An Investigation Into the Effects of Frequency-Modulated Transcutaneous Electrical Nerve Stimulation (TENS) on Experimentally-Induced Pressure Pain in Healthy Human Participants
Received 24 November 2008; received in revised form 25 February 2009; accepted 11 March 2009.
Abstract
Frequency-modulated transcutaneous electrical nerve stimulation (TENS) delivers currents that fluctuate between preset boundaries over a fixed period of time. This study compared the effects of constant-frequency TENS and frequency-modulated TENS on blunt pressure pain in healthy human volunteers. Thirty-six participants received constant-frequency TENS (80 pps), frequency-modulated TENS (20 to 100 pps), and placebo (no current) TENS at a strong nonpainful intensity in a randomized cross-over manner. Pain threshold was taken from the forearm using pressure algometry. There were no statistical differences between constant-frequency TENS and frequency-modulated TENS after 20 minutes (OR = 1.54; CI, 0.29, 8.23, P = 1.0). Both constant-frequency TENS and frequency-modulated TENS were superior to placebo TENS (OR = 59.5, P < .001 and OR = 38.5, P < .001, respectively). Frequency-modulated TENS does not influence hypoalgesia to any greater extent than constant-frequency TENS when currents generate a strong nonpainful paraesthesia at the site of pain. The finding that frequency-modulated TENS and constant-frequency TENS were superior to placebo TENS provides further evidence that a strong yet nonpainful TENS intensity is a prerequisite for hypoalgesia.
Perspective
This study provides evidence that TENS, delivered at a strong nonpainful intensity, increases pain threshold to pressure algometry in healthy participants over and above that seen with placebo (no current) TENS. Frequency-modulated TENS does not increase hypoalgesia to any appreciable extent to that seen with constant-frequency TENS.
Faculty of Health, Leeds Metropolitan University, and Leeds Pallium Research Group, Leeds, United Kingdom
Address reprint requests to Prof Mark I. Johnson, Faculty of Health, Leeds Metropolitan University, Civic Quarter, Leeds LS1 3HE, UK.
Supported by the Faculty of Health at Leeds Metropolitan University.
Potential conflicts of interest: MIJ occasionally facilitates TENS study days for health care practitioners that are sponsored by TENS companies and occasionally undertakes consultancy activities for TENS companies such as writing critical review documents.
ABSTRACT