buckle under

Buckle under, as opposed to buckle down, is a cliche which is used for describing a situation which you have consented to doing but quite reluctantly. This is when you are willing to do something or get some work done, but arent entirely thrilled about. If you are given a project at work which you are reluctant to do but have agreed to taking on, you might say that you are buckling under; such as buckling under the pressure.