Currently it is possible to collapse all Swimlanes under Active Sprints using the hotkey -.

For customer who are planning several sprints at the same time, or have large backlogs, it would be helpful to extend this shortcut to the Backlog page as well. Currently they have to collapse every sprint they are not planning whenever the page is refreshed, which can be annoying when planning large numbers of sprints.

From a support case: 

As I groom the backlog, I am having to scroll up and down and review stories from different future sprints to move things around its cumbersome and inefficient to individually collapse each future sprint each time I do refresh.