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.

Expect a positive start to the stock market today, as the Dow Jones Industrial Average (DJINDICES:^DJI) gained 50 points, or 0.3%, in premarket trading this morning. With the Dow 5% off of its record high close to 2013, investors spent the last week focused on the Federal Reserve's stimulus policies and on the economies of emerging markets. But corporate earnings are taking center stage as dozens of companies report quarterly results today, including Under Armour (NYSE:UAA), Visa (NYSE:V), and Time Warner Cable (UNKNOWN:TWC.DL).

Under Armour this morning posted a massive 35% jump in fourth-quarter revenue, to $683 million -- well ahead of the 22% rise that Wall Street expected. And that sales boost powered a 27% profit improvement, to $0.59 a share. In a quarter that saw most retailers struggle, Under Armour was able to book significant growth in its apparel and footwear businesses while improving gross margin by a full percentage point, to 51.3%. The company also provided an aggressive outlook for 2014 that called for 22% sales growth, thanks to what CEO Kevin Plank called "tremendous momentum" in the company's businesses. Under Armour stock is up 11% in premarket trading.

Time Warner today posted a 16% rise in quarterly profit, to $1.89 a share. Sales ticked higher by 2%, to $5.6 billion, as weakness in the residential business was offset by strong broadband sales. Time Warner booked a huge loss of customers, which it blamed on the programming dispute with CBS. Still, the company said those negative trends reversed toward the end of the quarter as subscriber growth returned. The cable provider also boosted its quarterly dividend by 15%, to $0.75 a share. Time Warner's stock is up 0.5% in premarket trading.

Finally, Visa this morning turned in surprisingly strong fourth-quarter results. Earnings rose 14%, to $2.20 a share, on an 11% jump in revenue to $3.2 billion. Analysts had expected profit of $2.16 a share and sales of $3.1 billion. Visa saw a healthy boost in total payment volume, and international transactions significantly improved as well. But the best news for investors was that expenses grew at a much slower pace than revenue, which pushed the company's operating margin up from 63% to nearly 66%. Visa's stock is up 3.4% in premarket trading.