Comparison of Different Quadriceps Femoris Isometric Strengthening Methods in Healthy Young Women
Phase: NA
Conditions: Muscle Strength
Sponsor: Pamukkale University

Comparison of Different Quadriceps Femoris Isometric Strengthening Methods in Healthy 
Young Women 
Authors 
Bilge Basakcı Calik1, Elif Gur Kabul1, Meryem Buke, Fatma Unver1, Filiz Altug1 
Affiliations 
1 School of Physical Therapy and Rehabilitation, Pamukkale University, Denizli, Turkey 
Running Tittle: Comparison of Different Quadriceps Strengthening 
Corresponding author 
Bilge BAŞAKÇI ÇALIK 
E-mail: fztbilge@hotmail.com 
Tel: 00.90.2582964282/Fax:00.90.2582964494 
Pamukkale University, School of Physical Therapy and Rehabilitation, Kınıklı 20070, Denizli, 
TURKEY. 

ABSTRACT 
Background:It has been reported in previous studies that more motor units are fired with 
electrical stimulation than voluntary muscle contraction, and even high intensity currents 
provide 10-30% more contractions than voluntary muscle contraction.  
Objective:This study was planned to compare the effectiveness of high voltage pulsed 
galvanic (HVPG) stimulation, Russian current and isometric exercise on quadriceps femoris 
(QF) isometric muscle strength in healthy young women. 
Methods:Forty-six healthy young women were included in the study (mean age=21.02 ± 
1.27). Before and after the training, the dominant side QF isometric muscle strength of 
participants was assessed with the Isokinetic Dynamometer (Humac Norm Testing 
Rehabilitation System, CSMI Medical Solutions, USA). The peak torque and average torques 
of the participants were recorded after the test. The training was planned as HVPG current for 
the the first group (n = 16), as Russian current for the second group (n = 15) and as isometric 
strengthening for the third group (n = 15). All treatments were performed under 
physiotherapist supervision for a total of 15 sessions for 3 days a week for 5 weeks.  
Results:The peak torque and average torque delta values were calculated to determine the 
increase in isometric muscle strength of Quadriceps Femoris. No statistical difference was 
found between the groups when the peak torque and average torque delta values were 
compared (p> 0.05). 
Limitations:The number of participants and duration of follow-up were inadequate to 
determine  can help to future resarchs. 
Conclusions:The highest rate of change belongs to the HVPG group in terns of increasing the 
Quadriceps Femoris isometric muscle strength, therefore, we recommend that it is preferred in 
clinical practice.  
Keywords: Quadriceps femoris, isometric force, HVPG, Russian current, Exercise 

INTRODUCTION 
Neuromuscular electrical stimulation (NMES) is a non-invasive treatment modality 
that stimulates motor neurons with low-amplitude electrical currents to induce voluntary 
muscle contractions. 1,2 A healthy muscle strength can be improved by active exercise against 
resistance or by NMES. There are many articles in the literature about increasing muscle 
strength, whether exercise is more effective than electrical muscle stimulation or electrical 
muscle stimulation than exercise and no clear consensus has been reached on which is more 
effective .3-6 In many studies, electrical stimulation was applied either alone or combined with 
exercise to improve QF muscle strength of healthy subjects. 7-11 
Faradic current, Russian current and HVPG currents are frequently used clinically for 
the purpose of strengthening the healthy muscle by electric stimulation. If the frequency of the 
current is high enough, tetanic muscle contraction can be obtained, same as in maximal 
voluntary contraction by stimulation. 12 According to a study by Kots, high-intensity currents 
have been claimed to provide 10-30% more contractions than voluntary muscle contractions. 
Faradic current is not preferred in our study because of the length of the transition period 
(1000μs) and the short number of pulses (1-60 pulses / sec). 13 In this study, the Russian 
current and another high-intensity current, HVPG current, were selected from the high-
intensity currents as Kots proposed, in order to strengthen the healthy muscle.  
Russian currents are a high frequency current of 2500 Hz and reduce the resistance of 
the skin and it would penetrate deeper and reach deeper motor nerves. Kots has stated that in 
professional athletes, Russian current practice can increase  maximal voluntary contraction of 
the muscle by 40% This technique provides maximum strength gain without fatigue due to 
long rest period.13 
HVPG current is a new form of neuromuscular electrical stimulation. This current 
began to be widely used in the 1970's.14 It has been shown that when the voltage is increased 

and the transition period of the electric current is reduced, deeper tissues can be excited 
without undergoing damage. 15 In the case of HVPG current applications, there is less tissue 
resistance or reaction capacity than low voltage applications.  This feature is the theoretical 
explanation for that HVPG is more effective and can be better tolarated. The greatest 
advantage of the HVPG current is that it has a higher electrical motion gain than other 
methods. Thanks to this low impedance due to its superiority, it penetrates the skin more 
easily and depolarizes the nerve fibers and provides continuity of tissue healing. 16-17 When 
compared to other neuromuscular stimulators, high-voltage intermittant current has the 
advantage of high electrical mobility which is the voltage. Due to its low impedance, it 
penetrates the skin more easily and can be better tolarated. Because of the high voltage, the 
skin resistance reduces spontaneously.11 
Isometric or static strength training is exercises performed without joint movement 
and changing muscle length during muscle contraction. Strength increase depends on the 
amount and duration of contraction, the intensity of contraction, the intensity of training and 
the joint angle.18-19 Isometric training can increase strength in a spesific muscle or muscle 
groups. It has been reported that the contraction should be continued for 3-10 seconds in order 
to increase the strength.19-20 
When we review the literature, we see that NMES and different exercise programs are 
widely used to strengthen QF muscles in healthy individuals. However, these studies differ 
from our study. Baskan et al. (2011) applied isometric exercise training and Russian flow to 
strengthen the QF muscle and assessed the strength increase as concentric force in isokinetic 
system while Silva et al. (2018) has performed isometric and eccentric force evaluation in 
isokinetic system after eccentric training with NMES and NMES alone.7,8 Romero et al. 
(1982) found that isometric muscle strength increased by 31% in the isokinetic system after 
electrical stimulation in healthy subjects.21 However, we did not find a study evaluating the 

isometric strength increase of the QF muscle with isokinetic system by applying two different 
NMES and isometric exercise methods. For this reason, we used methods that increase muscle 
isometric strength, such as Russian current, HVPG current and isometric exercise, to increase 
QF muscle strength in healthy women and evaluated we evaluated isometric force parameter 
wiht the isokinetic system.   
MATERIALS AND METHODS 
Forty-six healthy women (mean age = 21.02 ± 1.27 years) were included in the study 
between 18-30 years of age. Participants' QF isometric muscle strength (torque 
measurements) was assessed twice before and after training with the Isokinetic Dynamometer 
(Humac Norm Testing Rehabilitation system, CSMI Medical Solutions, USA). Participants 
were divided into three groups for training purposes (Figure 1). The training was performed 
on the dominant side QF muscle.  The training was planned as HVPG current for the the first 
group (n = 16), as Russian current for the second group (n = 15) and as isometric 
strengthening for the third group (n = 15). HVPG current was applied for 20 minutes. Russion 
current was applied for 10 minutes for the second group. The strengthening exercises in the 
third group were applied as 10 maximal contractions of 10 seconds and 10 seconds between 
each contraction. Both exercise and stimulation applications were performed after the body 
and knee were positioned and stabilized at 75 ° flexion and 60° flexion angle, respectively.  
All treatments were performed under physiotherapist supervision for a total of 15 sessions for 
3 days a week for 5 weeks.  Demographic data are given in Table 1. 
Inclusion criteria for the study: 
- 
Willingness to participate in the study. 
- 
Not having knee complaints such as pain, lockout, morning arrest, swelling, 
difficulty in walking. 
- 
Not having any orthopedic or neurological disability. 

Exclusion criteria from the study:  
- 
Exercising regularly for the last six months. 
- 
Presence of cardiovascular, pulmonary, orthopedic and neurological problems 
which may prevent exercise. 
The criteria for dismissing from the study: 
- 
Those who can not complete the assessment. 
- 
Those who have any disease status in the evaluation and training process. 
- 
Those who have started to do sport regularly during the training period. 
- 
Those whose date were incomplete. 
- 
Those who do not participate 75% of the training. 
The ethical approval of the study was taken at the Ethics Committee of Non-
Interventional Clinical Researches of Pamukkale University at the meeting no. 08 dated 
06.06.2017. All participants were informed verbally and an informed consent form was 
signed. 
Evaluation 
Muscle strength, Isokinetic strength measurement:  
The dominant side QF isometric muscle strength (torque measurements) of the 
participants was assessed with the Isokinetic Dynamometer (Humac Norm Testing 
Rehabilitation System, CSMI Medical Solutions, USA). Before the test, participants were 
subjected to a standard warm-up of 5 minutes and evaluations were carried out using a 
standard seat. The back of the seat was angled 105 ° backward to provide 75 ° flexion at the 
body. The knee was positioned at an angle of 60 ° and was fixed with bands around the body, 
waist, hip and ankle. Participants had no previous experience with isokinetic dynamometer 
testing, therefore; it was started with a trial whose protocols were same with QF isometric 
muscle strength measurement protocols. Then participants QF isometric muscle strength was 

measured by three 10-second maximal isometric contraction. Rest periods of 3 seconds 
between each contraction were given. Each participant held the sides of the seat with both 
hands during the test. Verbal encouragement was made throughout the whole test to obtain 
maximum strength from the participants. The peak torque and average torques of the 
participants were recorded after the test. 
High Voltage Pulsed Galvanic Current: 
HVPG, was applied by using “Endomed 982”. The instrument was automatically set to 
a pulse rate of 100 μs while the pulse frequency was set to 60 pulses / sec. In order to avoid 
fatigue, the intermittant form of the current was selected and the transition time / rest time was 
set to 4 sec. impulse / 12 sec. The total output voltage of the device ranged from 0 to 500 volts 
and the current intensity was increased until the sensible contraction of the applied muscle 
was achieved without causing too much sense of discomfort. Stimulation was performed after 
the body and knee were positioned and stabilized at 75 ° flexion and 60 ° flexion angle, 
respectively. One of the 6 * 8 cm carbonated electrodes was placed in the distal portion of the 
vastus medialis, while the other one was placed in the proximal portion of the vastus lateralis. 
This placement was intended to stimulate a large proportion of the muscle fibers of the QF 
muscle.22 The HVPG was applied for a total of 20 minutes. Current intensity was increased to 
obtain optimal muscle contraction. 
Russian Current 
 
In the treatment with the Russian current, a protocol developed by Kots, also known  
in the literature as "Russian Technique", was used. In the treatment with the Russian 
movement, a protocol developed by Kots, also known as "Russian Technique", was used in 
the literature. There were 10 muscle contractions per treatment session in this protocol. Each 
contraction lasted for 10 seconds and a resting time of 50 seconds were given for the next 
contraction (transition: rest ratio was 1/5).13 Russian current “Endomed 982” was applied 

using a model device at a frequency of 2500 Hz with a transition time of 400 μs. The position 
of the participants in the application and the placement of the electrodes were same as the the 
other application. Current intensity was increased until tetanic muscle contraction was 
obtained. 
Isometric Exercise: 
The body and knee of the participants in the isometric exercise group were  positioned 
and stabilized at 75 ° flexion and 60 ° flexion angle, respectively as in the stimulation groups. 
Participants were asked to do 10 repetitions as 10 seconds of maximum voluntary contractions 
and 10 seconds of rest. 
Statistical analysis: 
The data was analyzed by SPSS (version 21.0) packet program. The Shapiro Wilk test 
was used to test whether the data was appropriate for normal distribution. Continuous 
variables were given as mean ± standard deviation and categorical variables were given as  
number and percentage. The Wilcoxon test was used for the data oblatined at baseline and at 
the end of 5th week and the Kruskal Wallis test was used to compare delta values. 
Significance level was accepted as p <0.05 in statistical test results. 
RESULTS 
The study included 46 young women with a mean age of 21.02 ± 1.27 years, which 
was planned to compare the efficacy of HVPG, Russian currents and exercise on quadriceps 
muscle strength enhancement in healthy women. But 32 women completed the protocol (Fig. 
1). No injuries were reported related with training. The participation rate in the treatment 
sessions was 95%. There was no statistically significant difference between the demographic 
data of the groups (p> 0.05) (Table 1). 
Results of comparison of post-training and delta values of groups: 

The quadriceps isometric muscle strength was significantly increased in all groups in 
terms of peak torque and average torque values after training compared to pre-training values 
(p <0.05) (Table 2). When comparing the peak torque and average torque delta values, it was 
found that there was no statistical difference between the groups in terms of peak torque (p = 
0.691) and average torque (p = 0.901) delta values. The highest increase was found in the 
HVPG stimulation group (Table 3). 
DISCUSSION 
It was found that three different methods were effective in increasing isometric muscle 
strength, but not superior to each other, in the result of this study evaluated by isokinetic 
method on isometric QF muscle strength of three different methods, HVPG, Russian currents 
and isometric exercise in healthy women participants. 
In the literature, it has been shown in many studies that electrical stimulation in 
healthy individuals provided an increase in muscle strength.7-10, 23-25 It has been determined 
that Type II muscle fiber is selectively increased following muscle stimulation by electrical 
stimulation. Type II muscle fibers have more specialized resistance than Type I muscle fibers, 
and selective increase in Type II muscle fiber increases general muscle strength. In addition, a 
high amount of activity can be loaded into the muscles by activating large-scale motor units 
during muscle activation with electrical stimulation.26 It has also been reported that with 
isometric exercise the motor unit synchronization can be increased by 5%, thus a higher 
power increase can be provided by increasing muscle potency.27 
Strength training can cause additional complications such as muscle spasms, fatigue 
and delayed muscle pain. It has been reported in the literature that 10 applications may be 
performed 2 or 3 times a week to reduce possible side effects.20 It has also been reported that 
in a study examining the effect of the frequency of exercise on muscle strength increase, three 

times a week electrical stimulation was casused significant increase.29 We planned our 
treatment to reduce these side effects to be three days a week with 10 repetitions. 
When the efficiency of electrical stimulation to muscular functions is examined, the 
characteristic of the current is an important criterion. When the effect of the biophysical 
current and the Russian current applied on QF muscle on knee extension torque was 
compared, it has been found that they created similar effects.30 In another study, Currier et al. 
(1983) performed 15 sessions of 3 sessions per week for 5 weeks in total to investigate the 
effects of electrical stimulation and isometric exercise on QF muscle of healthy individuals. 
The increase in strength was found in each training groups after the training, however groups 
did not have any advantage over each other.3 The effectiveness of strength training on QF 
muscle with electrical stimulation and voluntary muscle contraction in Mayo clinical 
biomechanical laboratory and the results were reported to be similar.10  
Taspinar et al. (2011) emphasized that electrical stimulation alone is not enough to 
increase muscle strength, and that training programs involving voluntary muscle activation 
should be included in the rehabilitation program while there are studies in the literature 
reporting that electrical stimulation and exercise practices have similar effects.8 
In studies that the evaluations were performed with the isokinetic system; Bircan et al. 
(2002) applied strenght training on QF muscle strenght with interferential current and low 
frequency biphasic symmetrical current and have reported after four weeks of training that 
there was an increase in strength in both groups but no difference between the groups.31 
Unlike our study, low and medium frequency currents were used in this study and the change 
in muscle isotonic strength  was evaluated with the isokinetic system. Baskan et al. (2011) 
obtained progression in terms of  muscular strength, performance and isotonic muscle strength 
in the isokinetic system in both groups after Russian current and maximal voluntary isometric 
exercise on healthy QF muscle and have reported that both applications had no superiority to 

each other.7 The stimulation and exercise method used in this study is similar to ours however, 
despite  isometric training was given in order to increase strength, it was seen that  isotonic 
strength in the isokinetic system was evaluated. In addition, in a recent study in the literature, 
eccentric training with and without NMES was applied to improve the healthy QF muscle and 
isometric and eccentric strength increases in the isokinetic system were evaluated.9 In our 
study, we evaluated the effect of 5-week isometric exercise and two different neuromuscular 
electrical stimulation applications on isometric force with the isokinetic system. It has been 
reported in the literature that electrical stimulation may increase the isometric strength at 
different levels. 32,33   
 In the literature, it is seen that NMES and exercise applications are used to increase 
the strength in healthy QF, and the results created by NMES and exercise were similar. Our 
results are also parallel to this similarity. 
We believe that the individual's current situation and needs are important in deciding 
between the choice of NMES or exercise.  For example, we believe that the use of NMES 
may be the reason for preference in preserving the functional state of the muscles in some 
cases such as surgical or traumatic conditions that require the immobilization process, in 
young children and elderly people who are difficult to communicate, can not concentrate 
enough to exercise. Isometric exercise; have some advantages such as not requiring 
equipment, providing an increase in strength without adding the burden on joints  in the early 
period after the injury,  prevention of atrophy in long immobilization situations especially in 
elderly individuals.  
In the literature, it seems appropriate to use the HVPG current among the other 
currents to increase muscle strength due to that it creates less less variation compared to other 
currents on the biophysical properties of the skin such as skin temperature and elasticity.11 In 
our study, we did not obtain superiority between the two currents we used, Russian and 

HVPG. However, HVPG group has the highest rate of change in QF isometric muscle 
strength increase, therefore; we recommend that it can be preferred in clinical practice. We 
believe that it is necessary to plan studies with more sessions to determine the superiority of 
the applications relative to each other. 
CONCLUSION 
 We determined the isometric strength increase in healthy QF by both NMES 
applications and isometric exercise method as a result of our study, and we see that these three 
applications have similar effects in terms of isometric muscle strength. Increased isometric 
muscle strength is an important parameter to maintain joint stability and to maintain muscle 
strength during injuries or early postoperative period and should be included in training and 
assessment methods. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Figure1: Flowchart of the study. 
Pre-training evaluation 
Pre-training evaluation 
Post-training evaluation 
(n=11) 
Post-training evaluation 
(n=11) 
Post-training evaluation 
(n=10) 
Week-0 
Week 6 
Healthy young women 
N= 46 
5 dropouts 
Randomization 
HVPG 
(n=16) 
Russian current 
(n=15) 
Isometric exercise 
(n=15) 
Pre-training evaluation 
Week 1=20min x 3 
Week 2=20min x 3 
Week 3=20min x 3 
Week 4=20min x 3 
Week 5=20min x 3
Week 1=10minx3 
Week 2=10minx3 
Week 3=10minx3 
Week 4=10minx3 
Week 5=10minx3
Week 1=(10secx10) x3 
Week 2=(10secx10) x3 
Week 3=(10secx10) x3 
Week 4=(10secx10) x3 
Week 5=(10secx10) x3
4 dropouts 
5 dropouts 
Week 1-5 

Table 1: Demographic data 
 
HVPG 
 (n=11) 
Russian current 
(n=11) 
Isometric exercise 
(n=10) 
Age (Years)  
20.63± 1.68 
21.09 ± 0.94 
21.2 ± 1.13 
Weight (kg) 
59.18 ± 12.15 
56.45 ± 8.39 
58.1 ± 9.67 
Height (m) 
1.64 ± 0.59 
1.63 ± 0.51 
1.61 ± 0.69 
BMI (kg/m²) 
21.82 ± 4.09 
20.99 ± 2.60 
22.31 ± 3.65 
BMI: Body mass index, HVPG: High Voltage Pulsed Galvanic 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Table 2: Intragroup analysis for pre-post quadriceps isometric muscle strength  
 
HVPG 
(n=11) 
Russian current 
(n=11) 
Isometric exercise 
(n=10) 
 
Pre-
training 
Post- 
training 
p 
Pre-
training 
Post- 
training 
p 
Pre-
training 
Post- 
training 
p 
Peak 
torque 
157 ± 
25.13 
 
172.18 ± 
27.41 
 
0.013* 
147.63 ± 
30.21 
157.18 ± 
29.79 
 
0.029* 
156.60 ± 
26.9 
 
164.1 ± 
28.38 
 
0.014* 
Average 
torques 
138.54 ± 
28.3 
 
154.81 ± 
27.92 
 
0.007* 
130.54 ± 
29.45 
 
141.45 ± 
30.72 
 
0.006* 
137.5 ± 
26 
148.9 ± 
28.22 
 
0.007* 
HVPG: High Voltage Pulsed Galvanic, Wilcoxon Signed Rank Test, * p<0.05 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Table 3: Intragroup analysis for maximum torque and average torque delta values 
 
HVPG 
(n=11) 
∆% 
 
Russian current 
(n=11)  
∆% 
 
Isometric exercise 
(n=10) 
∆% 
 
p 
Peak 
torque 
-10.14±11.54 
-7.11±9.22 
-4.0±4.85 
0.691 
Average 
torques 
-13.25±17.58 
 
-8.99±9.77 
 
-8.46±6.1 
 
0.901 
HVPG: High Voltage Pulsed,Galvanic ∆%: percantage change Kruskal- Wallis Test