For top Olympic sprinters, the 100-meter dash is over in less than 10 seconds: power, speed, focus, and effort concentrated in one short burst.

To win, from start to finish, they have to give the race their all.

Or not.

Before a race, Usain Bolt always seemed relaxed. He smiled. He waved to the crowd. He appeared to enjoy the attention and the moment.

During the first 30 meters or so of a race (the "drive phase"), Bolt kept his head down, body forward. Then he slowly straightened ... and for the last 40 to 50 meters, when the race could be won or lost, Bolt actually relaxed: Shoulders loose, hands unclenched, face muscles slack.

Relaxation, not extreme effort, was the key to success.

Or take nine-time Olympic gold medalist Carl Lewis, a notoriously poor starter. Lewis often trailed the leaders at the 40-meter mark yet somehow managed to pass everyone by the end of the race. Many assumed Lewis had to push even harder to overcome his poor starts.

Instead, Lewis actually relaxed. Instead of clenching his fists and grimacing with effort, Lewis stayed within himself, trusting that preparation and technique -- not "extra" effort in the moment -- would pay off. 

Lewis, like many exceptional performers, took advantage of what a sprint coach who studied Lewis would later call the "85 percent rule."

The premise is simple. If you're at 85 percent -- if you aren't striving and straining and operating at the very limit of your ability -- you have room to think. You have room to adapt. You have room to assess your performance, evaluate the responses of and interact with the people around you.

In short, you have room to relax.

Which means your performance will be better.

Even though you're only working at 85 percent.

The premise works in nearly any pursuit. Take Hugh Jackman; on the Tim Ferriss Show podcast, Jackman said: "If I were the coach and Hugh Jackman was on my team, I wouldn't put more pressure on him, push him more. I wouldn't yell at him, scream."

Jackman feels his best moments have come from doing the research, doing the work, doing the preparation, and then leaving room for impulse and spontaneity. "I actually think you need to risk being bad," Jackman said, and "just let it be."

Keep in mind the 85 percent rule doesn't work unless you put in the work ahead of time. Bolt put in the work; that's why he was so confident before a race. That's why he could relax. He knew he was ready. 

Confidence -- and the ability to relax a bit, work at 85 percent, and let it flow -- came from preparation.

Because if you aren't prepared, even 100 percent effort won't be enough.

Make the 85 percent rule work for you

Say you land a meeting to pitch an important customer -- maybe even an enabling customer.

First, put in the effort ahead of time. Know your stuff. Know how you'll respond to questions. Know how you'll react to objections.

Prepare for what you'll do if something goes wrong: Your prototype malfunctions, key people aren't in the room, your schedule time gets cut short, etc. 

Then, on the day, focus on getting off to a good start. Keep your head down for the first little bit. Focus on getting into stride.

And then relax. Let your preparation and practice -- and your skill and experience -- take over, and operate at 85 percent. 

At 85 percent, you'll be able to read the room. At 85 percent, you'll be able to adapt to whatever happens.

At 85 percent, you'll be able to smile, and engage, and establish genuine rapport.

At 85 percent, you'll appear more confident and self-assured -- because you actually will be.

Which means your performance will actually improve.

Even though you won't be trying as hard.