Speculators in IMM yen futures reversed into a net short position in the period ended April 20, from a net long position the prior period, data from the Commodity Futures Trading Commission showed on Friday.
The data from the CFTC's Commitments of Traders report on speculative positioning are used by analysts as an indicator of future market direction.
For example, extreme net long speculative positions often signal a decline in the currency, especially if that position conflicts with the positioning of the more influential commercial players.
Speculators generally are trend followers seeking to pick a precise top or bottom in the market.
Speculators in yen futures notched a net short position of 6,044 contracts in the period ended April 20, compared with a net long position of 24,760 contracts in the previous week.
"One source of fuel the dollar has been drawing from against the yen, namely squeezing long yen speculative positions, has been exhausted. It is going to be fairly hard work from here for the dollar. It could be quite a struggle for the dollar to move above 110.0 yen," Callow said.