The reason why one lower leg can't collapse (fold, pull in) into the upper leg is that it has been bent a little bit. Normally it's because one has been sitting on Walkstool on uneven ground and/or been putting all pressure on one or two lower legs (perhaps from leaning back- or forwards to pick up something). This could result in one lower leg being bent and also hard to pull out. What cold be done is to get a new lower leg of the same model by ordering at www.walkstool.com under Spareparts. However, before ordering one should check if also the upper leg has been bent. The easiest way to do so is to take out one of the other lower legs and pull it into the upper leg. If this can't be done then the upper leg has been bent too and then it's not much one can do but buying a new Walkstool. Next time be careful not to put pressure on one or two lower legs which we also mention in our blue leaflet that comes with each Walkstool.