"Calm down. Just calm down."

Those were the words I repeated over and over to myself as I waited to start my second triathlon with a swim in the Schuylkill River in Pennsylvania.

I was anxious, and couldn't seem to get my nerves in order. No matter how hard I tried, I wasn't able to calm down. As a result, my performance in that swim was one of the worst I've ever had.

Had I known then the power of three simple words, the outcome would have been very different.

I'll tell you those three words in a moment. First, let's talk about anxiety--because it's important to understand why anxiety sabotages your performance.

Why anxiety sabotages your performance

We all feel anxiety when faced with high-stakes situations, especially those that take us out of our comfort zones.

If you have a speech to give, an investor to pitch, or an important negotiation, anxiety can often rear its ugly head just before it's time for you to do your thing.

Pre-performance anxiety is especially troublesome because it can decrease your self-confidence. It also drains your working memory, which is responsible for your ability to hold, process, and employ information.

As a result, your subsequent performance at the task suffers.

Most people feel that trying to calm down is key to getting you ready to deliver a stellar performance--but that can actually make things worse.

That's because attempting to suppress or hide your anxiety increases it. One study showed that participants who tried to suppress their anxious feelings before delivering a taped speech experienced an increased heart rate from baseline compared to those who redirected their feelings.

It turns out: Trying not to think of something makes you think of it more.

You can't afford to let that happen to you. Especially for the opportunities you've worked so hard to get.

So how do you disperse your anxiety?

The simple way to overcome pre-performance anxiety

Get excited. Specifically, say to yourself, "I am excited."

It doesn't even matter if you aren't feeling excited when you say the words. The act of expressing them out loud makes a tangible impact.

A series of research studies conducted by Allison Wood Brooks of Harvard Business School found that people who said "I am excited" just before tackling an anxiety-inducing task--giving a speech, taking a math test, singing in front of strangers?--felt more excited about the task. They also performed better than those who tried to just "calm down."

The reason why this works? Even though anxiety and excitement are opposite emotions and have different effects on your performance, the experience you feel with these emotions is similar.

Both are high-arousal--as opposed to calmness, which is low-arousal. Because of the similarities in the way your body experiences anxiety and excitement, it's much easier to transition from anxiety to excitement than it is to calmness.

But there's another reason why this strategy works so well for pre-performance anxiety: When you switch your mindset from calmness to excitement, you re-frame how you view the task before you.

When you're trying to get yourself to calm down, research shows, you tend to look at the situation as a threat. When you're excited, you're likely to view completing the task as an opportunity. You can focus on all the benefits of what could happen. You feel more in control.

The next time you find yourself experiencing pre-performance anxiety for an important task, skip trying to calm down. Instead, take control, get excited, and embrace the opportunity that lies before you.