What is Strong?

I was browsing through some videos on a home cycle trainer when I came across this motivational video that pondered the question of, "What is Strong?"

The video is only made up of around 50 words that attempt at showing you how to find strong.

Though what I get from the video is it's last statement, "Maybe strong is just what you have left when you've used up all your weak."

Watch the video from Youtube below

Is it muscle? Or is it something more? Is it measured in miles or milliseconds? Is it your best time or your worst day? Maybe strong is just what you have left when you've used up all your weak...

The video is part of an ad by running shoe company, Saucony.

What is Strong?