Why use an ergonomic foot rest?  A multitude of reasons to use a foot rest exist and vary by the individual.  When seated at your ergonomic chair, your knees should be at a 90 degree or slightly larger angle.  If you feet are lower than that, you'll stress your back.  Thus an adjustable foot rest is a must for shorter people or anyone whose workstation is too high, but what about the rest of the world?  Sitting all day is hard on the body and can put some people at risk for blood clots in the lower legs.  Movement can help prevent circulatory problems in your feet and legs.  The ability to move is what makes a foot rest ergonomic.   Movement can also improve your energy level and alterness, improving productivity.