Manual materials handling activities can cause high stresses on the musculoskeletal system. The dynamic nature of these tasks, such as lifting, preclude the use of the traditional concepts of human strength: isometric and isotonic contractions. Instead the novel development isokinetic muscle contraction has expanded the study of dynamic muscle strength. Isokinetic contractions occur against a lever arm which controls the velocity of movement and offers resistance proportional to the muscle dynamic tension developing capacity at every point in the range of motion. Thus the maximum demand can be placed on the muscle at any time, and, by selecting appropriate velocities, muscle power can be maximized. The proposal is to quantify the dynamic strength of those muscle groups that relate to MMH activities in a four-phase research plan. (1) Investigate in detail the dynamic properties of muscle strength for those muscle groups used most often in manual material handling activities. (2) Compare the measurement of these properties on th stationary Cybex isokinetic dynamometer with those measured on the portable Mini-Gym isokinetic dynamometer through correlation analysis. (3) Devise dynamic strength tests that would be representative of the actions and muscle grops for manual materials handling activities and that could be easily implemented for pre-employment strength testing. (4) Compare the dynamic strength tests with existing static and psychophysical tests and with predictions from dynamic models.
