The principles behind ergonomics are also described in this chapter. Biomechanics refers to the effect of physics on the human body; gravity, resistances, and external loads, in addition to others, have effects on our bodies on the job that must be quantified and studied in order to perform proper job analysis. For example, the force of gravity on our body is normally opposed by posture; efforts must be made on the job to provide ways to support proper posture that counteracts downward forces acting on the spine due to gravity. The biomechanics of holding are also explored, as holding and carrying objects are shown to be very common work activities - creating objects of the right size and shape can make them easier to grip and hold in a way that diminishes WRMSDs; training and evaluation of proper holding positions of a worker is also emphasized. The influence of dynamic motion is also explored in this chapter - static muscle work and dynamic work involve sustained contractions and repeated brief contractions of muscles during the process of working, respectively. Static work is shown to be directly tied to musculoskeletal disorders, while dynamic work simply leads to whole-body fatigue, making a worker less productive in the long run.
When conducting ergonomic work design, jobs must be designed to have physical dimensions that allow at least 90 percent of a workforce to comfortably do every job needed of them, without excessive repetition or pacing. This is the overall goal of job design and analysis, as ergonomic concerns are evaluated to the point where a job environment and relevant tasks are made possible for most workers. Recognizing signs of fatigue and designing a workplace to minimize fatigue however possible is the key to properly healthy and productive workers. Efforts must not just be made to improve the overall acceptability of the environment; the workforce must also be made physically fit. Incorporating exercise programs and fitness initiatives and incentives for workers is also said to increase their total body load; these include stretching exercises and other aerobic exercise meant to stretch muscles and increase bloodflow. Job rotation is also offered as a solution to whole-body fatigue in workers.
This chapter provides a wonderful blueprint for exactly how a job should be evaluated by ergonomic standards. In essence, the author delineates exactly what it is about a job that can lead to damage in the body and productivity of a worker, citing the biomechanics of holding, gripping and posture to show the ways in which a workplace can inadvertently harm its workers. By going through a process of classifying specific types of injuries and stresses on particular sections of the human body, the priorities of management toward finding solutions to the most potentially damaging activities can be accommodated.
The differentiation between static and dynamic muscle work demonstrates the much greater threat that static muscle work has on back disorders; it seems as though these types of contractions test the functional strength of multiple extremities and muscles in the hands and legs, adding compressive force and leading directly to WRMSDs. One of the most helpful parts of the chapter are the many charts and graphs used to illustrate metrics such as Maximum Voluntary Contraction (MVC) and the use of different kinds of force on various leg lifts. These measures help to quantify just how damaging poorly-performed physical actions to perform work-related tasks can be, and show the incredible importance of proper posture and angle when performing these tasks.
The suggestions regarding how to address these work-related stressors are also incredibly helpful; noting the importance and prevalence of exercise and fitness, as well as job rotation, helps managers to craft their own ergonomics programs that will help their workers become more productive over time. By noting the types and intensities of muscle contractions for most major muscle movements, and how they affect the worker individually, allows for the reader to understand more completely the preciseness with which proper posture and job environment initiatives must be studied and addressed. These create concrete design goals for ergonomic programs in a workplace that will deal with the problems of scheduling rest times, rotations, and arranging work environments to be more comfortable for workers.
Eastman-Kodak Company. (2003). Kodak's Ergonomic Design for People at Work.