Fig. 2

EMG patterns of 11 trunk motor task in the non-CLBP and CLBP group. The concatenated EMG envelops of 11 trunk motor tasks in all participants with and without CLBP. The mean of the EMG envelopes for all Non-LBP and LBP participants are plotted as a line and the standard deviation as a shading around it. The amplitude is normalized by the maximum value for each trunk muscle over all 11 tasks. Then, each muscle vector in the data matrix was standardized to have unit variance, such that the activity in each muscle was equally weighted. Of note, the five LBP participants had the more affected area of LBP on the right side and the remaining ten were on the left side. Thus, the EMG data on the right side in these five LBP participants were replaced with the EMG data on left side vice versa, so that all LBP participants had the affected area on the left side of trunk muscles (please see the “Methods” section)