For the standard limit of risk assessment, instead of using action limit and maximal permissible limit, as in the previous version, the revised guide uses lifting index (LI) to indicate the potential risk associated with manual lifting tasks
. If LI [less than] 1, it is assumed that more than 99% of all men and 75% of all women have adequate strength to perform the lifting task
with a nominal risk of lower back injury.
This can be illustrated by evaluating a repetitive lifting task
in which the load to be lifted is reduced.
Teamwork can be used to reduce the load on an individual performing a heavy lifting task
and is particularly useful when an object is bulky and mechanical aids are not available.
How the worker performs the task could drastically affect the MAWLs, given that these values might be confounded with moment arm distance from the spine during the lifting task
. Chaffin and Page (1994) found that the MAWL values used as safe limits were higher than recommended biomechanically predicted load limits.
Pressure within the abdomen potentially creates an extension moment on the spine (Bartelink, 1957; Morris, Lucas, and Bresler, 1961), thereby reducing the tension in the back muscles that is required to complete an exertion or lifting task
. Reduced tension in the back muscles also reduces the mechanical loads transmitted to the spine.
This study did account for research on the kinetic effects of lumbosacral support in healthy young men during a specifically controlled lifting task
employing restricted lifting strategies.
The manual lifting task
chosen for analysis is one in which both hands are involved symmetrically and movement occurs almost exclusively in the sagittal plane.
* The task is a lifting or lowering task * Twisting motions occur * Containing handle design is an issue * The task is a lifting task
* The weight lifted is 20 lbs or more * Repetition is not an issue * The task involves repetitive lifting * The task involves awkward (non-standard) positions * The task is performed using one hand
The effects of speed, frequency, and load on measured hand forces for a floor to knuckle lifting task
. Ergonomics, 35, 833-843.
Figure 3 shows the REBA analysis implemented to the device lifting task
by the workers.
Finally, as an application example, the TSA module has been used together with a surface-ElectroMyoGraphic (sEMG) signal acquisition system to implement an assistive device able to support the user during a lifting task
involving his/her forearm, and preliminary results are reported.