Static load refers to muscles that are kept tense for extended periods. A muscle contraction sustained for greater than 20 seconds can reduce blood flow. Reduced blood flow causes localized fatigue at a much quicker rate than would be expected if the same amount of work was performed in a dynamic manner. Moreover, statically loaded muscles also take longer to recover from fatigue than muscles fatigued from dynamic work. The end result is that statically loaded muscles are more prone to injury. Manipulating a tool in an outstretched arm is an example of a static position. Moreover, in this position the rotational forces that act on the tool, exponentially increase the static load experienced by the worker. 

The postural muscles are some of the largest and most active muscles in the body, thus even maintaining optimal posture for extended periods can be considered a static load and lead to discomfort and pain. Workers should be encouraged to periodically change their posture, even for a short period. Standing versus sitting, widening the stance or propping the feet up on a footrest while sitting, can help to redistribute blood flow.