**4. Biomechanical stress exerted on back when lifting panels as a source of exposure**

Ref. [4] analyzed the four most common techniques (three horizontal and one vertical) used to lift a drywall panel and showed that each lifting technique exerted a minimum of 655 lb. disc compression force on the low back (L5/S1 region) of the

workers whether for a 60 lb., 80 lb. or 100 lb. drywall panel. The same study found that low back loading while lifting a 100 lb. drywall panel exceeds 760 lb., the maximum value recommended by NIOSH in the Work Practices Guide for Manual Lifting. All four lifting techniques also involved risk of perturbation in postural balance [5].

Yuan et. Al., [2] found that the average disc compression force during installation of drywall panels exceeded value of 760 lb. (3400 N) disc compression force, set by NIOSH as the recommended action limit. The highest value of disc compression force in this study was found to be 1721 lb. (7748.8 N) and was sustained for an average of 8.5% of the total 8 hour work shift, or around 41 minutes.
