File
Stenlund T.C.1, Häger C.K.1, Lundström R.2, Lindroos O.3, Öhberg F.2, Rehn B.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 complex mechanical shocks (perturbations) that disturbs the seated balance of the driver. The perturbations, commonly in lateral directions, are suggested to be hazardous to the spine and associated with musculoskeletal pain among professional drivers. However, the muscle and kinematic reactions caused by perturbations, especially complex, in seated positions are scarcely studied.
Purpose: To describe and compare seated postural reactions due to single-sided perturbations (SSP) or double-sided perturbations (DSP) in healthy adults.
Methods: Twenty healthy male participants (18 - 43 ys) were seated on a movable platform and exposed to 5 single-sided perturbations (SSP) and 15 double-sided perturbations (DSP) with accelerations of approximately 13 m/s2 in lateral directions. During the DSP the platform accelerated in one direction followed by an acceleration in the opposite direction, divided into fast, medium and slow depending on the time to direction change. Evoked muscle activities were recorded with surface electromyography (EMG) bilaterally in the upper neck, trapezius, erector spinae and external oblique. The activities were further normalized to maximum voluntary contractions (MVC). Kinematics were simultaneously recorded for the neck, trunk and pelvis segments using inertial sensors.
Results: The evoked EMG amplitudes were significantly (p 0.001) higher for the fast DSP compared the other perturbations. The most intense muscle activity was found in the external obliques with more than 10% of an MVC both for the SSP and the DSP. The erector spinae and upper neck was less than 10% of an MVC while the trapezius activity was less than 2% of an MVC. The kinematics showed a greater range of motion of the neck and trunk during the DSP compared to the SSP.
Conclusion(s): Perturbations with higher complexity, especially the fast DSP, evoked larger seated postural reactions compared to the SSP. Still the rather low muscle activity together with the small range of motions do not imply a high risk for musculoskeletal overload.
Implications: When recovering the seated balance after a perturbation, the external obliques were the most active muscles and seem of importance for stabilising the whole spinal column. Specific physical training for the external obliques may be important for professional drivers.
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.
