

Citation: Muniz-Pardos, B.;
Zelenkova, I.; Gonzalez-Aguero, A.;
Knopp, M.; Boitz, T.; Graham, M.;
Ruiz, D.; Casajus, J.A.; Pitsiladis, Y.P.
The Impact of Grounding in Running
Shoes on Indices of Performance in
Elite Competitive Athletes. Int. J.
Environ. Res. Public Health 2022, 19,
1317. https://doi.org/10.3390/
ijerph19031317
Academic Editors: Roberto
Alonso González Lezcano,
Francesco Nocera and Rosa
Giuseppina Caponetto
Received: 24 November 2021
Accepted: 23 January 2022
Published: 25 January 2022
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International  Journal  of
Environmental Research
and Public Health
Article
The Impact of Grounding in Running Shoes on Indices of
Performance in Elite Competitive Athletes
Borja Muniz-Pardos 1,2,3
, Irina Zelenkova 2,3
, Alex Gonzalez-Aguero 1,2,3
, Melanie Knopp 4
, Toni Boitz 4,
Martin Graham 4, Daniel Ruiz 4
, Jose A. Casajus 2,3,5
and Yannis P. Pitsiladis 3,6,7,8,*
1
Faculty of Health and Sports Science (FCSD), Department of Physiatry and Nursing, University of Zaragoza,
50009 Zaragoza, Spain; bmuniz@unizar.es (B.M.-P.); alexgonz@unizar.es (A.G.-A.)
2
GENUD (Growth, Exercise, Nutrition and Development) Research Group, Department of Physiatry and
Nursing, University of Zaragoza, 50009 Zaragoza, Spain; iz@i1.ru (I.Z.); joseant@unizar.es (J.A.C.)
3
International Federation of Sports Medicine (FIMS), 1007 Lausanne, Switzerland
4
adidas Innovation, adidas AG, 91074 Herzogenaurach, Germany; Melanie.Knopp@adidas.com (M.K.);
Toni.Boitz@adidas.com (T.B.); martin.william.graham@adidas.com (M.G.); daniel.ruiz@adidas.com (D.R.)
5
Faculty of Medicine, Department of Physiatry and Nursing, University of Zaragoza, 50009 Zaragoza, Spain
6
School of Sport and Health Sciences, University of Brighton, Eastbourne BN20 7SN, UK
7
Centre for Exercise Sciences and Sports Medicine, FIMS Collaborating Centre of Sports Medicine,
University of Rome “Foro Italico”, 00135 Rome, Italy
8
European Federation of Sports Medicine Associations (EFSMA), 1007 Lausanne, Switzerland
*
Correspondence: y.pitsiladis@brighton.ac.uk
Abstract: The introduction of carbon ﬁber plate shoes has triggered a plethora of world records in
running, which has encouraged shoe industries to produce novel shoe designs to enhance running
performance, including shoes containing conductor elements or “grounding shoes” (GS), which
could potentially reduce the energy cost of running. The aim of this study was to examine the
physiological and perceptual responses of athletes subjected to grounding shoes during running.
Ten elite runners were recruited. Firstly, the athletes performed an incremental running test for
VO2max and anaerobic threshold (AT) determination, and were familiarized with the two shoe
conditions (traditional training shoe (TTS) and GS, the latter containing a conductor element under
the insole). One week apart, athletes performed running economy tests (20 min run at 80% of the
AT) on a 400 m dirt track, with shoe conditions randomized. VO2, heart rate, lactate, and perceived
fatigue were registered throughout the experiment. No differences in any of the physiological or
perceptual variables were identiﬁed between shoe conditions, with an equal running economy in
both TTS and GS (51.1 ± 4.2 vs. 50.9 ± 5.1 mL kg−1 min−1, respectively). Our results suggest that a
grounding stimulus does not improve the energy cost of running, or the physiological/perceptual
responses of elite athletes.
Keywords: earthing; environmental physiology; running performance; running economy; shoe
technology; grounding
1. Introduction
During the past ﬁve years, shoe designs have experienced a great technological
revolution, which has been accompanied by a plethora of world records in all long-
distance running events (i.e., from 5000 m to marathons, in both male and female athletes).
Joyner et al., recently suggested that the factors potentially explaining the recent records
in long-distance running are the physiological and training factors, in addition to shoe
technology and drafting [1]. However, the abrupt drop in world records across all distances
since 2017 suggests that shoe technology has a major contribution when compared to the
other factors (i.e., training methods, the physiology of athletes, and drafting are factors that
have not substantially changed in the last 5 years) [2].
Int. J. Environ. Res. Public Health 2022, 19, 1317. https://doi.org/10.3390/ijerph19031317
https://www.mdpi.com/journal/ijerph
Int. J. Environ. Res. Public Health 2022, 19, 1317
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The most popular shoe technology for road running includes a carbon ﬁber plate (CFP)
within the sole, a light and highly reactive foam, and a stack up to 40 mm in thickness. This
technology has been shown to reduce the energy cost of running during a ﬁxed exercise
intensity (traditionally between 14 and 18 km h−1) by approximately 4%, when compared
to non-CFP shoes [3–5]. This improved running economy (RE) seems to be elicited by
an increase in energy return caused by the action of passive elastic recoil, which in turn
increases stride length and contact times, reduces step frequencies, and slightly increases
the peak forces upon ground contact, when compared to non-CFP shoes [3,6,7].
The great popularity and effectiveness of CFP shoes has encouraged the shoe industry
to explore new forms of shoe designs to optimize both health and performance during
running. The implementation of “grounding” in humans purports to take advantage of the
prolonged contact between an individual and the ground, and the potential transmission of
energy between the two. Previous research states that the “direct contact of humans with
the earth or using a metal conductor changes the electric potential on the surface of the body,
as well as within the entire human organism” [8]. While the etiology of this potential effect
is difﬁcult to explain from a biophysiological perspective, previous ﬁndings have shown
that the direct contact of an individual with the ground may reduce inﬂammatory processes,
mood, pain, and stress at rest [9–11] and during exercise [8,9], with some studies suggesting
that grounding technology may have a medical application. For example, previous research
has suggested that the implementation of grounding is beneﬁcial for mood, and may be
especially beneﬁcial in cases of depression, anxiety, stress, and trauma [11,12].
In relation to the existing research on grounding and exercise, an informative pilot
study examined the effects of grounding on muscle physiology in response to exercise-
induced muscle damage, and observed faster muscle recovery times under the grounding
condition compared to the placebo [13]. The same group performed a more comprehensive
follow-up study [14], observing that grounding signiﬁcantly reduced creatine kinase (CK)
levels 24 h post-exercise when compared to the placebo, suggesting that grounding may
reduce acute muscular damage post-exercise. Following these early studies on grounding
and muscle damage, a further study focused on the impact that this technology may
have during aerobic exercise [8]. Sokal et al. claimed that the indirect contact of cyclists
with the ground (through a metal conductor) while exercising elicited an increase in
the electrical potential of the body when compared to those in the control group (not
grounded). This study further reported that the observed increase in electrical potential
with was accompanied by a greater decrease in blood urea concentrations during and after
a 30 min cycling test at 50% of VO2max, indicating, according to the authors, a decreased
physiological stress [8]. While these previous studies showed a beneﬁt of grounding on
the muscle recovery and physiological stress of healthy subjects in response to different
modes of exercise (i.e., resistance training and cycling), the impact of this technology while
running is unknown.
Given the imminent introduction of grounding technology in running shoes, and the
absence of rigorous scientiﬁc evidence of its effects, adding conductor elements within the
shoe and employing a well-controlled experimental design, would allow for the assessment
of any putative effects of this technology (i.e., grounding technology in running shoes)
during running. This is especially important given the recent controversy that novel shoe
technologies are negatively impacting the integrity and fairness within sport [2,15]. A
recent critical review [2] highlighted how novel shoe designs are revolutionizing the world
of sport, as numerous National, European, World, and Olympic records have been broken
over an extraordinarily short time period (i.e., since the introduction of CFP shoes). In
addition to this controversy, there is a lack of well-controlled and rigorous studies in the
ﬁeld that focus on the impact of shoe designs on running performance [2], which makes
the true performance beneﬁts of certain shoe technologies difﬁcult to determine.
Considering the reduced physiological stress and muscle damage witnessed in subjects
while performing other physical activities (i.e., strength exercises and cycling), it is impor-
tant to examine the impact of grounding on the physiological and perceptual responses to
Int. J. Environ. Res. Public Health 2022, 19, 1317
3 of 10
running, especially considering the interest of shoe companies in incorporating grounding
technology into running shoes, and the potential fairness/integrity issues that may result if
a performance beneﬁt is demonstrated. Therefore, the main aim of the present study was
to compare the RE and physiological stress of well-trained runners while running in either
grounding shoes (GS) or traditional training shoes (TTS).
2. Materials and Methods
2.1. Participants
Ten highly-trained male runners (age = 27 ± 7 years; weight = 64.6 ± 6 kg;
height = 176.3 ± 5.4 cm) were recruited for the present study. Upon recruitment, all
subjects received and signed an informed consent form in order to participate in the study.
Subjects were required to meet the following inclusion criteria: (1) to train a minimum of
50 km week−1, (2) to have a personal best under 35:00 min:s in 10 km or 17:30 min:s in
5 km, (3) to be healthy and without any musculoskeletal injury.
2.2. Procedures
The present study design required runners to visit either the laboratory or the track
on two occasions, both separated by a period of 7 days to avoid any residual fatigue. Visit
1 included a VO2max test, ventilatory threshold determination, and shoe familiarization
in the laboratory; Visit 2 included 20 min RE tests at 80% of the anaerobic threshold, on
a 400 m dirt track, with the order of the two shoe conditions randomized (Figure 1). A
dirt track was selected over a traditional synthetic PU rubber track to avoid any material
interference between the ground and the athlete. The present study was approved by the
Ethics Committee of Aragon (CEICA, num. 17/2021).
2.3. Shoe Conditions
Two shoe conditions were tested: the traditional training shoe (TTS) and the grounding
shoe (GS), with these being visually identical as shown in Figure 1. Shoes with grounding
potential contained a conductor element around the insole, and aimed to diminish the
physiological stress experienced by the athlete during running as they run in closer contact
with the ground. The insulation and thermal permeability of the shoes were considered
similar, given that the same material was used for both experimental and non-experimental
shoes, with the exception of the conductor element. Both uppers consisted of the same
knitted textile, produced and supplied at the same time for both types of shoe (Figure 1).
The GS upper included a textile webbing containing yarn that encouraged electrical charge
to ﬂow through the material. The material was stitched into the collar area, and ran
through the midsole to connect with the rubber on the outsole that contacts the ground.
The TTS outsole included conventional rubber, while the GS outsole included rubber that
encouraged the ﬂow of electrical charge. The manufacturers labelled the shoes with a
number in red or blue according to the two shoe conditions, and this setting was used by
the research team to keep the study design double-blinded (See Figure 1). Additionally,
as each athlete may have become subjectively biased during the familiarization trial, all
blue/red labels were obscured with tape in Visit 2. All athletes had their own pair of shoes
for each shoe condition.
2.4. Visit 1. Maximal Oxygen Uptake and Ventilatory Threshold Determination
On the ﬁrst day, athletes were subjected to a skin temperature test and a SARS-CoV-2
antigen test, in order to participate in this study. Upon testing negative, informed consent
was signed by all participants, and medical history and pre-participation screening was
also completed. The laboratory assessments performed during the ﬁrst day included:
Anthropometric and body composition assessments. The parameters measured were
as follows: weight, height, height from sitting position, foot length, calf circumference and
fold, and thigh circumference and fold. Percent body fat, muscle mass, and bone mass were
assessed with a DXA scan (Hologic Corp., Bedford, MA, USA). Body fat, body water, and
Int. J. Environ. Res. Public Health 2022, 19, 1317
4 of 10
muscle mass were also assessed via bioimpedance (TANITA BC 780-S MA, Tanita Corp.,
Tokyo, Japan).
Public Health 2022, 19, x FOR PEER REVIEW 
4 of 11 
 
Figure 1. Image of the right grounding shoe (A) and traditional training shoe (B) for one of the elite 
athletes. 
2.3. Shoe Conditions 
Two shoe conditions were tested: the traditional training shoe (TTS) and the 
grounding shoe (GS), with these being visually identical as shown in Figure 1. Shoes with 
grounding potential contained a conductor element around the insole, and aimed to 
diminish the physiological stress experienced by the athlete during running as they run 
in closer contact with the ground. The insulation and thermal permeability of the shoes 
were considered similar, given that the same material was used for both experimental and 
non-experimental shoes, with the exception of the conductor element. Both uppers 
consisted of the same knitted textile, produced and supplied at the same time for both 
types of shoe (Figure 1). The GS upper included a textile webbing containing yarn that 
encouraged electrical charge to flow through the material. The material was stitched into 
the collar area, and ran through the midsole to connect with the rubber on the outsole that 
contacts the ground. The TTS outsole included conventional rubber, while the GS outsole 
included rubber that encouraged the flow of electrical charge. The manufacturers labelled 
the shoes with a number in red or blue according to the two shoe conditions, and this 
setting was used by the research team to keep the study design double-blinded (See Figure 
1). Additionally, as each athlete may have become subjectively biased during the 
familiarization trial, all blue/red labels were obscured with tape in Visit 2. All athletes had 
their own pair of shoes for each shoe condition. 
 
Figure 1. Image of the right grounding shoe (A) and traditional training shoe (B) for one of the
elite athletes.
Maximal aerobic capacity test. All subjects were previously familiarized with VO2max
testing. Prior to the VO2max test, subjects laid down for 5 min, and resting electrocar-
diograms and blood pressure tests were performed and assessed by experienced medical
doctors to ensure athletes did not have any cardiological issues. Participants breathed
through a low dead space mask, with air sampled at 60 mL min−1. Before each test,
two-point calibrations of the gas sensors were completed, using a known gas mixture
(16% O2 and 5% CO2) and ambient air. Ventilatory volume was calibrated using a 3 L
(±0.4%) syringe. Firstly, subjects performed a self-paced warm-up, and prior to the com-
mencement of the test, subjects were instrumented with a portable metabolic analyzer
(Cosmed K5, Cosmed Srl, Rome, Italy) and a heart rate device (Polar H10, Polar Electro,
Kempele, Finland). A short-ramp incremental protocol was used (i.e., 13–16 min) as this has
been shown to be the most appropriate assessment for identifying individual physiological
events in well-trained runners [16–18]. The protocol consisted of a 3 min run at 10 km h−1
and a 1% gradient on a treadmill (h/p/cosmos, Nussdorf—Traunstein, Germany), followed
by increases of 1 km h−1 min−1 until volitional exhaustion. Heart rate was monitored
throughout the test, and overall perception of effort (RPE) and speciﬁc RPE for the legs
were registered immediately after the test. This test enabled the determination of VO2max
(deﬁned as the highest 30 s mean values obtained during the test) and individual anaerobic
threshold (IAT), determined through visual assessment conducted by two experienced
exercise physiologists. Each individual speed for subsequent shoe trials were determined
Int. J. Environ. Res. Public Health 2022, 19, 1317
5 of 10
at the 80% of the IAT velocity. This VO2max test involved the subjects’ preferred shoe, and
served to objectively quantify individual running speed for subsequent RE trials (avoiding
the impact of the slow component of oxygen uptake given the repeated square-wave design
of the RE tests on the second visit). Visit 1 also involved the familiarization of the different
running shoes during a light, 5 min run with each pair of shoes, in preparation for Visit 2.
2.5. Visit 2. Running Economy Tests
During the second visit, indices of performance, with particular focus on RE, were
assessed for each shoe condition, determined on a 400 m dirt track. Air temperature and
humidity were recorded at the beginning and end of the experimental sessions using a
portable meteorological station, and all trials were performed either in the early morning
or late evening to avoid extreme environmental conditions. Participants breathed through
a low dead space mask, with air sampled at 60 mL min−1. Before each subject’s ﬁrst
trial, the portable metabolic analyzer was calibrated following the calibration procedures
aforementioned. The shoe conditions were randomly assigned, and both runners and
assessors were blinded to the shoe condition. Brand new socks were used for each RE
trial to avoid excessive humidity within the shoe, as this could impact grounding effect.
Body mass was measured before and after each test. Each runner warmed up for 15 min
with their preferred training shoes prior to being equipped with the portable metabolic
analyzer. Pre-trial blood lactate was measured from a single drop of whole blood from
the ﬁngertip using a lactate meter (Lactate Pro 2, Arkray Europe, B.V., Amstelveen, the
Netherlands), and pre-trial heart rate and RPE were also collected. Athletes performed two
20 min exercise bouts at 80% of their IAT velocity for each shoe condition, with a 20 min
rest in between (Figure 2). The duration of this RE protocol was longer than traditional
RE tests (4–6 min) used in previous studies examining shoe designs [3–5]. The reason for
this was to allow for a longer contact time between the athlete and the earth, which is
crucial for obtaining a dose–response relationship. Lactate, whole-body RPE, and legs-only
RPE (1–10 scale) were recorded at min 1, 3, and 15 of recovery following both trials, and
heart rate and ventilatory parameters were monitored throughout the test. A researcher
(and experienced cyclist) paced all runners at their individual speed using a bicycle. The
RE elicited by each shoe condition was determined as the mean VO2 between min 10 to
min 15, as steady state was ensured during this period. To reduce the noise in the ventilatory
measurements, a 7-breath averaging method was performed.
Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 
6 of 11 
 
fingertip using a lactate meter (Lactate Pro 2, Arkray Europe, B.V., Amstelveen, the 
Netherlands), and pre-trial heart rate and RPE were also collected. Athletes performed 
two 20 min exercise bouts at 80% of their IAT velocity for each shoe condition, with a 20 
min rest in between (Figure 2). The duration of this RE protocol was longer than 
traditional RE tests (4–6 min) used in previous studies examining shoe designs [3–5]. The 
reason for this was to allow for a longer contact time between the athlete and the earth, 
which is crucial for obtaining a dose–response relationship. Lactate, whole-body RPE, and 
legs-only RPE (1–10 scale) were recorded at min 1, 3, and 15 of recovery following both 
trials, and heart rate and ventilatory parameters were monitored throughout the test. A 
researcher (and experienced cyclist) paced all runners at their individual speed using a 
bicycle. The RE elicited by each shoe condition was determined as the mean V̇O2 between 
min 10 to min 15, as steady state was ensured during this period. To reduce the noise in 
the ventilatory measurements, a 7-breath averaging method was performed. 
 
Figure 2. Protocol for the running economy trials at 80% of the anaerobic threshold (AT). 
2.6. Statistical Analysis 
Means and standard deviations (mean ± SD) were calculated for all variables. An a 
priori sample size calculation (G*Power software, version 3.1.9.3, Heinrich-Heine-
Universität Düsseldorf, Düsseldorf, Germany) was performed using the running 
economy data reported in a previous study testing different shoe designs in well-trained 
athletes (Barnes et al., 2018). The V̇O2 data for both the control and grounded shoe (53.61 
± 2.20 vs. 51.26 ± 2.23 mL kg−1 min−1, respectively) were used to generate a correlation 
20 min
20 min
20 min
15 min
warm-up
20 min
Shoe 1
Shoe 2
80% AT
80% AT
15’
15’
3’
3’
1’
1’
rest
rest
Rating of 
perceived 
exertion
Lactate
sample
Heart rate
recording
Gas
analysis
Shoe
condition
Body
mass
Figure 2. Protocol for the running economy trials at 80% of the anaerobic threshold (AT).
Int. J. Environ. Res. Public Health 2022, 19, 1317
6 of 10
2.6. Statistical Analysis
Means and standard deviations (mean ± SD) were calculated for all variables. An a pri-
ori sample size calculation (G*Power software, version 3.1.9.3, Heinrich-Heine-Universität
Düsseldorf, Düsseldorf, Germany) was performed using the running economy data re-
ported in a previous study testing different shoe designs in well-trained athletes
(Barnes et al., 2018). The VO2 data for both the control and grounded shoe (53.61 ± 2.20 vs.
51.26 ± 2.23 mL kg−1 min−1, respectively) were used to generate a correlation coefﬁcient
of 0.45 and a Cohen’s d of 1.01. A two-tailed t-test revealed that a total sample size of
10 subjects was required to obtain statistical power of 0.80 and an alpha of 0.05. A Shapiro–
Wilk test revealed normal data distributions across all studied variables. Student’s t-tests
for paired samples were applied between TTS and GS shoe conditions in order to examine
the differences between metabolic and RE data (HR, VO2, RER). Signiﬁcant values were set
at p ≤ 0.05 and effect sizes (Cohen’s d) were also calculated. The Statistical Package for the
Social Sciences (SPSS) version 23.0 (SPSS Inc., Chicago, IL, USA) was used to perform the
statistical analyses.
3. Results
A final sample of 10 athletes completed the present study, with no drop-outs. These athletes
were national to international level runners/triathletes, with two of them having participated in
major sporting events (Olympic Games and World Championships). Table 1 presents the mean
and individual descriptive characteristics of the sample, showing a fairly homogeneous fitness
level across all runners (i.e., mean VO2max of 78.4 ± 3.8 mL kg−1 min−1).
Table 1. Descriptive characteristics of the participants.
ID
Age
(years)
Weight
(kg)
Height
(cm)
BMI
(kg m−2)
Bioimpedance
(Fat %)
VO2max
(mL kg−1 min−1)
Athlete 1
31.0
78.5
180.3
24.1
12.7
76.0
Athlete 2
25.7
65.7
177.8
20.8
5.5
82.3
Athlete 3
35.0
64
174.3
21.1
10.4
80.3
Athlete 4
20.8
68.9
186.3
19.9
11.8
83.6
Athlete 5
31.1
57.0
171.0
19.5
3.0
78.0
Athlete 6
26.2
59.3
170.2
20.5
11.2
77.8
Athlete 7
38.2
66.0
176.5
21.2
3.8
78.5
Athlete 8
25.0
72.5
177.7
23.0
7.0
77.3
Athlete 9
20.6
64.9
171.2
22.1
8.9
80.5
Athlete 10
18.1
64.0
183.0
19.1
8.5
69.9
Mean ± SD
27.2 ± 6.6
66.1 ± 6.2
176.8 ± 5.4
21.1 ± 1.6
8.3 ± 3.4
78.4 ± 3.8
A Student’s t-test for paired samples revealed no signiﬁcant difference in RE values
between TTS and GS conditions (51.1 ± 4.2 vs. 50.9 ± 5.1 mL kg−1 min−1, respectively,
p = 0.779, Cohen’s d = 0.092). Figure 3 shows both mean and individual values for VO2.
Additionally, blood lactate was not different between shoe conditions at min 1 (p = 0.793),
min 3 (p = 0.250), and min 15 (p = 0.641) post-exercise (Figure 4). Both whole-body and
legs-only RPE values were also not signiﬁcantly different between TTS and GS at min 1
(p = 1.0 and p = 0.273, respectively), min 3 (p = 0.443 and p = 0.591, respectively), and
min 15 (p = 0.168 and p = 0.591, respectively) post-exercise (Figure 4). Finally, HR val-
ues were not signiﬁcantly different between TTS and GS during exercise (150.1 ± 15 vs.
151.0 ± 16 bpm, respectively, p = 0.461, Cohen’s d = 0.244; Figure 4).
Int. J. Environ. Res. Public Health 2022, 19, 1317
7 of 10
Additionally, blood lactate was not different between shoe conditions at min 1 (p  0.793), 
min 3 (p = 0.250), and min 15 (p = 0.641) post-exercise (Figure 4). Both whole-body and 
legs-only RPE values were also not significantly different between TTS and GS at min 1 (p 
= 1.0 and p = 0.273, respectively), min 3 (p = 0.443 and p = 0.591, respectively), and min 15 
(p = 0.168 and p = 0.591, respectively) post-exercise (Figure 4). Finally, HR values were not 
significantly different between TTS and GS during exercise (150.1 ± 15 vs. 151.0 ± 16 bpm, 
respectively, p = 0.461, Cohen’s d = 0.244; Figure 4). 
 
Figure 3. Mean and individual running economy values (mL kg−1 min−1) of the 10 athletes running 
in traditional training shoes (grey column) and in grounding shoes (black column). 
Figure 3. Mean and individual running economy values (mL kg−1 min−1) of the 10 athletes running
in traditional training shoes (grey column) and in grounding shoes (black column).
Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 
8 of 11 
 
 
Figure 4. Blood lactate (A), whole-body rate of perceived exertion (RPE; B), and legs-only RPE (C) 
during the recovery period after running in the traditional training shoe (TTS, gray solid line) or 
grounding shoe (GS, black solid line). Heart rate during the running economy trial in both TTS and 
GS trials (D). Dashed lines represent overlapping mean values between shoes. 
4. Discussion 
The main findings of the present study show that grounding technology applied to 
shoe designs does not provide a physiological/perceptual response over traditional 
training shoes in well-trained athletes. The RE, blood lactate, heart rate, and perceptual 
response of these athletes, exercising at 80% of their IAT during 20 min on a 400 m dirt 
track, were not different between shoes conditions. 
De
ite
e iou
o
i i
fi di
u
e ti
that
ou di
te h olo y ha
0
1
2
3
4
5
6
min 1
min 3
min 15
RPE value (1–10)
Recovery time
135
140
145
150
155
160
165
170
Heart rate (bpm)
0
0.5
1
1.5
2
2.5
min 1
min 3
min 15
Blood lactate concentration (mmol·L–1)
Recovery time
A
C
TTS
GS
B
0
1
2
3
4
5
6
7
min 1
min 3
min 15
RPE legs value (1–10)
Recovery time
D
Figure 4.
Blood lactate (A), whole-body rate of perceived exertion (RPE; B), and legs-only
RPE (C) during the recovery period after running in the traditional training shoe (TTS, gray solid
line) or grounding shoe (GS, black solid line). Heart rate during the running economy trial in both
TTS and GS trials (D). Dashed lines represent overlapping mean values between shoes.
Int. J. Environ. Res. Public Health 2022, 19, 1317
8 of 10
4. Discussion
The main ﬁndings of the present study show that grounding technology applied
to shoe designs does not provide a physiological/perceptual response over traditional
training shoes in well-trained athletes. The RE, blood lactate, heart rate, and perceptual
response of these athletes, exercising at 80% of their IAT during 20 min on a 400 m dirt
track, were not different between shoes conditions.
Despite previous promising ﬁndings suggesting that grounding technology has posi-
tive effects on the physiological responses (i.e., reduced acute inﬂammatory processes) of
humans at rest [7,8], very limited research has focused on the implementation of ground-
ing during exercise, with only two studies focusing on the effectiveness of grounding in
reducing muscular damage after exercise-induced DOMS. This is the ﬁrst study to examine
the impact of grounding in shoes during running, which makes the comparison with
previous studies challenging due to the unique nature of running for the implementation
of this technology (i.e., intermittent contact time with the ground). Our ﬁndings, however,
differ from those of Sokal et al. [8], who claimed that all recreational cyclists within their
study experienced physiological attenuation at rest, during a 30 min exercise at 50% of
their VO2max, and during recovery, indicated by decreases in blood urea; however, these
authors failed to include any individual data. It is also worth noting that these biochemical
parameters were not measured immediately prior to grounding/placebo conditions, and
therefore group-by-time interactions could not be determined, which limits the interpre-
tation of these results. Additionally, one would expect both blood urea and creatinine
concentrations to remain unchanged following the exercise protocol used by these authors
(a single bout of light exercise for 30 min). Blood urea and creatinine levels have been shown
to increase after prolonged, strenuous exercise as a result of increased protein catabolism
and/or impaired renal function [19], which is unlikely to have occurred during the ex-
ercise protocol proposed by Sokal et al. The difference between the groups observed by
Sokal et al., interpreted in the context of our present ﬁndings, are more likely due to day-
to-day inter-individual variability in blood urea, or some potential methodological issues
during data collection, rather than due to physiological stress attenuation during exercise.
In a subsequent study, Sokal et al. presented additional data from the same aforementioned
experiment [20], focusing on the effects of grounding on VO2 uptake, blood glucose, lactate,
and bilirubin concentrations. The 42 subjects included in this study were divided into two
subgroups (n = 21) according to their VO2max, therefore, both groups had a comparable
cardiorespiratory ﬁtness (Group A = 50.8 vs. Group B = 50.7 mL kg−1 min−1). The study
design followed a double-blind, crossover protocol between Groups A and B. During the
ﬁrst testing day, Group A was under the placebo condition and Group B was under the
grounding stimulus, with these conditions interchanged during the second day of testing.
These authors reported a signiﬁcantly reduced VO2 uptake (numeric data not shown by the
authors) at the end of the exercise with the grounding stimulus only in Group B, when com-
pared to the placebo. The study design employed by Sokal et al. [8,20] has limited reliability,
given that their experimental tests were performed on different days, which may have biased
the results. Day-to-day variability and the lack of a familiarization trial may have potentiated
the learning effects only for Group B (i.e., the group with the grounding stimulus during the
second day). These results should, therefore, be interpreted with caution.
To our knowledge, the two aforementioned studies are the only two experiments
focusing on the effects of grounding on the biophysiological responses of humans during
submaximal exercise. However, the important methodological issues described above, and
the use of cycling being the only mode of exercise, limits the interpretation of the current
literature and its comparison with the present study. In our experiment, we used a double-
blind, randomized, crossover design, with tests for all experimental conditions performed
on the same day. We are aware that the conductor element within the shoe was not in
permanent contact with the ground (i.e., intermittent contact time during running), and we
did not measure muscle activity, nor foot/stride mechanics, during running, which may have
provided more information and potentially revealed an effect. However, to ensure a sufficient
Int. J. Environ. Res. Public Health 2022, 19, 1317
9 of 10
contact time, we designed a longer than usual RE protocol (i.e., 20 min bouts; Figure 2), so that
we could identify a potential dose–response relationship over time. Despite these rigorous
experimental procedures, our results show that grounding technology did not have any
impact on the measured responses during running when compared to traditional training
shoes. Previous research showed a decrease in muscle damage in response to high-intensity
strength exercises in subjects under grounding conditions [13,14] when compared to a
placebo. These ﬁndings would suggest that grounding technology may have a role to play
as a muscle recovery method, which in turn could translate into a beneﬁt for runners when
performing higher intensity exercise (i.e., above the anaerobic threshold) in which muscle
fatigue and acidosis occur to a greater extent. Nonetheless, future research using larger
sample sizes and examining foot mechanics (especially contact times) would be required to
conﬁrm our ﬁndings. Other shoe designs currently available on the market that include a
CFP and a high midsole stack height made of compliant, resilient, and lightweight foam,
seem the most effective shoe modality to date. This technology has shown to improve RE
by increasing the midsole longitudinal bending stiffness, favoring a decrease in the range
of motion of the metatarsophalangeal joint [3,21,22].
5. Conclusions
In conclusion, our results suggest that grounding in shoe designs is not an effective
alternative for well-trained athletes to improve their running efﬁciencies, and/or their
physiological/perceptual responses during submaximal exercise. However, there are
intrinsic limitations that should be considered. Potential grounding effects could have
been missed during our study as running does not allow constant contact between the
athlete and the ground, which could have potentially biased the results. In relation to
this, lower caliber athletes may have beneﬁted from this technology given their ground
contact times are greater than faster, elite athletes; an issue that could not be addressed
in the current study. Future research may therefore consider additional sports in which
athletes remain in constant contact with the ground (e.g., race-walking, cross-country skiing,
powerlifting). Despite these limitations, our study followed a high-quality methodological
protocol (double-blind, randomized, crossover design) using a homogeneous sample of
highly trained athletes (as represented in Table 1), which suggests that our conclusions are
reliable for this speciﬁc population.
Author Contributions: Conceptualization and methodology: B.M.-P., I.Z., M.K., D.R., J.A.C. and
Y.P.P.; formal analysis: A.G.-A., J.A.C., I.Z., B.M.-P.; writing—original draft preparation: B.M.-P., I.Z.,
A.G.-A.; review and editing: B.M.-P., I.Z., A.G.-A., M.K., T.B., M.G., D.R., J.A.C. and Y.P.P.; supervision:
Y.P.P. and J.A.C. All authors have read and agreed to the published version of the manuscript.
Funding: This study was supported by a contract from adidas AG with the University of Zaragoza,
Spain (Project: “Testing support for innovation project”; number 2021/0348).
Institutional Review Board Statement: The present study was approved by the Ethics Committee
of Aragon, Spain (CEICA, num. 17/2021).
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: The datasets used and analyzed within the present manuscript will be
available from the corresponding author/ﬁrst author upon request.
Acknowledgments: We wish to thank the athletes involved in this study for participating.
Conﬂicts of Interest: M.K., T.B., M.G., D.R. are employees of adidas AG. B.M.P., I.Z., A.G.A., J.A.C.,
Y.P.P. have no conﬂicts of interest relevant to the content of this article.
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The Impact of Grounding in Running Shoes on Indices of Performance in Elite Competitive Athletes.
Muniz-Pardos, Borja,Zelenkova, Irina,Gonzalez-Aguero, Alex,Knopp, Melanie,Boitz, Toni,Graham, Martin,Ruiz, Daniel,Casajus, Jose A,Pitsiladis, Yannis P