Force, Stress & Strain
Stress measures how much force is spread over an area. We are concerned with stresses on the various tissues in the larynx, of course; these stresses can be applied in many directions. For instance, a stress applied in a direction toward the surface of the tissue (or any area) is called compressional stress, and the amount of such a stress is known as pressure. Those stresses which point away from the surface are called tensile stresses, while those applied along a surface (tangentially) are shear stresses.
The way that the tissue responds to various stresses is called strain. These responses include stretching of the tissue, contraction or shortening, thickening, or thinning of the tissue. Typically, if tissue changes shape/size in one dimension, an opposite deformation will take place in another dimension. For instance, shortening the vocal folds causes them to become thicker, but stretching them to make them longer results in them becoming thinner.
Some typical types of stress in the vocal folds are compressional stress from the folds colliding tens or hundreds of times per second, tensile stresses from the Bernoulli effect, and shear stresses from the folds rubbing and sliding along each other during oscillation.
Force Elongation Curve
A common way to study tissue response to stretching forces is to hook up a small piece of vocal fold tissue to a stretching device, and measure its response to stretching forces, thus generating a graph called a force-elongation curve. The curve for human tissue indicates that only a small force is needed to stretch the tissue initially, but then progressively larger forces are needed to stretch the tissue further. Thus, the tissue becomes stiffer as it is lengthened. Ultimately, enough stretching causes the tissue to break.
So..be careful how you use your voice because like any muscle if misused or abused it will start showing signs of wear and tear…. and stress..!