ORIGINAL ARTICLE Effects of Carrier Frequency of Interferential Current on Pressure Pain Threshold and Sensory Comfort in Humans Roberta Ceila Venancio, PT, MSc, a Stella Pelegrini, PT, MSc, a Daiane Queiroz Gomes, PT, a Eduardo Yoshio Nakano, PhD, b Richard Eloin Liebano, PT, PhD a From the a Physical Therapy Department, University of the City of Sa˜o Paulo (UNICID), Sa˜o Paulo; and b the Department of Statistics, University of Brası´lia (UnB), Brası´lia, Brazil. Abstract Objective: To assess the effect of carrier frequency of interferential current (IFC) on pressure pain threshold (PPT) and sensory comfort in healthy subjects. Design: A double-blind randomized trial. Setting: University research laboratory. Participants: Healthy subjects (NZ150). Interventions: Application of the IFC for 20 minutes and measures of PPT collected in the regions of the nondominant hand and forearm. Main Outcomes Measures: We measured PPT and comfort at frequencies of 1kHz, 2kHz, 4kHz, 8kHz, and 10kHz. Results: There was a significant increase in PPT in the 1-kHz group when compared with the 8-kHz and 10-kHz groups. There was a greater discomfort in the 1-kHz and 2-kHz groups. Conclusions: IFC with a carrier frequency of 1kHz promotes a higher hypoalgesic response during and after stimulation than IFC with carrier frequencies of 8kHz and 10kHz. Carrier frequencies of 1kHz and 2kHz are perceived as more uncomfortable than carrier frequencies of 4kHz, 8kHz, and 10kHz. Archives of Physical Medicine and Rehabilitation 2013;94:95-102 ª 2013 by the American Congress of Rehabilitation Medicine Interferential current (IFC) is a medium-frequency electrical current amplitude-modulated in low frequency, generated by the superimposition of 2 currents of medium-frequency slightly out of phase. 1,2 It is a type of electrotherapy that theoretically reaches deep tissues by means of the use of a carrier frequency in the kilohertz range with the aim of overcoming the electrical impedance offered by the skin. 1,3-8 Although this claim has been widely reported in the literature, it has been recently questioned because skin impedance to low-frequency pulsed currents depends on the phase duration, not the pulse frequency. 9-11 Moreover, some studies have failed to show differences in hypoalgesic response between IFC and low-frequency pulsed currents delivered by transcutaneous electrical nerve stimulation devices. 5,12,13 Never- theless, IFC is one of the most common types of electrical current used in Canada 14 and England. 15 Medium-frequency alternating currents (MFACs) are defined as currents in the frequency range of 1 to 10kHz and are often used in rehabilitation. IFC is a simple and noninvasive treatment often used to induce analgesia, 16 elicit muscle contractions, 17 and reduce edema. 2,18 Although some mechanisms of pain control with IFC have been proposed in the literature, the exact mechanism of action for this effect is still unknown. 5,19-21 The most popular theory used to explain IFC analgesia is the gate control theory of pain. 19,20 Modern IFC equipment permits that the carrier frequency of the current can be adjusted in accordance with the therapeutic goal. It is claimed that the frequency of 2kHz is more appropriate to elicit muscle contractions and strengthening, whereas the frequency of 4kHz is ideal to generate hypoalgesia. 18,22 However, this information usually comes from electrotherapy textbooks and equipment manuals and not as results of scientific studies. Moreover, there are conflicts in the literature about the ideal Presented in part to the World Confederation for Physical Therapy Congress, June 20e23, 2011, Amsterdam, The Netherlands. Supported by the National Council for Scientific and Technological Development (CNPq) (process no: 471382/2010-8). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Clinical Trial Registration No.: ACTRN12610001015033. 0003-9993/13/$36 - see front matter ª 2013 by the American Congress of Rehabilitation Medicine http://dx.doi.org/10.1016/j.apmr.2012.08.204 Archives of Physical Medicine and Rehabilitation journal homepage: www.archives-pmr.org Archives of Physical Medicine and Rehabilitation 2013;94:95-102