Limitations
One limitation is that due to one drop-out and missing data caused by lost contact of electrodes, a perfect balance between groups of the original study design was not achieved, especially for the EMG data. Two of the four missing data sets for EMG regarded LES, and they were related to the two prismatic loupes. However, most measured variables were not impacted by the missing data, and the amount of missing data comprised only a small portion of the total amount of data. Previous studies (