Measuring Back Strain

Most backaches are cumulative, the result of thousands of movements that add up to overuse and strain. Old diagnostic tools made it hard—or expensive—to identify which movements pushed the back beyond its limits. In particular, the continuous assessment of physical exposures was too costly and too time consuming, but with advances in technology “a new age in exposure assessment is developing,” according to Peter Johnson, whose ergonomics lab in the Department of Environmental and Occupational Health Sciences in the UW School of Public Health and Community Medicine specializes in measuring occupation-related physical exposures.

Observation alone, even by a trained ergonomist, cannot capture all events, particularly infrequent isolated events, and direct measurement methods such as muscle electromyography (EMG) and lumbar motion monitors can be somewhat invasive and cost up to $20,000. What has been needed is a simple and relatively inexpensive device to measure a worker’s posture and torso movements over the course of a whole work shift.

Johnson helped developed just such an instrument, the Virtual Corset™. This pager-sized unit, strapped to a worker’s back, arms, or chest, can collect a continuous record of the worker’s posture, which should help researchers better understand work-related musculoskeletal disorders. Johnson collaborated with Vermont-based Microstrain, Inc., to develop the system, which costs less than $1,000 and is small enough to be used in the field. Its two megabytes of memory can collect a day’s data, opening up new avenues for ambulatory exposure assessment. Ambulatory measurement can help researchers better understand the relationship between cumulative postural exposures, load patterns, and musculoskeletal disorders.

Johnson’s team developed the device for the Pacific Northwest Agricultural Safety and Health center as part of a project to create tools to measure physical exposures during agricultural and forestry work. In cooperation with the Field Research and Consultation Group, in the same department, the team wants to assess and compare two tree fruit harvesting methods—traditional ladders and mobile platforms. Mobile platforms are four-wheel, self-guided, all-terrain vehicles with one or two elevated platforms that move slowly down a row of fruit trees and can carry up to six workers.

The Washington tree fruit industry is experimenting with the introduction of mobile platforms as a way to improve harvesting productivity and fruit quality, while reducing ladder-related injuries. The Virtual Corset will allow researchers to track how the mobile platform affects the physical loads on the upper arms, shoulders, and back.

Kathy Hall is communication director for the Department of Environmental and Occupational Health Sciences. A version of this article first appeared in the 2003–2005 Biennial Report of the Department of Environmental and Occupational Health Sciences.