Citation: Jaén-Carrillo, D.;
Roche-Seruendo, L.E.;
Molina-Molina, A.; Cardiel-Sánchez,
S.; Cartón-Llorente, A.;
García-Pinillos, F. Inﬂuence of the
Shod Condition on Running Power
Output: An Analysis in
Recreationally Active Endurance
Runners. Sensors 2022, 22, 4828.
https://doi.org/10.3390/s22134828
Academic Editors: Robert Crowther
and Carlo Ricciardi
Received: 2 June 2022
Accepted: 23 June 2022
Published: 26 June 2022
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sensors
Article
Inﬂuence of the Shod Condition on Running Power Output:
An Analysis in Recreationally Active Endurance Runners
Diego Jaén-Carrillo 1
, Luis E. Roche-Seruendo 1
, Alejandro Molina-Molina 1,2,*
, Silvia Cardiel-Sánchez 1,
Antonio Cartón-Llorente 1
and Felipe García-Pinillos 2,3
1
Campus Universitario, Universidad San Jorge, Autov A23 km 299, Villanueva de Gállego,
50830 Zaragoza, Spain; djaen@usj.es (D.J.-C.); leroche@usj.es (L.E.R.-S.); scardiels@usj.es (S.C.-S.);
acarton@usj.es (A.C.-L.)
2
Department of Physical Education and Sport, University of Granada, 18016 Granada, Spain;
fegarpi@gmail.com
3
Departamento de Educación Física, Deporte y Recreación, Universidad de La Frontera, Temuco 4780000, Chile
*
Correspondence: amolinam@usj.es; Tel.: +34-625538520
Abstract: Several studies have already analysed power output in running or the relation between
VO2max and power production as factors related to running economy; however, there are no studies
assessing the difference in power output between shod and barefoot running. This study aims to
identify the effect of footwear on the power output endurance runner. Forty-one endurance runners
(16 female) were evaluated at shod and barefoot running over a one-session running protocol at
their preferred comfortable velocity (11.71 ± 1.07 km·h−1). The mean power output (MPO) and
normalized MPO (MPOnorm), form power, vertical oscillation, leg stiffness, running effectiveness
and spatiotemporal parameters were obtained using the Stryd™ foot pod system. Additionally,
footstrike patterns were measured using high-speed video at 240 Hz. No differences were noted in
MPO (p = 0.582) and MPOnorm (p = 0.568), whereas signiﬁcant differences were found in form power,
in both absolute (p = 0.001) and relative values (p < 0.001), running effectiveness (p = 0.006), stiffness
(p = 0.002) and vertical oscillation (p < 0.001). By running barefoot, lower values for contact time
(p < 0.001) and step length (p = 0.003) were obtained with greater step frequency (p < 0.001), compared
to shod running. The prevalence of footstrike pattern signiﬁcantly differs between conditions, with
19.5% of runners showing a rearfoot strike, whereas no runners showed a rearfoot strike during
barefoot running. Running barefoot showed greater running effectiveness in comparison with shod
running, and was consistent with lower values in form power and lower vertical oscillation. From a
practical perspective, the long-term effect of barefoot running drills might lead to increased running
efﬁciency and leg stiffness in endurance runners, affecting running economy.
Keywords: barefoot; footstrike; stiffness; sensor; wearable
1. Introduction
Endurance running events range from 3000 m to over 160 km in ultra-marathons.
Nowadays, both the number of runners in endurance races and the number of organised
races have increased. For example, 19,076 runners (19.51% women) ﬁnished the half
marathon in Valencia in 2020 (Spain). The lower limb muscles execute three distinctive
functions during such events: (i) force and power generation; (ii) shock absorption; and
(iii) store and release elastic energy [1], thus compromising running economy. Endurance
runners experienced improvements in muscle strength and power, among others, after an
8-week training intervention directly affecting running economy and, thus, performance [2].
The novel appearance of wearable devices capable of obtaining kinetic and kinematic data
during running offers sports practitioners a new way to quantify workload by acquiring
valuable metrics such as spatiotemporal parameters, power, and leg stiffness.
Sensors 2022, 22, 4828. https://doi.org/10.3390/s22134828
https://www.mdpi.com/journal/sensors
Sensors 2022, 22, 4828
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Although a wide range of endurance runners tend to collide with the ground ﬁrst with
the heel when shod [3], the switch from shod to barefoot running implies a tendency toward
a midfoot (MFS) or forefoot strike pattern (FFS), inﬂuencing factors such as contact (CT) and
ﬂight time (FT), step frequency (SF), step length (SL), loading rate and leg compliance [4–7].
While leg stiffness increases with barefoot running in comparison to shod running [8], a
signiﬁcant reduction in running dynamic stability was found when changing from shod
to barefoot conditions [9]. Moreover, greater activation levels in the intrinsic muscles of
the foot have been found with the stance phase in barefoot running, in comparison with
shod running, producing adjustment during the compression of the longitudinal arch. This
results in a greater ability to recoil elastic energy when running barefoot [10,11].
The recent appearance of wearable power meters on the running scene may change
training and competition by providing power output values for endurance runners. These
sensors may allow us to monitor and quantify workload from a fair and objective perspec-
tive with accurate replication, as they already do in cycling [12]. Velocity and both the
body height and weight of a runner, as well as external conditions such as slope and wind,
may inﬂuence power output in running [13,14]. Although the level of agreement between
power meter systems in running and two theoretical models for power output analysis
has been assessed [15], the lack of scientiﬁc evidence for the use and interpretation of such
metrics in endurance runners may prevent sport practitioners from adopting them as a
means to monitor and assess running performance. A recent wearable system (i.e., Stryd™)
calculates power production while running, separating this metric into two parts: power
and form power. Apparently, power reﬂects the power output associated with changes in
the athlete’s horizontal movement. Form power, however, represents the power output
production caused by the combination of the oscillatory up and down movements of the
centre of mass and lateral power when the athlete moves forward. This system employs
mathematical calculations to estimate these two parameters from kinematic data collected
from the described movements executed by the runner’s foot [16]. In addition, in a recent
review [17], the Stryd foot pod was noted for its reliability and compatibility with metabolic
power, compared to other commercially available portable running power devices.
While several studies have already analysed power output in running [18,19] and
others have investigated the relation between VO2max and power production [16,20], to
the best of the authors’ knowledge, there are no studies assessing the difference in power
output between shod and barefoot running. In order to bridge this gap, this study aims to
identify the effect of footwear on power output in endurance runners. It is hypothesised
that increased effectiveness, leg stiffness and power production would be identiﬁed in
barefoot running.
2. Materials and Methods
2.1. Subjects
Forty-one recreationally active endurance runners (25 males; age = 28.5 ± 6.9 years;
height = 1.73 ± 0.08 m; body mass = 68.2 ± 11.6 kg), recruited by convenience, volunteered
to take part in this study. All the participants were 18 years of age or older, capable of
running 10,000 m in under 50 min (44.02 ± 4.22 min), injury-free for the last 6 months
and were completing no fewer than 2 running sessions per week, therefore meeting the
inclusion criteria. Every participant signed a formal consent form, aligned with the bioethics
of the World Medical Association’s Declaration of Helsinki (2013). Once the objectives and
procedures of the study were explained, participants were assured that they were free to
leave the study at any time. The study was approved by the Ethics Committee of San Jorge
University (009-18/19), from which sport sciences students were recruited.
2.2. Procedures
Participants completed two testing trials over a one-session running protocol at their
preferred comfortable velocity (11.71 ± 1.07 km·h−1) for data collection at the San Jorge
University Biomechanics Laboratory (Zaragoza, Spain) in April 2019. Both trials were
Sensors 2022, 22, 4828
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completed on a motorised treadmill with a slope maintained at 0% (HP cosmos Pulsar
4P; HP cosmos Sports & Medical, Gmbh, Nußdorf, Germany). Participants warmed up
for 5 min on the treadmill where the velocity was increased and decreased several times
until a comfortable velocity was achieved [21]. For each trial, participants completed two
successive 3 min running bouts (i.e., shod for the ﬁrst and barefoot for the latter), separated
by a 2 min period to change from shod to barefoot condition. Since power output [19] and
spatiotemporal parameters [22] reach a steady state in less than 2 min, data were recorded
during both running trials and 6–8 strides were analysed [23].
2.3. Materials and Testing
Both body weight and height were measured for each participant, utilising a weigh-
ing scale (Tanita BC-601; TANITA Corp., Maeno-Cho, Itabashi-ku, Tokyo, Japan) and a
stadiometer (SECA 222; SECA Corp., Hamburg, Germany), respectively.
For this study, a commercially available wearable power meter, Stryd™ (Stryd Summit
Powermeter; Stryd, Inc., Boulder, CO, USA), was clipped on the laces of the runner’s
shoe when running shod and placed and secured with tape on the runner’s instep during
barefoot running (Figure 1). This lightweight, reinforced carbon-ﬁbre foot pod (weight:
9.1 g) is based on a 6-axis inertial motion sensor (3-axis gyroscope, 3-axis accelerometer)
and provides kinetic and kinematic data. During barefoot running, participants ran with
socks to avoid friction injuries to the soles of their feet caused by the treadmill belt. When
running shod, participants wore their traditional training shoes. The power meter was
linked to the manufacturer’s mobile application (StrydApp, version 5.13), downloaded on
a smartphone (iPhone 8, Apple Inc., Cupertino, CA, USA), for recording data.
Sensors 2022, 22, x FOR PEER REVIEW 
3 of 9 
 
 
University Biomechanics Laboratory (Zaragoza, Spain) in April 2019. Both trials were 
completed on a motorised treadmill with a slope maintained at 0% (HP cosmos Pulsar 4P; 
HP cosmos Sports & Medical, Gmbh, Nußdorf, Germany). Participants warmed up for 5 
min on the treadmill where the velocity was increased and decreased several times until 
a comfortable velocity was achieved [21]. For each trial, participants completed two suc-
cessive 3 min running bouts (i.e., shod for the first and barefoot for the latter), separated 
by a 2 min period to change from shod to barefoot condition. Since power output [19] and 
spatiotemporal parameters [22] reach a steady state in less than 2 min, data were recorded 
during both running trials and 6–8 strides were analysed [23]. 
2.3. Materials and Testing 
Both body weight and height were measured for each participant, utilising a weigh-
ing scale (Tanita BC-601; TANITA Corp., Maeno-Cho, Itabashi-ku, Tokyo, Japan) and a 
stadiometer (SECA 222; SECA Corp., Hamburg, Germany), respectively. 
For this study, a commercially available wearable power meter, Stryd™ (Stryd Sum-
mit Powermeter; Stryd, Inc., Boulder, CO, USA), was clipped on the laces of the runner’s 
shoe when running shod and placed and secured with tape on the runner’s instep during 
barefoot running (Figure 1). This lightweight, reinforced carbon-fibre foot pod (weight: 
9.1 g) is based on a 6-axis inertial motion sensor (3-axis gyroscope, 3-axis accelerometer) 
and provides kinetic and kinematic data. During barefoot running, participants ran with 
socks to avoid friction injuries to the soles of their feet caused by the treadmill belt. When 
running shod, participants wore their traditional training shoes. The power meter was 
linked to the manufacturer’s mobile application (StrydApp, version 5.13), downloaded on 
a smartphone (iPhone 8, Apple Inc., Cupertino, CA, USA), for recording data. 
 
Figure 1. Representation for the placement of the Stryd™ power meter clipped on the laces of the 
runner’s shoe (left picture) and placed and secured with tape on the runner’s instep during barefoot 
running (central and right picture). 
Average power output (w; ratio of total of watts generated to total run time), form 
power (w; previously described), mean power output (w (MPO)), normalised MPO (w/kg 
(MPOnorm)), vertical oscillation (cm; quantity of up and down movement generated dur-
ing running), leg stiffness (kN/m; ratio of the maximal force at the initial touchdown to 
the maximum leg compression at the middle of the stance phase) and running effective-
ness (kg/N; ratio of speed to power) were obtained using the Stryd™ power meter. 
Additionally, the running spatiotemporal parameters of contact time (time the foot 
spends in contact with the ground (CT)), flight time (time from toes-off to initial contact 
of the same foot (FT)), step length (distance covered between initial contact of one foot 
and the initial contact of the other foot (SL)) and step frequency (number of ground con-
tacts that occurred in a minute (SF)) were also measured utilising the Stryd™ system, 
which has been previously validated for such purposes [18]. 
The foot strike pattern (FSP) exhibited by the participants was recorded using high-
speed video at 240 Hz (Imaging Source DFK 33UX174, The Imaging Source Europe 
Figure 1. Representation for the placement of the Stryd™ power meter clipped on the laces of the
runner’s shoe (left picture) and placed and secured with tape on the runner’s instep during barefoot
running (central and right picture).
Average power output (w; ratio of total of watts generated to total run time), form
power (w; previously described), mean power output (w (MPO)), normalised MPO (w/kg
(MPOnorm)), vertical oscillation (cm; quantity of up and down movement generated
during running), leg stiffness (kN/m; ratio of the maximal force at the initial touchdown to
the maximum leg compression at the middle of the stance phase) and running effectiveness
(kg/N; ratio of speed to power) were obtained using the Stryd™ power meter.
Additionally, the running spatiotemporal parameters of contact time (time the foot
spends in contact with the ground (CT)), ﬂight time (time from toes-off to initial contact of
the same foot (FT)), step length (distance covered between initial contact of one foot and
the initial contact of the other foot (SL)) and step frequency (number of ground contacts
that occurred in a minute (SF)) were also measured utilising the Stryd™ system, which has
been previously validated for such purposes [18].
The foot strike pattern (FSP) exhibited by the participants was recorded using high-
speed video at 240 Hz (Imaging Source DFK 33UX174, The Imaging Source Europe GmbH;
Bremen, Germany). The camera was placed perpendicular to the treadmill from a sagittal
Sensors 2022, 22, 4828
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view at 2 m from the centre of the treadmill and at a height of 0.30 m, which has been
previously validated for such a purpose [24]. Three different FSP were identiﬁed in the
present study [4]: rearfoot strike pattern (RFS), where the heel contacts the ground ﬁrst;
MFS, in which the outside edge of the foot contacts the ground ﬁrst; and FFS, where the
forefoot touches down ﬁrst.
2.4. Statistical Analysis
Descriptive data are shown as mean (±SD), frequency and percentage. To determine
the differences between nominal variables, McNemar’s test was used. The mean differences
between values were analysed via pairwise mean comparisons (t-test) and the magnitude
of the differences was expressed by means of the Cohen’s d effect size (ES) and interpreted
as trivial (<0.19), small (0.2–0.49), medium (0.5–0.79) and large (≥0.8) [25]. All statistical
analyses were performed using SPSS (version 25, SPSS Inc., Chicago, IL, USA) and statistical
signiﬁcance was accepted at α = 0.05.
3. Results
Signiﬁcant differences (p < 0.05) were found in spatiotemporal gait characteristics
during running when comparing shod and barefoot conditions (Table 1). When running
barefoot, lower values for CT (p < 0.001, ES = 0.46) and SL (p = 0.003, ES = 0.13) were
obtained with greater SF (p < 0.001, ES = 0.59), compared to those reported during shod
running at the same comfortable velocity. The prevalence of FSP signiﬁcantly differs
(p < 0.034) between conditions, with 19.5% of runners showing RF, 56.1% MF and 24.4% FF
during the shod condition, whereas no runners showed RF during barefoot running, with
31.8% and 68.2% showing MF and FF, respectively.
Table 1. Spatiotemporal gait characteristics during running shod and barefoot at comfortable velocity.
Shod Condition
Barefoot Condition
p-Value (d)
FSP (n, %) ˆ
RF
8 (19.5)
0 (0)
0.019
MF
23 (56.1)
13 (31.8)
0.033
FF
10 (24.4)
28 (68.2)
0.012
CT (s)
0.261 (0.020)
0.252 (0.019)
<0.001 (0.46)
FT (s)
0.111 (0.018)
0.108 (0.017)
0.053 (0.17)
SL (m)
1.11 (0.15)
1.09 (0.15)
0.003 (0.13)
SF (spm)
162.06 (8.06)
166.99 (8.22)
<0.001 (0.59)
ˆ indicates that a McNemar test was conducted to compare frequencies; d: Cohen’s d effect size; FSP: foot strike
pattern; RF: rearfoot; MF: midfoot; FF: forefoot; CT: ground contact time; FT: ﬂight time; SL: step length; SF: step
frequency.
The comparisons between conditions (i.e., shod vs. barefoot) revealed no differences
in MPO (p = 0.582, ES = 0.02) and MPOnorm (p = 0.568, ES = 0.03), whereas signiﬁcant
differences were found in form power, in both absolute (p = 0.001, ES = 0.14) and relative
values (p < 0.001, ES = 0.33), running effectiveness (p = 0.006, ES = 0.36), stiffness (p = 0.002,
ES = 0.20) and vertical oscillation (p < 0.001, ES = 0.48) (Table 2).
Table 2. Power output and related parameters during running shod and barefoot at comfortable
velocity.
Shod Condition
Barefoot Condition
p-Value (d)
MPO (W)
210.05 (44.16)
210.73 (44.24)
0.582 (0.02)
MPOnorm (W/kg)
3.07 (0.32)
3.08 (0.32)
0.568 (0.03)
Form power (W)
69.95 (12.51)
68.28 (12.19)
0.001 (0.14)
Form power (%)
33.6 (2.8)
32.7 (2.7)
<0.001 (0.33)
Running effectiveness
0.95 (0.05)
0.97 (0.06)
0.006 (0.36)
Leg Stiffness (kN/m)
10.26 (1.86)
10.65 (1.93)
0.002 (0.20)
Vertical oscillation (cm)
7.93 (0.98)
7.48 (0.90)
<0.001 (0.48)
d: Cohen’s d effect size; MPO: mean power output; MPOnorm: normalised mean power output.
Sensors 2022, 22, 4828
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4. Discussion
This study sought to determine the effect of footwear on power output in long distance
runners, comparing data collected by the Stryd™ system during both shod and barefoot
running. The main ﬁnding of this study was that endurance runners showed greater
running effectiveness when running barefoot in comparison with shod running, being
consistent with lower values in form power and lower vertical oscillation. Additionally, our
ﬁndings support those by previous studies reporting biomechanical alterations in runners
who changed from traditional shoes to barefoot while running, such as the adoption of MFS
or FFS, higher SF, and both shorter CT and SL [4–7]. Given the novelty of power output
in endurance running, there is a lack of scientiﬁc evidence regarding this metric and, in
particular, with power output in barefoot running, making this discussion challenging.
From a biomechanical standpoint, the tendency towards the runner’s adoption of
MF or FF when switching from traditional running shoes to barefoot is supported by
Lieberman and colleagues, as they stated that habitually shod runners adopted ﬂatter foot
positions at the initial contact when barefoot running [4]. In the same line, the runner’s
showed signiﬁcantly higher SF (3%) when running barefoot (166.99 ± 8.22 spm, p < 0.001)
during the present study; this reinforces previous works [5,6], which found that habitually
shod runners signiﬁcantly increased their SF when barefoot running [5] and as velocity
increased [6]. Likewise, Cochrum and colleagues reported that barefoot running at 50%
VO2max resulted in a 2.4% shorter SL in comparison with shod running conditions [6],
endorsing the ﬁndings reported here, where SL is signiﬁcantly shorter in barefoot running
(1.83%) in comparison with running in shod conditions (1.09 ± 0.15 m and 1.11 ± 0.15 m,
respectively; p < 0.05) at a comfortable velocity.
Signiﬁcantly smaller CT was also reported in barefoot running (0.252 ± 0.019 s,
p < 0.001), supporting previous studies [5,7]. Divert and colleagues [5] reported that CT
signiﬁcantly increased in shod running, and Lussiana and colleagues [7] found shorter CT
when comparing minimalist to traditional shoes. Although all these studies share shod–
barefoot comparison in their procedures, the slight differences may be due to their different
methodologies. While our participants completed one single, steady-state, comfortable
velocity testing session on a motorised treadmill at a maintained slope of 0%, the studies
discussed above are based on an incremental gradient protocol [7], a two-session protocol
made up of six running bouts of 4 min [5], and four treadmill running testing sessions [6]. It
should also be noted that none of those studies utilised the Stryd™ power meter to analyse
the spatiotemporal parameters, in either the shod or barefoot condition.
Considering that it has been proposed that the addition of 100 g to the foot reduces
running economy by 1% [5,26], barefoot running would optimise the stretch-shortening
cycle behaviour, buffering and releasing elastic energy [27] and increasing leg stiffness by
the adoption of a plyometric movement pattern [28]. Moreover, as the foot’s core muscle
system produces an adaptation during compression of the longitudinal arch, which results
in increased ability to recoil elastic energy over the stance phase [10,11], one might expect
greater power output in barefoot running compared to running in the shod condition. It
should be noted that the footwear condition does not inﬂuence MPO or MPOnorm, but
it does signiﬁcantly inﬂuence form power (watts and percent), running effectiveness, leg
stiffness and vertical oscillation in endurance runners.
Given that power can be deﬁned as the product of force and velocity [29], and that in
the present study both running bouts (i.e., shod and barefoot) were executed at the same
comfortable velocity for every participant, it seems reasonable that MPO and MPOnorm
remained stable under both footwear conditions. The power output values reported in the
present study during shod running (210.05 ± 44.16 W) are supported by those found by
previous works using the Stryd™ power meter at the same running velocity [15,19].
From a practical application of MPO in endurance runners, the Functional Threshold
Power is a performance index referring to the highest MPO maintained for around 60 min
running without the onset of fatigue [30], commonly used to determine training intensities
(i.e., training zones) and quantify athletes’ responses to training stimuli [30,31]. In a recent
Sensors 2022, 22, 4828
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study, MPO and MPOnorm have shown a strong relationship with the Functional Threshold
Power at submaximal running from 10 min to 30 min [32]. Our results have shown no
signiﬁcant differences for MPO and MPOnorm between the shod and barefoot running
conditions, suggesting no changes in load intensities between the two footwear conditions.
Thus, a runner could maintain their training loads based on watts. However, the authors
recommend being cautious with this information as intra-articular loads could be different
due to biomechanical changes caused by barefoot running, such as the change in FSP from
RFS to FFS, greater ankle stiffness, lower impact load and brake load, greater knee ﬂexion
at ground contact, and reduced tibialis anterior muscle activity, among other factors [33].
Regarding form power, and according to the manufacturer’s manual (https://www.
stryd.com/guide (accessed on 1 June 2022)), most athletes would exhibit form power
ranging from 30 to 100 W. The ﬁndings reported in our study show signiﬁcant differences
between both running conditions (69.95 ± 12.51 W when shod, 68.28 ± 12.19 W when
barefoot) and seem to align with the manufacturer’s statement. It can be argued that form
power relates to leg stiffness and vertical oscillation in endurance running in different ways.
It is known that lower-limb stiffness varies across footwear conditions, resulting in increased
leg stiffness when barefoot in comparison to shod running [5,7,8,10,27]. This statement is
supported in the present study as the leg stiffness values are signiﬁcantly greater in barefoot
running (10.65 ± 1.93 kN/m). Since increased leg stiffness optimizes elastic energy recoil
and enhances running economy [34], it is reasonable to ﬁnd lower values of form power
and increased leg stiffness in barefoot running, making the reverse equally valid in shod
running. The values for vertical oscillation exhibit signiﬁcant differences between shod
(7.93 ± 0.98 cm) and barefoot running (7.48 ± 0.9 cm). The signiﬁcantly lower values found
in barefoot running demonstrate that runners show less vertical oscillation as they run,
positively affecting running economy [35,36], which is also associated with the increased
leg stiffness found under this footwear condition [7], consequently producing lower form
power under this footwear condition.
The Stryd™ system also offers a running effectiveness metric. This novel metric
is referred to as the ratio of running velocity to power (https://www.trainingpeaks.
com/blog/wko4-new-metrics-for-running-with-power/ (accessed on 1 June 2022)). The
ﬁndings reported here align with the proposed values for this value (i.e., ~1 kg/N),
showing signiﬁcantly higher effectiveness (p < 0.005) in barefoot running (0.97 ± 0.06
kg/N). Although it has not been reported before, this metric might be useful for coaches
and practitioners as white papers have stated that the closer the running effectiveness
value to 1 kg/N, the more effective runners are at transforming external power into ve-
locity (https://docs.google.com/document/u/2/d/e/2PACX-1vTzjH-Ns_GInUm4lAxi3
cVOQpzzKcWNF6VEX271s-QGYFHjwMgyLhhmu5i21-1_CaC3eL0B817rQo8k/pub (ac-
cessed on 1 June 2022)). This metric must not be used interchangeably with running
economy as they are completely different parameters. However, following the statements
of the aforementioned white papers, running effectiveness might represent running econ-
omy from a mechanical standpoint.
Regarding running economy, referred to as the energy required to maintain submax-
imal velocity efforts [37], several studies have not found signiﬁcant differences between
shod and barefoot running [38,39]. These studies did not control FSP, which may inﬂu-
ence these comparisons [5]. Of note, after controlling for maximal oxygen consumption
(VO2max) and footwear conditions (i.e., barefoot, minimal, and traditional running shoes),
Cochrum et al. [6] stated that barefoot running provides less metabolic beneﬁt over cush-
ioned shoes. This ﬁnding is supported by previous work, whose authors suggested that
the design of cushioned shoes offers metabolic savings compared to barefoot running [28].
Our results, in contrast, provide evidence that barefoot running can be more metabolically
beneﬁcial than running in shoes. In addition, we believe that the transition from running in
traditional shoes to less cushioned shoes, minimalist or barefoot running should be carried
out gradually, as has already been recently proposed in a 10-week pain and injury free
retraining program [40].
Sensors 2022, 22, 4828
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The ﬁndings described here are based on entirely mechanical parameters; therefore,
they should not be transferred to physiological terms. These ﬁndings should also not be
extrapolated to injury management or competition, as we detailed the changes that occur
in shod and barefoot running regarding kinetic and kinematics parameters.
Finally, there are some limitations to consider. Firstly, the protocol was completed on a
motorised treadmill at a comfortable velocity, preventing the readers from extrapolating
these ﬁndings to other velocities. The participants wore their own running shoes in shod
running, therefore increasing the ecological validity of the study. It would be of interest for
the research community to assess running power output and related metrics considering
different types of footwear, given the current revolution in the design of running shoes.
The participants were habitually shod runners; therefore, the novelty of the task might
inﬂuence the outcomes of barefoot running. Ultimately, the lack of scientiﬁc evidence on
this topic made the discussion section especially complex. However, notwithstanding the
aforementioned limitations, the present study offers new insights into the power production
in endurance running, as well as the use of power meters and the interpretation of the
metrics they provide, which might be of high value for clinicians, coaches and athletes who
aim to introduce this metric into training and competition.
5. Conclusions
The results obtained show that, besides the already known spatiotemporal gait char-
acteristic adaptations, barefoot running reported greater values in running effectiveness
in comparison with shod running, being consistent with lower values in form power and
lower vertical oscillation related to running economics. Future studies are needed to exam-
ine whether the long-term effect of short periods of barefoot running might contribute to
increased running efﬁciency and leg stiffness in endurance runners, which would affect
running economy.
Author Contributions: D.J.-C., L.E.R.-S. and F.G.-P. deﬁned the experimental design and conceptual-
ized the approach. D.J.-C., A.M.-M., S.C.-S. and A.C.-L. collected the data. D.J.-C. and F.G.-P. carried
out the statistical analysis. D.J.-C. wrote the paper. All authors reviewed the manuscript for scientiﬁc
content. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: The study was conducted in accordance with the Declaration
of Helsinki, and approved by the Ethics Committee of San Jorge University (009-18/19).
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Acknowledgments: The authors would like to acknowledge the study participants involved in
recruitment.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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Influence of the Shod Condition on Running Power Output: An Analysis in Recreationally Active Endurance Runners.
Jaén-Carrillo, Diego,Roche-Seruendo, Luis E,Molina-Molina, Alejandro,Cardiel-Sánchez, Silvia,Cartón-Llorente, Antonio,García-Pinillos, Felipe