It means, when you are accelerating upwards, as the elevator picks up speed, the reading on the spring will be more and you will feel heavy.

也就是说当你向上做加速运动时,就像电梯加速的时候,弹簧的读数会增大,你会觉得自己变重了

耶鲁公开课 - 基础物理课程节选

You feel heavy and it reads more because the poor spring not only has to support you from falling through the floor, but also accelerate you counter to what gravity wants to do.

你感到自己变重以及读数增加,因为现在弹簧不仅要支撑你,不让你掉下来,还要抵消重力的作用让你加速

耶鲁公开课 - 基础物理课程节选