You don't need an awful lot of force to disengage most clipless pedals. I've been on the M520s since I first started riding seriously less than 2 years ago. This includes as a relative noob on a brand new grade 2 sprain (suffered during a trail running relay and rehabbed very poorly in the first few days). I kept the tension at the lowest setting and still have it there. Though I have had some pop-outs when I've hit potholes. I think the mechanism has simply loosened a bit with time.