Case Study

Repetitive Stress: Improved EWAS Takes Aim at Worker Injuries

Published: November 3, 2007

New technology is helping position an old injury-prevention research tool developed for the poultry industry at the cutting edge of in situ biomechanical monitoring.

Nearly 10 years ago, the Georgia Tech Research Institute (GTRI), in association with Georgia Tech’s School of Applied Physiology, created an Ergonomic Work Assessment System (EWAS) to track the positioning and arm movements of workers as they deboned poultry. The project, part of the Agricultural Technology Research Program, was intended to identify and then avoid the factors leading to repetitive stress injuries.

The improved EWAS developed this year, with support from the poultry industry, provides a more accurate and detailed assessment by taking advantage of technology that wasn’t available in the ’90s, namely position-tracking technology typically used to create computer animation.

“It measures arm position in three dimensions,” says GTRI Research Engineer Jonathan Holmes. “You strap the system onto your arm and move your arm around, and you can watch it moving on a screen beside you.”

The EWAS arm strap contains sensors that measure forearm and wrist orientation as well as upper arm and shoulder activity. Separate modules on the back provide a global reference for the position sensors. Muscle response is monitored through electromyography, a technique for determining the level of electrical activity in muscles. Torque and grip force on the knife are calculated through special sensors by a method developed by Liberty Mutual Research Institute for Safety, which is teaming up with the Georgia Tech design team for that part of the system development.

As a worker wearing the arm strap cuts poultry, the aggregate data of the back and arm position, muscle response, grip force, and torque is transmitted wirelessly to a laptop computer allowing researchers to study relationships among force, exertion, posture, and repetition. The information can be used both to boost work efficiency on the factory floor and to correct inefficient movements.

More importantly, EWAS can help researchers assess the dynamics of muscle group interactions in job rotation schemes designed to reduce disorders such as carpal tunnel syndrome. This cumulative trauma results when tendons in the wrist become inflamed due to repetitive activity. Symptoms include burning, tingling, or numbness in the fingers; discomfort in the wrist, forearm, or upper arm; and difficulty in gripping.

“By monitoring these forces and positions, you can put numbers to physical motions and get a good idea of what is good and what is bad,” says Holmes. “You can determine if they are using certain muscles too much, or if they are bending their wrist too far – you can draw a lot of conclusions from that data that will eventually help us determine which risk factors appear to impact injuries.”

In many industries, workers who are required to perform repetitive tasks at a fast pace may be at risk for injury unless they take periodic breaks or find ways to reduce the stress and repetition of the job. EWAS can help identify when those breaks need to be scheduled and improve the current job rotations. EWAS analysis might reveal that a different knife handle shape or blade reduces wrist movement or the force required to perform a task. The position or height required to perform a certain job might be changed, or workers might be rotated more often from a difficult procedure.

Although being developed and field tested for the poultry industry, EWAS is applicable to a variety of tasks ranging from keyboard operation to heavy manual work. The system’s portability and small size means testing can be done in the workplace itself, which yields more realistic and accurate information than testing in a lab setting.

The group is also investigating the development of studies to monitor the back. They plan to pursue development of training or physical devices that can reduce back injuries resulting from back instability conditions.