Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of performance athletic apparel maker Under Armour (NYSE: UA) dashed up as much as 11% today, fueled by a solid fourth-quarter earnings report.

So what: Fourth-quarter revenue was up 36% from last year while diluted earnings per share jumped 47% from the prior year. It's hard to argue with that. Even after excluding a $0.04 EPS bump from a tax benefit, the company's bottom line still easily topped the $0.37 that analysts were looking for. And as if that wasn't enough, the company also raised its full-year outlook for 2011. It now sees revenue growth of 25% to 27% for the year.

Now what: If there's anything to potentially quibble with, it's Under Armour's stock price, which, after doubling over the past year, now trades at 38 times expected 2011 earnings per share. Of course a high earnings multiple has been a pretty consistent presence throughout Under Armour's history as a public company and -- recession aside -- its blazing growth has thus far kept the stock chugging along. The company is now hoping that the introduction of its Charged Cotton T-Shirt -- its first product in the large market for cotton athletic apparel -- will help keep the growth engine's furnace well-stoked.

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