The Limitations of Strength Duration Curve as Electrodiagnostic Tool for Muscle and Peripheral Nerve in Physical Therapy
Abstract
The strength duration curve or S-D curve is widely used in physical therapy for diagnosis and treatment of muscle and peripheral nerve injury patients. Since it costs less than the nerve conduction velocity test and other electromyography procedures. The S-D curve is a logarithm plot of the threshold current versus pulse duration required to stimulate excitable tissue which represent the integrity of the muscle and nerve complex. Although the neurophysiological basis for the S-D curve has been established and published long ago, there are many factors that affect the reliability and validity of chronaxie measurement such as stimulus waveform, electrode characteristics, stimulator output impedance, tissue inhomogeneity and temperature. In practice, physical therapist should obtain with a cathode rectangular pulse delivered from a constant-current stimulator and also test the given nerve supply to various muscles for the most reliable S-D curve.
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