This ergonomics principle promotes dynamic physical movement in the workplace on an on-going basis.
Stand or Walk?
Most people have carried a backpack at some point. Picture this scenario - you are with a group of friends going for an extended hike; your backpack weighs 50# and you have put it on your shoulders. What do would rather do: stand in one place for the next 30 minutes OR take that same backpack and start to walk for the a few miles?
To a person, everyone agrees that it is much better to walk not to stand. We intuitively know that movement is superior to maintaining one position. In other words, we need to move to be comfortable.
That is what this ergonomics principle is all about and there are sound physiological reasons why this is the case.
Metabolism
To accomplish work, the body is able to take in nutrients, convert them into chemical energy and then ultimately into mechanical energy (e.g., muscular contraction) and heat. This is metabolism. Glucose and oxygen are stored in relatively small amounts within the muscle tissue. Consequently, to sustain performance continuous flow of oxygen and energy-rich blood into the tissue in addition to removal of metabolic waste products is required.
Static Muscle Contraction
Type of muscular effort has been shown to have a profound impact on blood flow. Static muscle contractions (the muscle shortens but no joint movement occurs) results in blood vessel compression due to internal muscle pressure. At contraction levels of 60% and greater of the maximum voluntary contraction of the muscle, blood flow ceases.
The muscle depends on the quite limited initial reserves stored internally. Waste products accumulate and only short duration contractions are possible.
Dynamic effort
On the other hand dynamic muscle contractions are the alternating contracting and relaxing of muscle groups to perform tasks. I
n terms of enhancing performance and controlling fatigue, dynamic muscle contractions are a significant improvement over static muscle contractions.
Dynamic muscle activity promotes blood and fluid flow by acting as a pump to increase oxygen and nutrition to the working muscles and helps to remove the waste products of metabolism.
Most people have carried a backpack at some point. Picture this scenario - you are with a group of friends going for an extended hike; your backpack weighs 50# and you have put it on your shoulders. What do would rather do: stand in one place for the next 30 minutes OR take that same backpack and start to walk for the a few miles?
Type of muscular effort has been shown to have a profound impact on blood flow. Static muscle contractions (the muscle shortens but no joint movement occurs) results in blood vessel compression due to internal muscle pressure. At contraction levels of 60% and greater of the maximum voluntary contraction of the muscle, blood flow ceases. 
On the other hand dynamic muscle contractions are the alternating contracting and relaxing of muscle groups to perform tasks. I