Increasing Intensity of TENS Prevents Analgesic Tolerance in Rats

  • Karina L. Sato
    Physical Therapy and Rehabilitation Science, Carver College of Medicine, The University of Iowa, Iowa City, Iowa
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  • Luciana S. Sanada
    Physical Therapy and Rehabilitation Science, Carver College of Medicine, The University of Iowa, Iowa City, Iowa

    Department of Neuroscience and Behavioral Science, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
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  • Barbara A. Rakel
    Department of Nursing, Carver College of Medicine, The University of Iowa, Iowa City, Iowa
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  • Kathleen A. Sluka
    Address reprint requests to Kathleen A. Sluka, PT, PhD, Professor, Graduate Program in Physical Therapy and Rehabilitation Science, 1-252 Medical Education Building, University of Iowa, Iowa City, IA 52242.
    Physical Therapy and Rehabilitation Science, Carver College of Medicine, The University of Iowa, Iowa City, Iowa
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Published:August 03, 2012DOI:


      Transcutaneous electrical nerve stimulation (TENS) reduces hyperalgesia and pain. Both low-frequency (LF) and high-frequency (HF) TENS, delivered at the same intensity (90% motor threshold [MT]) daily, result in analgesic tolerance with repeated use by the fifth day of treatment. The current study tested 1) whether increasing intensity by 10% per day prevents the development of tolerance to repeated TENS; and 2) whether lower intensity TENS (50% MT) produces an equivalent reduction in hyperalgesia when compared to 90% MT TENS. Sprague-Dawley rats with unilateral knee joint inflammation (3% carrageenan) were separated according to the intensity of TENS used: sham, 50% LF, 50% HF, 90% LF, 90% HF, and increased intensity by 10% per day (LF and HF). The reduced mechanical withdrawal threshold following the induction of inflammation was reversed by application of TENS applied at 90% MT intensity and increasing intensity for the first 4 days. On the fifth day, the groups that received 90% MT intensity showed tolerance. Nevertheless, the group that received an increased intensity on each day still showed a reversal of the mechanical withdrawal threshold with TENS. These results show that the development of tolerance can be delayed by increasing intensity of TENS.


      Our results showed that increasing intensity in both frequencies of TENS was able to prevent analgesic tolerance. Results from this study suggest that increasing intensities could be a clinical method to prevent analgesic tolerance and contribute to the effective use of TENS in reducing inflammatory pain and future clinical trials.

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