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Motion Analysis

We are developing custom software to analyse motion data collected from two different systems; one is a low-cost system called V-Scope (Litek Advanced Systems, Ltd.), the other is made by Qualysis.

The V-Scope is a hybrid infrared/ultrasound system; three 'towers' (placed in a known location) send out infrared to the markers placed on a subject. Each marker responds to the infrared with a pulse of ultrasound. Each tower receives this, and can calculate the distance to the marker. Using three towers allows for triangulation to calculate the 3-D positions of the markers. Up to eight markers may be used with the V-Scope. However, it is line-of-sight based, thus making it impossible to examine complex motions.

While the motion data acquisition hardware was bought 'off the shelf,' it does not come with analysis software. We have written our own programs (Windows-based) to perform all analysis; you can read an abstract that was presented at the 1995 Combined Orthopedic Research Societies Meetings which describes some of our preliminary work. Currently we are in the process of improving this software and migrating it to MATLAB (The MathWorks, Inc.)

The system is mounted on a cart, allowing us to move it around to different parts of the Institute. We have been using it mainly for gait analysis, having subjects walk on a treadmill and collecting multiple gait cycles (40 seconds to a minute), which were then overlaid and averaged, thus providing an 'average' gait cycle for that session of walking (and eliminating a lot of noise). To monitor more complex or faster motion, we need a more sophisticated system.

After much investigation and deliberation, we have a 6-camera MacReflex system from Qualisys . The cameras sample at 60 Hz. and are infra-red, with each camera providing its own illumination for the scene; reflective markers are placed on the subject. The system allows tracking of up to 50 markers. We have had good success monitoring several different kinds of motion with the system; thus far. most of our work has involved different types of hopping and jumping. We intend to use it to examine balance and to develop a test for proprioception. It also uses the Biopac Systems MP100 to interface to EMG or other electrical signals. We use the Qualisys software to acquire the data and construct the 3-D representation from the data acquired by the cameras; for analysis we import the data into MATLAB. We are most interested in examining repetitive motions (e.g., gait, hopping) where we can overlay multiple trials in order to 'average out' the effects of, say, one bad step.

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EMG (and other things electronic)

We use a Noraxon Telemyo EMG system, which is capable of monitoring up to 8 channels of EMG (surface or fine-wire) simultaneously. It is a telemetered system, giving the athlete freedom to move while being tested. Additionally, we use the Telemyo unit to sample input from:

• force transducers
• electrogoniometers
• accelerometers
• foot switches (can be used to sync with motion analysis systems).
• dynamometers such as Cybex or Biodex

By combining measurements of muscle activity with data such as torque and joint position/angle, we can get a much clearer picture of what is really happening.

Rounding out our set of biomechanics tools is a force plate, specifically the Kistler 9286AA force plate. This is a portable force plate with an integrated amplifier, which interfaces to the Biopac MP100, described above. When using this, we can measure force (vertical and shear) and moments, as well as center of pressure, along with eight channels of EMG. Combined with the MacReflex motion analysis system, we have the capability of performing complete kinetic and kinematic analysis on a wide range of motion.

Recently, we purchased the scientific analysis software package DATAPAC 2000 from Run Techologies (developing our own software to do all our analysis was proving to take too long). In conjunction with the Noraxon hardware and a laptop, we now have a fully portable acquisition and analysis system.

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Metabolic Testing

NISMAT's research facility is also equipped with a metabolic cart (which is in turn connected to an EKG), allowing simultaneous measurements of oxygen consumption and heart rate. Determination of maximum oxygen consumption has long been a standard measure of cardiovascular fitness. Additionally, anaerobic threshold (ventilatory threshold) measurement is routinely done with the same equipment, so that exercise prescription can be made tailored to the individual's own fitness level. These tests provide the basis for much of our research. Using a lactate analyzer, we can measure lactate in the blood immediately following or even during a bout of exercise. Finally, when coupled to motion analysis we are able to examine the economy of walking and examine the impact of abnormal gait on economy. In much the same way as some cars are economical with respect to gas consumption, individuals' motion economy determines how hard their cardiovascular system must work.

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Flexibility Testing

Flexibility testing examines the biomechanic properties of human skeletal muscle. At NISMAT, we perform flexibility testing in vivo using the custom device shown. While making simultaneous electrogoniometric, force, and EMG measurements, a subject's leg is raised to the point of maximum tolerable stretch. These data are then analyzed using custom software to examine acute and chronic changes in stiffness.