Force levels of trunk muscles
During bending and lifting a weight of 15 kg co-contraction increases by only 1.5% MVC
(van Dieen et al., 2003b).
During walking rectus abdominis has a average activity of 2% MVC and external oblique 5% MVC (White & McNair, 2002).
Co-contraction in standing is less than 1% MVC rising up to 3% MVC when a 32 Kg weight is added to the torso. With a back injury it is estimated to raise these values by only 2.5% MVC for the unloaded and loaded models (Cholewicki et al., 1997).
In standing, ES, psoas and QL are virtually silent! In some subjects there is no detectable EMG activity in these muscles
(Andersson et al., 1996)