Stocks pushed back downward on Friday, sending the market to its worst levels of the year, and creating even more fear about the future for the seven-year-old bull market. The Dow finished down almost 400 points after having been off more than 500 points earlier in the day. Other major market benchmarks were also down between 2% and 3%.

Many energy stocks fell sharply as oil dropped below the $30-per-barrel mark, but some non-energy stocks were also among the poorest performers on the day. Intel (NASDAQ:INTC), Sarepta Therapeutics (NASDAQ:SRPT), and Sprint (NYSE:S) were among notable decliners Friday.

Intel fell 9% despite posting better-than-expected results for the fourth quarter in its earnings announcement last night. The chip giant said that it managed to limit its revenue losses for the quarter to 4%, and earnings of $0.74 per share were more than $0.10 better than the consensus forecast. Intel also projected that its full-year revenue gains would be better than expected.

Yet investors focused on the prospect for gross margins to slump early this year. Moreover, the company's data-center business didn't see the strength that some had hoped for. Given the importance of cloud computing and enterprise servers to Intel's future strategy, the shortfall there carried more weight than the less forward-looking segments of the tech giant's business.

Sarepta Therapeutics plunged 55% after the FDA issued a review of the company's eteplirsen, an experimental treatment for Duchenne muscular dystrophy. The agency said that it had concerns about how Sarepta designed the trial of the drug, as well as the drug's efficacy and Sarepta's statistical analysis in the trial.

With an advisory panel set to meet to discuss eteplirsen next week, investors were worried that the negative review would lead to a vote from the panel against recommending approval of the drug. Such a vote wouldn't necessarily stop the FDA from approving the drug, but advisory-panel opinions carry a lot of weight with regulators. A rejection would mark a huge setback for Sarepta, which has already faced long delays in the approval process.

Finally, Sprint dropped 10%. The broadband-network company reportedly is looking to relocate its radio towers away from private leases toward lower-cost properties owned by government entities in order to reduce overall expenses. Cost reductions of an estimated $1 billion would be a positive for Sprint's bottom line, but some investors believe that further savings will be needed in order for the carrier to remain competitive against its main competitors in the U.S. market.

Analysts have seen recent signs of subscriber defections away from rival carriers to Sprint as being a short-term positive, but there's a lot of skepticism over whether the ongoing price wars will actually produce a winner, or rather just pull down profits for the entire industry. Given the similar experience that the telecom industry went through with long-distance telephone service, investors are right to worry about Sprint's long-term financial health.