changing nature of work meaning in English

工作性质的改变

Professor gai explains how the changing nature of work has contributed to the difficulty of defining the middle class , when he says that " in the past , people worked with their physical strength . but now , more and more people work with their minds , their brains .
盖浙生教授则从职务要求的改变来说明定义中产阶级的困难：过去的工作都是劳力的，现在则有越来越多的劳心工作而我们通常视劳心者为中产阶级。