Its been a few years but I have used SRT strain gauges for similar measurements. They are made of resistive metal that changes resistance, albeit very small changes, in response to being stretched or compressed. You use them in one or two legs of a wheatstone bridge. They were commonly used to measure the tensile strength of materials. I was using them to measure blood pressure. They were replaced with piezo elements (crystal). Here is a pic of an SRT metal strain gauge. They come in various sizes and simply glued to a surface.
Pete
