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An impulse-momentum exercise system was instrumented for collection of kinematic and kinetic data during shoulder exercise. The objective of this study was to quantify the dynamics of an exercise system that utilizes a weighted shuttle (22.2 N) traveling on a rail system and evaluate its efficacy as an exercise and rehabilitative tool. Two healthy adults (mean age. 30.0 years) were tested utilizing 2 protocols. The first protocol required the subject to maintain tension in the system while externally rotating the upper arm from neutral to 90° relative to the shoulder and then internally rotating back to the initial position. In me second protocol, the range of motion was similar, but each subject was instructed to carry out the exercise as rapidly as possible without regard to the tension in the rope, thus creating an impulsive load. Average peak loads up to 87.9 and 137.0 N were recorded using the first and second protocols. respectively. Average maximum loads using the second protocol were approximately 50 N greater than those using the first protocol (p < .05). Representative calculations demonstrated that less mechanical work was performed during the first protocol (−3.8 to −45.9%). Qualitatively the shuttle acceleration curves appear dramatically different, although similar average peak accelerations are achieved during use (4.12 vs. 3.47 m/s2, protocol I vs. protocol 2, respectively).
T.C. Phillips, J.F. Orwin, L.T. Brody, R.P. McCabe, and R. Vanderby Jr. are with the Division of Orthopedic Surgery at the University of Wisconsin, Madison, WI 53706. S.S. Kohles is with the Departments of Biomedical and Mechanical Engineering at Worcester Polytechnic Institute, Worcester, MA 01609-2280.