`©Journal of Sports Science and Medicine (2005) 4, 66-75
`http://www.jssm.org
`
`Research article
`
`THE EFFECTS OF NEUROMUSCULAR ELECTRICAL
`
`STIMULATION TRAINING ON ABDOMINAL STRENGTH,
`
`ENDURANCE, AND SELECTED ANTHROPOMETRIC
`
`MEASURES
`
`John P. Porcari 1 (cid:13), Jennifer Miller 1, Kelly Cornwell 1, Carl Foster 1, Mark
`
`Gibson 1, Karen McLean 2 and Tom Kernozek 2
`
`1 Department of Exercise and Sports Science, University of Wisconsin-La Crosse, USA
`2 Department of Physical Therapy, University of Wisconsin-La Crosse, USA
`
`Received: 24 December 2004 / Accepted: 11 February 2005 / Published (online): 01 March 2005
`
`ABSTRACT
`We studied the effects of self-administered neuromuscular electrical stimulation (NMES) on changes in
`strength, endurance, selected anthropometric measures, and subject’s perceived shape and satisfaction of
`the abdominal wall. Twenty-four adults (experimental group) stimulated their abdominals 5 days per
`week (20-40 minutes per session) for 8 weeks and refrained from engaging in any additional exercise
`during the study. A control group (N=16) refrained from exercising the abdominals or engaging in any
`other exercise training during the study. Subjects were tested at the beginning, mid-point, and end of the
`study. Isometric strength of the abdominal muscles was tested using a isokinetic dynamometer,
`endurance was measured using the ACSM curl-up test, abdominal circumference was measured using a
`steel tape measure, and body shape and satisfaction were assessed via questionnaire. The stimulation
`group had a 58% increase in abdominal strength, whereas the control group did not change. The
`stimulation group also had a 100% increase in abdominal endurance versus a 28% increase in the control
`group. Waist circumference decreased by of 3.5 cm in the stimulation group compared to no significant
`change in the control group. All 24 subjects in the stimulation group felt that their midsections were
`more “toned” and “firmed” and 13/24 (54%) felt that their posture had improved as a result of the
`stimulation. None of the control group subjects reported changes in these parameters. There were no
`significant differences in body weight, BMI, or skinfold thickness over the course of the study in either
`group. NMES, as used in the current study, resulted in significant improvements in the muscular strength
`and endurance of the abdominal region, as well as subject’s perceived shape and satisfaction of the mid-
`section.
`
`KEY WORDS: Fitness, training, isometric.
`
`INTRODUCTION
`
`Neuromuscular electrical stimulation (NMES) has
`been used been used for many years by physical
`therapists to retard atrophy in denervated muscle and
`to maintain or
`improve muscular strength
`in
`
`immobilized muscle following surgery. In the 1960’s,
`Kots used NMES with elite athletes in the former
`Soviet Union (Kots, 1977) and found strength
`improvements of 30-40%, using what came to be
`known as “Russian stimulation”. He even suggested
`that NMES might be more effective than exercise
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`alone for strength development.
`In recent years, fitness equipment companies
`have tried to market the benefits of NMES as another
`in the long line of “get-fit-quick” schemes. The
`potential to attain “rock-hard abs” or “buns of steel”
`without having to actually exercise is an attractive
`lure for many people who do not have the time or
`motivation
`to engage
`in
`traditional exercise
`programs. One area that has drawn considerable
`attention is the mid-section. Alon and colleagues
`conducted a series of studies that investigated the
`effects of NMES on the strength and endurance of the
`abdominal region (Alon et al., 1987; 1992; Alon and
`Taylor, 1997). They found that NMES to the
`abdominal musculature was well
`tolerated and
`resulted in strength improvements ranging from 14-
`22%. Alon et al. (1992) also found that 5 days of
`stimulation was better than 3 days at inducing
`changes (Alon et al., 1992). Similarly, when NMES
`was applied to induce contraction of the knee
`extensors or plantar flexors, strength gains in the
`range of 17-31% have been found (Balogun et al.,
`1993; Currier and Mann, 1983; Maffiuletti et al.,
`2002; Romero et al., 1982; Selkowitz, 1985). A
`common finding among these studies was that the
`stimulation was reasonably comfortable, allowing
`subjects to obtain muscular contractions in excess of
`60% of their maximal voluntary contraction (MVC).
`Trying
`to capitalize on
`the vanity of
`consumers, a number of companies have incorporated
`NMES technology into abdominal stimulation belts
`and pad systems. A well-controlled study from our
`laboratory
`(Porcari et al., 2002)
`found no
`improvement in muscle strength, body composition,
`or physical appearance using one of
`these
`commercially available stimulators. The lack of
`positive results was attributed to the poor quality of
`the stimulators themselves and the uncomfortable
`nature of the stimulation, which prevented subjects
`from attaining sufficiently intense contractions to
`improve strength. The results of this study prompted
`the Federal Trade Commission (FTC) to remove
`several NMES belt products from the market (Green,
`2002).
`A relatively new abdominal stimulation belt on
`the Slendertone FLEXTM (Compex
`the market,
`Technologies, Minneapolis, MN), has been cleared
`for use by the Federal Drug Administration (FDA) to
`strengthen, tone, and firm the abdominal muscles.
`Two studies conducted by the manufacturer found
`that use of this system improved isometric strength,
`isometric and dynamic endurance, and a number of
`self-perceived outcome measures (Caulfield et al.,
`2002; Cullinane et al., 2002). However, given the
`inherent bias characteristic of
`in-house studies,
`independent
`evidence
`of
`the
`accuracy
`of
`manufacturer claims is desirable. Accordingly, the
`
`independently
`to
`this study was
`purpose of
`investigate the effects of 8 weeks of NMES on
`similar parameters.
`
`METHODS
`
`Subjects
`Forty-one volunteer subjects were recruited from the
`La Crosse area community to participate in the study.
`Inclusion criteria required the subjects to be between
`the ages of 25-50 years old, to have a Body Mass
`Index (BMI) between 18-30, and not have been
`involved in any type of formal abdominal training
`program within the previous 6 months. In addition,
`subjects with a cardiac pacemaker, any abdominal
`implants, or who were currently pregnant or had been
`pregnant within the past 3 months were not eligible to
`participate in the study. The 41 individuals were
`randomly assigned into two groups: a control group
`and a stimulation group. Both groups were instructed
`not to alter their diet or engage in any additional
`exercise over the course of the 8-week study period.
`All subjects provided informed consent. The protocol
`was previously approved by the Institutional Review
`Board for the Protection of Human Subjects. Subjects
`in the stimulation group were paid $100 to participate
`in the study in order to assure compliance with the
`study protocol. In addition they got to keep the
`stimulation belt they had used for training. Subjects
`in the control group received a free stimulation belt at
`the conclusion of the study.
`
`Testing
`Both groups underwent an identical battery of tests at
`the beginning, midpoint (4 weeks), and end (8 weeks)
`of the study. The testing consisted of a series of
`questionnaires,
`skinfold
`measurements,
`circumference measurements, abdominal strength
`assessment,
`and measurement
`of
`abdominal
`endurance. Height and weight were also measured
`using a standard laboratory scale.
`
`Questionnaires
`Subjects were asked to fill out three questionnaires:
`the Shape Evaluation Scale (Caulfield et al., 2002;
`Cullinane et al., 2002), the Body Satisfaction Scale
`(Caulfield et al., 2002; Cullinane et al., 2002), and
`Rosenberg’s Self-Esteem Scale (Rosenberg, 1989).
`The Shape Evaluation Scale assesses perceived
`abdominal shape using a set of ten dichotomous
`items taken to describe various aspects concerning
`the shape and appearance of the abdominal region.
`The items are rated on a five point semantic
`differential scale. The Body Evaluation Scale consists
`of 12 items that measure feelings about body shape
`on a five point Likert scale ranging from “strongly
`agree” to “strongly disagree.” Rosenberg’s Self-
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`Abdominal electrical muscle stimulation
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`
`Esteem Scale consists of 10 items on a four point
`Likert scale that refer to aspects of self-esteem
`including pride in self, general competence, and
`equal worth to others.
`
`Skinfold and circumference measurements
`All skinfold and circumference measurements were
`made by the same research assistant throughout the
`study. Skinfold measurements were made at two sites
`using Lange
`callipers
`(Cambridge Scientific
`Industries, Inc., Cambridge, MD): an umbilical site
`and a suprailiac site. For the umbilical measurement,
`a vertical skinfold was taken one inch to the right of
`the umbilicus. For the suprailiac skinfold, a diagonal
`skinfold was taken just above and slightly forward of
`the iliac crest. Three measurements were taken at
`each site and the closest two measurements were
`averaged for use in the analysis.
`Abdominal and waist circumferences were
`measured using a steel tape measure. For the
`abdomen, the smallest horizontal circumference was
`measured in the area between the ribs and the iliac
`crest: the level of the natural waist. The waist
`circumference was measured horizontally at the level
`of the umbilicus. Two measurements were taken at
`each site and the average of the two measurements
`was used in the analysis.
`
`Front to back anthropometry
`The diameter of the torso at the level of the largest
`protrusion of the abdomen was measured using a pair
`of large, sliding calipers. The measurement was made
`from the side, with the anthropometer blades in
`contact with the middle of the spinal column in the
`back and just touching the abdomen in the front. Two
`measurements were taken and the average of the two
`measurements was used in the analysis.
`
`Abdominal endurance
`the
`Abdominal endurance was assessed using
`American College of Sports Medicine (ACSM) paced
`curl-up test (Figure 1). The test was conducted using
`a prerecorded audiotape. The subject laid supine on a
`padded exercise mat, with knees bent at 90 degrees
`(as verified via a goniometer) and both arms
`extended to the sides with fingers touching a piece of
`masking tape. A second piece of tape was placed 12
`cm beyond the first. At the start of the tape (cadence
`of 40 curl-ups per minute), the subjects lifted their
`shoulder blades off the mat and slid their fingers
`forward until their fingertips touched the second strip
`of tape. Subjects performed as many curl-ups as
`possible without stopping. The test was terminated
`when the subjects could no longer keep up with the
`cadence or could not reach the second strip of tape.
`The prerecorded audiotape included 6 warm-up
`repetitions before the actual test began.
`
`
`
`
`
`
`Figure 1. Starting and ending positions for the
`muscular endurance tests.
`
`Abdominal strength
`Abdominal strength was assessed using an isokinetic
`dynamometer (Cybex 6000, USA, Figure 2). The
`subject laid supine on a movable bench in a bent knee
`position. The
`lever
`arm of
`the
`isokinetic
`dynamometer was set at 180 degrees (horizontal with
`the ground) and the padded extension was placed just
`below the nipple line on the lower third of the
`sternum. The height of the bench was adjusted for
`each subject so that the extension arm remained at
`180 degrees. Each subject was given several practice
`trials to make sure the position of the lever arm was
`comfortable on their chest. Subjects then performed
`five isometric contractions, with approximately 30
`seconds between each repetition. The average torque
`for the highest two repetitions was used in the
`analysis.
`
`Training
`the stimulation group underwent
`in
`Subjects
`stimulation 5 times per week for 8 weeks. The
`abdominal stimulation system consisted of a
`contoured neoprene belt with detachable, pre-gelled
`electrodes that are connected to the stimulator
`without externally visible leads. The electrodes were
`replaced at the end of the 3rd and 6th weeks of the
`study. Each subject was given their own belt and had
`to attend a minimum of two supervised sessions per
`week for the first 2 weeks of the study, and one
`supervised session per week for the remainder of the
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`
`study. All other sessions were conducted on their
`own. During each stimulation session, subjects were
`encouraged
`to
`increase
`the amplitude on
`the
`stimulator to the highest tolerable level in order to
`achieve the strongest possible contractions. They
`were instructed not to perform volitional contractions
`in conjunction with the stimulator and were allowed
`to conduct the stimulation sessions in any positions
`they preferred. After every session, the subject
`recorded the average level of intensity used as well as
`the peak intensity achieved during that session.
`During Week 1, the subjects completed two
`sessions using Program 1 (20 minutes per session),
`and three sessions using Program 2 (25 minutes per
`session). During Weeks 2-4, the subjects used
`Program 3 (30 minutes per session) for all of their
`stimulation sessions. During Weeks 5-8, subjects
`used Program 4 (40 minutes per session) for all of
`their stimulation sessions (Table 1).
`
`Statistics
`Differences between groups, gender, and time (Pre-
`test, 4 Week, and 8 Week) were assessed using a 3-
`way ANOVA with repeated measures for each
`variable. Differences within each group were
`assessed using a 2-way ANOVA (gender X time)
`with repeated measures. If there was a significant F
`ratio, Tukey’s post-hoc tests were used to assess pair-
`wise comparisons. Differences in change scores
`between the control and stimulation groups at each
`time point (Pre-test to 4 Week and Pre-test to 8
`Week) were assessed using independent t-tests with a
`Bonferoni adjustment of the alpha level (.05).
`
` Table 1. Slendertone FLEXTM stimulator parameters.
`
`Time Frequency
`Pulse
`On
`Duration
`Time
`sec
`µsec
`
`
`200
`2.0
`200
`2.5
`200
`2.0
`
`
`Figure 2. Starting and ending positions for the
`isometric strength test.
`
`RESULTS
`
`All 41 subjects successfully completed the study.
`Data for one male in the stimulation group were not
`used in the analysis, due to unreliable testing results.
`
`Rump
`Up
`sec
`
`2.0
`2.0
`2.0
`
`Ramp
`Down
`sec
`
`2.0
`2.0
`2.0
`
`Off
`Time
`sec
`
`2.0
`2.5
`2.0
`
`Interphase
`Delay
`µsec
`
`140
`140
`140
`
`min
`
`1
`18
`1
`
`Hz
`
`70
`70
`70
`
`
`1
`23
`1
`
`
`1
`28
`1
`
`
`1
`38
`1
`
`
`60
`60
`60
`
`
`50
`50
`50
`
`
`50
`50
`50
`
`
`200
`200
`200
`
`
`200
`200
`200
`
`
`200
`200
`200
`
`
`2.0
`3.5
`2.0
`
`
`2.0
`4.5
`2.0
`
`
`2.0
`5.5
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`2.0
`2.0
`
`
`2.0
`3.5
`2.0
`
`
`2.0
`4.5
`2.0
`
`
`2.0
`5.5
`2.0
`
`
`140
`140
`140
`
`
`140
`140
`140
`
`
`140
`140
`140
`
`
`Program 1
`Warm-up
`Treatment
`Cool-down
`
`Program 2
`Warm-up
`Treatment
`Cool-down
`
`Program 3
`Warm-up
`Treatment
`Cool-down
`
`Program 4
`Warm-up
`Treatment
`Cool-down
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`Abdominal electrical muscle stimulation
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`Table 2. Descriptive characteristics of the subjects at the beginning of the study. Data are
`means (±SD).
`Age (yrs) Height (m) Weight (kg)
`Gender
`Groups
`Stimulation
`44 (4) *
`1.78 (.05)
`88.1 (7.0)
`Males (n=12)
`45 (4) *
`164 (.05)
`69.3 (7.0)
`Females (n=12)
`
`Control
`39 (8)
`177 (.06)
`83.0 (8.6)
`Males (n=8)
`40 (6)
`163 (.05)
`67.1 (6.5)
`Females (n=8)
`
`* Significantly different than Control group (p < 0.05).
`
`BMI
`28.1 (2.1)
`26.0 (2.7)
`26.5 (2.6)
`25.3 (2.9)
`
`
`Descriptive characteristics of the subjects who were
`used in the analysis are presented in Table 2. The
`only significant difference between the groups at the
`start of the study was in age, with the control group
`being significantly younger than the stimulation
`group.
`The stimulation group was urged to use as high
`an intensity as possible on the stimulator in order to
`elicit the most vigorous contractions. The average
`intensity and the peak intensity for each workout
`were recorded in a daily log. A weekly summary of
`the data is presented in Table 3. Subjects were also
`asked to rate the strength of the contraction they felt
`they were getting from the stimulator on a scale of 0-
`10 (0 = no contraction, 10 = maximal tolerable
`contraction). At the mid-point in the study, subjects
`rated the strength of contraction as 8.2 ± 1.2. At the
`end of the study, subjects rated the strength of
`contraction as 8.5 ± 1.5.
`
`Table 3. Stimulator average and peak intensity
`values used during the study. Data are means (±SD).
`Week
`
`Males Females Overall
`1
`Average
`61 (20)
`64 (16)
`62 (17)
`
`Peak
`71 (20)
`77 (15)
`74 (17)
`2
`Average
`80 (15)
`84 (13)
`82 (14)
`
`Peak
`90 (15)
`93 (10)
`91 (13)
`3
`Average
`87 (12)
`88 (11)
`87 (11)
`
`Peak
`94 (12)
`95 (6)
`95 (10)
`4
`Average
`90 (8)
`90 (10)
`90 (9)
`
`Peak
`97 (6)
`98 (4)
`97 (5)
`5
`Average
`93 (4)
`92 (9)
`93 (7)
`
`Peak
`99 (1)
`98 (3)
`98 (2)
`6
`Average
`94 (3)
`93 (9)
`93 (7)
`
`Peak
`99 (0)
`98 (3)
`99 (2)
`7
`Average
`95 (2)
`93 (9)
`94 (6)
`
`Peak
`99 (0)
`98 (3)
`99 (2)
`8
`Average
`95 (3)
`93 (8)
`94 (6)
`
`Peak
`99 (0)
`98 (3)
`99 (2)
`
`
`
`Changes in abdominal strength and endurance
`
`are presented in Table 4. The stimulation group had
`58% improvement in isometric abdominal strength
`over the course of the study. The control group did
`not change. Results were similar for both males and
`females.
`
`the stimulation and control groups
`Both
`increased their abdominal endurance over the course
`of the 8 weeks. The stimulation group increased by
`100% and the control group increased by 28%,
`yielding a net
`improvement of 72% for
`the
`experimental group. Results again were similar for
`males and females.
`Data regarding body composition measures are
`presented in Table 5. There were no significant
`changes in body weight, Body Mass Index, umbilical
`skinfold, or suprailiac skinfold for either group over
`the course of
`the study. Overall, abdominal
`circumference decreased by 2.6 cm and waist
`circumference decreased by 3.6 cm in the stimulation
`group, with results being similar for males and
`females. The control did not change over the course
`of the study. There was also a significant decrease in
`the front-to-back diameter (1.4 cm) of the mid-
`section in the stimulation group. There were no
`changes in abdominal circumference, abdominal
`circumference, or front-to-back diameter in the
`control group.
`Total scores for the three questionnaires are
`presented in Table 6. Results for both the Shape
`Evaluation Scale and the Body Satisfaction Scale
`were identical. Males and females had significant
`improvements in their scores at both the 4 Week and
`8 Week testing points, and these changes were
`significantly greater
`than
`the control group.
`Consistent with these results were the answers to two
`other questions that were presented to subjects in
`written form at the end of the study. Subjects were
`asked if they felt their abdominal muscles felt more
`“firm” and “toned” after using the Slendertone
`FLEXTM for 8 weeks. All 24 subjects responded
`positively. They were also asked if they felt that their
`posture had improved as a result of using the
`Slendertone FLEXTM. Thirteen of the 24 subjects
`(54%) responded that they felt it had improved their
`posture. There was not a significant improvement in
`the total score for the Self-Esteem Scale (Table 6).
`
`DISCUSSION
`
`that NMES
`this study found
`The results of
`significantly increased the isometric strength and
`dynamic endurance of the abdominal musculature.
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`Table 4. Changes in body composition measures over the course of the study. Data are means (±SD).
`Variables
`Groups
`
`Pre-test
`4 Week
`8 Week
`Body
`Stimulation Males
`88.1 (7.0)
`88.1 (7.4)
`87.6 (7.8)
`Weight (kg)
`
`Females
`69.3 (7.0)
`69.5 (6.3)
`67.0 (6.6)
`
`
`Overall
`78.7 (11.8)
`78.8 (11.7)
`78.3 (11.9)
`Control
`
`Males
`83.0 (8.6)
`83.7 (8.6)
`84.0 (8.9)
`
`
`Females
`67.1 (6.5)
`67.1 (6.3)
`66.6 (6.0)
`
`
`Overall
`75.0 (11.0)
`75.4 (11.3)
`75.3 (11.6)
`Body Mass
`Stimulation Males
`28.1 (2.1)
`28.1 (2.3)
`27.9 (2.4)
`Index
`
`Females
`25.6 (2.7)
`26.0 (2.5)
`25.9 (2.6)
`
`
`Overall
`27.0 (2.6)
`27.0 (2.6)
`26.9 (2.7)
`Control
`
`Males
`26.5 (2.6)
`26.7 (2.5)
`26.8 (2.6)
`
`
`Females
`25.3 (2.9)
`25.3 (2.9)
`25.1 (2.9)
`
`
`Overall
`25.9 (2.8)
`26.0 (2.7)
`26.0 (2.8)
`Umbilical
`Stimulation Males
`29.0 (4.1)
`28.9 (4.1)
`30.0 (3.7)
`Skinfold(mm)
`
`Females
`22.1 (5.0)
`22.2 (5.5)
`22.9 (5.1)
`
`
`Overall
`25.6 (5.7)
`25.6 (5.8)
`26.4 (5.7)
`Control
`
`Males
`28.6 (7.3)
`29.3 (7.1)
`28.9 (6.9)
`
`
`Females
`22.3 (6.2)
`22.5 (5.3)
`21.7 (5.7)
`
`
`Overall
`25.4 (7.3)
`25.9 (7.0
`25.3 (7.1)
`Suprailiac
`Stimulation Males
`15.4 (3.4)
`14.4 (3.3)
`15.0 (3.4)
`Skinfold
`
`Females
`15.8 (5.0)
`14.9 (5.0)
`15.0 (5.4)
`(mm)
`
`Overall
`15.6 (4.2)
`14.7 (4.2)
`15.0 (4.4)
`Control
`
`Males
`14.9 (3.4)
`14.0 (4.7)
`15.0 (3.4)
`
`
`Females
`15.1 (4.8)
`15.5 (4.4)
`15.4 (3.7)
`
`
`Overall
`15.0 (4.3)
`14.8 (4.4)
`15.2 (4.0)
`Abdominal
`Stimulation Males
`96.6 (4.6)
`96.3 (5.3)
`94.1 (6.0) *#
`Circumference
`
`Females
`82.4 (6.3)
`82.3 (5.3)
`79.6 (5.4) *#
`(cm)
`
`Overall
`89.5 (9.0)
`89.3 (8.9)
`86.9 (9.3) *#
`Control
`
`Males
`91.8 (6.7)
`91.7 (7.4)
`91.9 (6.9)
`
`
`Females
`81.6 (6.4)
`81.5 (8.0)
`81.0 (7.3)
`
`
`Overall
`86.7 (8.2)
`86.6 (9.1)
`86.4 (8.9)
`Waist
`Stimulation Males
`101.2 (4.2)
`99.8 (5.0)
`97.9 (5.5) *#
`Circumference
`
`Females
`92.2 (5.9)
`90.1 (6.4) *
`88.4 (7.7) *#
`(cm)
`
`Overall
`96.7 (6.8)
`94.9 (7.5) *#
`93.1 (8.1) *#
`Control
`
`Males
`94.8 (6.7)
`94.9 (7.4)
`94.8 (7.1)
`
`
`Females
`86.5 (7.8)
`86.3 (8.2)
`86.0 (7.0)
`
`
`Overall
`90.7 (8.2)
`90.6 (8.8)
`90.4 (8.2)
`Front-to-Back
`Stimulation Males
`25.8 (1.4)
`24.8 (1.7)
`24.3 (2.1) *
`Anthropometry
`
`Females
`23.1 (2.1)
`22.4 (2.2)
`22.0 (2.6)
`(cm)
`
`Overall
`24.5 (2.2)
`23.6 (2.3) *
`22.0 (2.6)
`Control
`
`Males
`24.3 (2.9)
`23.8 (3.0)
`23.9 (2.6)
`
`
`Females
`21.3 (2.6)
`21.3 (2.3)
`23.0 (2.8)
`
`
`Overall
`22.6 (3.0)
`22.6 (2.7)
`23.0 (2.8)
`* Significantly different than Pre-test (p < 0.05).
`# Change for the Stimulation group is significantly different than the Control group at the same time
`point (p < 0.05).
`
`The strength gain of 58% is almost double that found
`by other researchers (Alon et al., 1987; 1992; Alon
`and Taylor, 1997; Ballantye and Donne, 1999). The
`most obvious explanations for this finding is that the
`length of the current study was 8 weeks, versus 4
`weeks in studies conducted in Alon’s laboratory. The
`length of the study conducted by Ballantyne and
`Donne was 6 weeks in length, and their data
`suggested that the benefits of NMES tended to
`plateau after 4 weeks. In the current study a plateau
`was not realized. Strength improved by an average of
`34% after 4 weeks and increased another 24% in the
`subsequent 4-week period. Another plausible
`explanation
`for
`this discrepancy
`is
`that
`the
`stimulation protocol was different between the two
`
`studies. In the current study stimulator “on time”
`increased from 4.5 to 5.5 seconds after the 4th week,
`and the length of the stimulations sessions increased
`from 30 minutes to 40 minutes. In the study by
`Ballantyne and Donne, stimulation parameters stayed
`constant throughout the 42-day period.
`For abdominal endurance,
`the stimulation
`group had a 100% increase in curl-up performance.
`However, the control also had a 28% increase over
`the 8-week study period. The increase in the control
`group was attributed to a learning effect and was
`subsequently subtracted from the results of the
`stimulation group to yield a net improvement of 72%.
`Alon et al. (1987) did not find a significant
`improvement in abdominal endurance following
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`

`

`72
`
`Abdominal electrical muscle stimulation
`
`
`
` Table 5. Changes in abdominal strength and endurance over the course of the study. Data are means (±SD).
`Variables
`Groups
`
`Pre-test
`4 Week
`8 Week
`Abdominal
`Stimulation Males
`75.5 (27.3)
`99.9 (25.4) *#
`119.3 (25.0) *#
`Strength
`
`Females
`37.6 (13.6)
`51.5 (15.7) *
`59.0 (12.7) *#
`(N·m)
`
`Overall
`56.6 (28.7)
`75.8 (32.2) *#
`89.2 (36.4) *#
`Control
`
`Males
`78.4 (17.4)
`82.2 (16.9)
`84.9 (19.1)
`
`
`Females
`41.1 (10.7)
`45.6 (8.5)
`45.6 (9.8)
`
`
`Overall
`59.7 (23.8)
`63.9 (22.9)
`65.2 (25.1)
`Abdominal
`Stimulation Males
`39 (20)
`61 (40)
`80 (53) *#
`Endurance
`
`Females
`31 (11)
`43 (10)
`60 (27) *#
`(repetitions)
`
`Overall
`35 (16)
`52 (30) *#
`70 (42) *#
`Control
`
`Males
`34 (17)
`36 (16)
`44 (17)
`
`
`Females
`29 (14)
`29 (14)
`38 (15)
`
`
`Overall
`32 (15)
`32 (14)
`41 (16) *
` * Significantly different than Pre-test (p<.05)
` # Change for the Stimulation group is significantly different than the Control group at the same time
`point (p<.05)
`
`NMES applied to the abdominals. However, the
`endurance task was a timed isometric holding task
`that was terminated based on decreased torque
`development. Goniometer fluctuation caused by
`thorax movements made decisions to terminate the
`test unreliable, as evidenced by the fact that the
`control group had a 112% increase in holding time
`(versus 144% in the stimulation group, p > 0.05).
`Ballantype and Donne (1999) did find highly
`significant improvements in isometric endurance of
`154% and 114% at joint angles of 0° and 10° percent,
`respectively. They also found a 33% increase in
`dynamic abdominal endurance when using an
`incremental, timed curl-up test. The inconsistent
`results are probably a reflection of the fact that
`methods and procedures for testing and training
`varied considerably between studies.
`The stimulation group also had a 2.6 cm
`decrease in abdominal circumference, a 3.6 cm
`
`Table 6. Changes in questionnaire responses over the course of the study. Data are means (±SD).
`Variables
`Groups
`
`Pre-test
`4 Week
`8 Week
`Shape
`Stimulation Males
`23.9 (3.5)
`30.5 (3.5) *#
`32.8 (2.9) *#
`Evaluation
`
`Females
`19.7 (4.4)
`26.0 (6.9) *#
`30.1 (7.2) *#
`Scale
`
`Overall
`21.8 (4.5)
`28.3 (5.2) *#
`31.5 (5.5) *#
`Control
`
`Males
`27.4 (6.5)
`28.5 (6.5)
`28.9 (6.3)
`
`
`Females
`22.1 (3.8)
`22.6 (2.5)
`24.0 (3.5)
`
`
`Overall
`24.8 (5.8)
`25.6 (5.6)
`26.4 (5.5)
`Body
`Stimulation Males
`28.3 (5.6)
`37.2 (6.1) *#
`39.7 (6.2) *#
`Satisfaction
`
`Females
`28.6 (4.5)
`36.7 (7.7) *#
`38.3 (8.2) *#
`
`Overall
`28.4 (5.0)
`36.7 (6.8) *#
`39.0 (7.1) *#
`Scale
`
`Control
`Males
`32.0 (5.8)
`30.3 (6.0)
`32.0 (5.6)
`
`
`Females
`30.0 (5.5)
`32.1 (5.8)
`32.1 (5.9)
`
`
`Overall
`31.0 (5.5)
`31.2 (5.7)
`32.1 (5.6)
`Self-Esteem
`Stimulation Males
`33.6 (5.8)
`34.3 (4.5)
`34.9 (4.7)
`
`Females
`36.3 (3.5)
`36.7 (3.6)
`37.1 (2.7)
`Scale
`
`Overall
`34.9 (4.8)
`35.5 (4.2)
`36.0 (3.9)
`
`Control
`Males
`32.3 (3.2)
`31.1 (2.6)
`31.0 (3.1)
`
`
`Females
`34.5 (2.6)
`33.0 (3.0)
`32.8 (3.3)
`
`
`Overall
`33.4 (3.0)
`32.1 (2.9)
`31.9 (3.2)
`
`* Significantly different than Pre-test (p < 0.05).
`# Change for the Stimulation group is significantly different than the Control group at the same
`time point (p < 0.05).
`
`decrease in waist circumference, and a 1.4 cm
`decrease in front-to-back diameter. These changes
`were significant in that they occurred despite any
`changes in body weight or umbilical or suprailiac
`skinfolds. None of the other studies reviewed found
`significant changes in girth measurements as a result
`of NMES. However, most of the other studies
`(Currier and Mann, 1983; Porcari et al., 2002;
`Romero et al., 1982) measured thigh girth. An
`increase in strength of the thighs would not be
`expected to decrease circumference of the thighs
`muscles in the absence of significant weight loss. If
`anything,
`the
`resultant hypertrophy would be
`manifest as an increase in thigh girth.
`An increase in the strength of the abdominal
`muscles could theoretically reduce the circumference
`of the mid-section. Since, one of the roles of the
`abdominal musculature is to support the abdominal
`contents, it follows that strengthening the abdominal
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`

`

`Abdominal electrical muscle stimulation
`
`
`73
`
`
`muscles could in effect “pull in” the abdomen, much
`like a girdle. This effect would decrease both the
`circumference and front-to-back diameter of the
`waist.
`In support of
`the decrease
`in waist
`circumference was the fact that 13 out of 24 (54%)
`subjects in the stimulation group felt that their cloths
`fit better around the mid-section at the conclusion of
`the study. None of the control group subjects reported
`any change in how their clothes fit.
`Another role of the abdominal muscles is to
`maintain posture (Juker et al., 1998; Mulhearn and
`George, 1999). Thirteen of the 24 (54%) subjects felt
`that using NMES improved their posture. This is
`theoretically possible if the increase in strength of the
`abdominal muscles pulled the pelvis up in the front,
`thus decreasing the spinal curve in the lower back.
`Perceptually, every one of the subjects felt that
`their abdominal muscles felt more “firm” and “toned”
`after using NMES for 8 weeks. These feelings were
`supported by significant improvements on the scores
`for the Body Shape Scale and the Body Satisfaction
`Scale. These results are in agreement with the
`findings of Caulfield et al. (2002) and Cullinane et al.
`(2002), who also found abdominal NMES to provide
`self-perceived benefits.
`Despite the fact that subjects perceived their
`abdomens to be more firmed and toned, they did not
`have significant improvements in their self-esteem.
`Individual items on the self-esteem questionnaire
`indicated
`that
`the subjects did not feel more
`confident, compare their shape more favorably to
`others, or feel healthier after completing the study.
`This was probably due to the fact that even though
`the subjects felt that their abdomens were stronger
`and firmer, they didn’t perceive themselves to look
`any different because
`they did not
`lose any
`subcutaneous fat.
`The big question is: Why did this study have
`such positive results when studies using other
`commercially available NMES products found little
`improvement in many of the same parameters? The
`answer probably is related to the strength of the
`electrically induced contractions attained by subjects
`in the current study. In order to improve the strength
`of a muscle, whether through resistance training or
`NMES, the muscle must be overloaded above a
`critical threshold. While this threshold can be as low
`as 30% of MVC
`in deconditioned
`individuals
`(Mueller, 1959), it must typically be in the range of
`60-80% of MVC to induce changes (Currier and
`Mann, 1983; Selkowitz, 1989; Soo et al., 1988). The
`studies that have shown a positive benefit using
`NMES (Currier and Mann, 1983; Muffiuletti, 2002;
`Selkowitz, 1985) have all utilized contractions in
`excess of 60% of pre-training MVC. Selkowitz
`(1985) reported a strong relationship between the %
`MVC utilized for training and the magnitude of
`
`strength improvement. In the study by Porcari et al.
`(2002) that found no benefit of NMES, the elicited
`contractions were less than 20% of MVC.
`In the current study, the strength of contraction
`was not assessed directly, but subjects were asked to
`rate the strength of contraction they felt they were
`receiving on a scale of 0 (no contraction) to 10
`(maximal tolerable contraction). Subjects rated the
`contractions as 8.2 at the mid-point of the study and
`8.5 at the conclusion of the study. While it is
`impossible to translate this into a % MVC value, it is
`obvious
`that subjects were obtaining
`forceful
`contractions.
`The ability of the product used in this study to
`elicit strong contractions is most likely due to two
`factors. First, the NMES unit uses large, pre-gelled
`electrodes. Thus, the electrical current applied to the
`muscle is spread out over a large area. In the study
`by Porcari et al. (2002), the electrodes were made of
`rubber and water was used as the conducting
`medium. This made
`the electrically
`induced
`contractions very uncomforta