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 USANA Health Sciences (NYSE:USNA) have gained 10%, after rising throughout the day, in response to a strong earnings report and positive forward guidance.

So what: USANA reported fourth-quarter revenue of $168.5 million, and earnings of $1.27 per share, both results beating analyst expectations of $165.6 million, and $1.21 per share. Operating cash flow was also strong, with a $29.2 million result. The company offered guidance for the upcoming year of $700 million to $720 million in annual revenue, and adjusted 2013 EPS of $5.10 to $5.25. USANA's EPS guidance came in well in advance of the $4.84 that Wall Street was looking for, and the Street's top-line projection of $701.6 million hit the low end of the company's guidance range.

Now what: USANA's results offer a firm rebuttal to the bear attack led by Bill Ackman on fellow multilevel marketing company Herbalife (NYSE:HLF) that sank many stocks in the sector at the end of last year. USANA is enjoying its best growth in China and Southeast Asia, where a 17.4% rise in the number of active Associates drove 21.3% greater sales. The company has nearly 60% of its float shorted at the moment, which could result in further short squeezes in the near future -- but it's also bound to make this stock volatile in either direction. Are you ready for a wild ride?

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