Comparing the effect of grip technique, Beggs et al. (2011) investigated the use of either the double overhand or over-under grip technique on upper trapezius muscle activity and found no difference between conditions at either 60 or 80 % of 1RM. (strengthandconditioningresearch.com)
With this in mind, research has found that starting a shoulder shrug in 30 of glenohumeral abduction (i.e., arms slightly out to the sides), which is a component of slight scapula upward rotation, generated greater upper trapezius muscle activity in comparison with the shrug with the arms at the side (1). (nicktumminello.com)
It appears that the middle and upper trapezius display superior muscle activity during the bent over row, while middle trapezius muscle activity seems not to be affected by stability at the hand or seated row technique. (strengthandconditioningresearch.com)