participants were assigned to complete several tasks on one of four gadgets—a hand-held device, a tablet, a laptop or a desktop. Then, the researcher tested subjects' willingness to interrupt another person, a power-related behavior. He left each subject alone in the room with instructions to come get him if he didn't return in five minutes. Subjects who worked on the hand-held device waited significantly longer before interrupting him, compared with those on desktops, and some didn't come out at all, suggesting their low-power posture sparked feelings of powerlessness.

Breaking old body-language habits takes practice, sometimes years. Pamela Lentz used to wave her hands while speaking on her job as a principal at a management-consulting firm, making some co-workers "think I was too emotional or too passionate," says Ms. Lentz, a Leesburg, Va., management consultant. She also tended to fold her arms across her chest while listening, drawing criticism that she lacked presence. "It looks as if you are withdrawing from the conversation," she says. Her body language was holding her back in her career, colleagues told her.

She worked with executive coach Tim Allard on changing her posture and movements. "We wanted her to project calmness and confidence," says Mr. Allard, co-owner of Odyssey Inc., a Charlottesville, Va., executive and business consulting firm. He videotaped her and, with Ms. Lentz's permission, asked her subordinates for feedback.

Ms. Lentz began leaning forward and placing her hands firmly on the table when speaking. She also put an elastic band around her wrist and snapped it now and then when her hands were hidden under a table or desk, to remind her to keep them still when she began speaking.

Gradually, as she practiced the new habits, says Ms. Lentz, "I felt more in control, and I was having more impact in the discussions." She was soon promoted to partner.

Write to Sue Shellenbarger at sue.shellenbarger@wsj.com