Lubricating greases have to be mechanically stable. This means that when a bearing arrangement containing grease is subject to vibration, the grease shall not soften to such an extent that the grease leaks out from the housing. A good quality grease will be resistant to such mechanical forces.
SKF developed the V2F grease test rig in order to be able to recommend mechanically stable greases to its bearing customers.
Datasheet for V2F