To keep the arm stretched out, the arm muscles must work statically. The muscles continue to be tensed as long as the arm is stretched. This tension reduces blood flow and cuts off the supply of oxygen.
Muscles can actually work without oxygen, but waste products such as lactic acid are not transported away. It is the accumulation of waste products that makes us tired and causes pain. The problem doesn’t go away until we take our arm down and the blood flow returns to normal.
In nursing, there are many routines that require static muscular work. Light static work, for instance at a computer, can also cause irritations in the muscles and muscle attachments, if muscles are not allowed to relax sometimes. After a while – your sensitivity determines how long – static work can lead to long-term problems.
It is highly important for muscles, and the body's wellbeing, that blood can pulse through. By avoiding unnecessary muscle tension, taking frequent short breaks, varying muscular work and adapting our working environment, we can avoid muscle tension-related problems.
The Difference Between Static and Dynamic Work
Have you ever cut a piece of wood with a hand saw? Sawing clearly illustrates the difference between static and dynamic work. The arm that saws is working dynamically, while the other arm, holding the piece of wood in place, is working statically.
The dynamics consist of the muscle alternately tensing and relaxing. When the muscle is relaxed, the blood vessels expand and the blood can stream into it. When it is tensed, the blood vessels are pressed together and no blood reaches the muscle. The muscle receives oxygen and nutrients via the blood, which also carries away waste products. Running is a good example of dynamic muscular work.