A Discussion of Job Content Validation and Isokinetic Technology. Gary Soderberg, Ph.D., PT, FAPTA i March 2006

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1 A Discussion of Job Content Validation and Isokinetic Technology Gary Soderberg, Ph.D., PT, FAPTA i March 2006 Testing of human function is difficult because of the great capability associated with our movements. Numerous tests have been developed for the assessment of our physical abilities with the intent of studying function from the microscopic to macroscopic level. What each of these tests attempts to do is to assure that the test is appropriate and meaningful, that is, does the test truly provide a result that is meaningful and applicable. These concepts should be used when attempting to test human performance relative to the work environment. While numerous tests have been developed and used, questions have been raised as to which test protocol is the most valid in determining a person s physical capability to perform in the work place. Content Validation is the primary validation of any test form that initially speaks to its capability to measure human function in the workplace. Content validation satisfies the question of whether the form of measuring human ability (isokinetics in this case) is reflective of and associated with the content requirements of the job. The first task in this process is to conduct a comprehensive ergonomic assessment of each job classification s tasks or work behaviors that are important elements of job performance. Physical work demands can be reduced to four general classifications: push, pull, lift and carry. Each job must be subcategorized and measured, preferably in terms of torque (Newton-meters (Nm) =.7376 foot-pounds), range of motion, frequency and duration of tasks. Isokinetics does not require the measurement of human function to match the performance of the human movement being tested. Isokinetic testing satisfies this match in that as joint torques are required to perform the various tasks associated with the work environment, the isokinetic testing measures the capacity of the joints to exert the torques required to perform these tasks. A foremost advantage of isokinetic testing is the capability to determine maximum torque generating capability under a broad spectrum of movement velocities. The test velocity can be selected based on the requirements of a specific job or selected movement of interest, thus matching the job to be performed. While most testing request maximum effort, the dynamometer only resists the magnitude of the effort. Thus, this system has been known to produce the perfectly accommodating resistance so that in the instance where the subject reduces the magnitude of their effort the machine would only apply an accommodating magnitude or torque. Test procedures typically isolate one joint for testing, the exception being the spine, where motion at multiple motion segments is required for the trunk flexion and extension testing. Some would consider the testing of upper extremity joints and the knee in the non-weight bearing position as a limitation of isokinetic testing. However, all forms of testing of human joints have limitations. Further, there is general acceptance among researchers, health care

2 2 practitioners, and ergonomists that results of the isolated joint tests are valid and applicable to the work environment. For example, the job task analysis (JTA) of a landscape laborer (Appendix) accurately reflects the essential physical job demands for this job classification. The employee is required to exert between 51 and 100 pounds of force frequently (up to 66% of the workday) in lifting, carrying, pushing and pulling involving sandbags, plants, shoveling, etc. While not frequent, the employee is also occasionally required (up to one-third of a work-day) to exert over 100 pounds of force in moving materials. The actual joints involved in these tasks principally involve general leg and trunk control necessary to provide body stability. Specifically, scapular, shoulder and elbow torques are required, as well as is stability to hold the wrist so the hand can be used to grip. The moving of materials would primarily be from the front of the body towards either side, such as in digging a hole in the ground. The required joint torques would be the greatest at the scapula and shoulder complex and at the elbow. A job would necessitate that the required torque be generated to complete each specific component of the specific task associated with this job. Therefore, an applicant for the landscape laborer position will have to have the requisite strength (ability to generate the minimum torque), by muscle group, required of each task along the necessary range of motion throughout the workday to execute these job demands as a condition of employment. At a minimum, a young male employee should be able to generate approximately 50 Nm of torque at the shoulder when shoveling dirt in a forward direction at a normal, or usual rate of shovel movement. Elbow torques would be about 60 Nm to hold the joint in a fixed 90 degree position. Trunk and knee joints would have to be stabilized and held in a constant position as well. Specific torques necessary to perform tasks is highly dependent on the angle at which each of these joints is held during task performance. Isokinetic testing objectively and accurately determines, independently, the torque of each joint representing approximately 83% of the muscle groups (knees, shoulders, trunk) specifically engaged in materials handling or movement (pushing, pulling, lifting and carrying) that the person being tested can generate. The torque generated from these muscle groups should at least equal, and preferable exceed, the torque required to perform the physically demanding tasks specific to the job. Simply stated, isokinetics measures the degree to which candidates have identifiable ability to exert joint torques which can then be compared to the minimum torques required of a job (content matching) that has been determined to be important in successful performance on the job. Assuring that employees can generate adequate torques at the joints performing the required motion avoids the likelihood that abnormal mechanics and biomechanics are used, avoiding the potential for injury, particularly if repetitive motions are being used. Testing of several joints (shoulder, knee and trunk) provides sufficient information to indicate whether the candidate is able to perform the tasks required for a specific job. References Abrnethy PJ, Jurimae J. Cross-sectional and longitudinal uses of isoinertial, isometric, and isokinetic dynamometry. Med Sci Sports Exerc 1996; 28:

3 3 Anderson MA, Gieck JH, Perrin D, et al. The relationships among isometric, isotonic and isokinetic concentric and eccentric quadriceps and hamstring force and three components of athletic performance. J Orthop Sport Phys Ther 1991;14: Barber SD, Noyes FR, Mangine RE, et al. Quantitative assessment of functional limitations in normal and anterior cruciate ligament deficient knees. Clin Orthop 1990; Cahalan TD, Johnson ME, Chao EYS. Shoulder strength analysis using the Cybex II isokinetic dynamometer. Davies GJ. A Compendium of Isokinetics in Clinical Usage. S and S Publishers, Onalaska WI, Delitto A, Irrgang JJ, Harner CD: Relationship of isokinetic quadriceps peak torque and work to one legged hop and vertical jump in ACL reconstructed knees. Phys Ther 1993;73:S85 (abstract). Dolny DG, Collins MG, Wilson T, et al. Validity of lower extremity strength and power utilizing a new closed chain dynamometer. Med Sci Sports Exer; 2001; 33: Dvir Z, Keating J. Reproducibility and validity of a new test protocol for measuring isokinetic trunk extension strength. Clin Biomech 2001; 16: Gaines JM, Talbot LA. Isokinetic strength testing in research and practice. Biol Res Nurs. 1999;1: Griffin JW, Tooms RE, VanderZwaag RC, et al. Eccentric muscle performane of elbow and knee muscle groups in untrained men and women. Med Sci Sports Exerc. 1993;25: Hill AV. First and Last Experiments in Muscle Mechanics. University Press, Cambridge, Karlsson J, Lundin O, Lossing IW, et al. Partial rupture of the patellar ligament-results after operative treatment. Am J Sports Med 1991;19: Kannus P. Isokinetic evaluation of muscular performance: implications for muscle testing and rehabilitation. Int J. Sports Med 1994;15 Suppl 1:S Kroemer K. An isoinertial technique to assess individual lifting capacity. Hum Factors 1983;25: Lechner DE, Jackson JR, Roth DL, et al. Reliability and validity of a newly developed test of physical work performance. J Occup Med 1994;36: Murphy AJ, Wilson GJ. The assessment of human dynamic muscular function: a comparison of isoinertial and isokinetic tests. J Sports Med Phys Fitness 1996;36: Newton M, Waddell G. Trunk strength testing with iso-machines. Part 1. Review of a decade of scientific evidence. Spine 1993;18:

4 4 Noyes FR, Barber SD, Mangine RE. Abnormal lower limb symmetry determined by function hop test after anterior cruciate ligament rupture. Am J Sports Med 1991;19: Reizebos ML, Paterson DH, Hall CR et al. Relationship of selected variables to performance in women s basketball. Can J. Appl Sport Sci 1983;8: Sachs RA, Daniel DM, Stone ML, et al. Patellofemoral problems after anterior cruciate ligament reconstruction. Am J Sports Med 1989;17: Soderberg GL. Kinesiology: Applications to Pathological Motion. Williams and Wilkins, Baltimore, Swarup M, Irrgang JJ, Lephart S. Relationship of isokinetic quadriceps peak torque and work to one legged hop vertical jump. Phys Ther 1992;72:S88 (abstract). Tegner Y, Lysholm J, Lysholm M, et al. A performance test to monitor rehabilitation and evaluate anterior cruciate ligament injuries. Am J Sports Med 1986;14: Westblad P, Svedenhag J, Rolf C. The validity of isokinetic knee extensor endurance measurement with reference to treadmill running capacities. Int J Sports Med 1996;17: Wilk K, Romaniello WT, Soscia SM, et al. The relationship between subjective knee scores, isokinetic testing, and functional testing the ACL-Reconstructed knee. J Ortho Sports Phys Ther 1994;20: Wiklander J, Lysholm J. Simple tests for surveying muscle strength and muscle stiffness in sportsmen. Int J Sports Med 1987;8:50-54.

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7 7 i Dr. Soderberg is recently retired as Director of Physical Therapy Research, and Professor of Physical Therapy, Missouri State University, Springfield, MO, and Chief Scientist Emeritus of Cost Reduction Technologies, LLC.