To test the hypotheses that, as compared with pulsed current with the same pulse duration, kilohertz frequency alternating current would not differ in terms of evoked-torque production and perceived discomfort, and as a result, it would show the same current efficiency.
A repeated-measures design with 4 stimuli presented in random order was used to test 25 women: (1) 500-microsecond pulse duration, (2) 250-microsecond pulse duration, (3) 500-microsecond pulse duration and low carrier frequency (1 kHz), (4) 250-microsecond pulse duration and high carrier frequency (4 kHz). Isometric peak torque of quadriceps muscle was measured using an isokinetic dynamometer. Discomfort was measured using a visual analog scale.
Currents with long pulse durations induced approximately 21% higher evoked torque than short pulse durations. In addition, currents with 500 microseconds delivered greater amounts of charge than stimulation patterns using 250-microsecond pulse durations (P < 0.05). All currents presented similar discomfort. There was no difference on stimulation efficiency with the same pulse duration.
Both kilohertz frequency alternating current and pulsed current, with the same pulse duration, have similar efficiency for inducing isometric knee extension torque and discomfort. However, neuromuscular electrical stimulation (NMES) with longer pulse duration induces higher NMES-evoked torque, regardless of the carrier frequency. Pulse duration is an important variable that should receive more attention for an optimal application of NMES in clinical settings.
From the Physical Education Department (FVM, MB, AV), Physiotherapy Division (TPL, KAM, GC, JLQD), and Electrical Engineering Department (APLB), University of Brasilia, Federal District, Brazil; and Centre d’Expertise de la Performance G. Cometti, UFR STAPS, Université de Bourgogne, Dijon, France (NB).
All correspondence and requests for reprints should be addressed to: João Luiz Quagliotti Durigan, PhD, University of Brasília, College of Ceilândia, Federal District, Centro Metropolitano, conjunto A, lote 01, 72220-900, Brasília, DF, Brazil.
This project was supported by the Fundação de Amparo à Pesquisa do Distrito Federal (FAPDF; process no. 193.000.862/2014), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; process no. 447529/2014-5), and by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES; process no. 88881.068106/2014-01).
AV held a PhD grant sponsored by CNPq (process no. 132387/2010-7). TPL and KAM held a scientific initiation fellowship sponsored by CNPq (106927/2013-2).
Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.