Standard Interpretations - (Archived) Table of Contents|
April 14, 1992
MEMORANDUM FOR: REGIONAL ADMINISTRATORS ATTENTION: DEPUTY REGIONAL ADMINISTRATOR FROM: THOMAS J. SHEPICH Director Directorate of Technical Support Subject: Evaluation and Recommendations for the Peak Performance System.As you requested at the New York Regional Administrators meeting, the following information concerns the Peak Performance Motion Analysis System now available within the Office of Ergonomic Support. Please see that your ergonomic specialists receive this information.
Peak Performance Motion Analysis System
The Peak Performance motion analysis system generates computer graphic representation of human movement and its kinematic elements (i.e., displacement, velocity, acceleration) from video tape. The system can, if used properly, provide detailed information regarding the stresses placed on the musculoskeletal system via dynamic biomechanical modeling. Biomechanics uses the laws of physics and engineering concepts to describe motion undergone by the various body segments and the forces acting on these body segments during normal daily activities. This information gives the analyst insight into what specific changes should be made to a workstation or task methods that would reduce the ergonomic risk factors placed on the worker. With respect to dynamic manual activities, such information cannot be acquired solely through the use of the NIOSH Lift Guide. The system does, however, have limitations that must be considered if it is used in the context of performing an ergonomic evaluation.
By using the Peak Performance system, manual materials handling activities such as lifting, lowering, pushing, and pulling, can be analyzed directly from video tape. Utilizing computer programming to create the appropriate biomechanical model (a series of mathematical equations) the following ergonomic stressors can be calculated with regard to their magnitude and changes across the time required to perform the activity.
* The compressive force placed on the spinal column of the low back (L5/S1 disc).
* The anterior/posterior shear force placed on the spinal column of the low back (L5/S1 disc).
* The moments (torques) placed on the elbow, shoulder, and hip joints.
* The percentage of maximum voluntary torque generated at the elbow, shoulder, and hip joints for the below average, average, and strongest male or female workers.
* The severity and relative duration (percentage of total task time) of back flexion, shoulder flexion/abduction, and wrist deviation.This data can be acquired from video tape taken of workers performing jobs in their actual occupational settings, under normal working conditions, without disrupting the ongoing operations of the business.
It should be noted that several limitations must be taken into consideration when using the Peak Performance system to generate occupational biomechanical data for ergonomic analysis:
* The calculated ergonomic stressors are estimates based on assumptions regarding weight distribution, the force on the hands, the location of joint centers, and muscle activation/orientation. The more assumptions that are required to perform a particular analysis, the greater the potential error in the accuracy of the calculations.
* Because the system relies on two-dimensional analysis, the tasks evaluated must be symmetric (the right and left sides of the worker must be mirror images of one another). The system becomes ineffective as a tool of analysis when the subject performs asymmetric activities which are more realistic and more frequently found in occupational settings.
* To use the system properly, the CSHO must adhere to the following guidelines: (1) The camera must be stationary at all times; (2) The subject must be video taped at an angle that captures their entire upper body either in profile, a full frontal view, or a full posterior view; (3) an object of known length must be in the same field of view as the worker; (4) A stationary point must be in the field of view at all times; (5) The weight and dimensions of the load must be recorded; (6) The weight and gender of the operator must be recorded. The nature of the work and or work environment may prevent the camera operator from following these guidelines.
* The biomechanical modeling utilized in this system is adequate for simple handling tasks such as lifting, lowering, pushing, and pulling. However, for faster and more biomechanically complex tasks (such as typing), the system would prove ineffective as a tool of ergonomic analysis.RECOMMENDATIONS
To achieve the most utility from of the Peak Performance system, compliance Safety and Health Officers should be provided with the guidelines included in this memo regarding how to video tape occupational activities. In addition, if this system is to be used in the context of enforcement, the biomechanical data generated should be considered only as a single piece of evidence supplemented and supported by the following criteria where possible:
* Physiological Evidence - the estimated metabolic energy expenditure required on the part of the worker to perform the task. These estimates should be compared to recommended guidelines set forth by the National Institute of Occupational Safety and Health as well as the American Industrial Hygiene Association.
* Psychophysical Evidence - the subjective estimate of the maximum weight or force the worker feels he or she can safely handle given the type of exertion, the frequency of the exertion, and the physical parameters of the job. This evaluation is accomplished by comparing the actual weights handled by the worker to data tables containing the maximum weights acceptable to industrial populations. "Acceptable" in this context, is defined as the maximum load a worker feels they can handle without straining, becoming unusually tired, weakened, overheated, or out of breath.
* Epidemiological Evidence - the evidence found in the OSHA 200 and 101 forms of an employer that documents the prevalence of musculoskeletal injuries and illnesses in the workplace and directly associates these injuries and illnesses to the task which is being evaluated. The job turn over rate and employee interviews should be taken into consideration as well.
The ultimate potential of the Peak Performance system to assist in the mission and function of the Office of Ergonomic Support has not, as of yet, been fully realized. This goal will only be achieved with more practical application of the device in order to discover more of it's benefits and limitations in the occupational setting. Thus, when the field believes that this system may assist in the issuance of citations, it is essential that the CSHO call the Office of Ergonomic support to discuss the specific task to be modeled before submitting videotapes. The contact point for this is Brian Carnahan at FTS 523-0478.
cc: Leo Carey
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