This past Sunday, I was at the US Open watching a match between Top 10 player Jelena Jankovic and Belinda Bencic, who’s ranked 58th. Jelena had a healthy lead in the first set when a close line call was reversed in Belinda’s favor. Jelena was clearly upset and went on to lose the next few games and the set in a tiebreaker, and eventually the match, giving Belinda the underdog an exciting victory.

There have been countless times when top players have gotten a bad call or been down a set or two — and fought their way back to win the match. But after that line call, it was crystal clear, without even seeing the scoreboard, that Jelena was going to lose; she had given up. The tell? Her body language. After each point, she shuffled slowly across the court, her head down, shoulders slumped.

The thing is, just by changing her body language, Jelena could very well have turned the match around.

It’s no revelation that how carry yourself is a clue as to what you’re feeling. Think about what an animal does when it feels threatened: it tries to make itself as small as possible, curling up and crouching close to the ground in order not to be seen by a predator.

In a performance situation — whether in sports or the office — the physical signals that your morale is low often boosts the confidence of your “opponent” (or lowers a colleague’s confidence in you, as the case may be). That’s why professional tennis player Li Na, currently ranked No. 3, focuses on exuding strong body language: “I don’t want to show the opponent how weak I am,” she says.

In a power pose, however, you’re comfortable taking up space and being seen. Your eyes and chin are up, shoulders back, feet apart, arms spread wide or on your hips.

The good news, as Harvard professor Amy Cuddy has found in her research (see her popular TED talk here), is that — even if you don’t feel like it — simply holding a “power pose” for as little as two minutes increases testosterone and confidence, and makes people feel measurably more powerful and willing to take risks.

Two minutes, guys. Whatever your version of being on center court or the field is — a team meeting, sales negotiation, job interview, investor pitch — the power to affect your results starts with your body language. Are you controlling the message it’s sending?