Effects on Isometric Force Induction, Tolerance and Fatigue of Burst-modulated Kilohertz Frequency (Neo-Russian and Aussie) and Low Frequency (Rectangular Biphasic Symmetrical) Neuromuscular Electrical Stimulation in Healthy Subjects
Phase: NA
Conditions: Healthy
Sponsor: Instituto Universitario de Ciencias de la Salud Fundación H.A. Barceló

 
 
 
 
 
 
 
 
 
 
 
ELECTRICAL STIMULATION WITH DFIFERENT CURRENTS: THE EFFECTS 
ON FORCE, TOLERANCE AND FATIGUE IN HEALTHY SUBJECTS 
 
      
 
 
 
 
 
A u t h o r :  R o n z i o ,  O s c a r  
A c a d e m i c  U n i t :  I n s t i t u t o  H . A .  B a r c e l ó  -  B u e n o s  A i r e s  C a m p u s   
 
N C T 0 3 3 4 0 3 3 7  –  L a s t  r e v i e w e d  o n  0 1 - 1 2 - 2 0 1 9  
  

 
2 
 
KEY WORDS: neuromuscular electrical stimulation - instrumentation - isometric muscle 
strength - pain threshold - muscle fatigue. 
THEORETICAL FRAMEWORK  
Electrical stimulation  
Electrical stimulation is the use of electric currents in order to generate a muscle contraction. 
The objectives of this therapy are replacing insufficient voluntary contraction, prevention or 
treatment of atrophy, treatment of sarcopenia, muscle strengthening and performance. (1) 
Neuromuscular electrical stimulation (NMES) is used when the peripheral nervous system is 
unharmed, acting on the nerve (1-3), aiming to generate muscle contraction with no voluntary 
activation or functional movement by the patient. (4).   
The result of training, whether by electro-stimulation or by voluntary contraction, will be in 
relation to the force produced in the sessions. In order for muscle strength and trophism to be 
maintained, minimum contraction levels of 20% of the maximum voluntary isometric 
contraction (MVIC) must be repeatedly attained. Peaks of strength of 30 to 50 % of maximum 
voluntary isometric contraction (MVIC) are required to improve muscle performance (5). To 
achieve hypertrophy, values of 50 to 60% of MVIC must be reached (6). Other variables that 
affect strength gain with NMES are the type of contraction elicited and the angle at which the 
training is performed. (7) 
The magnitude of the contractile response in neuromuscular stimulation is related to the 
parameters of the electrical current, such as pulse duration, intensity, frequency, and contraction 
and relaxation times (8). These variables should allow maximum force peaks to be generated 
with minimum nociceptive sensation (9).  
Current variables used in electrical stimulation 
Currents used in neuromuscular electrical stimulation have a pulse width of less than 1 ms (10) 
and an intensity between 1 and 120 mA. Pulsed currents can be classified, in terms of their 
waveform, as single-phase and two-phase. Two-phase currents, in turn, can be symmetric, 
compensated asymmetric and uncompensated asymmetric.  

 
3 
In low frequency pulsed currents it is possible to modify the phase duration or width, pulse 
duration or width and its frequency. (2, 3) New research also includes a variable called intra-
pulse interval, but this is not yet available in conventional equipment. (8)   
Medium frequency currents, on the other hand, have a carrier frequency (achieving pulses 
without in-between pauses) and a modulation frequency (the number of times the current is 
modulated or varies in one second). This modulation can be in on-off packages, determining a 
duty cycle (Duty Cycle = Emission Time / (Emission Time + Pause Time) or in intensity. 
Russian, Neo-Russian and Australian currents are modulated in on-off packages (also called 
burst modulated currents). (2, 3) 
In addition, currents for electrical stimulation must have ramp-up, ramp-down, contraction time 
and relaxation time (pause), in order to resemble a voluntary contraction. These values are 
adjustable and their unit is seconds. (11) 
The higher the intensity, pulse duration and/or frequency, the greater the contraction. Increasing 
these parameters will increase discomfort and fatigue. (12) 
Medium frequency neuromuscular electrical stimulation 
In the classical literature, medium frequency currents include Russian currents and interferential 
currents (11). Subsequently, Neo-Russian currents were added to this list, whose equipment 
emission differs in several technical aspects from conventional Russian currents (13) and, more 
recently, Aussie currents have been added as well (14). 
Russian currents 
Although Russian currents are very popular in Latin America, there is not much scientific 
evidence and the studies conducted by their inventor, Kots, are controversial. The author studied 
the strength gains, but the patient population comprised teenagers, which could explain why 
there was a large increase in this variable. Another controversial issue is that, in order to 
determine the optimal times of contraction and relaxation, instead of using Russian current, he 
used low-frequency monophasic currents of 1 ms pulse duration and then extrapolated this to 
Russian stimulation. This was called 10-50-10 (10-second contraction, 50-second pause, 10 
repetitions) (15). 
The classical Russian current has a sinusoidal waveform, with a pulse duration of 0.4 ms (400 
us), a carrier frequency of 2500 Hz, modulation frequency of 50 Hz and a duty cycle of 50 % 

 
4 
(10 ms emission, 10 ms pause) (Fig. 4). It has achieved strength increases when applied in 
combination with isometric exercises (7, 11). 
Neo-Russian currents 
Neo-Russian currents have a symmetrical biphasic rectangular rather than a sinusoidal 
waveform, with the same pulse duration and carrier frequency as Russian currents. They differ 
from them in that their modulation frequency can also be changed (1 to 120 Hz) and different 
duty cycles can be chosen other than 50%. (13).  
These features offer some advantages over Russian currents. Firstly, by varying their 
modulation frequency, they can stimulate different types of muscle fibers, such as I, IIa, IIb and 
IIc  (1). On the other hand, by using duty cycles lesser than 50 % the motor response is higher 
(16) and fatigue is less (17). 
Australian or Aussie currents 
In 2010, Ibramed company released a new current called Aussie in the Latin American market, 
which claims to be more comfortable and to induce greater force than Russian and low 
frequency currents. It has a sinusoidal waveform and uses, in its electro-stimulation mode, a 
pulse width of 1 ms, 1000 Hz carrier frequency, modulated in burst of 4 ms on-time and 16 ms 
off-time when modulated at 50 Hz (14). Unlike the Russian current, this one does not consider 
the duty cycle, as it keeps the burst time steady and modifies the pause between one and the 
next to vary the modulation frequency (14, 18). 
In order to determine the ideal carrier frequency, a first study was conducted using 1 and 35 
KHz (18). Subsequently, the experience was repeated with frequencies from 0.5 to 20 KHz with 
different modulations (1 to 100 % duty cycle). The results showed that to achieve maximum 
torque, a carrier frequency of 1 KHz with a duty cycle of 20% should be used. When comfort 
is the objective, the use of a carrier frequency of 2500 Hz is recommended, as it provides a 
good balance between maximum voluntary isometric contraction (MVIC) and comfort (17). 
Ward then compared low-frequency single-phase current with conventional Russian and Aussie 
currents (14). In this study, he used two phase durations for the single-phase ones, one of 200 
us (0.2 ms), corresponding to the phase duration of the Russian current, and another of 500 us 
(0.5 ms), which coincides with the Aussie one (14). A weakness found in this work is that, 
being these unidirectional currents, the way of connecting the electrodes should have been 
standardized, since the negative electrode is more depolarizing than the positive one, thus 
affecting the force induced in the contraction. The negative pole should be connected to the 

 
5 
active electrode, on the motor point (4, 11). If this is the way it was done, it has not been properly 
described in the methodology. (14) 
So far, then, no comparison has been made between Aussie and Neo-Russian currents (with a 
biphasic rectangular waveform) at different duty cycles, nor with RBS, which is the waveform 
most commonly used by good quality portable personal electro-stimulators. Unfortunately, 
Ward's studies also fail to include the fatigue variable, which is of utmost importance in daily 
practice (14, 18). 
Low-frequency currents, rectangular biphasic symmetrical 
Low frequency currents differ structurally from medium frequency currents in that they are 
made up of only one pulse every certain time rather than of a packet of pulses like medium 
frequency currents. Within the low frequency currents we can find the symmetrical biphasic 
(charge-balanced), the unbalanced asymmetrical biphasic, the monophasic and the balanced 
asymmetrical biphasic. All these are also called faradic. (3) It is now suggested that, instead of 
using these waveforms, low frequency rectangular biphasic symmetrical (RBS) waveforms 
should be used, which are available in higher-quality, and therefore more expensive, portable 
equipment. The waveform is important, even when these currents are used for electro-analgesia 
in its TENS (trans-cutaneous electrical nerve stimulation) mode, because it results in better 
analgesic effects. (19) 
According to initial research, RBS are more tolerable and induce greater force than Russian 
currents (5, 9, 20, 21). Other authors, however, suggest that there is no difference in discomfort 
rates between medium and low frequency currents (22). Fukuda, on the other hand, claims he 
has found no difference in the force generated by each of these currents, but the intensity 
reached with Russian currents, as well as their tolerance, were higher (23). 
Some authors have also studied the fatigue induced by currents, their findings indicating that 
low frequency currents cause less fatigue, which makes them more suitable, as they maintain 
the induced force at similar levels during more contractions along the session (20). 
Force – Maximum force induced by electrical stimulation 
Force is defined as "the ability of a muscle to actively generate tension, regardless of the specific 
condition under which such tension is being measured (slow-speed or fast-speed contraction, 
shortening or lengthening condition)" (24). 

 
6 
When electro-stimulation is applied, an increase in muscle tension is generated, even when the 
patient does not engage in any voluntary contraction. In research studies seeking to find out 
which one is the best current, the operator increases the current intensity to the maximum 
tolerable by the patient and measures the Electrically-Induced Contractions (MEIC) (12, 14, 
16, 20, 21, 23, 25-30). Another variable having an influence on the MEIC is the frequency of 
the electrical current, being it directly proportional (31). 
There is a directly proportional correlation between MEIC and the strength gain of a training 
session. The scalar magnitude of the force variable is the Newton (N) (5). 
Force measurement or dynamometry 
The force variable is measured with dynamometry. There are isometric and isokinetic 
dynamometers. The latter allows to measure force in a concentric, eccentric and isometric 
manner, thus providing a greater amount of data. The isokinetic dynamometer has been used in 
several of the articles where MEIC and MVIC are analyzed (5, 7, 23, 25, 32). Others, on the 
other hand, opt to use isometric dynamometers with load cells (9, 33). It has been noted that, 
despite their much lower cost, they are very reliable (6, 24, 34, 35). 
The methodology used with isometric dynamometry to measure the MVIC consists in 
performing three maximum isometric contractions of 3 seconds duration (5), with a 120-second 
interval between one and the other (5, 9, 36). The best of the 3 repetitions should be considered 
(23). The subject should be seated in a therapeutic chair with the hip at 110° (23), with the trunk 
well stabilized with straps (37). The knee should be placed in 90° flexion (9, 26, 38-40). The 
patient is instructed to cross his arms over his chest and relax (5). 
The MEIC is usually normalized with the MVIC, being expressed as a percentage of the latter 
(%MVIC). (20, 23) 
Sensory, motor and pain thresholds in electrical stimulation and their correlation with 
tolerance 
The sensory threshold was defined as the level of applied current, slowly increased, at which 
the subject first perceives cutaneous sensation. The motor threshold is the current intensity 
required to produce a threshold contraction. The pain threshold is the intensity producing an 
unpleasant sensation (18). Thresholds vary in women during the different phases of the 
menstrual cycle, regardless of whether they use contraceptives or not; therefore, in research 
involving this variable it is always convenient to recruit only men in order to homogenize the 
sample (41). 

 
7 
To measure the discomfort generated by the current, the visual analogue scale (VAS) is 
commonly used, thus establishing a quantitative variable (20, 21). 
When intensity (mA) is used as a variable, it is important to verify that the intensity reported 
by the equipment is the one actually emitted. This measurement is made with an oscilloscope 
connected to the output of the equipment, with a resistive load of 1 KOhm (42). 
Fatigue 
Fatigue is a multidimensional concept combining physiological and psychological aspects. In 
physiology, fatigue is the exercise-induced decrease in the ability to generate strength due to 
central and peripheral changes. The movement itself is preceded and accompanied by brain 
activities related to the preparation and execution of the movement, which have been correlated 
with the perception of effort (43). 
Muscle-specific (peripheral) fatigue can be measured using electro-stimulation through the 
MEIC (43). 
Fatigue in electrical stimulation  
During the application of NMES the force decreases. Some authors claim that the magnitude 
of fatigue is influenced by pulse width, frequency and intensity of electro-stimulation. As 
frequency is increased, the MEIC increases as well, which in turn increases metabolic 
consumption, thus generating fatigue (31). 
Several authors have studied the effect of electro-stimulation with surface electrodes on fatigue, 
finding that medium frequency currents generate more fatigue than low frequency ones (5, 20). 
There are various experimental models to study peripheral fatigue, but the one most used 
consists of applying electrical stimulation, reducing the central component (31). 
There is no doubt that Laufer was one of the authors who researched on electro-stimulation- 
induced fatigue the most. To this end, she used a protocol which starts by measuring the MVIC 
to normalize the data. Then, she measures the MEIC during 21 repetitions, considering the first 
contraction as a hundred percent and the following contractions as a percentage of the first one 
(17). The next step is counting the number of contractions that were equal to or less than 50% 
of the initial strength, thus determining which current is more fatiguing (20). 
Another option for calculating this variable is the determination of the Fatigue Index (FI), which 
consists of describing the percentage of reduction of the force induced between the first phase 

 
8 
(Pinit) and last phase (Pfinal), where a higher value indicates less fatigue and an FI = 1 implies 
that no fatigue has occurred. This formula is: FI=1-(Pinit-Pfinal)/Pinit (44). 
OBJECTIVES 
General 
1.  To compare induced isometric force, tolerance and fatigue in healthy subjects from 18 
to 30 years of age, with Neo-Russian, Aussie and RBS currents, in the period from 11-
30-2017 to 12-30-2017. 
Specific 
1.1. To evaluate the isometric force induced by Neo-Russian, Aussie and RBS currents by 
means of isometric dynamometry in healthy subjects from 18 to 30 years of age. 
1.2. To compare the isometric force induced in healthy subjects aged 18 to 30 years by the 
different currents in order to determine which one induces greater force. 
1.3. To evaluate the tolerance of Neo-Russian, Aussie and RBS currents using the Pain 
Visual Analogue Scale (VAS) in healthy subjects from 18 to 30 years of age. 
1.4. To compare tolerance in healthy subjects aged 18-30 years to the three types of current 
in order to determine which one is less unpleasant.  
1.5.  To evaluate fatigue upon application of Neo-Russian, Aussie and RBS currents by 
means of a fatigue test with isometric dynamometry in healthy subjects from 18 to 30 
years of age. 
1.6.  To compare the fatigue induced by the different currents in healthy subjects between 
18 and 30 years of age in order to determine which of the three produces less fatigue. 
MATERIALS AND METHODS 
a. Design type 
Experimental, crossover, randomized study (45). 
 
 
b. Location 
The data collection was carried out in the "Ronzio Terapia Física Especializada" Center, 
located at Mendoza 2096, 2 B, in the Autonomous City of Buenos Aires, Argentina, in 
the period from 11-30-2017 to 12-30-2017. 
 

 
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c. Universe 
Students pursuing a degree in Kinesiology and Physiatry at the Instituto Universitario 
de Ciencias de la Salud Fundación H.A. Barceló (Autonomous City of Buenos Aires, 
Argentina), at Universidad Maimónides (Autonomous City of Buenos Aires, Argentina) 
and at the Universidad Nacional Arturo Jauretche (Florencio Varela, Buenos Aires, 
Argentina). 
 
d. Population 
Composed of 255 individuals, male (5, 41, 46), students pursuing a degree in 
Kinesiology and Physiatry at the Instituto Universitario de Ciencias de la Salud 
Fundación H.A. Barceló (Autonomous City of Buenos Aires, Argentina), at Universidad 
Maimónides (Autonomous City of Buenos Aires, Argentina) and at the Universidad 
Nacional Arturo Jauretche (Florencio Varela, Buenos Aires, Argentina). 
 
e. Sample 
Composed of 30 individuals according to the sample size estimate.  
 
f. Sample size 
To determine the required sample size, a pilot test was carried out prior to the study, in 
which the 3 types of electrical stimulation were randomly applied to 5 subjects. In order 
to estimate the variability of the sample, the global standard deviation of the 15 
measurements was considered (SD=19.58%). A sample size for a Two-tailed T-Test 
was estimated, assuming an alpha error of 0.05, a power of 0.8 and a delta of 10%. For 
a crossover design only 1/2 of the calculated sample size is required, since the same 
subject contributes to all 3 groups. This results in a sample size of 30 subjects (47). The 
distribution coefficient was 1:1. (48) 
 
g. Sampling:  
Consecutive non-probability. 
 
h. Criteria 
a. Inclusion: Available, healthy, male volunteers between 18 and 30 years of age, with 
right-dominant lower limb, who are physically active (9, 41). 

 
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b. Exclusion: Having a right-dominant lower limb injury, skin lesions in the quadriceps 
area, having a pacemaker, cardiovascular or neurological diseases (18, 25). Subjects 
who have exercised 72 hours before the protocol (49, 50). 
c. Elimination: Missing one or both appointments for evaluation, the patient’s own 
decision to abandon the protocol while it is being carried out, intolerance to the 
procedure (51). 
 
i. Randomization:  
In order to minimize the potential bias of the order in which interventions are initiated 
(e.g., the effect of fatigue), the randomization sequence was generated prior to starting 
work 
(9, 
23, 
25, 
52). 
The 
number 
2 
generator, 
available 
at 
http://www.randomization.com/, was used for situations where subjects must receive all 
interventions in random order, with balanced permutations, forming 5 x 6 blocks for the 
three currents of interest (53). The results of said distribution were as follows: 
 
1. Aussie - RBS - Neo-Russian. 
2. RBS - Neo-Russian – Aussie. 
3. Aussie - Neo-Russian - RBS. 
4. RBS – Aussie - Neo-Russian. 
5. RBS - Neo-Russian – Aussie. 
6. Aussie - RBS - Neo-Russian. 
7. Aussie - Neo-Russian - RBS. 
8. Aussie - Neo-Russian - RBS. 
9. Neo-Russian – Aussie - RBS. 
10. Neo-Russian – Aussie - RBS. 
11. Aussie - RBS - Neo-Russian. 
12. Neo-Russian – Aussie - RBS. 
13. Neo-Russian - RBS – Aussie. 
14. Aussie - Neo-Russian - RBS. 
15. Neo-Russian - RBS – Aussie. 
16. Neo-Russian - RBS – Aussie. 
17. Aussie - RBS - Neo-Russian. 
18. RBS - Aussie - Neo-Russian. 
19. RBS - Aussie - Neo-Russian. 
20. Aussie - RBS - Neo-Russian. 

 
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21. Neo-Russian – Aussie - RBS. 
22. Neo-Russian - RBS – Aussie. 
23. Neo-Russian - RBS – Aussie. 
24. Neo-Russian – Aussie - RBS. 
25. RBS - Aussie - Neo-Russian. 
26. RBS - Neo-Russian – Aussie. 
27. Aussie - Neo-Russian - RBS. 
28. RBS - Aussie - Neo-Russian. 
29. RBS - Neo-Russian – Aussie. 
30. RBS - Neo-Russian – Aussie. 
j. Blinding  
The subject was blindfolded so that he would not watch the procedure. The study 
subject did not know the type of current applied and the operator was alien to the work 
and unaware of the hypothesis. The database was coded in order to conceal the 
interventions from the statistical analyst (25, 45). 
k. Ethical aspects  
This protocol was submitted to the Instituto Universitario De Ciencias De La Salud, 
Fundación H. A. Barceló as a research project and was approved by resolution number 
HSC 5745. In addition, it has the relevant clinical trial registration at Clinical Trials 
U.S.A. (www.clinicaltrials.gov), identifier: NCT03340337. 
Participants were given a written document entitled "Information letter and Written 
Consent for Volunteer’s Participation" and also an "Informed Consent" document 
explaining the objectives and purposes of the study, the experimental procedures, any 
known short or long-term risks, possible discomforts; benefits of the procedures applied; 
duration of the study; suspension of the study in the event of negative effects or when 
sufficient evidence of positive effects does not justify continuing with the study, and the 
subjects’ freedom to withdraw from the study at any time they want. The document also 
indicated that the information provided by all participants in the study will be kept 
confidential in the event that the results are presented in scientific events and/or 
published. In case of acceptance, the subject proceeded to sign said documents. 
 
l. Procedures 
a. Checking the emission of the equipment and measuring the intensity 

 
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The emission of the equipment was corroborated by connecting a resistive load of 
1 Kohm to a PC-based oscilloscope Owon brand, model VDS2062 of 60MHz and 
100MHz bandwidth, then measuring the current intensity. (42) It was also verified 
that the waveforms emitted by the equipment correspond to the theoretical 
characteristics of the currents studied.  
During the MEIC measurement, the intensity shown on the equipment's display was 
recorded and the real intensity was checked on the oscilloscope, considering the 
latter. Some equipment show on their display the peak to peak (PP) intensity, 
therefore, the value from the isoelectric line to the peak of the positive phase, called 
Vamp, was considered for all of them. (54) 
Since the oscilloscope reports voltage, Ohm's law was used to calculate the 
intensity. (3, 11, 55) 
b. Measuring MVIC 
This data was used for normalization of the MEIC. A short 10-minute walk was 
taken to warm-up (23). An isometric dynamometer with load cell and computer 
interface, Fisiomove® brand, Isoforce® model, was used. The patient was 
positioned in a therapeutic chair with the hip at 110° (23, 31), stabilizing the trunk 
(at chest level) and the hip (at the level of the anterior superior iliac spines) with 
straps (37). The knee was placed in 90° flexion (9, 26, 31, 38-40). A goniometer 
was used to correctly position the joints at said angles (12). The patient was 
instructed to cross his arms over his chest and relax (5). The subject was blindfolded 
to prevent him from watching the procedure. The measuring system was attached 
to the distal end of the right lower limb by means of an ankle brace. The subject 
was instructed to perform 3 maximum 3-second contractions with an interval of 120 
seconds between each of them  (9, 23). The best of the 3 repetitions was considered  
(31, 52). Whenever the third one was the best, additional measurements were taken 
until a decrease in torque was obtained in order to determine the maximum (56). 
Work and rest times were controlled by a chronometer and also by the dynamometer 
software. The best of the three contractions and, when necessary, the request for 
additional repetitions to obtain the best one, was automatically determined by the 
software, which also served to store the data that was later transferred to an Excel 
2016 table. 
c. Detecting motor points and positioning electrodes 
The motor points were detected for the correct positioning of the electrodes, which 
allows to increase the generated force (9, 22). First, the skin was cleaned with a 

 
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cotton soaked in alcohol. To detect the points, a Globus brand 600 Pro model 
equipment was used, in which an ad hoc program was executed, with continuous 
emission at 5 Hz, 200 us. In order to locate the motor point of the internal vastus, a 
self-adhesive dispersive electrode of 2" x 4" (5.08 x 10.16 cm) was placed on the 
proximal third of the right thigh, to then search for it with the active electrode –
metal strut-type, wrapped with cotton wool soaked in tap water and covered with 
conductive gel- until determining the point of greatest contraction at the same 
intensity. For the motor point of the anterior rectus, a self-adhesive dispersive 
electrode was placed on the motor point of the internal vastus of the right thigh, to 
then search for it with the active electrode, -metal strut-type, wrapped with cotton 
wool soaked in tap water and covered with a conductive gel- until determining the 
point of greatest contraction at the same intensity. 
Once these points were marked, unused self-adhesive electrodes -Pro-Patch® 
brand, model ProM-030, 2" x 4" (5.08 x 10.16 cm) 2, 57)- were placed on them (52, 
57). Two electrodes were used for each patient. 
d. Measuring MEIC 
After measuring the MVIC, the subject was allowed to rest for 120 seconds (while 
searching for motor points), to then perform the MEIC assessment with all three 
types of electrical currents, which were applied in random order so that the effects 
of one current would not influence the results of the next (23, 25). The 
randomization sequence is the one mentioned above, generated through 
www.randomization.com (53). 
The same isometric dynamometer was used, positioning the subject as indicated 
above. (5, 9, 12, 23, 26, 31, 37-40). 
The patient was asked not to make any voluntary contraction or collaborate in any 
way, but just let the electrical stimulation generate the contraction (20). 
With each type of current, the intensity was increased until it reached the maximum 
tolerable by the subject, which situation was communicated to the operator (23, 25, 
32, 52). Upon reaching said intensity, it was noted down accordingly, and then 3 
contractions of 3 seconds duration were measured by isometric dynamometry, with 
a 120-second pause between them. Once the 3 contractions with the first current 
were measured, the second and then the third type of electro-stimulation followed, 
in the order as randomly determined (9, 23, 25, 52). An interval of 120 seconds was 
also taken between the determinations of the MEIC with each current, in order to 
minimize fatigue (9). The best of the 3 repetitions was considered (9, 23, 31, 52). 

 
14 
Whenever the third one was the best, additional measurements were taken until a 
decrease in torque was obtained in order to determine the maximum (56). 
Work and rest times were controlled by a chronometer and also by the dynamometer 
software. The best of the three contractions and, when necessary, the request for 
additional repetitions to obtain the best one, was automatically determined by the 
software, which also served to store the data that was later transferred to an Excel 
2016 table. 
The following parameters were used to perform the MEIC tests (Table 1): 
 
VARIABLE 
NEO-RUSSIAN 
AUSSIE 
RBS 
Emission mode 
Synchronic 
Synchronic 
Synchronic 
Waveform 
Rectangular 
biphasic 
symmetrical 
Sinusoidal 
Rectangular 
biphasic 
symmetrical 
Carrier frequency 
2500 Hz 
1000 Hz 
- 
Phase duration 
200 us 
500 us 
200 us 
Pulse width 
400 us 
1000 us 
400 us 
Modulation 
frequency 
50 Hz 
50 Hz 
50 Hz 
Duty cycle 
50 % 
20 % 
- 
Burst duration 
10 ms. 
4 ms. 
- 
Ramp-up 
1 sec. 
1 sec. 
1 sec. 
On time 
3 sec. 
3 sec. 
3 sec. 
Ramp-down 
1 sec. 
1 sec. 
1 sec. 
Rest time 
120 sec. 
120 sec. 
120 sec. 
Table 1: Parameters for electrical stimulation during MEIC measurement. 
 
e.   Normalizing MEIC data 
In order to normalize the data, MEIC will be expressed as percentage of MVIC (% 
MVIC) (17, 20, 23, 52, 58).The calculation was done in an Excel 2016 table. The 
formula was the following: 
 
% MVIC = (MEIC / MVIC) x 100 
 

 
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f.   Determining tolerance to each type of electrical stimulation 
After recording the MEIC with each current, the subject was given a VAS scale and 
was asked to indicate how unpleasant he found the electro-stimulation, with 0 (on the 
left) being "no pain" and 10 (on the right) the equivalent of "crying in pain". 
Numerical data from the VAS was transferred to a Microsoft® Excel® 2016 table 
(20, 21, 57, 59). 
Although an uncomfortable stimulus may not necessarily generate less force, what is 
sought is balance between these variables (14). That is why, considering that a current 
is more effective for electro-stimulation the more force it induces and the less 
discomfort it generates, the coefficient between the % MVIC and the VAS was 
calculated, thus establishing the "ratio" value through the following formula: 
 
Ratio = % MVIC / VAS 
g. Measuring fatigue  
The fatigue induced by the three types of electrical stimulation was measured after 
one week of washout period (20). 
The same isometric dynamometer was used, positioning the subject as indicated 
above. (5, 9, 12, 23, 26, 31, 37-40). 
The motor points were detected and two unused self-adhesive electrodes were placed 
on them (9, 22, 52, 57). 
The patient was instructed to cross his arms over his chest and to relax (5). The 
subject was blindfolded to prevent him from watching the procedure. The studied 
subject did not know the order of the procedures applied and the evaluator was not 
aware of the working hypothesis, thus defining a double-blind study (25, 45). The 
measuring system was attached to the distal end of the right lower limb by means of 
an ankle brace (9). 
The patient was asked not to make any voluntary contraction or collaborate in any 
way, but just let the electrical stimulation generate the contraction (20). The intensity 
was increased until it reached the maximum tolerable by the subject, which situation 
was communicated to the operator (23, 25, 32, 52). Data was taken from the MEIC 
of 21 contractions (20), consisting of 1 second of ramp-up, 3 seconds of contraction, 
1 second of ramp-down (60) and 5 seconds of rest time. The dynamometer was 
configured to collect data for 320 seconds and then the peak values of each of the 21 
contractions were manually reviewed and transferred to Microsoft® Excel® 2016. 

 
16 
This variable was identified as maximum voluntary isometric contraction in fatigue 
test (MEIC-F). 
The following parameters were then used to perform the fatigue test (Table 2): 
 
VARIABLE 
NEO-RUSSIAN 
AUSSIE 
RBS 
Emission mode 
Synchronic 
Synchronic 
Synchronic 
Waveform 
Rectangular 
biphasic 
symmetrical 
Sinusoidal 
Rectangular 
biphasic 
symmetrical 
Carrier frequency 
2500 Hz 
1000 Hz 
- 
Phase duration 
200 us 
500 us 
200 us 
Pulse duration 
400 us 
1000 us 
400 us 
Modulation 
frequency 
50 Hz 
50 Hz 
50 Hz 
Duty cycle 
50 % 
20 % 
- 
Burst duration 
10 ms. 
4 ms. 
- 
Ramp-up 
1 sec. 
1 sec. 
1 sec. 
On time 
3 sec. 
3 sec. 
3 sec. 
Ramp-down 
1 sec. 
1 sec. 
1 sec. 
Rest time 
5 sec. 
5 sec. 
5 sec. 
Table 2: Parameters for electrical stimulation during fatigue test. 
h. Normalizing data from the fatigue variable 
Each repetition was expressed as a percentage of MVIC, using the acronym %MVIC-
F, with the following formula:  
% MVIC-Fx = (MEIC-Fx x 100)/MVIC 
Where "x" is the repetition number. 
i. Determining fatigue 
After normalization and determination of %MVIC-Fx, repetition 1 (%MVIC-F1) was 
considered to be 100 %. This variable was coded as R1. Then, it was calculated what 
percentage of R1 the subsequent repetitions corresponded to (where "x" is the 
repetition number: x = 2, 3..., 21 ), by means of the following formula: 

 
17 
Rx = (%MVIC-Fx x 100) / MVIC-F1 
The number of repetitions equal to or lower than 50% was then counted, thus 
determining the fatigue induced by each type of electrical stimulation (20).   
i. Calculation of the fatigue index (FI): The data collected during the fatigue test of 
the %MVIC-F were transferred to Microsoft® Excel® 2016 and the percentage 
decrease of the first as compared to the last contraction was calculated using the 
following formula (61): 
FI = 1- (%MVIC-F1 - %MVIC-F21) / %MVIC-F1 
m.   Flowchart 
The experimental design is summarized in Figure 1:
 
Fig. 1: Flowchart of the experimental design. 
n.   Statistical processing of data 
The systematization was computerized and quantitative. The data was transferred to 
Microsoft® Excel® 2016, creating a database in which the data, tables and graphs were 

 
18 
normalized. IBM SPSS software, version 22.0 (IBM Corp., Armonk, NY, USA) was used for 
data analysis. A p-value < 0.05 was considered significant.  
Continuous variables were expressed with their mean and standard deviation when assuming a 
normal distribution. Otherwise, the median and the interquartile range (IQR) were reported. 
Categorical variables were reported with their frequency and percentage. 
To meet the specific objectives in 1.2, 1.4 and 1.6, an analysis of the variance of a repeated 
measurement factor was performed in order to determine the effect of three wave types (Aussie, 
NR and RBS) on the %MVIC, tolerance level and fatigue. Independent analyses were 
performed for each outcome variable. Bonferroni correction was applied for the a posteriori 
analyses, as appropriate. Results were expressed as mean difference and their respective 95% 
CI. The assumption of normality was evaluated using the Shapiro-Wilk test. The presence of 
outliers was determined by visual inspection of the box charts. The sphericity assumption was 
evaluated by means of the Mauchly test. When it was not possible to apply the parametric 
ANOVA test, the non-parametric Friedman test and the Wilcoxon test for Bonferroni-corrected 
samples were used for multiple comparisons. 
To meet the specific objective in 1.2, it was analyzed which current shows the highest value of 
%MVIC (%MVIC-Neo-Russian vs. %MVIC-Aussie vs. %MVIC-RBS). 
In order to comply with the specific objective in 1.4, it was analyzed to which of the currents 
the subjects referred a lower VAS value (VAS-Neo-Russian vs. VAS-Aussie vs. VAS-RBS) 
and which of the currents obtained a better ratio, calculated by using the formula mentioned 
above (Ratio-Neo-Russian vs. Ratio-Aussie vs. Ratio-RBS). 
To meet the specific objective in 1.6, a comparison was made considering the number of 
repetitions ≤ 50% of the initial value between the 3 different waves. No assumption of normality 
was made at any of the levels as assessed by the Shapiro-Wilk test (p<0.001) for which the 
Friedman test was used for related samples. For post hoc comparisons the Wilcoxon Test for 
related samples was used with Bonferroni correction for multiple comparisons (R ≤ 50%-Neo-
Russian vs. R ≤ 50%-Aussie vs. R ≤ 50%-RBS). In addition, a comparison was made between 
%MVIC-F1 vs. %MVIC -F21 using the Wilcoxon Test for paired samples.  
To compare fatigue rates between AU, RS and RBS groups, the Friedman non-parametric test 
was used with the Wilcoxon test for post hoc comparisons. Bonferroni correction was applied 
for post-hoc comparisons.  
 

 
19 
SOURCES AND INSTRUMENTS 
• Notebook with Windows, Microsoft Office 2016 package, SPSS 22, Endnote X7. 
• Owon PC-based oscilloscope, model VDS2062 60MHz and 100MHz bandwidth.  
• Fisio-Move® brand computerized digital isometric dynamometer, model Isoforce® 
with its corresponding accessories and software. 
• Bench made ad-hoc to fasten the dynamometer and position the patient.  
• Velcro straps. 
• Blindfolding eye mask. 
• Constant current electrical stimulator, Neo-Russian current transmitter, Ibramed® 
brand, Neurodyn II® model. 
• Constant current electrical stimulator, Aussie® current transmitter, Ibramed® brand, 
model Neurodyn Aussie Sport®. 
• Constant current electrical stimulator, RBS wave transmitter, Globus® brand, model 
600 Pro®. 
• Self-adhesive electrodes, Pro-Patch® brand, model ProM-030, 2" x 4" (5.08 x 10.16 
cm). 
RESOURCES 
This work was financially supported by the Instituto Universitario de Ciencias de la Salud 
Fundación H.A. Barceló, approval No. HSC 5745. 
Measurements were made at the "Ronzio Terapia Física Especializada" Center. 
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