Effect of
Electromyostimulation
Training on Muscle
Strength and Sports
Performance
Kayvan M. Seyri, MSc, NSCA-CPT*D, CSCS, NASM-PES, CES1 and Nicola A. Maffiuletti, PhD2
A.T. Still University, Kirksville, Missouri; and 2Neuromuscular Research Laboratory, Schulthess Clinic,
Zurich, Switzerland
1
SUMMARY
ELECTROMYOSTIMULATION (EMS)
IS A WIDELY USED METHODOLOGY
IN APPLIED SPORTS SCIENCE. IN
CONTRAST TO A TYPICAL VOLUNTARY CONTRACTION INITIATED BY
THE CENTRAL NERVOUS SYSTEM
(E.G., IN RESISTANCE TRAINING),
EMS INVOLVES INVOLUNTARY
CONTRACTIONS ELICITED BY
ELECTRICAL CURRENT APPLIED TO
THE MUSCLE. THE EFFECTIVENESS
OF THIS TECHNIQUE HAS BEEN
EVALUATED IN NUMEROUS STUDIES
EXAMINING STRENGTH AND PHYSICAL PERFORMANCE. OTHER REPORTS COMPARING SHORT-TERM
(I.E., #3 WEEKS) AND LONG-TERM
(I.E., $12 WEEKS) EMS APPLICATION
HAVE ALSO REPORTED DIFFERENTIAL RESULTS. THIS ARTICLE WILL
REVIEW RESEARCH EXAMINING
THE EFFECT OF EMS ON INCREASING STRENGTH AND POWER, ESPECIALLY IN SPORTS
PERFORMANCE.
QUICK DEFINITION AND
COMMON USE
E
lectromyostimulation (EMS)—
electrical muscle stimulation
or neuromuscular electrical
stimulation—involves artificially activating the muscle with a protocol
designed to minimize the discomfort
associated with the stimulus. EMS has
long been used to either supplement or
substitute voluntary muscle activation
in many rehabilitation settings, for
example, for re-education of muscle
action, facilitation of muscle contraction, muscle strengthening, and maintenance of muscle mass and strength
during prolonged periods of immobilization (14,18,28). EMS training programs have further been used to
improve muscle strength of healthy
individuals (6,7), and more recently,
EMS has been implemented in competitive athletes (21,33).
Typical settings of EMS exercise involve the application of electrical
stimuli delivered in intermittent trains
through surface electrodes positioned
in proximity of the muscle motor point
and preprogrammed stimulation units
(Figure 1). Owing to recent advances in
EMS technology, portable and relatively low-cost stimulators (300–500
U.S. dollars) can be purchased, thus are
being used by a growing number of
individuals. It is important to know the
stimulus parameters, how contractions
are triggered by EMS, and the effect of
Copyright Ó National Strength and Conditioning Association
EMS on neuromuscular function to
optimize its use and minimize the
possible risks. After a brief overview
of the methodological and physiological aspects of EMS, this article will try
to answer these important questions on
appropriate use of EMS in sports
training:
Does
EMS
improve muscle
strength?
Could
EMS
improve
sport
performance?
Recommendations and practical examples of EMS use will also be provided.
METHODOLOGICAL ASPECTS OF
EMS: THE MAIN PARAMETERS
The main stimulus parameters for
EMS, dictated by the physiological
characteristics of nerves and muscles,
include
Frequency (number of pulses per
second);
Intensity, or current amplitude
(probably the most important
parameter);
KEY WORDS:
maximal strength; jump ability; sprint
ability; strength training; sport
performance; neuromuscular electrical
stimulation
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Strength Training by Electrical Stimulation
Figure 1. Typical settings of isometric EMS exercise for the quadriceps muscle. MVC = maximal voluntary contraction.
Pulse characteristics (shape and
duration);
On/off cycle or duty cycle (to
minimize the occurrence of fatigue);
Ramping (to reduce contraction
abruptness and to improve comfort);
Electrode material, size, and
placement.
At present, there is no general consensus on the optimal stimulus parameters, so that considerable heterogeneity
exists between the different EMS
studies. There is nevertheless an informal agreement on some current
characteristics. For example, EMS
strength training is commonly realized
using biphasic symmetrical rectangular
pulses lasting 100–500 microseconds
and being delivered at a pulse rate of
50–100 Hz (35) to maximize the level
of evoked force (muscle tension). For
the same reason, current amplitude
should be at the maximum level
tolerated by the participants (18).
Unfortunately, a detailed and complete
description of the EMS procedures
(including stimulus parameters) is frequently lacking. Even if EMS parameters may facilitate the effectiveness of
EMS, the practitioners agree that there
is considerable subject variation in
response to EMS, and optimization
may relate more to the subject than to
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the stimulus parameters themselves
(20). Similarly, Lieber and Kelly (19)
suggest that the effectiveness of EMS
would not depend on external controllable factors (such as electrode size or
stimulation current) but rather on
some intrinsic anatomical/neuromuscular characteristics.
PHYSIOLOGICAL ASPECTS OF
EMS: MOTOR UNIT RECRUITMENT
During voluntary contractions, motor
units are activated according to their
size and threshold of recruitment, that
is, small low-threshold motor units are
recruited before large high-threshold
ones. On the other hand, when skeletal
muscles are artificially activated by
EMS, the involvement of motor units
is different from that underlying voluntary activation. The main argument
supporting this difference is that large
diameter axons are more easily excited
by electrical stimuli, which would alter
the activation order during EMS
compared with voluntary contractions
(9). However, human experiments
yielded contradictory findings with
some studies suggesting preferential/
selective activation of fast motor units
with EMS and others demonstrating
minimal or no difference between the
2 contraction modalities (for an overview of these studies, see (12)).
In a recent review article, Gregory and
Bickel (12) suggested that EMSinduced motor unit recruitment is
nonselective/random (also see (15)),
that is, muscle fibers are recruited
without obvious sequencing related
to their types; thus, EMS can be used
to activate fast motor units (in addition
to the slow ones) at relatively low force
levels. The principal differences in
motor unit recruitment between voluntary and stimulated contractions are
summarized in Table 1.
The main consequence of such unique
motor unit recruitment patterns is the
exaggerated metabolic cost of an EMS
contraction (36), which—compared
with a voluntary action of the same
intensity—provokes greater and earlier
muscle fatigue (16,34). According to
Vanderthommen and Duchateau (35),
these differences in motor unit recruitment and thus in metabolic demand between electrically evoked and
voluntary contractions constitute an
argument in favor of the combination
of these 2 modalities of activation in
the context of sports training.
EFFECT OF EMS TRAINING ON
MUSCLE STRENGTH
For unimpaired muscles, EMS training–induced strength gains are similar
Table 1
Comparison of motor unit recruitment between voluntary and EMS
contractions
Voluntary contraction
EMS contraction
Selective (slow to fast)
Nonselective/random (both slow and fast)
Asynchronous
Synchronous
Rather dispersed
Spatially fixed
Rotation is possible
Superficial (close to electrodes)
Complete (at maximal level)
Incomplete (even at maximal level)
(and complementary) to, but not
greater than, those that can be achieved
with traditional voluntary training. In
a recent systematic review of EMS
studies, Bax et al. (2) concluded that
for impaired quadriceps (postinjury or
postoperative subjects), EMS training
could be more effective than voluntary
training, whereas for unimpaired quadriceps (healthy subjects), the effectiveness of EMS training is generally lower
compared with those of voluntary
modalities. Training studies performed
in the past 20 years have also demonstrated that it is possible to obtain
significant improvements of muscle
strength—particularly for the lower
extremity muscles—in amateur and competitive athletes of all levels (Table 2).
EMS training–induced increases in
muscle strength are largely mediated
by neural adaptations, for example,
increased muscle activation (26), particularly in the case of short-term
training programs. On the other hand,
EMS regimens of longer duration can
elicit morphological changes in the
muscle (11). In their study, Gondin
et al. (11) demonstrated the time
course of neuromuscular adaptations
to EMS strength training. After 4
weeks of training, strength increases
were accompanied by increased
muscle activation, whereas the crosssectional area of the muscle was not
significantly modified. Interestingly,
both neural and muscular adaptations
mediated the strength improvements
observed after 8 weeks of EMS, similar
to the classical model proposed by Sale
(30) for neuromuscular adaptations to
voluntary strength training.
In summary, does EMS improve
muscle strength? Yes, but results differ
according to the muscle status:
For unimpaired muscles, EMS is
effective but not more than voluntary training;
For impaired muscles, EMS can be
more effective than voluntary training;
For athletes, EMS is effective for
increasing general not necessarily
specific strength.
These studies are examples of the
potential complementary role EMS
could play in conventional strength
training. The next avenue to explore is
how EMS could be practically applied
to various sports.
EFFECT OF EMS TRAINING ON
SPORT PERFORMANCE
Several studies involving individual and
team sport athletes have reported a
significant improvement in maximal
strength (as assessed using isokinetic or
isometric dynamometers), and in some
cases, even in anaerobic power production (vertical jump and sprint
ability, as assessed using contact mats
and photoelectric cells) after EMS
training (Table 2). These improvements are likely to affect the field
performance. However, because the
stress is applied during nonspecific
contractions (i.e., isometric in general),
excessive use of EMS could impair
motor coordination (13). Therefore,
performance of complex movements
requiring high levels of neuromuscular
coordination can only be obtained if
EMS is used in conjunction with
voluntary ‘‘technical’’ exercise, for example, plyometrics (25).
In the study of Maffiuletti et al. (25),
subelite volleyball players completed
5 sets of 10 consecutive vertical jumps
immediately after EMS of the thigh and
calf muscles. Jumps were completed
starting from a standing position, squatting down, and then extending the knee
in one continuous movement, so that
the first jump of a set was a countermovement jump and the 9 others were
a type of drop jump. To ensure maximal
intensity, hurdles and benches (approximately 40 cm) were used.
As a practical recommendation for both
individual and team sports, it is suggested that EMS training could be used
to enhance muscle strength and anaerobic performance without interfering
excessively with sport-specific training
(4,25,27). Therefore, EMS training
would be best used early in the
training season (i.e., at the beginning
of the preparatory training season), with
10–15 minutes of treatments, 2–3
sessions per week for 3–4 weeks
(21,24,27). Electrical current intensity
(in milliampere) and evoked force (as
a percentage of the maximum voluntary
contraction), which are strongly correlated (21), should be strictly and
consistently controlled to allow EMS
training intensity to be carefully quantified (22,32). It is recommended that
EMS should be administered, at least for
the first few training sessions (first week
of a training program), by athletic trainers or strength and conditioning coaches
who are familiar with the methodological and physiological aspects of EMS
exercise.
The main interest of using EMS in high
level sport is that this modality could be
considered as a new stimulus to favor
plasticity; that is, a new form of stress
from a neuromuscular and metabolic
point of view. EMS could be particularly useful for athletes whose performance has plateaued after several years
of training and competition, but it
would be supplementary to, rather than
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Strength Training by Electrical Stimulation
Table 2
EMS strength training in competitive sport
Year
1st author
Sport
Muscle
Weeks (x/wk)
Type of EMS (settings;
frequency [Hz])
Main findings
1989
Delitto (8)
Weightlifting
Q
6 (3)
I-LE; 2500
1989
Wolf (40)
Tennis
Q
3 (4)
C-S; 75
[ strength, sprint, jump
1995
Pichon (29)
Swimming
LD
3 (3)
I-OC; 80
[ strength, swimming
1996
Willoughby (38)
Basketball
BB
6 (3)
I-PC; 2500
1998
Willoughby (39)
Track and field
Q
6 (3)
C/E-LE; 2500
[ strength, jump
2000
Maffiuletti (24)
Basketball
Q
4 (3)
I-LE; 100
[ strength, jump
2002
Malatesta (27)
Volleyball
Q + TS
4 (3)
I-S; 105–120
[ strength, jump
2002
Maffiuletti (25)
Volleyball
Q + TS
4 (3)
I-LE/SC; 120
[ strength, jump
2005
Brocherie (4)
Ice hockey
Q
3 (3)
I-LE; 85
[ strength, sprint
2007
Babault (1)
Rugby
Q + TS + G
I-LE/CM; 100
[ strength, jump
2009
Maffiuletti (23)
Tennis
Q
3 (3)
I-LE; 85
[ strength, sprint, jump
2010
Billot (3)
Soccer
Q
5 (3)
I-LE; 100
[ strength, shoot
6 (1–3)
[ weightlifting
[ strength
[ = increased; BB = biceps brachii; C = concentric; CM = calf machine; G = gluteus; E = eccentric; I = isometric; LD = latissimus dorsi; LE = leg
extension; MT = motor threshold; OC = open chain; PC = preacher curl; Q = quadriceps; S = squat; SC = standing calf; TS = triceps surae; x/wk =
training sessions per week.
a substitute for, more traditional forms
of training (21). Another interest of
EMS for elite sportsmen is that a single
EMS bout is usually less time consuming (12–18 minutes) than traditional
volitional exercise sessions. This is
extremely appealing for athletes who
have a limited amount of time for
conditioning (e.g., tennis players). It is
not tempting to suggest that EMS
could replace traditional strength
training methods, but rather, EMS has
to be considered as an important
complement/supplement to conventional (voluntary) training programs (21).
strength and vertical jump performance.
Based on a pre- to posttraining comparison among 3 experimental groups
(weight training only, EMS only, and
weight training plus EMS), they suggested that supplementing dynamic
contractions with EMS could be more
effective than either EMS or weight
training in isolation for increasing knee
extensor strength and vertical jump
performance. These results are compatible with previous findings by the same
authors (38) who examined EMS
training–induced strength gains in
college basketball players.
As shown in Table 2, research in this
area has examined the effect of EMS
on performance enhancement of elite
and subelite (noninjured) athletes in
individual and team sports, such as ice
hockey, basketball, volleyball, soccer,
track and field, swimming, tennis,
weightlifting and rugby.
From all the EMS studies conducted in
competitive athletes, only one concentrated on long-term (12 weeks) training
effects in professional rugby players (1).
In this study, EMS was delivered to the
knee extensor, plantar flexor, and gluteus
maximus muscles of 15 experimental
subjects with 10 other individuals serving
as controls. After 12 weeks of carefully
monitored procedures, the EMS group
showed a significant increase in maximal
concentric/eccentric
torque,
squat
strength, and squat and drop jump
As an example, Willoughby and
Simpson (39) examined the effect of
EMS and dynamic contractions supplemented with EMS applied during
weightlifting exercises on knee extensor
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height, compared with the controls.
Based on these findings, 12 weeks of
EMS training had a significant effect on
muscle strength and power of elite rugby
players, although their specific skills like
scrummaging and sprinting were not
affected by EMS.
In summary, does EMS could improve
sport performance? If it is adequately
combined with technical training (e.g.,
plyometric) and logically integrated into
yearly training season, improvements
could be achieved in the following
capabilities:
Jumping ability (both general and
specific jumps)
Sprinting ability (including shuttle
sprints)
Other sport performances (swimming, weightlifting, and shooting)
PROBLEM STATEMENT AND
CONCLUSIONS
Numerous studies have shown the
effectiveness of EMS on healthy untrained and trained individuals including athletes. However, the significance
of the observed improvements is
partially compromised by factors such
Figure 2. Example of annual training plan, including EMS, for team sports (basketball). Inspired from Bompa (5).
as the pretraining status of the subjects,
lack of standardization of methods, or
testing protocols (31). For example,
while the study by Venable et al. (37)
on short-term EMS training found no
effect on muscular strength, vertical
jump performance, or power, a recent
study by Babault et al. (1) on long-term
EMS training reported significant increases in muscle strength and vertical
jump ability of elite athletes.
Some studies support EMS methodology and its training modalities in
enhancing the contractile quality of
muscle under isometric conditions
(12), whereas others support EMS in
combination with dynamic contractions to increase muscle strength (38).
Hence, any standardization methods
or testing protocol must take such
factors into consideration. Such disparities in the findings warrant further
systematic research that considers the
possible impact of those factors on
EMS effectiveness.
In conclusion, EMS has been confirmed to be an important complement
to conventional strength training programs for the enhancement of athletic
performance. EMS can also be applied
in conjunction with sport-specific
training in annual periodic training
schedules (Figure 2). However, as is
apparent in this brief literature review,
there is heterogeneity in the magnitude
of improvements between studies,
depending on factors such as EMS
intensity, the modality of EMS application, frequency, time course, recovery between EMS protocols, and
implementation of EMS into annual
periodic sports conditioning. Future
research should focus on reaching
a solid conclusion to ascertain its
effectiveness on athletic performance.
assistant professor at the University of
Burgundy in Dijon (France).
Kayvan Seyri is
the athletic performance trainer for
the U18 England
women’s National
Basketball Team
and the owner of
Kayvan Seyri’s
Personal Training
in London, United Kingdom.
3. Billot M, Martin A, Paizis C, Cometti C, and
Babault N. Effects of an electrostimulation
training program on strength, jumping, and
kicking capacities in soccer players.
J Strength Cond Res 24: 1407–1413,
2010.
Nicola A. Maffiuletti is the
director of the
Neuromuscular
Research Laboratory
at
the
Schulthess Clinic
in Zurich (Switzerland) and an
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