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

When the rate of GDP growth in the U.S. more than doubles in a single quarter, you'd think the stock market would go crazy. Today's revised second-quarter GDP estimates showed just that sort of acceleration: the annualized 2.5% growth seen in the April-June quarter easily exceeded the 1.1% growth seen in the January-March period. But that sub-3% uptick only sent the S&P 500 Index (SNPINDEX:^GSPC) three points, or 0.2%, higher, ending at 1,638. The following three stocks certainly did their part in holding the index back.

Today was a terrible day to be invested in coal, as evidenced by the two coal miners on today's list. The most severe decliner in the 500-stock index, Peabody Energy (NYSE:BTU) shed 3.8% Thursday. If you're familiar with the stock, the slide shouldn't shock you; Peabody shares are twice as volatile as the broader market, and as coal has become more controversial and less popular in recent years, so have the companies that produce the resource. 

Cliffs Natural Resources (NYSE:CLF), today's second-largest laggard, lost 3.1% Thursday. Peabody and Cliffs are birds of a feather, and birds of a feather typically fall together in the stock market. Similar companies often rise together, too, of course, and if a coal renaissance is in the works, these two businesses will be some of the most prolific gainers in the S&P. The only problem seems to be that the coal renaissance is devoid of da Vincis -- and Michelangelos, and pretty much any other metaphorical figure indicating a renaissance is even a possibility. Until coal can overcome its image as a "dirty" energy source and fight off the popularity of natural gas, these two may continue to struggle.

Finally, a familiar name graces the ranks of today's struggling stocks for a second straight day: J. C. Penney (NYSE:JCP) shareholders saw the stock decline 2.8%, the fourth straight day of declines in a week that saw hedge fund manager Bill Ackman's Pershing Square -- a major J.C. Penney shareholder for years -- liquidate its entire position, taking more than $400 million in losses in the process. While legendary investor George Soros has reportedly built a significant position in the department store's stock just as Ackman licks his wounds, there needs to be a more significant catalyst on the horizon before this stock becomes alluring.