Effects of upper-extremity movements on electromyographic activities of selected trunk muscles during leaning forward

Leaning forward has been accepted as a foundational approach to facilitate trunk-stabilizing muscles in the abdominal and lumbopelvic regions for patients with back pain during rehabilitation. However, how trunk muscles are activated and recruited during leaning forward performed under dynamic upper-extremity motion conditions is not completely understood.

To determine whether activation of selected trunk muscles changes depending on shoulder movements during leaning forward exercise in healthy young adults.

Twenty-four healthy adults (6 men and 18 women) participated in this study. The participants performed 3 types of leaning forward exercises: leaning forward alone (leaning forward 1), leaning forward with horizontal shoulder abduction (leaning forward 2), and leaning forward with shoulder flexion (leaning forward 3). Surface electromyography (EMG) was used to record activation of the erector spinae (ES), multifidus (MF), rectus abdominis (RA), and internal oblique (IO) on the dominant side.

There was a significant main effect of exercise type on the activation of the IO, RA, and MF muscles. Activation of the IO and MF during leaning forward 1 was significantly decreased compared to activation in leaning forward 2 and 3; the activation of IO and RA showed the greatest increase during leaning forward 3. Furthermore, the IO/RA ratio was significantly increased during leaning forward 2 and 3 in comparison to leaning forward 1; the MF/ES ratio was also significantly increased during leaning forward 3, compared with leaning forward 1.

The integration of shoulder movements during leaning forward exercises could be effective in the facilitation of EMG activity of IO and MF muscles, especially with shoulder flexion.