The trunk's contribution to postural control under challenging balance conditions.

BACKGROUND

The double inverted pendulum model is imprecise when applied to studies of postural control. Although multijoint analyses have improved our understanding of how balance is maintained, the exact role of the trunk remains unclear.

RESEARCH QUESTIONS

What is the trunk's contribution in postural control with respect to the other joints and how do trunk muscles control trunk kinematics?

METHODS

Thirty-six healthy athletes (handball, karate, long jump) performed a highly challenging balance task while the ground support was dynamically tilted in the sagittal plane. The center of force (CoF) as well as lower limb joint angles and the trunk-pelvis angle were respectively measured with a force platform and inertial measurement units. The amplitude, sway path and standard deviation of the CoF and the joint angles were then calculated. Electromyography was used to record the activity of the rectus abdominis, external obliquus, and erector spinae muscles. Multiple linear regressions were computed to determine the joints' and muscles' contributions (β-coefficients) in predicting CoF variables and trunk kinematics, respectively.

RESULTS

The linear combination of joint kinematic variables accounted for between 33 % and 75 % of the variance in the CoF. The ankle had the highestβ and was a significant predictor of all CoF variables. The trunk yielded the second highest β-coefficient and was a significant predictor of the CoF sway path. Electromyography variables accounted for no more than 35 % of the variance in the trunk kinematics, and erector spinae activity was the only significant predictor.

SIGNIFICANCE

The trunk appears to be the second most important element during this specific postural task, in the magnitude of body sway in particular. But neuromuscular control of these trunk processes is difficult to characterize with surface electromyography only. The trunk should be taken into account when seeking to improve overall postural control (e.g. during training, rehabilitation).