Traders work on the floor of the New York Stock Exchange August 5, 2011. [Photo/Agencies]

Stocks closed out their worst week in more than two years on Friday in a volatile session that saw the major indexes whip back and forth before the S&P 500 ended down less than a point.

More than 15.9 billion shares -- or more than twice the daily average volume -- traded in the busiest day in more than a year as investors plowed into cash-rich mega-cap stocks that had been beaten down in recent days as the market dropped.

The market's swings on Friday were fast and furious, with the Dow Jones industrial average covering 416.41 points from its session high to its intraday low.

The intense selling this week reflects frustration with sluggish economic growth and politicians' inability to address pressing concerns over high public debt in Europe and the United States.

Options volume hit a record, a sign investors were protecting their portfolios from further declines. The CBOE Volatility Index or VIX, Wall Street's so-called fear gauge, rose as high as 39.25 earlier, its highest level since May 2010, but ended at 32, up 1.1 percent.