To be honest, I have yet to find a quality mass gainer on the market. The problem with most mass gainers is that they are loaded with cheap sugars as a carb source. Not only can this lead to greater fat gain, it can make drinking them several times a day unhealthy.
Mechanical stress: physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion.
Stress is defined as force per unit area. It has the same units as pressure, and in fact pressure is one special variety of stress. However, stress is a much more complex quantity than pressure because it varies both with direction and with the surface it acts on.