Moments are forces that cause an object to rotate about an axis. Often the word "torque" is used inter-changeably with the word "moment". For example, pulling on a wrench causes the wrench (and nut) to rotate. Likewise holding an object in the hand causes the arm to rotate about the elbow, and the arm to straighten. In a similar fashion, when lifting, the trunk, limbs and object being lifted generate a moment about the spine.

When we lift an object, the moment created at the spine is offset by larger muscle moments acting in the opposite direction. How much larger depends on how fast we accelerate the trunk, limbs and object. The muscle moments create compressive forces on the spine that can be very large in comparison to the weight being lifted.

Moments are important because they are a good indicator of the compressive force or stress generated on the spine during lifting activities. It would seem intuitive that high compressive forces would be associated with high incidence of low back disorders. Indeed, the relationship between moments and injury development has been supported by the work of several researchers.

If we consider data published by Chaffin and Park ³ we see that work situations which result in low compressive forces on the spine have significantly fewer incidents of low back pain than work situations associated with high compressive forces on the spine. The incident rate of the highest compression force category was twice as high as the next category.

Reducing the moments and compressive forces on the spine reduces the incidence of injury. Chaffin & Andersson reported on several studies that "suggest…that re-engineering of jobs to reduce heavy lifting could significantly decrease both the incidence and severity of musculoskeletal disorders. The magnitude of such improvement in the injury and illness statistics is estimated by Westgaard and Aaras and Snook to be a 33% reduction in long-term sick leave."

Reducing the weight lifted, however, is not the only way to reduce the moments experienced by workers. Lifting techniques that emphasize more upright postures, smoother motions, and minimize reaching and twisting will greatly reduce moments, compression forces and the probability of injury.⁵ The LiftTrainer computes the instantaneous moment during lifting taking into account all of the factors which affect the size of the moment including the individual’s body make up, the weight of the object being lifted and the speed and smoothness of the lifting technique.

The LiftTrainer does more than just measure the moments, however. With its bio-feedback and one-on-one coaching protocol, The LiftTrainer can be used to quantify and then modify lifting behavior in a very objective way. This is a major advance that distinguishes The LiftTrainer from current training techniques.

One study of The LiftTrainer in a food distribution center demonstrated that on average, employees could reduce the magnitude of their peak moments by 35% in a single 30 minute training session. Re-testing 10 days later demonstrated that the benefit from the first session was retained to the second session.

As suggested above, this reduction in moments could translate directly into a lower incident rate. The amount of that reduction will depend on many things including the current level of incidents, how frequently the company conducts its training program, the reinforcing nature of its incentive systems and the amount of supervisory reinforcement exerted after training.

Because the ultimate payback can only be measured directly over several years, it is important that before commencing the program, historical data be obtained and objectives established for as many of the following categories of cost as possible:

- Lost time

- Medical expenses

- Absenteeism

- Turn-over

- Product Quality

In this way the program can be structured, analyzed, and actively managed to quantify both the long and short term payback.

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