Abstract
The intensity used during transcutaneous electrical nerve stimulation (TENS) in both, clinical practice and research studies, is often based on subjective commands such as “strong but comfortable sensation”. There is no consensus regarding the effectiveness dose of TENS. The objective was to determine the difference in the effect of spinal TENS on soleus H-reflex modulation when applied by two therapists instructed to apply the stimulation at a “strong but comfortable” intensity. Twenty healthy volunteers divided into two groups: Therapist 1 (n = 10) and Therapist 2 (n = 10). Both therapist applied spinal TENS and sham stimulation at the T10–12 spinal level for 40min in random order to each subject, at an intensity designed to produce a “strong but comfortable” sensation. To avoid habituation, the intensity was adjusted every 2min. Soleus H-reflex was recorded before, during, and 10min after TENS by an observer blinded to the stimulus applied. Despite the instruction to apply TENS at a “strong comfortable” level, a significant difference in current density was identified: Therapist 1 (0.67mA/cm2, SD 0.54) applied more than Therapist 2 (0.53mA/cm2, SD 0.57; p<0.001) at the onset of the intervention. Maximal peak-to-peak H-reflex amplitude was inhibited significantly more 10min following TENS applied by Therapist 1 (-0.15mV, SD 0.16) compared with Therapist 2 (0.04mV, SD 0.16; p = 0.03). Furthermore, current density significantly correlated with the inhibitory effect on peak-to-peak Soleus H-reflex amplitude 10 min after stimulation (Rho = -0.38; p = 0.04). TENS intensity dosage by the therapist based on the subjective perception of the participants alone is unreliable and requires objective standardization. In addition, higher current density TENS produced greater inhibition of the Soleus H-reflex.
Highlights
Transcutaneous electric nerve stimulation (TENS) is usually applied in the treatment of pain [1], and for sensorimotor dysfunction such as spasticity [2, 3]
The main objective of this study was, to quantify TENS intensity applied by two independent therapists who were instructed to apply the same intensity by evaluating the subjective sensation perceived by the participant
These findings support the need for a change in the paradigm of standardizing TENS intensity, which is currently based on subjective assessment of the evoked sensation, to one that requires objective calculation of stimulation based on current density, which in turn will help to demonstrate the effectiveness of this intervention for the neuromodulation of different pathologies
Summary
Transcutaneous electric nerve stimulation (TENS) is usually applied in the treatment of pain [1], and for sensorimotor dysfunction such as spasticity [2, 3]. Parameters of the current that influence the dosing of TENS application, such as frequency, pulse width, or intervention time, are expressed using objective values. The intensity is usually reported by subjective parameters, such as the intensity that produces a “strong but comfortable” sensation. [6, 7] In both clinical practice and TENS research studies, this application of intensity in terms of subjective perception could be influenced by the therapist’s interpretation. This may be a limitation when comparing the effectiveness of the intervention, especially taking into account that TENS produces intensity-dependent effects [5, 8,9,10,11,12]. No study has attempted a direct comparison of the current intensity applied and the subjective sensation of the stimulus nor the influence of different therapists on adherence to subjective instructions to define TENS intensity
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