Integrated application of miniature inertial movement sensing, electromyography and synchronized observation in ergonomics, rehabilitation and movement sciences.

Detailed biomechanical assessment of motion and joint load exposures in terms of net moments and forces has thus far been performed mainly in the laboratory. Video-based setups provide accurate 3D kinematics and have been used in combination with ground reaction force and EMG assessment in many fundamental and clinical applications. However, the relative complexity of setting up and calibrating the system after moving the cameras, the costs of buying and running a system and the restricted workspace all call for another solution for large-scale detailed assessment in the field, e.g. job and work place evaluations. Therefore in 1994 the Dutch AMBER / AmbuLab project line was initiated to result in a method for detailed 3D biomechanical assessment of motion, EMG and joint load in a fully ambulatory context. Ambulatory here was defined as: fully automatic assessment on the subject, independent from any artificial external references or connections, without hampering or stigmatizing the subject. Initially a method was developed around one typical application: ambulatory low back load exposure monitoring. Here load exposure is assessed in terms of net spinal moments and spinal forces through simple biomechanical models driven by fully dynamic 3D body posture and movement data together with muscle activation patterns assessed through miniature EMG sensors. Essential for data management and interpretation is the integration with observation and video data through wireless real-time synchronization. Typical other applications under investigation are: physical load estimation around other joints (shoulder, knee), general ‘free’ (human) motion analysis and ambulatory monitoring of other electrophysiological data.

AmbuLab methods
In the AmbuLab context the following enabling technologies were further developed and applied:

• Inertial motion sensing. Miniature movement sensor modules were developed which deliver full 3D rotational and partly translational kinematics of one body segment each. The modules combine signals from accelerometers, rate gyroscopes and magnetometers to accurately estimate 3D orientation, angular velocity, angular acceleration and linear acceleration during long recordings. Here the combined sensing of omnipresent global references (the earth gravitational field, Coriolis forces related to earth spin velocity and the earth magnetic field) enables accurate and stable, fully dynamic 3D kinematics assessment. Current developmental focus is on minimizing disturbance of the estimation quality by earth magnetic field distortions by near by metal masses.
• EMG driven estimation of physical load exposure under unknown free load handling. A method was developed for accurate estimation of back load exposure effects of unknown manual load handling through a quickly self-calibrating artificial neural networks (ANN) driven by EMG signals and kinematics data. The self-calibrating ANN was validated for sagittal plane net moment estimation and shown to perform well while only requiring a short, easy to perform set of calibration movements. Current focus is on development and validation of a 3D version.
• Miniature recording and integration of observational scoring facilities. A custom portable analog data acquisition unit was developed and applied in a series of pilot studies in the field. Currently a digital successor is being developed in which data acquisition and observational scoring is combined (according to ‘The Observer’ standards).
• Integrated wireless real-time synchronization with commercial digital video camcorders. This was implemented for cameras using the Ctrl-L or Lanc communication protocol to facilitate data reorganization and proper interpretation.

Aim of the meeting

• Discussion and exchange of expert knowledge about strengths and weaknesses / challenges and threats of ambulatory biomechanical motion and electrophysiological monitoring.
• Dissemination of the current AmbuLab project results to interested parties.

Program

1. Presentations/demonstrations current AmbuLab results (60 min)
   • Practical 3D inertial sensing. H. Luinge (University of Twente)
   • Application: Amber ambulatory back load exposure assessment. C.T.M. Baten (Roessingh Research and Development) and J. van Dieen (Vrije Universiteit Amsterdam)
   • Application: evaluating office work on the basis of health guidelines. M. de Looze (TNO Work and Employment)
   • Demonstration: AmbuLab concept ambulatory monitor. J.H. Smeding (Roessingh Research and Development), P. Slycke (Xsens Sports Technology), B. Loke and V. Kovacs (Noldus Information Technology bv)
2. Demonstrations and/or presentations by SIG participants (15-30 min)
3. General discussion (45 min): Integrated ambulatory monitoring: gadget or useful tool? Analysis of strengths, weaknesses, challenges and threats for integrated ambulatory biomechanical motion and electrophysiological monitoring.

References

• Baten, C.T.M.; Luinge, H.J.; Moerkerk, H. (2000). Estimating body segment orientation applying inertial sensing. Proceedings of the Sixth International Symposium on the 3-D analysis of Human Movement (Cape Town, South Africa).
• Baten, C.T.M. (2000). Ambulatory low back load exposure estimation. 14th Triennial Congress of the International Ergonomics Association (San Diego, USA).
• Looze, M.P. de; Boeken-Kruger, M.C.; Steenhuizen, S.; Baten, C.T.; Kingma, I.; van Dieen, J.H. (2000). Trunk muscle activation and low back loading in lifting in the absence of load knowledge. Ergonomics, 43, 333-344.
• Dieën, J.H. van; Nussbaum, M.A. (2000). Occupational biomechanics of the low back. Human Factors and Ergonomics Society (2000), 596.
• Luinge, H.J.; Veltink, P.H.; Baten, C.T. (1999). Estimating orientation with gyroscopes and accelerometers. Technol. Health Care, 7, 455-459.