A big client meeting. An investor pitch. A keynote address. In any of these situations, an extra shot of confidence can go a long way.

Turns out, it's easier to get that little boost than you might think. In a video recently posted by Stanford's Graduate School of Business, Deborah Gruenfeld, a professor of leadership and organizational behavior there, demonstrates a quick and simple way for you to boost your confidence level in just a few seconds.

Gruenfeld's basic message is that your posture doesn’t just reflect your level of confidence, insecurity, or anything else. Instead, your posture sends messages to your brain that tell you how to feel. If you need to feel confident, you want your posture to send your brain that message.

To illustrate her point, Gruenfeld asked her audience to do two brief exercises. The whole thing took less than five minutes, and I played along at my desk. Let's just say it works.

Ready to feel more confident? Here's how it works.

Sit up straight, or lean back a bit. Now, take up some space. Roll your shoulders back. Get your elbows away from your body, perhaps by putting your hands behind your head or putting your hand on the seat next to you. Stretch out your legs, or cross one foot over your knee so your legs make a triangle instead of a "lap."

If you’re having trouble getting in the spirit, pretend you're one of those people on the subway who nonchalantly takes up three seats when it’s standing-room only.

Stay put.

Now read these words out loud, with as much feeling as you can:

"I can’t do it. I feel so helpless. I am worthless."

In the video, this produces a round of laughing. There's more than a bit of cognitive dissonance going on. Your brain can't quite get the proper amount of meekness to come out when your body is saying, "Big! Bold! Powerful!" As Gruenfeld says, "It’s not the case that these thoughts are never in your head. But it's very hard to believe what you say when your body is telling you something different."

Now try this: Squinch yourself in. Keep your hands close to your body, and keep your knees together. You might even lean forward a bit and turn one foot in.

Got it?

And now read these words out loud, with feeling:

"I am totally in charge. I’m invincible. I’m on top of the world."

Doesn't work, does it? Says Gruenfeld, "It's not the case that our bodies only follow our psychology, but that we actually take cues from what our bodies are telling us, and the way we hold our bodies actually affects how powerful we feel and how powerfully we behave."

So part of what your parents told you is true: Sit up straight. Already, you're halfway there.