Comparison of bilateral abdominal muscles onset times during upper limb flexion in healthy subjects: Investigation of anticipatory postural responses

The present study was conducted to compare bilateral abdominal muscles onset times with that of dominant upper limb deltoid muscle associated with anticipatory postural responses in healthy participants.
In the current observational study, 20 healthy female individuals (mean age 25.3 yrs and BMI =22.36kg/m2) were studied. While they were performing rapid arm flexion in standing position with their dominant limb, electromygraphic data of Transverse Abdominus (TrA) and External Oblique (EO) in both sides and the deltoid muscle of dominant limb were recorded. The onset times of these muscles were the main measured parameter during anticipatory postural response. Wilcoxon signed-ranked test was used to compare bilateral abdominal muscles onset times.
Contra lateral TrA and EO were recruited prior to deltoid muscle, but in Ipsilateral side these muscles were activated primarily after deltoid. There were significant differences between abdominal muscles onset time in comparison between the two sides of the trunk (TrA: p=0.001, EO: p=0.005).
Feed-forward activation of the abdominal muscles, prior to perturbation due to rapid arm movements, was observed for one body side in healthy subjects but these muscles in Ipsilateral side were activated in feedback manner. The results of the present study show that abdominal muscles are a part of diagonal synergies related to transferring movement and torque efficiently produced by the moving limb. It seems that reciprocal pattern of TrA muscle activation is a more efficient pattern in comparison with co-contraction pattern previosely introduced.