Influence of a 4-Month Barefoot Training upon Muscle Activation of
Overload Controllers
Ana Paula da Silva Azevedo, Raísa Valvassori, Bruno Mezêncio, João G. O. Claudino,
Juliana Pennone, Murilo Alves de Souza, Fernanda O. M. dos Anjos, Alberto Carlos Amadio and
Julio Cerca Serrão
Laboratory of Biomechanics, School of Physical Education and Sport, University of São Paulo,
65 Professor Mello Moraes Avenue, São Paulo, Brazil
1 OBJECTIVES
Running has been a very important expression of
movement. The expansion of your practice has been
followed by a seeking for new strategies to improve
mechanical load control and performance. Thus, the
belief that barefoot running could be an effective
strategy to attend these objectives has been
reinforcing (Divert et al., 2005, Lieberman et al.
2010, Squadrone and Gallozzi, 2009).
In short-term, external load seems to be
increased during barefoot locomotion in subjects
who are inexperienced in this mechanical condition
(Cavanagh et al., 1981, De Wit et al., 2000).
Considering that the lower limb muscles, mainly
placed in thigh, are involved in the mechanical load
control (Novacheck, 1988), they could have their
activity increased either. However, there are
evidences that the human body could adapt to
barefoot situation, altering the control of mechanical
load and the muscle activation pattern in running
(Divert et al., 2005, Lieberman et al. 2010).
Nevertheless, few studies analyzed the long-term
effect of barefoot running upon the intensity of
muscular activation, and little is known about the
consequences of this strategy in subjects who are
inexperienced in this mechanical condition. Thus,
the investigation of lower limb muscles responsible
for the overload control during running, as biceps
femoris, vastus lateralis and rectus femoris,
(Novacheck, 1988) becomes crucial for the
understanding of barefoot adaptation’s process in
long-term.
Therefore, the purpose of this study was to
analyze the influence of 4 months of barefoot
training upon the muscle activation intensity of
biceps femoris, vastus lateralis and rectus femoris,
comparing the electromyiographic signal obtained
during barefoot and shod running, before and after
intervention.
2 METHODS
Twenty runners (13 men e 7 women; 33.2 ± 6.4
years; 72.6±14.2kg; 1.72±0.11m) without experience
in barefoot running were recruited for the study.
Participants were excluded if they had suffered any
structural injury in the last 12 months and/or had any
experience in barefoot running or with minimalist
shoes. All participants read and signed an informed
consent term. The experimental design was
approved by the local ethics committee.
During the 4 months of intervention, participants
ran progressively at the barefoot condition, starting
the training with 5% and ending with 20% of their
weekly training volume being performed without
shoes. The barefoot running training was performed
three times per week. The participants kept their
normal running training routine, using shoes, while
they were involved in this research.
Runners were evaluated at two different
moments: pre and post intervention. They ran during
10 minutes at 9 km.h
-1
on a treadmill, in two
conditions: shod and barefoot. The electromyo-
graphic signal (EMG) of the long head of biceps
femoris (BF), rectus femoris (RF) and vastus
lateralis (VL) of the right leg of each volunteer were
monitored. Nine acquisitions (10 seconds each) of
EMG for each experimental condition were
performed, with sampling frequency of 2600 Hz.
The acquisition of EMG signal occurred through
the Lynx-EMG System 1000 (Lynx Electronic
Technology LTDA.), composed by data acquisition
EMG1000-VxRy module, an Analog/Digital (A/D)
converter and the Lynx-AqDados program. Bipolar
surface electrodes "Double" (Hal Industry and Trade
LTDA), AgCl, were placed on muscle bellies and
connected to active preamplifiers AX1010 (Lynx
Electronic Technology LTDA.). The electrodes
placement in each muscle occurred according to the
criteria established by SENIAM (Surface
Paula da Silva Azevedo A., Valvassori R., Mezêncio B., G. O. Claudino J., Pennone J., Alves de Souza M., O. M. dos Anjos F., Carlos Amadio A. and
Cerca Serrão J..
Influence of a 4-Month Barefoot Training upon Muscle Activation of Overload Controllers.
Copyright
c
 2014 SCITEPRESS (Science and Technology Publications, Lda.)

Electromyography for the Non-Invasive Assessment
of Muscles). The muscle activation was assessed
through the calculation of the RMS (Root Mean
Square) of the EMG signal from each muscle
analyzed, only in the stance phase, during shod and
barefoot running. The signals were filtered by a
digital Butterworth band pass filter of 4th order
(cutoff frequency from 20 to 450Hz) and notch
filters of 60Hz, 120Hz and 180Hz. Data was
normalized by the maximum voluntary isometric
contraction (MVIC), obtained at the beginning of the
test session, prior to the running test. The statistical
analysis of data was performed in SigmaStat 3.5
(Systat, Germany) software. Data normality was
verified using the Kolmogorov-Smirnov test, while
homoscedasticity was checked by Levene's test. For
means comparison, an analysis of variance (one-way
ANOVA) for repeated measures was performed. The
level of significance adopted was p <0.05.
3 RESULTS
The Table 1 shows average values and standard
deviations for the RMS of the three selected
overload controllers muscles (BF, VL e RF) in both
shod and barefoot. No significant difference was
found for BF and RF. On the other hand, the VL was
significant different between experimental
conditions. Before intervention, the VL had an
activation intensity about 131% higher in barefoot
running (p=0.002) when compared to shod.
However, after 4 months of barefoot training, the
RMS of VL was significant smaller for barefoot
running than before the intervention, decreasing its
Table 1: RMS values (%MVIC) during stance phase of
running with shoes and barefoot in pre and post-
intervention.
Pre Post
Variables Shod Barefoot Shod Barefoot
BF
23,60 ±
7,69
50,90
±
10,50
20,4
±
10,50
52,60
±
10,50
VL
(*) (#)
17,80 ±
3,32
41,20
±
4,45
14,70
±
3,32
14,40
±
3,32
RF
29,60 ±
4,99
39,80
±
7,06
31,10
±
4,99
21,80
±
4,99
Legend: Long head of biceps femoris (BF), vastus lateralis (VL)
and rectus femoris (RF). (*) significant difference between the
conditions (shod and barefoot) in pre moment; (#) significant
difference between the moments (pre and post) in barefoot
condition.
activation in about 65% (p=0,017) after intervention
and showing a activation pattern similar to shod
running.
4 DISCUSSION
According to the results, individuals who are not
adapted to barefoot locomotion seemed to have a
higher intensity of muscle activation of overload
controllers muscles compared to shod condition
before intervention, mainly for VL. Studies showed
an increase of the external forces in barefoot running
to not adapted subjects (Cavanagh et al., 1981; De
Wit et al., 2000). Therefore, the greater muscle
activation without shoes is probably a response to
this possible increase in mechanical load, especially
VL which is directly involved in impact absorption
(Novacheck, 1988). Thus, despite representing an
intrinsic protection strategy, the greater muscle
activation at pre-moment may influence internal
load and energy expenditure in running.
However, 4 months of progressive barefoot
running training seemed to be efficient to promote
some adaptations in muscle activity intensity.
Barefoot training significantly reduced the muscle
activity of the VL, making it similar to running shod.
Thus, it’s possible to
conclude that a 4-monthy
barefoot running training has potential to decrease
the intensity of muscle activation of the lower limbs,
mainly the VL, in subjects who are not adapted to
locomotion under this mechanical condition.
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