Shares of MannKind Corp. rose more than 40 percent Thursday.

The Westlake Village biotech, maker of the Afrezza brand of inhalable insulin, made no announcement about the business, but Brian Orelli on the Motley Fool website speculated that the big move stemmed from short-sellers covering their position.

“The most likely reason for the massive increase today is a combination of MannKind's share price hitting a level that investors think is too low to sell, combined with a short interest,” he wrote in a post. “The end result is a ‘short squeeze’ in which short-sellers have to buy to close their short position. Those buyers have to increase their bid price to find a seller, which results in even more short-sellers deciding to end their position.”

Shares of MannKind MNKD closed Thursday up $1.11, or 41.3 percent, to $3.80 on the Nasdaq.