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In 2014, the American Physical Therapy Association (APTA) began recommending using the term “biophysical agents” to refer to physical agents and modalities. Also, the APTA Choosing Wisely campaign addressed the use of biophysical agents. Their first recommendation states: “Don’t employ passive physical agents except when necessary to facilitate participation in an active treatment program.”1 They further state that “The use of passive physical agents is not harmful to patients except when they communicate to patients that the passive, instead of active, treatment is appropriate.” These statements highlight the need to give careful consideration to the clinical indications for applying biophysical agents. The purpose of using biophysical agents is to alter pain, improve skeletal muscle activity, and promote tissue healing. The physical therapist assistant (PTA) has several adjunctive interventions at his or her disposal, each of which is determined by the physical therapist’s (PT) intervention goals documented in the POC.


The APTA policy statement on direction and supervision of the physical therapist assistant reads, “regardless of the setting in which the service is provided, the determination to utilize physical therapist assistants for selected interventions requires the education, expertise and professional judgment of a physical therapist as described by the Standards of Practice, Guide to Professional Conduct and Code of Ethics.”

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Acoustic streaming The atmospheric pressure at sea level, equal to 1 atmosphere absolute (ATA—760 mm Hg).
Accommodation The increased threshold of excitable tissue when a slowly rising stimulus is used. The quicker the rise time, the less time the nerve has to accommodate to the impulse.
Alternating current (AC) The uninterrupted bidirectional flow of ions or electrons that must change direction at least one time per second.
Amplitude The magnitude of the current. Amplitude controls are often labeled intensity.
Asymmetrical waveform A condition when the amplitude and duration characteristics between the two phases of the biphasic waveform differ in any manner.
Attenuation A measure of the decrease in ultrasound energy by absorption, reflection, or refraction.
Beam nonuniformity ratio (BNR) The ratio between spatial peak intensity and the average spatial intensity of an ultrasound beam.
Burst A series of pulses or brief periods of alternating current delivered consecutively and separated from the next series.
Cavitation Pulsation of gas bubbles in biological tissues in response to the passage of ultrasound.
Direct current The continuous, unidirectional flow of charged particles for at least 1 second.
Duty cycle The percentage of on-time to the total time of electrical current multiplied by 100%.
Endorphins Endogenous opioid-like peptides that reduce the perception of pain by binding to opioid receptors. (Also referred to as opiopeptins.)
Nerve conduction The transmission of an electrical impulse along a nerve fiber.
Piezoelectric effect The property of generating electricity in response to a mechanical force or changing shape in response to an electrical current (as in an ultrasound transducer).
Ramp-down time The time taken ...

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