SHORT-TERM ADAPTATION OF POSTURAL REACTIONS IN SEATED POSITION

Rehn B.¹, Häger C.K.¹, Lundström R.², Lindroos O.³, Öhberg F.², Stenlund T.C.¹

¹Umeå University, Community Medicine and Rehabilitation, Physiotherapy, Umeå, Sweden, ²Umeå University, Radiation Sciences, Biomedical Engineering, Umeå, Sweden, ³Swedish University of Agricultural Sciences, Forest Biomaterials & Technology, Umeå, Sweden

Background: Driving on irregular terrain causes mechanical shocks that may be hazardous for the musculoskeletal system, especially for the neck and lower back region of the spine. Postural reactions are necessary for stabilizing the spine after large external perturbations. Adaptation is important but is rarely studied for seated positions.

Purpose: The purpose was to describe and analyze the adaptation of seated postural reactions in a short-term perspective.

Methods: Five lateral perturbations (peak accelaration 13.3 m/s2) where delivered from a movable platform to twenty healthy male participants (18-43 ys) in a standardized seated position. Surface electromyography (EMG) was recorded bilaterally in upper neck, trapezius, erector spinae and external oblique. Muscle activities were normalised to maximum volontary contractions (MVC). Kinematics were simultaneously recorded with inertial sensors for the head, trunk and pelvis segments.

Results: EMG amplitudes for all muscles, except for the trapezius, significantly (p 0.05) decreased by 0.2% between the first and last perturbation. Neck angular displacements were reduced by more than 2.1° but there were no other kinematic adaptations. Notably, the mean EMG amplitudes did not exceed 10% of an MVC. Muscle onset latencies remained unchanged over time.

Conclusion(s): The adapted neuromuscular strategy during repeated postural reactions in seated positions seem to prefer a reduced EMG amplitude with minor kinematic alterations. Further research on long-term adaptations are warranted.

Implications: The modest size and the adaptation of the postural reactions for these experimentally induced mechanical shocks suggest no immediate harmful effect on muscles or joint structures.

Funding acknowledgements: Centre for Environmental Research in Umeå, Sweden. AFA Insurance and Ingabritt & Arne Lundbergs Research Foundation.

Topic: Occupational health & ergonomics

Ethics approval: The study was approved by the Regional Ethical Review Board in Umeå (No. 2014-228-32M)

All authors, affiliations and abstracts have been published as submitted.