Correlation of exercise level and electromyography of trunk stabilizer muscles during manual lifting among experienced back belt users

Abstract

The exercise level of the trunk stabilizer muscles (ELLS) is known to be associated with the ability to control back stability with the transversus abdominis (TrA) muscle. An important role of the TrA is feed forward activity necessary for preventing lower back injury (LBI). Therefore, it can be postulated that lifting workers who always wear a back belt for certain periods of time are at risk for decreasing activity in the TrA or other trunk muscles during lifting with or without a back belt. Objective: This study evaluates the correlation between the ELLS and electromyography (EMG) of selected trunk muscles during manual lifting with and without a back belt in experienced back belt users. Materials and Methods: Sixteen participants from a warehouse in Thailand, aged 22 to 44 years, were assessed for ELLS, which was indicated by values ranging from level 1 (weakest) to level 6 (strongest), and the EMG of selected trunk stabilizer muscles, including the rectus abdominis (RA), external abdominal oblique (EO), TrA/internal oblique (IO), erector spinae (ES), and multifidus (MF). The EMG data were recorded during manual lifting in a dynamic semisquat posture for conditions of lifting with and without a back belt. The results of the Pearson correlation coefficient between the ELLS and normalized EMG (NEMG) of the selected trunk muscles showed a positive significant correlation between the ELLS and TrA/IO activity only during lifting without a back belt (r p = 0.537, p = 0.032). However, there was no correlation between the ELLS and other selected muscles during lifting with or without back belt. This study demonstrates that ELLS indicates the importance of workers using the TrA during lifting without a belt. Therefore, a specific exercise program to improve the strength of the TrA is necessary for back belt users.