Performing tasks in stooped postures or manually handling materials can strain the muscles or sprain the ligaments surrounding the spinal joints in the lower back causing low back pain. Lifting cement bags can require stooping, lifting and carrying. With the reduced weight, using half-weight cement bags reduces the likelihood of strain and injury.
Half-weight cement bags (less than 51 pounds) reduce the amount lifted by mason tenders in each lift.
There have not been independent published studies measuring the effect of half-weight cement bags on reducing musculoskeletal disorders. Regardless, safety and health experts believe that masons will be less likely to develop musculoskeletal disorders if the weight of the bags is reduced from 94 lbs to below 50 lbs by using half-weight cement bags on the jobsite. While handling half-weight cement bags, spinal compression would be less compared to handling standard-weight bags. Thus, the risk of low back pain or back injury would be decreased.
With the use of half-weight cement bags, mason tenders would probably have to lift twice as many bags. However, lifting half-weight cement bags is less fatiguing and should not slow down productivity.
Research in exercise physiology has shown that lifting a weight near a person's maximum lift capability is much more exhausting then lifting even a slightly reduced weight. Exercisers can be expected to perform 12 lift repetitions with a weight that is about 70% of their maximum lift weight. Maximum productivity is likely to be achieved at even lower percentages of maximum lift weight. Productivity gains begin at the point where increase in repetion rate plus reduction in recovery time (both immediate and long term) exceeds time lost to multiple repetitions.
Safety and health experts believe reducing the risk of developing musculoskeletal disorders may lead to increased productivity because: 1) masons can work for longer periods with fewer breaks and less fatigue, and 2) there may be a reduction in lost time injuries.
Dan Anton, PT, PhD, ATC – Eastern Washington University, and Carlos Sanchez-Marin, DDS, MS – University of Iowa