International  Journal  of
Environmental Research
and Public Health
Article
Seven Weeks of Jump Training with Superimposed
Whole-Body Electromyostimulation Does Not Aﬀect
the Physiological and Cellular Parameters of
Endurance Performance in Amateur Soccer Players
Nicolas Wirtz 1,*
, André Filipovic 2, Sebastian Gehlert 2,3
, Markus de Marées 4,
Thorsten Schiﬀer 5, Wilhelm Bloch 2 and Lars Donath 1
1
Institute of Training Science and Sport Informatics, Department of Intervention Research in Exercise
Training, German Sport University Cologne, 50933 Cologne, Germany; l.donath@dshs-koeln.de
2
Institute of Cardiology and Sports Medicine, Department of Molecular and Cellular Sports Medicine,
German Sport University Cologne, 50933 Cologne, Germany; andre.ﬁlipovic@gmx.net (A.F.);
gehlert@dshs-koeln.de (S.G.); w.bloch@dshs-koeln.de (W.B.)
3
Institute of Sport Science, University of Hildesheim, 50933 Hildesheim, Germany
4
Section of Sports Medicine and Sports Nutrition, Faculty of Sports Science, Ruhr University of Bochum,
44801 Bochum, Germany; Markus.deMarees@ruhr-uni-bochum.de
5
Outpatient Clinic for Sports Traumatology and Public Health Consultation, German Sport University
Cologne, 50933 Cologne, Germany; t.schiﬀer@dshs-koeln.de
*
Correspondence: n.wirtz@dshs-koeln.de; Tel.:+49-221-4982-6044
Received: 6 January 2020; Accepted: 1 February 2020; Published: 10 February 2020


Abstract: Intramuscular density of monocarboxylate-transporter (MCT) could aﬀect the ability to
perform high amounts of fast and explosive actions during a soccer game. MCTs have been proven
to be essential for lactate shuttling and pH regulation during exercise and can undergo notable
adaptational changes depending on training. The aim of this study was to evaluate the occurrence and
direction of potential eﬀects of a 7-weeks training period of jumps with superimposed whole-body
electromyostimulation on soccer relevant performance surrogates and MCT density in soccer players.
For this purpose, 30 amateur soccer players were randomly assigned to three groups. One group
performed dynamic whole-body strength training including 3 x 10 squat jumps with WB-EMS (EG,
n = 10) twice a week in addition to their daily soccer training routine. A jump training group (TG,
n = 10) performed the same training routine without EMS, whereas a control group (CG, n = 8)
merely performed their daily soccer routine. 2 (Time: pre vs. post) x 3 (group: EG, TG, CG) repeated
measures analyses of variance (rANOVA) revealed neither a signiﬁcant time, group nor interaction
eﬀect for VO2peak, Total Time to Exhaustion and Lamax as well as MCT-1 density. Due to a lack
of task-speciﬁcity of the underlying training stimuli, we conclude that seven weeks of WB-EMS
superimposed to jump exercise twice a week does not relevantly inﬂuence aerobic performance or
MCT density.
Keywords: electrostimulation; soccer; lactate; VO2peak; monocarboxylate transporter
1. Introduction
The physical demands of soccer players have increased notably within the last 10 to 20 years due
to modern game tactics and their variability. For example, the ability of a team to successfully play
high pressing mainly depends on the physical characteristics of the players. The distances covered
in the higher intensities and the number of quick and explosive actions such as accelerations, turns,
and jumps have increased within the recent years [1–3]. A player’s capacity to perform numerous of
Int. J. Environ. Res. Public Health 2020, 17, 1123; doi:10.3390/ijerph17031123
www.mdpi.com/journal/ijerph
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those actions with a highly intense load is considered crucial in modern soccer. This ability relies on
(1) adequate intra- and intermuscular coordination of soccer-speciﬁc movements and (2) metabolism
that ensures proper energy delivery [4]. Both has been shown to be aﬀected by electromyostimulation
(EMS) training [5,6].
Jumps with superimposed Whole-Body EMS (WB-EMS) in addition to soccer training sessions can
be eﬀective for improving accelerations, turns, jumps, and kicking velocity [5]. WB-EMS potentially
supports the athlete achieving higher power outputs and faster sport-speciﬁc movement velocities
using resistance training [7] by increased ﬁring rates and synchronization of motor units, resulting
in a more pronounced activation of fast-twitch ﬁbers at relatively low force levels [8]. Previous
studies showed that local EMS is beneﬁcially aﬀecting muscle metabolism and can elevate energy
expenditure and carbohydrate oxidation to a higher degree than voluntary contraction only [9–11].
Moreover, WB-EMS seem to stimulate anaerobic glycolysis for energy production with higher lactate
accumulation [12,13]. The beneﬁcial eﬀects of EMS on transportation of lactate have to be taken into
account as lactate shuttling via monocarboxylate transporters (MCTs) has been shown to improve
high-intensity intermittent exercise performance [14,15].
MCTs are considered essential for lactate shuttling and pH regulation during exercise and can
undergo notable adaptational changes depending on physical activity levels [16,17]. Due to a 1:1 ratio of
lactate and H+ being transported by MCTs, an increase in the two isoforms MCT-1 and MCT-4 in skeletal
muscle reduce the intracellular pH perturbations [18]. In line with this, studies revealed that the density
of MCT-1 and MCT-4 proteins in muscle is elevated after a macrocycle of endurance training [19–21].
However, some training studies did not ﬁnd relevant increases in MCT-4 density [22–24]. It has been
assumed that MCT-1 production is more sensitive to physical stress than MCT-4. Since the biochemical
characteristics of MCT-1 favors lactate uptake, it has been suggested that erythrocytes provide a lactate
storage compartment in situations of physical exercise, thereby reducing the exercise-induced increase
in plasma lactate concentration [25].
Interestingly, Fransson et al. [26] showed remarkable changes in MCT-4 protein expression after
4 weeks of soccer speciﬁc training regimes like speed endurance (+30%) and small sided games (+61%)
in well-trained soccer players. An increase in MCT-1 and MCT-4 density in skeletal muscle after
6 weeks of strength training was however merely reported by Juel et al. [27]. No available study
investigated the eﬀects of WB-EMS on relevant endurance capacities like VO2max and MCT-1 and
MCT-4 in soccer players. Against this background, the aim of our 3-armed randomized controlled trial
was to elucidate whether WB-EBS supplemented to a traditional soccer training routine can improve
endurance capacities indices and MCT density of soccer players. Our primary hypothesis was that a
training program of jumps with superimposed EMS may pronouncedly stimulate MCT-1 and MCT-4
density. Our secondary hypothesis was that endurance performance surrogates will not be aﬀected by
the training program, because of the relatively low additional training volume and the subject´s high
overall training status.
2. Material and Methods
2.1. Participants
Only healthy ﬁeld soccer players were included which means no cardiovascular or metabolic
diseases and no preinjury in the tested muscle groups. Participants needed to compete on a regional
level for the last 3 years and train 2–4 session per week with strength and conditioning training contents
and play one soccer match per week. In a randomized control trial twenty-eight soccer players from
10 diﬀerent teams were assigned to three diﬀerent groups. Control group was assigned based on
preferences and availability, whereas both intervention arms have been assigned based on coin toss.
The EMS group (EG, n = 10) performed jumps with superimposed WB-EMS twice a week accompanied
by 3 × 10 squat jumps in addition to the daily soccer routine over a period of 7 weeks that is a suﬃcient
intervention period with WB-EMS to improve strength abilities [5,28,29]. To diﬀerentiate between the
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eﬀects caused by EMS and by the squat jumps and soccer training respectively, two control groups
were included. A jump training group (TG, n = 10) performed the same number of squat jumps
without EMS on the same days as the EG and a control group (CG, n = 8) that only performed the daily
soccer routine. All subjects were non-smokers. Basal anthropometric parameters of the subjects were
presented in Table 1.
This study was carried out in accordance with the recommendations of the “Ethics Committee of
the German Sports University Cologne”. All subjects gave written informed consent in accordance
with the Declaration of Helsinki. The protocol was approved by the “Ethics Committee of the German
Sports University Cologne” (06–02–2014).
Table 1. Anthropometric data (mean ± SD) and Total Training Load (arbitrary units) during the 7-weeks
intervention period calculated by Polar Team-2 Software according to training time spent in deﬁned
heart rates zones.
Group
Age [Year]
Height
[m]
Weight
[kg]
Bodyfat
[%]
relVO2peak
[ml/kg*min-1]
Sessions/
Week
Total Training Load
[a.u.]
EG (n = 10)
24.4 ± 4.2
1.82 ± 0.03
81.4 ± 5.3
12.9 ± 2.1
52.1 ± 3.4
3.4 ± 1.2
3431 ± 911
TG (n = 10)
21.1 ± 1.9
1.83 ± 0.06
79.7 ± 5.5
10.8 ± 2.8
56.3 ± 5.7
3.4 ± 1.3
3479 ± 1723
CG (n = 8)
23.6 ± 3.9
1.82 ± 0.05
79.7 ± 7.5
14.1 ± 3.6
54.3 ± 7.2
2.6 ± 0.7
2644 ± 1437
2.2. Daily Soccer Routine
The participants performed 3.2 ± 1.0 soccer training sessions per week and competed once a week
in the championships. The standard training sessions lasted approximately 90 min including technical
skill activities, oﬀensive and defensive tactics, athletic components with various intensities, small-sided
game plays and continuous play. In a normal training week during season with a match on Sunday
training was scheduled on Tuesdays, Wednesdays (optional), Thursdays and Fridays. Number of
training sessions and the training days varied according to the game schedule playing Sunday-Sunday
or Sunday-Saturday. The number of training sessions and the total training minutes were documented.
The training load was measured according to the training time spent in deﬁned heart rate zones during
soccer training or match via Polar Team-2 Software (Polar Electro, Büttelborn, Germany) (see Table 1).
The training load [arbitrary units] provided by the Polar-Software aims to determine internal training
load based on background variables (sex, training history, metabolic thresholds, and maximal oxygen
consumption [VO2max]) and parameters measured during training sessions (exercise mode, and
energy expenditure) (c.f. [30]). The heart rate zones (100–90%, 89–80%, 79–70%, 69–60%, 59–50%)
were deﬁned according to the individual maximum heart rate measured in the maximal ramp test
(see endurance test).
The players were asked to maintain their usual food intake und hydration according to the
recommendations for soccer players [31] and no nutrition supplementation was used. Additional
strength training was not allowed during the study.
All players had a constant training volume during the ﬁrst half of the season (July till December)
and were in a well-trained condition with a relative VO2peak of 54.2 ± 5.9 mL/kg·min−1. All players
regularly conducted strength training during ﬁrst half of the season and had overall experience in
strength training of 5.4 ± 3.9 years. The intervention period started after the three weeks mid-season
break from end of December till mid of January. During these three weeks the training load was
relatively low (moderate endurance training twice per week) in order to maintain ﬁtness level and not
negatively aﬀect Baseline testing.
2.3. WB-EMS Application and Protocol
In order to obtain a rest interval of 48 h between the two sessions and the championship game
on Sunday WB-EMS training was conducted on Tuesdays and Friday. All subjects abstained from
alcohol consumption for 24 h prior to and during the training intervention. The EMS Training was
conducted with a WB-EMS-system by Miha Bodytec (Augsburg, Germany). WB-EMS was applied
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with an electrode vest to the upper body with integrated bilaterally two paired surface electrodes for
the chest (15 × 5 cm), upper and lower back (14 × 11 cm), latissimus (14 × 9 cm), and the abdominals
(23 × 10 cm) and with a belt system to the lower body including the muscles of the glutes (13 × 10
cm), thighs (44 × 4 cm) and calves (27 × 4 cm). Biphasic rectangular wave pulsed currents (80 Hz)
were used with an impulse width of 350 µs [5]. The stimulation intensity (mA) was determined and
set separately for each muscle group (0–120 mA) by using a Borg Rating of Perceived Exertion [32].
The training intensity was deﬁned for each player in a familiarization session two weeks before and
set at a sub-maximal level that still assures a clean dynamic jump movement (RPE 16–19 “hard to
very hard”) and was saved on a personalized chip card. The EG performed 3 × 10 maximal squat
jumps with a set pause of 60 s (no currents) per session. Every impulse for a single jump lasted for
4 s (range of motion: 2 s eccentric from standing position to an knee angle of 90◦–1 s isometric–0.1 s
explosive concentric–1 s landing and stabilisation) followed by a rest period of 10 s (duty cycle approx.
28%). This results in an overall time of 8.5 min per session an eﬀective stimulation time of 2 min
per session. The players started with a 2–3 min standardized warm-up with movement preparations
including squats, skipping and jumps in diﬀerent variations (squat jumps, jumps out of skipping or
double jumps) at a light to moderate stimulation intensity. The players were told to slowly increase
the intensity every few impulses. The training started when the players reached the deﬁned training
intensity that was saved on the chip card from the last session according to the RPE 16–19 (“hard to
very hard”). The stimulation intensity was constantly increased individually every week (Tuesdays)
controlled by the coaches in order to maintain a high stimulation intensity. The intensity was increased
after the warm-up during the ﬁrst and the second set of 10 squat jumps starting from calves up to the
chest electrodes. The TG conducted the same standardized warm-up and performed the same amount
of jumps with identical interval and conduction twice per week without EMS. The CG only performed
the 2–4 soccer training session plus one match per week.
2.4. Experimental Protocol
2.4.1. Endurance Test and Assessment of Anthropometrics
For determination of the endurance parameters spirometry was performed on a WOODWAY
treadmill (Woodway GmbH, Weil am Rhein, Germany) one week before (Baseline) and after the
7-weeks intervention period (Post-test) (Figure 1). Furthermore, bodymass and body composition
were determined via bioelectrical impendence analysis (TANITA corp., Tokyo, Japan). Endurance
tests were conducted three days after the soccer match to assure adequate recovery and not negatively
inﬂuence performance. Respiratory gases were analyzed via the ZAN600-System and ZAN-Software
GPI 3.xx (ZAN Austria e.U., Steyr-Dietach, Austria), using standard algorithms with dynamic account
for the time delay between the gas consumption and volume signal. To calibrate the device according
to the manufacturer´s guidelines, a gas mixture consisting of 5% CO2, 16% O2, and rest nitrogen was
used (Praxair Deutschland GmbH, Düsseldorf, Germany). To measure the maximum oxygen uptake
(VO2peak), the subjects performed an incremental ramp test [33]. Thereby, the players performed a
warmup at moderate speed (3 m·s−1) with 1% incline for 3 min. In the last 30 s the incline was increased
to 2.5%. Subsequently, running speed was then increased every 30 sec by 0.3 m/s until subjective
exhaustion was reported. Heart rate was documented in the last 10s of a ramp stage. The VO2peak
was determined as average maximum oxygen uptake of the ﬁrst 20 s after ending the test. Additionally,
maximum heart rate, time to exertion (TTE) and maximum lactate concentration (Lamax) was recorded.
27 players completed the two endurance diagnostics. One player of the TG was removed from the
study due to an ankle joint injury prior to post testing.
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Figure 1. Timeline of endurance testing and muscle biopsy withdrawal during the study in the 2nd
half of the season.
2.4.2. Muscle Biopsies and Tissue Treatment.
Muscle biopsies via Bergström method [34] were taken from each player two weeks before
(Baseline) and in the week after the last training intervention (Post-test). All biopsies were obtained
under local anaesthetic from the middle portion of the vastus lateralis between the lateral part of the
patella and spina iliaca anterior superior 2.5 cm below the fascia. The muscle samples were freed from
blood and non-muscular material and embedded in tissue freezing medium (TISSUE TEK, Sakura,
Zoeterwoude, The Netherlands). Samples were frozen in liquid nitrogen-cooled isopentane and stored
at −80 ◦C for further analysis. The distance between the Baseline and Post-test incision was approx.
2.5 cm.
2.5. Immunohistochemistry
Muscle samples from 26 subjects were used for histology. 7 µm cross-sectional slices were obtained
from the frozen muscle tissue using a cryo-microtome Leica CM 3050 C (Leica Microsystems, Nußbach,
Germany) and placed on Polysine™ microscope slides (VWR International, Leuven, Belgium) [35].
Sections were ﬁxed for 5 min in −20 ◦C pre-cooled acetone and air dried for 10 min at room temperature
(RT), before blocking for one hour at RT with TBS (tris buﬀered saline, 150 mM NaCl, 10 mM Tris-HCl,
pH 7.6) containing 5% BSA (bovine serum albumin). After blocking, sections were incubated overnight
(4 ◦C) with primary antibody for MCT-1 (ab3538P; 1:500; Merck Millipore, Burlington, MA, USA) and
MCT-4 (sc-376140; 1:400; Santa Cruz Biotechnology, Dallas, TX, USA), diluted in 0.8% BSA. To conﬁrm
antibody speciﬁcity, control sections were incubated in TBS containing 0.8% BSA but without primary
antibody. After incubation, sections were washed 5 times short and twice for 10 min with TBS and
incubated for one hour with biotinylated goat anti-rabbit secondary antibody for MCT-1 (VECTOR
Laboratories, Burlingame, CA, USA), diluted 1:500 in TBS and goat anti-mouse for MCT-4 (VECTOR
Laboratories), diluted 1:400 in TBS, at RT.
After that, sections were washed again 5 times for 30 s and twice for 10 min before incubation
with ﬂuorescent Alexa 488 secondary antibodies (Life Technologies, Carlsbad, CA, USA); diluted 1:500
in TBS for an hour. Afterwards sections were blocked with 5% BSA (TBS-Tween) for 30 min. Slides
were then incubated overnight at 4 ◦C with A4.951primary antibodies (A4951; type-I myosin heavy
chain; Developmental Studies Hybridoma Bank, Iowa City, IA, USA) diluted 1:200 in 0.8% BSA.
On the third day, sections were washed 5 times short and twice for 10 min with TBS before
incubated again with secondary antibodies and ﬂuorescent Alexa 555 (red) diluted 1:500 in TBS for an
hour at RT. After washing again the samples, ﬁxed on microscope glass slides, were embedded with
aqualpolymount and stored at RT.
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2.6. Data Analysis
The analysis of immunoﬂuorescence stained myoﬁbers were conducted with a confocal laser
scanning microscope (LSM 510, Zeiss, Jena, Germany) at 63X fold magniﬁcation. For the analysis of
MCT density in sarcoplasm and myoﬁber membranes, two laser channels 543 nm (for Alexa 555) and
488 nm (for Alexa 488) were used.
Two separate line-scans were conducted per measurement of membrane and sarcoplasmic areas
of single myoﬁbers to determine the staining intensity for MCT 1 and MCT 4 and the means was used
for analysis (Figure 2). 1000 pixels were standardized analyzed per line scan along the membrane
and the sarcoplasm. MCT density was then calculated as the mean staining intensity of all pixels
along each line scan. For the analysis of type I ﬁbers, only the green channel (Alexa 488) was used for
analysis and the red channel (Alex 555) was used for ﬁber type determination. Laser intensity was
standardized for each subject without changing throughout the analysis.
Figure 2. Representative pictures of immunoﬂuorescence stained myoﬁber cross-sections showing
speciﬁc MCT-1 and MCT-4 staining (green) and type 1 myoﬁber staining (red) within membrane and
sarcoplasmic areas of myoﬁbers (10× fold magniﬁcation). (A) MCT-4 Posttest, (B) MCT-1 Posttest.
2.7. Statistical Analysis
To determine the eﬀect of the training interventions on endurance parameters, MCT-1 and MCT-4,
separate 2 (time: pre vs. post) × 3 (group: EG, TG, CG) mixed ANOVA with repeated measures
were conducted. ANOVA assumption of homogenous variances was tested using Maulchy-test of
Sphericity. A Greenhouse-Geisser correction was used when a violation of Mauchly´s test was observed.
To estimate overall time and interaction eﬀect sizes, partial eta squared (η2p) was computed with
η2p ≥ 0.01 indicating small, ≥0.059 medium and ≥0.138 large eﬀects [36]. If 2 × 3 mixed ANOVA
revealed a time*group interaction eﬀect on any variable, this eﬀect was further investigated using
Bonferroni post hoc tests for pairwise comparison. For all inferential statistical analyses, signiﬁcance
was deﬁned as a p-value less than 0.05. All descriptive and inferential statistical analyses were
conducted using SPSS 25® (IBM®, Armonk, NY, USA). Results were presented as means and standard
deviations (SDs). Figures were created with Prism 6 (GraphPad Software Inc., La Jolla, CA, USA).
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3. Results
3.1. Training Load
No signiﬁcant diﬀerences were observed between the groups in the total number of training
sessions (EG 23.9 ± 7.8; TG 25.9 ± 6.6; CG 18.1 ± 5.6 sessions), training minutes (EG 2103 ± 630; TG 1812
± 919; CG 1437 ± 381Min), and the total recorded training load via Polar Team-2 software (Table 1).
All subjects of TG and EG had a compliance of 100% (14 training sessions) for jump training and
WB-EMS sessions, respectively.
3.2. Endurance Parameters
2 × 3 (time × group) ANOVA of repeated measures revealed no signiﬁcant time, group or
interaction eﬀect for relative VO2peak, TTE and Lamax. No group diﬀerences were observed at Baseline
or Posttest in none of the analyzed parameters (Figure 3).
Figure 3. (A) Relative maximum oxygen uptake (relVO2peak), (B) maximal lactate concentration,
(C) maximal running time till exertion (TTE), and (D) maximal heart rate) determined at the endurance
ramp-test on the treadmill in EMS-Group (EG), Training-Group (TG) and Control-Group (CG) measured
before (Baseline) and after the 7 weeks intervention period (Posttest). Values are presented in means
± SD.
3.3. MCT-4
3.3.1. Type-I Fibers
The 2 × 3 (time × group) repeated measures ANOVA revealed no signiﬁcant time (p = 0.119,
η2p = 0.102), group or intervention eﬀect (p = 0.165, η2p = 0.145) for the MCT-4 density in the membrane
of type-I muscle ﬁbers. Regarding cytoplasm density of the MCT-4, a large signiﬁcant eﬀect over time
(p = 0.009, η2p = 0.26) was shown. No group*time eﬀect (p = 0.318, η2p = 0.095) was however observed.
Subsequent post-hoc analysis showed a signiﬁcant decrease in MCT-4 density after 7 weeks for TG
only (p = 0.005). No group diﬀerences were detected at Baseline and Posttest for MCT-4 density in
membrane and cytoplasm in type-I ﬁbers (Figure 4).
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3.3.2. Type-II Fibers
With respect to the membrane density of the MCT-4, no time eﬀect (p = 0.172, η2p = 0.079)
or group*time interaction (p = 0.315, η2p = 0.096) of type-II ﬁbers was shown. For the cytoplasm
density of the MCT-4 a large signiﬁcant main eﬀect for the factor time (p = 0.001, η2p = 0.382) was
observed in type-II ﬁbers. No group*time interaction eﬀect (p = 0.333, η2p = 0.091) was observed.
Subsequent post-hoc analysis showed a signiﬁcant decrease in MCT-4 distribution only for TG
(p = 0.004). No diﬀerences were shown between the groups at Baseline or Posttest for MCT-4 density
in the membrane and cytoplasm of the type-II ﬁbers (Figure 4).
Figure 4.
MCT-4 density in type-I ﬁber (A) membrane and (B) cytoplasm, and in type-II ﬁber
(C) membrane and (D) cytoplasm for EMS-Group (EG), Training-Group (TG) and Control-Group (CG)
measured before (Baseline) and after the 7 weeks intervention period (Posttest). Values are presented
in means ± SD.
3.4. MCT-1
3.4.1. Type-I Fibers
The 2 × 3 (time × group) repeated measure ANOVA showed no signiﬁcant eﬀect over time
(p = 0.230, η2p = 0.065) as well as no signiﬁcant group*time interaction eﬀect (p = 0.045, η2p = 0.246) for
MCT-1 density in the membrane. Post-hoc analysis showed a signiﬁcant decrease in density for the TG
(p = 0.032). For the cytoplasm density of the MCT-1 no main eﬀects over time (p = 0.114, η2p = 0.110) or
group*time (p = 0.416, η2p = 0.077) were found. No group diﬀerences were detected at Baseline and
Posttest for MCT-1 density in the membrane and cytoplasm of the type-I ﬁbers (Figure 5).
3.4.2. Type-II Fibers
The 2 × 3 ANOVA revealed a large signiﬁcant time eﬀect for cytoplasm MCT-1 (p = 0.009,
η2p = 0.269) but no group × time interaction eﬀect (p = 0.933, η2p = 0.006). However, no signiﬁcant
alternations in the cytoplasm were found in the three diﬀerent groups over time. For membrane density
of the MCT-1 neither a time (p = 0.104, η2p = 0.115) nor an interaction eﬀect (p = 0.480, η2p = 0.065)
was observed in type-II ﬁbers. Group comparison revealed no diﬀerences between the three groups
at baseline and post-testing for MCT-1 density in the membrane and cytoplasm of the type-II ﬁbers
(Figure 5).
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Figure 5. MCT-1 density in type-I ﬁber (A) membrane and (B) cytoplasm, and in type-II ﬁber (C)
membrane and (D) cytoplasm for EMS-Group (EG), Training-Group (TG) and Control-Group (CG)
measured before (Baseline) and after the 7 weeks intervention period (Posttest). Values are presented
in means ± SD.
4. Discussion
The main ﬁnding of this intervention is that 7 weeks of a dynamic WB-EMS program (2 sessions per
week) in addition to the regular soccer training does not relevantly inﬂuence endurance performance
indices as well as MCT-1 or MCT-4 density in the muscle. We surprisingly observed that MCT-4 density
in the cytoplasm and MCT-1 density in the membrane of type I muscle ﬁbers notably decreased in TG,
the group that completed jumps without EMS. Participants of all three groups (EG, TG, CG) did their
weekly soccer sessions since years and training volume and training intensity was not changed during
the intervention period. Thus, the results could be explained by the high overall training status of the
subjects. Due to the documented eﬀects of strength training on runner´s performance [37] and eﬀects
of EMS application on runner´s VO2max [6], we analysed eﬀects on some endurance parameter for EG.
Indeed, WB-EMS intervention with dynamic exercises and training status of the subjects (VO2max:
53 mL/min/kg) were similar to the study of Amaro-Gahete et al. [6]. However, the diﬀerential results
might be attributed to diﬀerences in current frequency (12–90 vs. 85 Hz), higher time under tension
(6 vs. 2 min) and higher intensities of exercises with superimposed EMS (strength and interval exercise
vs. jumps) in the cited study. With regard to the training status of the subjects and the general high
metabolic demand in soccer games and -training, the EMS stimulus could have been too low for further
adaptations in endurance capacities. Consequently, no changes were observed in any parameter
obtained during incremental treadmill running test. With respect to the results of Amaro-Gahete and
coworkers and in order to improve endurance parameter, it might be promising to adjust exercise to
higher training intensities, e.g., by shortening rest intervals of jumps or include other exercises within
high intensity intervals. The authors provided recommendations for an undulating modulation of
current adjustments [38], but without physiological explanation or reasoning. There are no studies
available that support these results and we found only one study that applied EMS during endurance
training. In this regard, Mathes and coworkers showed that, although metabolic stimuli and markers
of muscle damage were higher in cycling with superimposed EMS compared to cycling without EMS,
improvements of endurance performance and capacity were not signiﬁcantly diﬀerent between both
training methods [39].
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The disposed EMS-protocol concurrently to soccer training enhanced strength and myoﬁber
adaptations [40]. Furthermore it revealed to be eﬀective for accelerations, direction changes, vertical
jumping ability and kicking velocity in elite soccer players [5]. Training design was identical within the
present study. Improving such surrogate parameters of aerobic or anaerobic endurance capacities seems
also promising to improve indices of soccer performance. The ability to perform sprints with high
intensity bouts is inﬂuenced by anaerobic capacity. The ability to do that repeatedly critically depends
on the aerobic metabolism. Both metabolic pathways are inter-linked with each other. However,
for the recommendation of WB-EMS, it would be also important that no degradation occurs since
soccer players need concurrent abilities of strength, speed, and endurance in the sense of repeated
high-intensity actions.
MCT-1 and MCT-4 content in the muscle was not inﬂuenced by the intervention of EG. Interventions
that showed increases of MCT-1 and MCT-4 conducted higher intensities and metabolic demanding
exercises. It is known that high-intensity endurance training increases MCT-1 in trained subjects [41,42]
and strength training increases MCT-1 and MCT-4 in untrained subjects [27]. The training program of
3 × 10 maximum jumps and 10 s between each jump was seemingly less intense. Indeed, jumps are
metabolically demanding, but 10 s of rest enable adequate delivery of oxygen. Unfortunately, lactate
accumulation was not measured during training in the present study. However, hundreds of repeated
jumps with 8 s rest between the jumps can result in moderate steady state lactate concentrations of
3–4 mmol·L−1 [43]. It might be a question of the stimulus´ intensity or accumulation that need to be
analyzed in exercise constellations that increase metabolic stimulus like high intensity interval training.
The superimposed WB-EMS on/oﬀ-time ratio should be increased accordingly.
Our results show a signiﬁcant decrease in MCT-4 and MCT-1 content after jump training without
EMS (TG), which can be hardly explained, as EG and CG did not show signiﬁcant diﬀerences in MCT-4
and MCT-1 content. Although the EG and TG showed equal training load (see Table 1) generally,
high-intensity anaerobic eﬀort in soccer greatly varies according to the playtime and diﬀerent playing
position requirements within a squad [44,45]. Furthermore, there can be diﬀerences of intensity in
daily soccer training routine that could lead to ﬂuctuations of MCT´s. This speculation is indicated
by large standard deviations in total training load of TG (Table 1). Although subjects were assigned
to play and train as usual, it was not possible to adjust for this inﬂuence in the study. Replication
studies with accelerometer-based monitoring of the total loads are required to verify this issue.
Additionally, ﬁndings warrant further studies about strength training eﬀects to MCT. In this regard,
authors have demonstrated the importance of detailed characterization of the training stimulus and
the subjects [46,47]. A speciﬁcation of muscular time under tension and movement dynamics like
reactivity are missing in recent studies that dealt with EMS or MCT´s. The reduction eﬀect of MCT
could also be attributed to a shift of MCTs to the membrane. A previous study has shown that MCT-1
localisation after training in diabetic patients increased in the sarcolemma of muscle ﬁbers while the
sarcoplasmic content was reduced [48].
Some more limitations of the present study have to be mentioned for further research on the
eﬀects of WB-EMS to endurance capacities. Due to the small sample size the study has pilot character.
Since we did not measure lactate production during training, we are not able to characterize the
metabolic stimulus of the training. Moreover, the eﬀects of running performance mainly include
improved running economy, time trial performance and sprint performance all of which were not tested
in the current work. A more sports-speciﬁc testing set such as the Yo-Yo Intermittent Recovery test in
combination to sprint tests would have been useful in terms of ecological validity. A Further aspect of
limitation is that including players from diﬀerent teams can result in diﬀerences in training sessions
for the CG (Table 1). A more detailed documentation of players match and training loads would be
helpful to avoid bias. Future research may consider changing study design to evoke higher metabolic
stimuli by increasing time under tension, reducing rest intervals or increasing intervention duration.
However, the present training stimulus was designed to improve soccer speciﬁc high-intensity actions
and could be integrated into daily training on a professional level [5].
Int. J. Environ. Res. Public Health 2020, 17, 1123
11 of 13
5. Conclusions
We conclude despite ﬁndings that the disposed WB-EMS protocol can enhance strength [5]
and myoﬁber adaptations [40] it is not a potent stimulation to improve VO2max and lactate
transport proteins.
Author Contributions: Conceptualization: A.F. and N.W.; Methodology: A.F., T.S. and M.d.M.; Software: A.F.;
Validation: S.G., N.W. and A.F.; Formal Analysis: A.F.; Investigation: A.F., T.S. and M.d.M.; Resources: W.B.; Data
Curation: A.F.; Writing—Original Draft Preparation: N.W.; Writing—Review and Editing: L.D., S.G. and N.W.;
Visualization: A.F.; Supervision: L.D.; Project Administration: A.F.; Funding Acquisition: A.F. All authors have
read and agreed to the published version of the manuscript.
Funding: This research was funded by the German Federal Institute of Sport Science, grant number AZ
070101/16-17.
Acknowledgments: The authors would like to thank Bianca Collins, Benedikt Seeger, Anke Schmitz, and Anika
Voß for excellent technical assistance.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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Seven Weeks of Jump Training with Superimposed Whole-Body Electromyostimulation Does Not Affect the Physiological and Cellular Parameters of Endurance Performance in Amateur Soccer Players.
Wirtz, Nicolas,Filipovic, André,Gehlert, Sebastian,Marées, Markus de,Schiffer, Thorsten,Bloch, Wilhelm,Donath, Lars