Interdisciplinary Motion Capture Applications include muscle activation and vibration studies

By Michele Oliver, Ph.D., P.Eng*#.

Robert Jack, Ph.D. Candidate#.

and Taylor Murphy, M.Sc.(Biological Engineering) Candidate*

*School of Engineering

#Biophysics Interdepartmental Group,

University of Guelph, Guelph, Ontario, Canada N1G 2W1

The School of Engineering at the University of Guelph began offering degrees in Biological Engineering in 1969 and in 1973 became the first fully accredited Biological Engineering program in Canada. Within Biological Engineering, two current foci are Biomechanics and Biomedical Engineering. The school currently has three faculty members who specialize in these areas. When looking across the university campus, even though Guelph is a mid-sized institution, the university is in the enviable position of having a total of eight faculty members who conduct research in Biomechanics. The five other Biomechanics researchers reside in either Human Biology and Nutrition or the Ontario Veterinary College. Given that Guelph has evolved as an extremely interdisciplinary institution, inter-department and external collaboration is encouraged and fostered. As a result, many of the research projects using the Vicon system involve researchers and students from a number of departments and universities.

Motion Capture and EMG Laboratory

The permanent home of the newly installed (July 2004) six camera Vicon 460 motion analysis system is an approximately 16 square meter small volume capture laboratory. The six M2 cameras are attached to the walls along cylindrical bars at varying levels with permanent camera mounts to prevent lab personnel and subjects from tripping on cabling (Figure 1). The Vicon workstation is used to collect signals synchronized using a 64 channel analog to digital conversion board from various analog inputs including: an eight channel NoraxonTM telemetered EMG system, strain gauges, load cells, and BiometricsTM goniometers. The lab also contains a MicroscribeTM 3D digitizer which is used for some Vicon validation work as well as other animal and human cadaveric studies.

Funding to purchase the Vicon system was obtained from Canadian Foundation for Innovation New Opportunities and Ontario Innovation Trust grants.

CURRENT RESEARCH PROJECTS

Development of a Dynamically Moveable Armrest for Heavy Equipment Operators

Past research indicates that current lever operators are at risk of repetitive strain injuries as a consequence of exposure to ergonomically inadequate armrest design. It is the goal of the present research to design a more ergonomically sound armrest that will act to decrease muscle activation in the shoulder complex.

The laboratory set-up includes a mock-up of a typical North American excavator cab, including operator chair and hydraulic-actuation joystick (Figure 2). Data acquisition involves six Vicon M2 cameras capturing a customized upper limb marker set, as well as EMG data used to quantify muscle activation levels. Through the application of BodyBuilder software, upper limb kinematics and corresponding joystick angles are quantified in order to assess the movement patterns of the upper limb-joystick linkage (Figure 3). Once an arm movement pattern has been established, an armrest following a similar motion pattern will be designed using computer aided design and then tested using EMG and Vicon to determine the efficacy of the new design. An initial study was conducted to determine the most appropriate EMG normalization technique(s) to use in quantifying muscle activation patterns for joystick motion. During this study both EMG and Vicon data were collected (Murphy and Oliver, 2005).

[Murphy, T. and Oliver, M. A comparison of task and muscle specific isometric submaximal EMG data normalization techniques for the analysis of muscle loads during hydraulic-actuation joystick controller use. Accepted for presentation and publication at the 20th Congress of the International Society of Biomechanics and the 29th Annual Meeting of the American Society of Biomechanics, Cleveland, Ohio, August, 2005.]

Simulated Whole Body Vibration Studies Using Vicon and a 6 DOF Robotic Platform

Current literature regarding human responses to whole-body vibration (WBV) is limited with respect to understanding such areas as: the degree and patterns of muscle activation, effects of posture, effects of vibration exposure levels and types of exposures used, as well as the location and the number of acceleration measurements made on the body. In order to get a better understanding of the responses to WBV, more detailed studies need to be conducted, where many levels of the spine are measured for vibration transmission in concert with muscle activation measurements. At the University of Guelph, professors and graduate students from Engineering, Human Biology and Nutritional Science, Biophysics, and Psychology are beginning to conduct studies which aim to fill gaps in the literature.

Field data obtained from operating mobile machines fed into a 6 DOF robotic platform located in a laboratory in Human Biology and Nutritional Science at the University of Guelph will enable the researchers to conduct detailed postural measurements and to monitor the activation patterns of selected muscles. The Vicon system enables these researchers to investigate the effects of WBV exposures for frequencies up to 25Hz which is a very important frequency range for this type of investigation. The capabilities of the Vicon system allow for investigations into the transmission of translational and rotational WBV throughout the human spine, the influence of posture and WBV exposure on vertebral disc herniation, and the influence of WBV on spine stability, all of which are currently being explored at the University of Guelph with the Vicon 460 system.

Initial work which validates the use of the Vicon 460 motion capture system for the prediction of acceleration will be presented this summer at the upcoming combined meetings of the International Society of Biomechanics and the American Society of Biomechanics (Jack et al., 2005).

[Jack, R.J., Oliver, M., and Hayward, G. Validation of the Vicon 460 motion capture system for whole-body vibration acceleration determination. Accepted for presentation and publication at the 20th Congress of the International Society of Biomechanics and the 29th Annual Meeting of the American Society of Biomechanics, Cleveland, Ohio, August, 2005.]

Validation of a Hand and Forearm Marker Set

University of Guelph is one of a very few engineering schools in Canada to have permission to conduct studies on-site using human cadaveric specimens. A group of four, senior biological engineering students is designing a positioning jig for a cadaveric hand and forearm to be used in the validation of a hand/forearm Vicon marker set. Vicon will also be used to assess the positioning capabilities of the jig. The data will be collected using six tripods in a secure Biohazard laboratory located in the School of Engineering. So that the jig can be used in a future study, it will be made from CT compatible materials such that it will allow for the acquisition of CT images to be used in the development of a finite element model of the hand and wrist. Both of the above projects represent a cooperative venture between two researchers and a graduate student from the Guelph School of Engineering and a professor from the Division of Anatomy at the University of Toronto.

Development of Inverse Dynamics Upper Limb Models

Very few models of inverse dynamics exist for the upper limb. Models have been developed which quantify the forces and torques exerted by an operator on a hydraulic-actuation joystick over the full range of joystick motion including the hard endpoint which occurs when the operator has moved the joystick to the end of the range of motion. Using the forces and torque predicted from the joystick models, an inverse dynamics model is in the process of being created which quantifies joint reaction forces and moments in order to quantify loading on the wrist, elbow and shoulder. Vicon and BodyBuilder software are being used to quantify the various arm and joystick angles. Electromyography from selected upper limb muscles is being concomitantly monitored using the NoraxonTM telemetered EMG system.

Future Research

Given that the University of Guelph is renowned for interdisciplinary research, cooperation between departments both inside and outside of the university will continue to generate innovative applications for the Vicon system. As an example, a state-of-the art driving simulator obtained with Canadian Foundation for Innovation and Ontario Innovation Trust Funding is in the process of being commissioned. This represents a cooperative venture between researchers in Computer Information Systems and Psychology and has been installed in the engineering building which may open the door for future collaboration and uses for the Vicon system.