n recent years studies have shown that very low
levels of static loading are associated with muscle
fatigue. Bjorksten and Jonssor? have shown that static
muscle work maintained for over 1 h should not exceed
5-6% of maximal voluntary contraction (MVC).
Jonsson29 further suggested that static loading is acceptable
only if it is lower than 2% of MVC when
maintained for the entire working day. Grandjean**
quantifies static loading in three categories relating to
the forces required. If a high force is exerted static
muscle actions should be for less than 10 s; for a
moderate force, less than 1 min, and for a low force,
less than 4 min.