Stress/motion sensor

Im currently in the development stage of a lawn mower project and ive got an idea for a cutting system which detects stress on the blades.

There is a system on the market that when the stress on the cutting blades becomes to much the power supply is cut, but i want to develop this concept so that when the stress becomes to much, the cutting height of the blades can increase therefore reducing the stress and increasing the efficiency of the cut.

Anyone have an idea of the technology/mechanics involved? or if this is used in any other type of product/industry?