Journal of Physical Education and Sport
®
(JPES), 16(1), Art 7, pp. 38 - 45, 2016
online ISSN: 2247 - 806X; p-ISSN: 2247 – 8051; ISSN - L = 2247 - 8051 © JPES
38 -----------------------------------------------------------------------------------------------------------------------------------
Corresponding Author CELİL KAÇOĞLU, E-mail: ckacoglu@anadolu.edu.tr
Original Article
Acute effects of lower body electromyostimulation application with two different
frequencies on isokinetic strength and jumping performance
CELİL KAÇOĞLU
1
, MEHMET KALE
2
1,2
Coaching Education Department, Sport Sciences Faculty, Anadolu University, TURKEY
Published online: March 25, 2016
(Accepted for publication February 05, 2016)
DOI:10.7752/jpes.2016.01007
Abstract:
Electromyostimulation is commonly used for potentiation of muscle strength to supplement voluntary
muscle contractions. However, the acute effects of the lower body electromyostimulation on muscle
strengthening are poorly known. Fourteen moderately trained men exposed to three lower body
electromyostimulation sessions in nonconsecutive days under experimental conditions (30Hz, 100Hz) and
control condition (0Hz). Each subject participated in post-tests including squat jump, countermovement jump
and dominant concentric knee extension-flexion isokinetic strength at 60, 180, 300ºs-1. All tests performed 90
seconds after a single bout of lower body electromyostimulation with 90º static squat position for 16 seconds (4s
Electromyostimulation/4s rest) at maximal tolerated current intensity. Statistical analysis have shown that there
are significant increases in jump heights (p<0.05), rating perceived exertion (p≤0.001) and knee flexion torques
at 180 and 300ºs-1 angular velocities (p<0.05) for acute electromyostimulation with two experimental conditions
compared to control condition. Postactivation potentiation effect of conditioning contractions can be responsible
for mechanism under these significant differences. However, there were no significant differences between low
and high frequencies regarding 60º, 180º, 300ºs-1 extension and 60ºs-1 flexion knee isokinetic torques (p>0.05)
and all jump values (p>0.05). In conclusion, lower body electromyostimulation at low or high frequencies can
increase explosive strength regarding high-speed flexion torques and jump height in acute phase of moderately
trained men.
Keywords: acute effect, electromyostimulation, ısokinetic strength, jump performance, perceived exertion,
Potentiation
Introduction
The possibility to generate contractile activity of a muscle with an electrical current application on the
neuromuscular system has been known since the 18th century (Bax et al., 2005; Vanderthommen and Duchateau,
2007). The number of Electromyostimulation (EMS) studies has been enlarged in the last 30 years on healthy
individuals and EMS has been paid attention as a new training method for athletes. Yakov Kotz has claimed that
increased muscle strength (~%40) after short-term EMS training program with high frequency caused this
interest. There are a lot of studies (Strauss and Domenico, 1986; Holcomb, 2005; Kraemer and Mendryk, 1982;
Komi, 2008; Porcari et al., 2002; Walmsley et al., 1984; Yanagi et al., 2003) supporting or opposing these results
in literature.
High-frequency EMS training has increased its popularity as a method of strength training to increase
maximal voluntary strength of the lower limb muscles among healthy individuals and elite athletes in the last
few years (Maffiuletti et al., 2002a; Maffiuletti et al., 2002b; Malatesta et al., 2003; Marqueste et al., 2010;
Taifour et al., 2013). EMS has been accepted to be an important complement in rutin strength training programs
for the enhancement of athletic performance (Thorstensson et al., 1976) because it can provide more intense
contraction to the stimulated muscle and thereby induce greater adaptive responses (Borniquez et al., 1993;
Maffiuletti et al., 2000). LB-EMS application is an effective training method to enhance lower body power that
provides intense contraction to the stimulated leg muscles and thereby induces greater adaptive responses. Local
EMS application have shown positive effects on neuromuscular parameters in athletes and healthy individuals;
however; there are a few multi-joint EMS studies on the effects of athletic performance and therefore, the
feasibility and acceptability of this new training technology have turned out to be an important point (Kemmler
et al., 2012; Kraemer and Mendryk, 1982; Kale et al., 2014; Komi, 2008, Vanderthommen and Duchateau, 2007;
Porcari et al., 2002).
Acute EMS applications produced the similar physiological effects as conventional aerobic exercises.
Some studies have indicated that EMS training combined with aerobic exercises cause more energy consumption
(%17) than aerobic exercises (Kemmler et al., 2012; Hennessy et al., 2010). Therefore it is necessary to study on
the acute effects of EMS application on explosive power performances. In different EMS protocols,
theoretically, partial or complete neuromuscular adaptations seem possible, but the physiological effects are
CELİL KAÇOĞLU, MEHMET KALE
---------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------
JPES ®
www.efsupit.ro
39
different from each other. Also acute and chronic effects of EMS are still not clear. There are limited studies on
the effect of a single EMS training session on isokinetic strength and jumping performance. The purpose of the
present study was to investigate the acute effects of a lower body electromyostimulation (LB-EMS) bout on
maximal isokinetic strength of the dominant knee extensor-flexor muscles and vertical jumping performance.
Materials and Methods
In these study vertical jump including squat jump (SJ) to assess explosive power and counter movement
jump (CMJ) to assess elastic strenght performance of the lower extremity are tested. Maximal isokinetic strength
test of the knee extensor-flexor muscles at different angular velocities is also an acceptable test to evaluate leg
power. Heights of SJ and CMJ, and isokinetic maximal knee extensor-flexor torque values at three angular
velocities were assessed to examine the acute effects of LB-EMS during static squat movement. A randomized
crossover trial with moderately trained men was used to address the hypothesis of the acute effect of LB-EMS
during static squat movement on jumping performance and knee extensor-flexor torque values at three angular
velocities (60, 180 and 300º/s) of two different frequencies (low=30Hz and high=100Hz) with the control
condition frequency (0Hz). The current protocol allowed each subject to serve as his own control.
Participants
Fourteen moderately healty trained men, who routinely perform moderate intensity exercises at least
four times a week and 2-2.5 hours a day, voluntarily participated into the study. Descriptive statistics of the
subjects are given in the Table 1. The subjects were instructed not to be involved in any additional exercise and
not to consume any alcohol and caffeine. They had an ordinary pretraining diet for at least 24 hours before
measuring and testing sessions. Subjects were advised to be properly hydrated (~500ml) one hour before testing.
The laboratory temperature ranged from 23 to 25ºC during the tests. The study protocol was conducted in
compliance with the declaration of Helsinki and the study started after obtaining ethical approval from the
local ethics committee of Osmangazi University. Subjects having any injury risk were not included in this study.
All subjects were informed about the study protocol. The participants were notified about the potential risks and
benefits of the study and their written informed consent was taken.
Volunteers were recruited in some regional high schools and colleges in the city of Eskişehir, in Turkey.
Volunteers inclusion and exclusion criteria were established by the researcher before the beginning of the study.
Researchers screened volunteers using the following inclusion criteria from previous the study: (1) they were
selected from among healthy men, (2) age range is 13-26 years, (3) they have been doing physical
activity regularly at a moderate effort at least 2 years. Also, volunteers were excluded from the stuty for the
following reasons: (1) participating in any kind of experimental EMS studies, (2) having any risk of heart
disease, (3) epilepsy, (4) transient ischemic attack, (5) history of no stroke and these kind of neurological
disorders, (6) open wounds, (7) using of pacemaker and (8) having any health problems.
Table 1. Descriptives of participants (n=14)
Variables Mean ± SD
Age (year)
Height (cm)
Weight (kg)
Body Mass Index (kg.m²
-1
)
Body Fat Percentage (%)
Exercise Volume (h.wk
-1
)
Exercise Backround (year)
Rest Heart Beat (beat.min
-1
)
19.5±6.7
180.9±7.9
71.5±14.6
22.0±3.7
16.4±3.8
9.1±1.5
7.7±5.8
75.2±11.6
Procedures
All of the subjects participated into the study underwent LB-EMS applications at two different
frequencies of low (30Hz) and high (100Hz), and also control condition frequency (0Hz) in a random order. The
measurements and tests were made at the same time of the day in view of the chronobiological effects (09:00-
12:00am). Each subject participated in the same test conditions (0, 30 and 100Hz), a standart test day started
with warm-up session. After these session, tests were perfomed with SJ and CMJ and then dominant isokinetic
knee flexion/extension strength tests were taken. After that three days rest was given at least between each
condition tests and all measurements and all LB-EMS applications in these study were completed in a total of 17
days. The subjects participated in all the testing and the LB-EMS implementation to familiarize with the trial one
week before having the test session. Subjects performed all of the three experimental sessions (30Hz, 100Hz, and
0Hz) having at least one day off between the sessions. Each subject performed all measurement and test sessions
according to the study protocol. Maximal intensity comfortably tolerated at 30Hz and 100Hz frequencies of LB-
EMS applications for each subject were determined during the familiarisation period. Subjects had 90s rest on
sitting position after the end of the LB-EMS application. Squat jump (SJ) and counter movement jump (CMJ)
tests were performed with a wireless jump assessment device right after it (Freejump, Sensorize, Italy). Ninety
CELİL KAÇOĞLU, MEHMET KALE
---------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------
JPES ®
www.efsupit.ro
40
seconds after the end of jumping tests, subjects performed isokinetic strength tests with dominant knee knee
extensor-flexor muscles at three angular velocities (60, 180 and 300º/s) with an isokinetic dynamometer (Humac
Norm Testing & Rehabilitation System, USA). Verbal encouragement and required feedback were given to each
participant during each measurement, test, and LB-EMS application. In addition, the ratings of perceived
exertion during the LB-EMS application and the control condition frequency were determined with Borg Scale
(RPE; 6-20 Borg scale). Flow chart of the study design is given at Figure 1.
Fig. 1. Flow Chart of The Study
Lower body EMS application
Initially, anthropometric measurements were taken after 10min warm-up implemented with 5min
unloaded pedaling a cycle ergometer and then 5min various stretching and jumping exercises, respectively. The
strip electrodes (44x4cm for the thigh region and 27x4cm for calf region) were placed on the area of thigh and
calf muscles during the 2 minutes rest period after the warm-up session. Then, 16s EMS application was applied
bilaterally with an EMS application device (Miha Bodytec, Germany) at the maximal tolerated comfortably
current intensity that specified in the trial and familiarisation period. The current was applied to 4s with 4s rest
intervals with the specific current parameters that was described in the Table 2. None of the subjects reported
any serious discomfort during EMS application. Each subject retained the 90º static squat-position (Figure 2.)
throughout the LB-EMS application and rested in standing position during the rest intervals.
Fig.2. The 90º static squat LB-EMS position
Table 2. Electrical current parameters
Current Parameters EMS Application Settings
Stimulation Frequency
Pulse Duration
Current Break
Current Breadth
Current Type
Duration
Ramp-up Time
Current Intensity
30Hz / 100Hz
4s
4s
400µs
bipolar
16s
0s
100% maximal tolerated
Data collection and analysis
CELİL KAÇOĞLU, MEHMET KALE
---------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------
JPES ®
www.efsupit.ro
41
Anthropometry and body fat percentage measurements
Height was measured to the nearest +0.1cm between head's vertex point and foot using a wall mounted
stadiometer (Holtain Ltd, UK) after a deep inspration. The subjects without shoes wore short, t-shirt, and head at
frontal plane. Body weight and body fat percentage were measured with bioelectrical impedance analyser (Tanita
MC 180MA, Japan). Body weight was measured to nearest +0.1kg and during body fat percentage
measurements subjects without shoes wore short and they kept eyes forward in standing position. All the
measurements were taken two times by the same researcher and the mean values were recorded.
Jumping tests
Subjects were rested 90s in sitting position at the end of LB-EMS. The rest period after, squat jump (SJ)
and counter movement jump (CMJ) were tested using a waist belt shaped wireless jumping assessment device
(Freejump, Sensorize, Italy). Squat jump test is a variation of the vertical jump test method used to determine leg
explosive power. In this test, hands are placed on the waist throughout the test and starting position keep about
one second and then subject jumps vertically as high as possible without arm swinging or a downward
movement. Subjects flexed their knees until they felt a comfortable starting position where semi-squatting
position occurred normally at a knee angle of about 85º (Bosco and Komi, 1979). The subjects maintained their
posture at least 2 to 3s, which prevented the prestretching of muscles from any preliminary downward movement
before jumping. CMJ, where the muscles were prestretched before shortening in the desired direction, made use
of the stretch–shortening cycle. The subjects performed maximum vertical jump with hands kept on the hips,
started in an upright standing position following a preliminary downward movement by flexing the knee
approximately to the same knee angle as the starting position in SJ during CMJ. To provide standardization
during vertical jump tests, the subjects performed the jumps with the hands kept on the hips. The subjects
performed 2 maximum vertical jump in starting position and landed on the floor with the legs kept straight for
both SJ and CMJ. Each jump attempt was separated with a 1-minute rest period and the best attemps were
recorded for statistical assessment.
Isokinetic strength tests
Isokinetic concentric and concentric knee extension and flexion torques were tested at three angular
velocities (60, 180, and 300º/s) of dominant leg with a computer controlled isokinetic dynamometer (Humac
Norm Testing & Rehabilitation System, USA) at the end of 90s rest period following the jumping tests. Subjects
performed 5 maximal efforts with 60s rest intervals after each test at a given angular velocities as recommended
by Davies et al (Davies et al., 2000) and the highest value of these efforts was accepted as the peak torque.
Subjects performed three maximum efforts before testing at each angular velocity to warm-up. Each test started
after 30s rest period at the end of each angular velocity warm-up. The subjects were verbally encouraged during
all test process. The calibration of the isokinetic dynamometer was done according to CSMI (2003) before the
test sessions. Dynamometer attachments were adjusted to each subject before the tests. The range of motion of
the knee joint were adjusted to exactly 0-90º position as described by CSMI (2003) after the subjects placed in
the two-position seat of the dynamometer for the knee flexion/extension test. Dynamometer axis of rotation was
aligned with using the lateral femoral epicondyle. The calf pad was placed proximal to the lateral malleolus.
Each subject was confortably stabilized by straps including thigh, waist, and chest to minimize trunk and thigh
movements. Each subject gripped the handles located in each side of the seat throughout the test.
Ratings of perceived exertion
Subjects were asked to evaluate the intensity of the low and high of LB-EMS sessions (30 and 100Hz)
and control session (0Hz) on Borg’s rating of perceived Exertion (RPE) scale (Borg, 1982) between 6 (very
low) and 20 (very high). The same investigator also recorded these evaluations during each session.
Statistical analysis
A two-way analysis of variance (Friedman's ANOVA) with repeated measure was used to compare all
three conditions of each isokinetic strength measures and jump performances. If there was a significant
difference as a result of variance analysis, Wilcoxon test was used to determine statistical differences between
two of the three conditions. Descriptive statistics were applied to identify the chracteristics of the subjects on
each conditions, mean scores and standart deviation values were calculated for each participant's three conditions
in each isokinetic and jump performances. All data were expressed as mean ±SD that can be seen Table 3.
Statistical significance was set to a probability level of p≤0.05 at the %95 level of confidence. All statistical
analyses were run using the Statistical Package for the Social Sciences (IBM SPSS), version 20 for Windows
(SPSS Inc., Chicago, IL).
Results
The effects of acute LB-EMS application with multi-joint participation at maximal tolerated
comfortable current intensity on jumping performance, perceived exertion and isokinetic strength values are
given in the Table 3 and 4.
CELİL KAÇOĞLU, MEHMET KALE
---------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------
JPES ®
www.efsupit.ro
42
Jumping performances
As a result of the statistical analysis, a significant improvement in both SJ and CMJ height (p<0.05) was
obtained after the LB-EMS application. There were significant differences in LB-EMS applications among the
control, low and high frequency conditions in SJ (p<0.05), CMJ (p<0.05) (Table 3). There is a statistically
significant different in low- and high-frequency LB-EMS conditions (p<0.05) compared to the control condition
LB-EMS to control condition in SJ and CMJ (Table 4). There was no significant difference between low
frequency and high frequency LB-EMS in CMJ.
Ratings of perceived exertion
The perceived exertion rates significantly (p<0.001) increased during LB-EMS application in each of
low- and high frequencies compared to control condition LB-EMS frequency (Table 3). Perceived exertion
values were significantly higher in the low and high frequency LB-EMS conditions compared to the control
condition LB-EMS frequency (p≤0.001) and also high frequency LB-EMS condition compared to low frequency
LB-EMS condition (p<0.05).
Table 3. Comparisons and descriptive statistics (mean value ± SD) of dominant knee extension/flexion isokinetic
torque values (Nm), vertical jump performances (Cm) and rating of perceived exertion values after low, high and
control LB-EMS frequency conditions
† Nm = Newton meter. Differences between measurements are shown (* p ≤ 0.05 and ** p ≤ 0.001).
Ex:Extensor, Flex:Flexor
Isokinetic strength performances
It can be seen on the Table 3 that there are statistically significant differences in dominant knee flexion
torque values at 180º/s and 300º/s angular velocities (p<0.05) related to low, high and control condition LB-EMS
frequencies. There are no significant changes in other torque values at all three conditions. Knee flexion torque
values are significantly higher in the low and high frequency conditions compared to control condition at 180º/s
angular velocity (p<0.05) and the low and high frequency conditions compared to control condition at 300º/s
angular velocity (p<0.05) but not high frequency condition compared to low frequency condition at all torque
values (Table 4).
Table 4. Comparisons of dominant knee flexion isokinetic strength, vertical jump performance and ratings of
perceived exertion after low, high and control LB-EMS frequency conditions
Control - Low Control - High High - Low
Z-score P Z-score P Z-score P
180º/s Flexion
-2.835 0.006* -2.199 0.028* -0.440 0.660
300º/s Flexion
-2.795 0.005* -2.138 0.033* -0.175 0.861
SJ
-2.362 0.018* -3.081 0.002* -0.535 0.592
CMJ
-2.469 0.014* -2.439 0.015* 0.258 0.796
RPE
-3.316 0.001** -3.314 0.001** -3.108 0.002*
**p≤0.001; *p≤0.05
Note = The Z-scores are from a Wilcoxon two-sample rank-sum test.
Discussion
In this study we have observed that there are acute effects of a single bout of LB-EMS applications with
different frequencies (30Hz and 100Hz) on isokinetic strength and jump performance. The results have shown
Control
Frequency
(0Hz)
(n = 14)
Low
Frequency
(30Hz)
( n = 14)
High
Frequency
(100Hz)
( n = 14)
Chi-
Square
P
Extension
175.9±37.0 178.7±42.2 172.2±42.6 2.704 >0.05
60º/s
Flexion
120.0±26.0 122.8±44.2 129.0±33.6 1.811 >0.05
Extension
118.0±19.5 122.5±21.0 120.9±21.8 1.962 >0.05
180º/s
Flexion
98.5±14.7 109.5±16.4 108.2±17.7 8.618 <0.05*
Extension
87.2±13.1 93.0±13.1 92.9±17.0 3.000 >0.05
300º/s
Flexion
78.7±10.5 88.7±15.3 87.8±13.5 8.982 <0.05*
SJ
28.9±3.1 31.3±3.0 31.7±2.9 12.286 <0.05*
CMJ
32.0±2.7 33.8±3.5 34.0±3.1 11.511 <0.05*
RPE
6.0±0.0 14.2±1.5 15.9±1.9 27.111 <0.001**