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Unformatted text preview: REHABILITATION AND MUSCLE TESTING W.K. D URFEE P.A. I AIZZO University of Minnesota Minneapolis, Minnesota INTRODUCTION There is a growing need in clinical medicine to validate the quantitative outcomes of an applied therapy. In addition, the measurement of muscle function is an essential com- ponent of many neurological and physical exams. Muscle strength is correlated to function, work productivity, and general quality of life. Muscle function becomes compro- mised: (1) as we age, (2) when associated with a skeletal impairment, and/or (3) as a secondary consequence of many disease processes. Therefore, assessing muscle func- tion is an important clinical skill that is routinely used by neurologists, orthopedists, general practitioners, anesthe- siologists, and occupational and physical therapists. Eva- luation of muscle strength is used for differential diagnosis, to determine if an impairment or disability is present, to decide if a patient qualifies for treatment, and to track the effectiveness of a treatment. In a research setting, the measurement of muscle func- tion is used to further our understanding of the normal and potentially impaired neuromuscular system in human and/ or animal experiments. In such research, muscle function can be assessed at the intact individual level ( In vivo ), in chronic and acute animal models ( In situ ), within isolated muscle strips or even within single myofibrils ( In vitro ), and/or at the molecularbiochemical level. In this article, only whole muscle testing ( In vivo and In situ ) is discussed. There are several components of muscle performance. The American Physical Therapy Association uses various definitions to explain the characteristics of muscle function (1). Muscle performance is the capacity of a muscle to do work. Muscle strength is the force exerted by a muscle or group of muscles to overcome a resistance in one maximal effort. Instantaneous muscle power is the mechanical power produced by the muscle (muscle force times muscle velocity). Muscle endurance is the ability to contract a muscle repeatedly over time. Of these performance indi- cators, muscle strength is the one most commonly mea- sured when assessing the muscle function of intact humans. In assessing muscle strength, the conditions under which the muscle contracts must be specified so that the muscle test data can be interpreted properly. The following conditions are relevant: Isometric contraction: the muscle contracts while at a fixed length; Isotonic contraction: the muscle contracts while working against a fixed load, for example, a hanging weight; Isokinetic contraction: the muscle contracts while moving at a constant velocity; gene- rally, isokinetic contractions are only possible with the limb strapped into a special machine that imposes the constant velocity condition; Eccentric contraction: the mus- cle contracts against a load that is greater than the force produced by the muscle so that the muscle lengthens while contracting; and Concentric contraction: the muscle con-...
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