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What: Shares of fitness specialist GNC (NYSE:GNC) were getting pumped up today, gaining as much as 10% after reporting an impressive quarter.

So what: GNC was two out of three in its earnings report. The health supplement retailer beat earnings estimates by $0.04 cents, with a $0.50 EPS, but missed on revenue expectations. Sales increased 10.9% to $565 million, but that was still short of Wall Street's view at $573.6 million. Same-store sales at domestic locations increased 7.1%, and were up by 11.4% at franchise locations, both strong numbers. Guidance also topped the experts' projections as management sees EPS of $2.75-$2.80 in 2013. The consensus was at $2.72.

Now what: CEO Joe Fortunato touted the company's strong performance in 2012, noting improvements in market share and operating margins, and expanding the customer base. The increase in comparable sales is generally a good indicator of continuing growth, and the fifth quarter in a row that GNC has beaten estimates. The company appears to be firing on all cylinders, and I'd expect a strong 2013 from the retailer.

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Fool contributor Jeremy Bowman has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.