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Clinical Rehabilitation 2002; 16: 194199

Arnold 2002 10.1191/0269215502cr467

Address for correspondence: Cigdem Bircan, Dokuz EylulUniversity Medical Faculty, Department of PhysicalMedicine and Rehabilitation, Izmir, Turkey. e-mail:cigdem.bircan@deu.edu.tr

Efcacy of two forms of electrical stimulation inincreasing quadriceps strength: a randomizedcontrolled trial

Cigdem Bircan, Ozlem Senocak, Ozlen Peker, Aylin Kaya, Sebnem Akgol Tamc

, Selmin Gulbahar and Elif AkalinDepartment of Physical Medicine and Rehabilitation, Dokuz Eylul University Medical Faculty, Izmir, Turkey

Received 12th April 2001; returned for revisions 27th June 2001; revised manuscript accepted 1st September 2001.

Objective: To investigate whether electrical stimulation is effective in

improving quadriceps strength in healthy subjects and to compareinterferential and low-frequency current in terms of the effects on quadriceps

strength and perceived discomfort.

Design: Randomized, controlled study.

Setting: Physical Medicine and Rehabilitation Department in a university

hospital.

Subjects: Thirty medical faculty students, divided into three groups,

participated in the study.

Interventions: Group A received electrical stimulation with bipolar

interferential current while group B received electrical stimulation with low-

frequency current (symmetrical biphasic). Group C served as the control

group. Electrical stimulation was given for 15 minutes, ve days a week for

three weeks, at a maximally tolerated intensity with the knee fully extended

in the sitting position.

Main outcome measures: Before and after the study, quadriceps strength

was measured with a Cybex dynamometer isokinetically at the angular

velocities of 60/s and 120/s. The perceived discomfort experienced with

each type of electrical stimulation was quantied by the use of a visual

analogue scale (VAS).

Results: Statistically signicant increase in isokinetic strength was observed

after training in group A and group B. Increase in strength did not differ

between the stimulation groups. No signicant change in strength occurred in

group C. Perceived discomfort by the stimulation groups was not signicantly

different.Conclusion: Both interferential and low-frequency currents can be used in

strength training with the parameters used in this study.

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Electrical stimulation to increase quadriceps stength 19

Introduction

Neuromuscular electrical stimulation (NMES) isthe actuation of muscular tissue through theintact peripheral nervous system. There are vemajor categories of treatment programmes thatuse NMES. They include the use of NMES tostrengthen or maintain muscle mass both duringor following periods of enforced inactivity; tomaintain or gain range of motion; to facilitatemotor control; to reduce temporarily the effectsof spasticity; and to provide temporarily fororthotic substitution.1

Strengthening healthy muscles has receivedconsiderable attention in the literature but thereare conicting results concerning the efcacy ofelectrical stimulation (ES) on the healthy quadri-cep.2 Although many investigators have found ESto be effective in improving muscle force,312

there are other researchers who concluded thatES was not an effective method of increasingstrength in healthy subjects13 or that ES increasedisometric strength but not isokinetic strength.14

No widely accepted protocol exists for cliniciansusing electrical stimulation to improve musclestrength. Different stimulation parameters havebeen used and various electrical stimulators havebeen developed.

This study was designed to investigate whetherES is effective in improving quadriceps strengthin healthy subjects and to compare interferentialand low-frequency current in terms of the effectson quadriceps strength and perceived discomfort.

Methods

Thirty medical faculty students with an average

age of 23.20 years (range 2035 years) and no h is-tory of neuromuscular disease or knee disordersparticipated in the study. After giving their

informed consent, they were randomly assignedto three groups. Each group consisted of 10 sub-

jects (ve male, ve female). Group A receivedelectrical stimulation with bipolar interferentialcurrent with a carrier frequency of 2500 Hz and

amplitude modulation frequency of 80 Hz. Group

B received ES with low-frequency current. Thewaveform was symmetrical biphasic, with a phase

duration and frequency of 100 s and 80 Hz,

respectively. Stimulation was not applied tgroup C (control group). All subjects wer

requested to avoid changing their normal activ

ties during the study.Myomed 932 (Enraf Nonius, the Netherlands

was used to produce ES in both of the stimulation groups. Two rubber electrodes (6 8 cm

were placed over the right quadriceps femorimuscle, one of them below the inguinal ligamen

and the other one proximal to the patella. Eacelectrode was covered with a moist sponge pa

and secured by a circumferential velcro strapThe maximal tolerable stimulation intensity wa

given for 15 minutes, ve days a week for threweeks, with the knee fully extended in the sittin

position. Irrespective of the group assignmenonoff time of the stimulation was set as 13 s oand 50 s off. Ramp up time was 2 s and ramdown time was 1 s. Constant voltage mode wa

used in both of the groups. The current amplitude varied from 28 mA to 59 mA in group A an

32 mA to 56 mA in group B.

Before and after the study, quadriceps peatorque was measured with a Cybex Norm

dynamometer (Cybex International, IncRonkonkoma, New York, U SA) isokinetically a

60/s and 120/s (concentr ically) . During the testhe subject was placed in the sitting position wit

a backrest angle of 85 and the axis of rotatioof the dynamometer was aligned with that of th

knee. The lever arm of the dynamometer wasecured with a velcro strap just proximal to th

level of the malleoli. The subjects were stabilizein the test position by a belt around the shoul

ders and waist and a velcro strap around ththigh. Five trial contractions were performed a

each angular velocity, with a 20 s rest intervabetween the sets. The examiner provided verba

encouragement while the subjects were trying t

develop maximal voluntary muscle contractionand the dynamometer gave visual feedback.

The perceived discomfort experienced witeach type of ES was quantied by the use of 10-cm visual analogue scale (VAS).

A three-way analysis of variance (ANOVA

with repeated measures factors being time anspeed was used to determine signicant differences in quadriceps strength data. In additionWilcoxon test was used to compare pretrainin

and post-training peak torque values within th

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196 C Bircan et al.

Isokinetic peak torque values before and aftetraining in the groups are presented in Table 2Statistically signicant increase in isokinetstrength measured at the angular velocities o60/s and 120/s was observed after training igroup A (p < 0.05, p < 0.01, respectively). Isoknetic strength increases at the angular velocitieof 60/s and 120/s were also signicant in grouB (p < 0.01). There was no signicant change igroup C (p > 0.05). Figures 1 and 2 show quadrceps strength before and after training in thgroups at 60/s and 120/s, respectively.

When the two stimulation groups were compared in terms of isokinetic strength gains, no signicant difference was found between groups Aand B (p > 0.05).

Mean VAS score was 4.90 1.52 in group Aand 4.10 1.66 in group B. The difference wa

not statistically signicant (p > 0.05).

groups; and MannWhitney U-test was used tocompare strength gains (post-training peaktorque value minus pretraining peak torquevalue) and VAS scores between the two stimula-tion groups. Signicance was accepted for p