Muscle fibre directions of iliocostalis and multifidus: male-female differences.

The accuracy with which the fibre direction of the multifidus muscle can be predicted in females is comparable to that for males, and is well within the limits of accuracy obtainable in the placement of surface electrodes in relation to a reference line drawn on the skin, i.e. +/- 5 degrees. In females, the observed deviation of the iliocostalis fibres from the corresponding reference line may, however, add some degree of error to the proper orientation of electrode bars perpendicular to muscle fibres. It may thus be concluded that the surface recording of EMG power spectrum parameters of the iliocostalis in women cannot be carried out as accurately as for the multifidus muscle. Nevertheless, the resulting recording error associated with a possible orientation deviation of, for example, 13 degrees is rather small (3%) and may be acceptable for clinical research purposes.