NEW YORK (Reuters) - One notable factor in Wall Street’s monster rally on Wednesday was a record gain in an index of stocks that have the largest bets placed against them by market contrarians.

A trader works at his post on the floor of the New York Stock Exchange (NYSE) in New York, U.S.,December 26, 2018. REUTERS/Jeenah Moon

The Thomson Reuters United States Most Shorted Index rose 6 percent, the biggest percentage rise in its six-year history, as some investors moved to cover bearish bets on the 51 stocks in the index, some of which were at their lowest price in years.

The gain came as the Dow Jones Industrial Average surged more than 1,000 points in a single session for the first time, in a broad stock rebound that pulled the benchmark S&P 500 index back from the brink of a bear market.

“This is a short-covering rally,” said Michael Antonelli, managing director of institutional sales trading at Robert W. Baird in Milwaukee.

“The move you see is just everybody trying to get out of these super, super bearish positions that they have been in, that have been easy to make money in,” he said.

U.S. stocks have been battered this month by fears of slowing economic growth and worries about a potential conflict between the White House and the Federal Reserve, putting the S&P on pace for its worst December since the Great Depression.

“From the day the market opened in December, if you just went short the market every morning, you were making money at the close,” said Antonelli.

Short-sellers aim to profit by selling borrowed shares, hoping to buy them back later at a lower price.

The rally in heavily shorted names exerted pressure on short-sellers to at least partly cover their bets, analysts said.

“The shorts realize that they probably shouldn’t be too greedy here,” said Brett Ewing, chief market strategist at First Franklin Financial Services in Tallahassee, Florida.

Several components of the Thomson Reuters United States Most Shorted Index rose sharply from multi-year lows on Wednesday.

Shares of home furnishing retailer Bed Bath & Beyond Inc BBBY.O, which on Monday fell to a two-decade low, rose 9 percent on Wednesday. Snap Inc SNAP.N, which dropped to a record low last week, rose 4.6 percent. Shares of California Resources Corp CRC.N rebounded 22 percent from their lowest since early March.

Abercrombie & Fitch Co ANF.N, another component of the index, rose 10.5 percent.