A new study from Fidelity Investments shows 401(k) participants managed to recoup much of their losses from one of the worst market downturns in history. And savers who were consistent over the past decade have actually seen their account balances increase by nearly 150 percent.

Average 401(k) account balances ended the year at $64,200, up another 5.7 percent from the end of the third quarter and up 28 percent for the year, according to Fidelity.

"The good news is that many workers, in spite of the economy, chose to save in their 401(k)s throughout 2009, and as the markets recovered, so did many Americans' account balances," said Jim MacDonald, president of Workplace Investing at Fidelity Investments. "When we took a longer-term view and looked at the past decade, we found that many participants were able to significantly grow their nest egg, despite periods of great market volatility."

Between 1999 and 2009, account balances climbed nearly 150 percent from $65,800 to $163,900. This growth is attributed to participant and employer contributions, dollar cost averaging and market returns, according to Fidelity.