Static Stretching Alters Neuromuscular Function and
Pacing Strategy, but Not Performance during a 3-Km
Running Time-Trial
Mayara V. Damasceno1, Marcos Duarte2, Leonardo A. Pasqua1, Adriano E. Lima-Silva3,
Brian R. MacIntosh4, Roˆ mulo Bertuzzi1*
1 Endurance Performance Research Group, School of Physical Education and Sport, University of Sa˜o Paulo, Sa˜o Paulo, Sa˜o Paulo, Brazil, 2 Biomedical Engineering, Federal
University of ABC, Santo Andre´, Sa˜o Paulo, Brazil, 3 Sports Science Research Group, Department of Physical Education and Sports Science, Federal University of
Pernambuco, Vitoria de Santo Anta˜o, Pernambuco, Brazil, 4 Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
Abstract
Purpose: Previous studies report that static stretching (SS) impairs running economy. Assuming that pacing strategy relies
on rate of energy use, this study aimed to determine whether SS would modify pacing strategy and performance in a 3-km
running time-trial.
Methods: Eleven recreational distance runners performed a) a constant-speed running test without previous SS and a
maximal incremental treadmill test; b) an anthropometric assessment and a constant-speed running test with previous SS; c)
a 3-km time-trial familiarization on an outdoor 400-m track; d and e) two 3-km time-trials, one with SS (experimental
situation) and another without (control situation) previous static stretching. The order of the sessions d and e were
randomized in a counterbalanced fashion. Sit-and-reach and drop jump tests were performed before the 3-km running
time-trial in the control situation and before and after stretching exercises in the SS. Running economy, stride parameters,
and electromyographic activity (EMG) of vastus medialis (VM), biceps femoris (BF) and gastrocnemius medialis (GA) were
measured during the constant-speed tests.
Results: The overall running time did not change with condition (SS 11:35600:31 s; control 11:28600:41 s, p = 0.304), but
the first 100 m was completed at a significantly lower velocity after SS. Surprisingly, SS did not modify the running
economy, but the iEMG for the BF (+22.6%, p = 0.031), stride duration (+2.1%, p = 0.053) and range of motion (+11.1%,
p = 0.0001) were significantly modified. Drop jump height decreased following SS (29.2%, p = 0.001).
Conclusion: Static stretch impaired neuromuscular function, resulting in a slow start during a 3-km running time-trial, thus
demonstrating the fundamental role of the neuromuscular system in the self-selected speed during the initial phase of the
race.
Citation: Damasceno MV, Duarte M, Pasqua LA, Lima-Silva AE, MacIntosh BR, et al. (2014) Static Stretching Alters Neuromuscular Function and Pacing Strategy,
but Not Performance during a 3-Km Running Time-Trial. PLoS ONE 9(6): e99238. doi:10.1371/journal.pone.0099238
Editor: Franc¸ois Hug, The University of Queensland, Australia
Received November 28, 2013; Accepted May 12, 2014; Published June 6, 2014
Copyright:  2014 Damasceno, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by Sa˜o Paulo Research Foundation (FAPESP: 2011/10742-9). Mayara Vieira Damasceno and Leonardo Alves Pasqua were
supported by a master scholarship from Sa˜o Paulo Research Foundation (FAPESP: 2011/02769-4 and 2010/13913-6), www.fapesp.br. The funders had no role in
study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: bertuzzi@usp.br
Introduction
The manner in which runners distribute their speed during a
competition is defined as pacing strategy [1]. It has been widely
recognized that the pacing strategy adopted by athletes can
substantially impact performance in long-distance running [1].
During these competitive events, endurance athletes usually adopt
a pacing strategy with a speed distribution consisting of three
distinct phases. These phases are characterized by a fast start,
followed by a period of slower speed during the middle of the race,
and a significant increase in running speed towards the end [2,3].
It has been previously demonstrated that the strategy with the
highest speeds reached during start phase (i.e. fast start) is
advantageous for increasing oxygen uptake early and decreasing
the use of anaerobic energy reserves [4]. Additionally, a fast
acceleration relies on the ability to generate high forces, suggesting
an importance of neuromuscular system for the start phase [5].
The rating of perceived exertion (RPE) [6] can be evaluated
during a running race in order to verify how effort and perceived
difficulty relate to actual speed. More recently, Faulkner et al. [7]
observed that when speed distribution during long-distance
running was characterized by the triphasic speed distribution
profile described above (so-called ‘‘U shaped’’ pacing strategy), the
RPE increases linearly. It has been hypothesized that this linear
profile of RPE during a time trial test reflects a centrally-regulated
control system that is dependent on a patterned disturbance to
muscular homeostasis. It is believed that this system regulates the
pattern and magnitude of muscular activation to maintain the
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physiological strain at a tolerable level and to prevent premature
exercise termination [8].
In addition to a centrally-regulated system, it has been proposed
that pacing strategy can be influenced by some physiological
feedback [9,10] and neuromuscular [11] performance changes.
For example, Lima-Silva et al. [12] observed that long-distance
runners who had higher running economy (RE) were able to adopt
a more aggressive pacing strategy, employing faster velocities at
the start phase (first 400 m) in a 10-km running race. In addition,
it has been proposed that neuromuscular factors related to force
production and muscular recruitment must also be considered
when investigating the determinants of endurance performance
[2,13]. Considering the highest speeds reached during the start
phase, it seems plausible to assume that the neuromuscular
variables related to force production might also be important
determinants of pacing strategy and success in long-distance
events.
Static stretching (SS) is commonly used as part of a warm-up
routine for athletes, yet SS has received considerable attention
because it seems to have an acute negative effect on activities that
are strength- and power-dependent [14,15]. Previous studies have
reported that an acute session of SS resulted in impairments on
sprint performance [16,17] and in jump height [14,15,18]. For
example, Sayers et al. [17] observed a negative effect on the
acceleration phase of a sprint test after SS. This impaired
performance induced by SS treatment may be related to an
inability to maximally activate muscle. Avela et al. [19] reported
that there were significant decreases in maximal voluntary
contraction (23.2%) and EMG (19.9%) following 1 h of passive
stretching of the triceps surae. Collectively, these data suggest that
SS results in reduced capacity of the skeletal muscle to produce
explosive force and this could result in a reduction in speed during
the acceleration phase of a long-distance race. Furthermore, SS
has been reported to increase the energy cost of running [20], but
there is not universal agreement on this [21]. Collectively, these
consequences of SS would be expected to alter pacing strategy and
consequently the performance during a 3 km time-trial.
To date, no study has considered the potential negative
influence of SS on pacing strategy during a long-distance running
event. Since force generating capability is an important determi-
nant of endurance performance [13], it is attractive to suspect that
prior SS treatment could alter the acceleration phase during a
long-distance event. Thus, the main objective of the current
investigation was to analyze the acute effect of SS on pacing
strategy adopted during a 3-km running time-trial. It was
hypothesized that SS would increase the energy cost of running,
reduce the capacity of lower limbs to produce explosive force, and
reduce the initial speed in a 3-km running time-trial.
Methods
Participants
Eleven male, recreationally trained long-distance runners (mean
age: 35.766.1 years; height: 1.7660.08 m; mass: 79.7611.3 kg;
maximal oxygen uptake: 51.063.0 mlNkg21Nmin21) volunteered to
participate in this study. All participants regularly competed in 10-
km running races at regional levels, and their best performances in
10-km competitions ranged from 35–45 minutes. They were
included if they had been training for the last 2 years without
interruption and for at least three times per week with a minimum
weekly volume above 30 km. The study was conducted at the
beginning of the year during a non-competitive period. The
subjects performed only low-intensity continuous aerobic training
(,60% maximal oxygen uptake) and reported no previous
strength or plyometric training experience. None of the partici-
pants were receiving any pharmacological treatments or had any
type of neuromuscular disorder or cardiovascular, respiratory or
circulatory
dysfunction.
The
participants
received a
verbal
explanation about the possible benefits, risks and discomfort
associated with the study and signed a written informed consent
before participating in the study. Procedures were in accordance
with the Helsinki Declaration of 1975, and this investigation was
approved by the Ethics and Research Committee of the University
of Sa˜o Paulo.
Experimental design
Participants visited the laboratory on five separate occasions,
with at least 48 h between sessions, over a three-week period.
Figure 1 gives a pictorial view of the experimental design. In the
first session, the participants completed one 6-min, constant-speed
test by running at 12 kmNh21 without previous SS treatment
(control condition) and a maximal incremental treadmill test. Ten
minutes of passive recovery was allowed between these two tests.
In the second session, anthropometric measurements and one 6-
min, constant-speed running test at 12 kmNh21 with previous SS
treatment (experimental condition) was performed. Drop jump
familiarizations were conducted at the end of the first and second
visits after 20 minutes of passive recovery. The order of
presentation for components of the first and second visits was
counterbalanced. In the third session, the participants performed a
3-km time trial test familiarization on an outdoor 400-m track. In
the fourth and fifth sessions, the participants performed a 3-km
time trial test either with or without previous SS treatment. For the
experimental condition, the runners performed a sit-and-reach test
and a drop jump before and after SS to determine the impact of
SS
on range
of motion and the
stretch-shortening
cycle,
respectively. These tests were also performed in the control
condition before the 3-km time trial. The order of presentation for
components of the fourth and fifth visits was counterbalanced. The
duration of each experimental session was approximately 50
minutes. All of the tests were performed at the same time of day for
a given subject, at least 2 h after the most recent meal. The
subjects were instructed to maintain their training program during
the study period, but they were asked to refrain from any
exhaustive or unaccustomed exercise during the preceding 48 h of
any experimental test and to refrain from taking nutritional
supplements during the experimental period.
Laboratory tests
Anthropometric
measurements.
Anthropometric
mea-
surements were performed according to the procedures described
by Lohman [22]. Participants were weighed to the nearest 0.1 kg
using an electronic scale (Filizola, model ID 1500, Sa˜o Paulo,
Brazil). Height was measured to the nearest 0.1 cm using a
stadiometer. Skinfold thickness was measured to the nearest
0.2 mm at eight body sites (i.e., triceps brachii, suprailiac,
abdominal, chest, subscapular, midaxillar, anterior thigh and calf)
using a Harpenden caliper (West Sussex, United Kingdom). The
median of three values was used for data analysis. Measurements
were performed by an experienced investigator. Body density was
estimated using the equation of Jackson and Pollock [23], and
body fat was estimated using the equation of Brozek et al. [24].
Maximal incremental test.
A maximal incremental running
test was performed on a motorized treadmill (model TK35,
CEFISE, Nova Odessa, Brazil). After a warm-up at 8 kmNh21 for
5 min, the speed was increased by 1 kmNh21 every minute until
exhaustion. The participants received strong verbal encourage-
ment to continue as long as possible. Expired gases were measured
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by a metabolic measurement cart (Cortex Metalyzer 3B, Cortex
Biophysik, Leipzig Germany) to determine VO2 and carbon
dioxide output (VCO2) and were subsequently averaged over 30-s
intervals throughout the test. Before each test, the metabolic cart
was calibrated using ambient air and a gas containing 12% O2 and
5% CO2. The turbine flowmeter was calibrated using a 3-L
syringe (Quinton Instruments, Seattle, WA, USA). Heart rate
(HR) was monitored during the test with a HR transmitter (model
S810, Polar Electro Oy, Kempele, Finland) coupled to the gas
analyzer. Maximal heart rate (HRmax) was defined as the highest
value obtained at the end of the test. Maximal oxygen uptake
(VO2max) was determined when two or more of the following
criteria
were
met:
an
increase
in
VO2
of
less
than
2.1 mlNkg21Nmin21 between consecutive stages, a respiratory
exchange ratio greater than 1.1, and reaching 610 bpm of the
maximal age-predicted heart rate [25].
Constant-speed test.
To analyze the impact of an SS bout
on running parameters, the participants performed two constant-
speed tests (experimental vs. control condition) on a motorized
treadmill (model TK35, CEFISE, Nova Odessa, Brazil). Before
the
tests,
the
athletes
performed
a
standardized
warm-up
consisting of a 5-min run at 8 kmNh21, followed by a 3-min
passive recovery. The treadmill speed was adjusted to 12 kmNh21
after the warm-up, and the subjects ran for 6 minutes at this speed.
The test began with the participant’s feet astride the moving belt
and hands holding the handrail. For the experimental condition,
the athletes performed the test immediately after the SS treatment.
The VO2 over the final 30 seconds was taken as the steady-state
VO2 for that speed. Running economy (RE) was defined as
described by Fletcher et al. [26]. Taking the average RER over the
same 30 seconds, the caloric equivalent of the VO2 (kcalNl21O2)
was determined [27], and the caloric unit cost was calculated using
equation 1:
Caloric unit cost (kcal.kg1. km1)
~VO2
. caloric equivalent. s1. BM1. K
ðEq:1Þ
Where VO2 is measured in liters per minute, caloric equivalent
is in kilocalories per liter, speed (s) is in meters per minute, body
mass (BM) is in kilograms, and K is 1000 mNkm21.
The resting metabolic rate was not subtracted because it cannot
be confirmed that resting metabolic demand continues at the same
rate while running. Stride parameters and EMG signals were
simultaneously measured from the left leg during the last 10 s of
the constant-speed tests. Disposable dual Ag/AgCl snap electrodes
with a 1 cm diameter and a 2-cm center-to-center spacing
(Noraxon, Scottsdale, AZ, USA) were placed on the belly of the
vastus medialis (VM), biceps femoris (BF) and gastrocnemius
medialis (GA) before starting the tests. The guidelines published by
SENIAM
[Surface
Electromyography
for
the
Non-Invasive
Assessment of Muscles (SENIAM)] were followed for skin
preparation, electrode placement and orientation. Electrode
positions were marked with small ink tattoos on the skin during
the first testing session to ensure that electrode placement over the
entire experimental period would be consistent [28]. The EMG
signals were recorded with a telemetric EMG system, which had a
gain of 1000 times, a bandwidth (23 dB) over 10 to 500 Hz, and a
common mode rejection ratio .85 dB and was relayed to the
computer via a 16-bit A/D converter (Telemyo 900, Noraxon,
Scottsdale, AZ, USA).
The EMG data were band-pass filtered at 20–400 Hz, and an
envelope representing the muscle activation was determined using
a moving RMS filter with a window of 50 ms. The period of
activation of each muscle during a stride was determined as the
period where the signal was above a threshold of 15% of the
Figure 1. Pictorial view of the experimental design.
doi:10.1371/journal.pone.0099238.g001
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maximum activity of that muscle during the trial for at least
100 ms. These parameters were selected based on the signal-noise
relationship of the EMG data and were visually verified to
correctly identify periods of muscle activation. For each bout of
EMG activation, we calculated the integrated EMG (iEMG),
defined as the area under the EMG versus time curve divided by
the period of activation.
A video camera (GR-DVL9800U, JVC Inc., Wayne, NJ, USA)
was used to record frontal plane images at 120 Hz during the last
10 s of running. Stride parameters were measured simultaneously
with EMG using Noraxon’s Myoresearch software (Version 1.08).
Using frame-to-frame video analysis, ten steps were analyzed.
Contact time was defined as the time from ground contact of the
left foot until the time that the same foot left the ground. The flight
time was determined from the time when the left foot left the
ground to the time prior to the next contact of the same foot. The
stride time was defined as the time from ground contact of one foot
to the next ground contact of the same foot (i.e., contact time+
flight time). Given that contact time was ,250 ms and images
were captured at 120 Hz sampling rate, the experimental
uncertainty of digital instruments in our case was ,8 ms,
corresponding to an uncertainty of 3.2%. This is acceptable
considering the between subjects variability of the measurements
was larger.
Field tests
3-km running test.
To analyze the impact of SS on pacing
strategy, participants individually performed a 3-km run on an
outdoor 400-m track on three different days (familiarization,
experimental, and control conditions). These running time-trial
tests were performed with an interval of at least 48 h between
them. Before each time-trial, the participants did 10 minutes of
warm-up at 8 kmNh21. They were instructed to maintain regular
water consumption within six hours of testing, and water was
provided ad libitum during the entire event. The participants were
instructed to finish the race as quickly as possible, as they would in
a competitive event. Verbal encouragement was provided during
the entire event. However, runners were not advised of their lap
splits. Speed was registered every 100 m via a global positioning
system (GPS Forerunner 305, Garmin, Kansas City, Oregon,
EUA). RPE was reported by participants every 400 m using the
Borg 15-point scale [6]. Copies of this scale were laminated and
reduced to 10 cm by 5 cm, and they were affixed to the wrist of
the dominant arm of the individuals. The 3-km running tests were
performed at the same time of day and in similar conditions.
Ambient temperature and humidity were provided by the Institute
of Astronomy, Geophysics and Atmospheric Sciences of the
University of Sa˜o Paulo, Brazil. The mean 6 SD values for
temperature and humidity were 24.163.9uC and 63.069.7%,
respectively.
The sit-and-reach and drop jump tests were performed before
and immediately after the SS in the 3-km running time-trial
session with previous SS, and they were performed before the 3-
km running time-trial session without SS. In the former situation,
these tests were performed to verify the effectiveness of SS on the
range of motion and capacity of lower limbs to produce explosive
force, respectively. The sit-and-reach test was used because it
provides a global measure of hamstring, hip, and lower back
flexibility [29]. The participants sat with their bare feet pressed
against the sit-and-reach box. Knees were extended, and the right
hand was positioned over the left. Participants were then asked to
push a ruler transversely located over the box as far as possible on
the fourth bobbing movement. Each subject performed 3 trials of
the sit-and-reach test, and the best trial was used for analysis. After
the sit-and-reach test, the participants were instructed to perform a
drop jump. The jump height was determined by flight time, which
was measured by a contact mat (MultiSprint, Hidrofit, Brazil).
Athletes stepped off a 40 cm box and attempted to achieve the
greatest vertical height with a short ground contact time (close to
200 ms) [30]. Subjects were instructed to minimize knee flexion
and extension during the drop jump, and a demonstration was
provided by the investigators. All jumps were performed with
hands on hips, and five repetitions were performed with a 30-s rest
between jumps. The largest and smallest values were rejected, and
the average of the remaining 3 jumps was calculated and used for
statistical analysis.
Intervention protocol
Static stretching.
The stretching treatment used in the
present study was similar to that described in Samogin-Lopes et
al. [31]. The SS involved seven different exercises for the lower
limbs, including 5 unassisted and 2 assisted exercises. Briefly, the
exercises performed were unassisted straight-leg stand and toe
touch,
unassisted
standing
quadriceps
stretching,
unassisted
hamstrings and back stretching, unassisted hurdler’s stretching,
unassisted standing calf stretching, assisted quadriceps and hip
stretching, and assisted thigh stretching. Each exercise was
performed three times, and each time the stretching position was
maintained for 30 seconds. The magnitude of stretch was sufficient
to yield a score of 8–9 on the Borg CR10 scale [6]. The total
duration of time required for completion of the SS treatment was
approximately 20 minutes.
Statistical analyses.
Data normality was assessed by the
Shapiro-Wilk test, and all variables showed a normal distribution.
All data are reported as means and standard deviations (6SD). A
paired t- test was used to determine differences between non-
stretching and SS treatments for RE, EMG, drop jump height, sit-
and-reach test, flight time, contact time and stride time. Repeated
measures analysis of variance with two factors (distance x
condition), followed by a Bonferroni adjustment to compare the
alterations in the speed and RPE during the 3-km time trials. The
level of significance was set at p#0.05. All statistical analyses were
conducted using the SPSS statistical package (version 16.0,
Chicago, USA). Smallest worthwhile change (SWC; clinically
beneficial effect) was also determined for performance parameters
using the method described by Batterham and Hopkins (32). A
Cohen’s unit of 0.2 was used to determine the SWC. The
uncertainty in the effect was expressed as difference and 90%
confidence limits (difference 695% CL) and as likelihoods that the
true value of the effect represents substantial change (harm or
benefit). When clear interpretation could be made, a qualitative
descriptor was assigned to the following quantitative chances of
benefit: ,1%, almost certainly not; 1–5%, very unlikely; 5–25%,
unlikely or probably not; 25–75%, possibly or may be; 75–95%,
likely or probably; 95–99%, very likely; .99%, almost certainly
(32). Where the chances of benefit or harm were both calculated to
be $5%, the true effect was deemed unclear.
Results
Laboratory tests
Table 1 shows the anthropometric and physiological charac-
teristics of the participants. Table 2 shows the variables measured
during the RE tests. No significant differences were observed in
the caloric unit cost of running (p = 0.128) or HR between the
conditions (p = 0.317). The iEMG for the BF muscle was
significantly higher in the SS condition, compared to the control
condition (p = 0.031). No significant changes in iEMG were
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observed in either VM (p = 0.419) or GA (p = 0.212). The stride
time was significantly longer in the SS condition (p = 0.053) than
in the control, but no differences were observed for contact time or
flight time.
Field tests
Variables measured during time-trial tests performed with and
without previous static stretching are presented in figure 2. The
speed-distance curve during 3-km running showed a classical U-
shape in both conditions. It was detected that the first section
(100 m) was completed at a significantly slower speed in the SS
condition (very likely harmful, 21.161.0 km.h21 95% CL),
compared with the control condition (p = 0.036). However, the
overall running time to cover 3-km running during the control
condition (11:28600:41min:s) was not significantly different from
that
during
the
SS
condition
(11:35600:31min:s)
(trivial,
7.0613.9 s 95% CL). The RPE increased significantly over time
in both conditions (p = 0.001). The RPE in the SS condition was
statistically greater than that in the control condition only during
the first 800 m (p = 0.019). Following SS, the athletes also
demonstrated reduced drop jump height (p = 0.001) and improved
performance on the sit-and-reach test (p = 0.0001) relative to
measures obtained prior to SS protocol. There were no differences
in drop jump height (p = 0.351) and sit-and-reach test (p = 0.262)
before the 3-km running when the control and experimental
situations were compared.
Discussion
The main objective of the present study was to investigate the
impact of SS on pacing strategy and performance during a 3-km
running time-trial. To the best of our knowledge, this is the first
study to analyze the influence of this exercise-induced impairment
in neuromuscular function on the pacing strategy adopted during
a long-distance run. The main finding was that the SS resulted in a
slow-start strategy during a 3-km running time-trial. We also
observed an impaired drop jump performance and a higher
perceived exertion during the first 800 m.
Acute effects in neuromuscular function after SS treatments
have led to changes in isometric peak torque, range of motion,
height in vertical and drop jumps [14,18,33]. In the current study,
it was found that an SS bout resulted in an 11% increase in the sit-
and-reach test and a 9.2% decrease in drop jump height before the
3-km running time-trial. These findings are similar to previous
investigations. Young and Elliott [34] demonstrated that SS
significantly decreased drop jump performance by 6.9% in
recreational
athletes.
Furthermore,
Behm
and
Kibele
[18]
demonstrated that SS for lower limbs significantly decreased the
drop jump height (24.6%) and increased the range of motion
measured by the sit-and-reach test (+12.1%) in physically active
subjects. These data show that the magnitude of modification in
flexibility and jump performance after SS treatment demonstrated
in the current study was similar to that reported in the literature.
Data from the current study also showed that reduced ability to
produce force after the SS protocol was accompanied by a higher
iEMG of the BF and stride time during constant-speed running
test. It is well recognized that BF activation plays a key role in the
control of knee extension and in the generation of the knee flexion
force in the late swing phase before foot contact during running
[35]. Thus, the higher iEMG of the BF after the SS protocol might
have reflected an increased motor unit recruitment in order to
maintain the running mechanics and compensate the reduced
passive forces that would otherwise have served this purpose. In
turn, this increased muscle activation may have contributed to the
perception of effort as indicated by the RPE.
Previous
findings
have
indicated
an
inverse
relationship
between RE and flexibility [20]. In the present study, it was
found that SS produced a significant increase in range of motion,
as measured by the sit-and-reach test (362 cm), but the RE
measured at 12 kmNh21 was not statistically altered. These data
were similar to the study of Allison et al. [21], who showed that the
statistical changes detected in range of motion (2.760.6 cm),
isometric strength (25.663.4%) and countermovement jump
Table 1. Anthropometric and physiological characteristics of
the participants.
Variable
Mean ± SD
Age (years)
35.766.1
Height (cm)
173.369.0
Body mass (kg)
67.967.4
Body fat (%)
10.062.7
VO2max (ml.kg21.min21)
51.063.0
HRmax (beats.min21)
18466
RERmax
1.260.1
HRmax: maximal heart rate, RERmax: maximal respiratory exchange ratio.
doi:10.1371/journal.pone.0099238.t001
Table 2. Variables measured during the constant-speed tests with or without previous static stretching.
Control
Static stretching
RE (ml.kg21.min21)
41.362.8
40.463.0
CUC (kcal.kg21.km21)
1.0360.07
1.0060.08
iEMGVM(mV)
60621
64623
iEMGGA (mV)
77627
95.3638
iEMGBF(mV)
73626
94631*
Contact time (ms)
256626
250632
Flight time (ms)
443642
452637
Stride time (ms)
697641
710641*
Values are means 6 SD; RE: running economy; CUC: caloric unit cost; VM: vastus medialis; GA: gastrocnemius medialis; BF: biceps femoris. *Significantly different from
control condition (p#0.05).
doi:10.1371/journal.pone.0099238.t002
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height (25.563.4%) were not accompanied by changes in the RE
after SS. Similarly, Hayes and Walker [36] observed that static
and dynamic stretching improved range of motion, but both
treatments had no impact on the RE. Therefore, it seems that
acute improvement in range of motion after SS is not associated
with modification in the RE.
In relation to pacing strategy, our results revealed that runners
adopted a slow start after SS. This reduced running speed during
initial phase of the 3-km running time trial seems to be related to
lower ability to produce force, as evidenced by decreased drop
jump height and increased stride time found after the SS protocol.
Previous studies have suggested that the ability to produce force is
an essential determinant of endurance performance without being
necessarily related to energy demand of running (e.g. running
economy) [37,38]. This occurs because middle and long-distance
runners must be able to maintain a relatively high speed over the
course of a race [39]. In particular, the acceleration phase requires
a great level of muscle contraction in order to overcome inertia.
Because the SS have a negative acute effect on the neuromuscular
system [14,15], its deleterious effect might be more pronounced in
the start phase of a long-distance running. These results are in
accordance with previous studies that reported reduced running
sprint performance after a SS protocol [16,17]. Taken together,
these findings suggest that the SS induces a slow start in a 3-km
running time trial due its negative influence in the neuromuscular
system, impairing the acceleration phase of a long-distance event.
Interestingly, our results showed that the slow start induced by
SS treatment was accompanied by an increase in the RPE. It has
been suggested that RPE may reflect increased motor unit
recruitment [40]. It is believed that collateral innervations are
sent directly from the motor to the sensory areas in the brain,
contributing to the increase of the RPE response during exercise
[41]. Thus, it is plausible to suggest that the brain might have
interpreted the efferent signals from increased motor unit
recruitment of the BF as the first cues for running speed
adjustments. Based on this finding, it is plausible to suggest that
the greater RPE found during the start phase after SS may reflect
an increased neural drive resulting from intention to produce the
same amount of force and thus maintain a high initial running
speed. This is in agreement with a previous suggestion that RPE
has a relevant role in the speed control during the start phase of a
running race [42].
Results of the present study revealed that despite the slow start,
runners were able to maintain the overall running performance.
Figure 2. Variables measured with and without previous static stretching treatment. A and B panels show the running speed and rating of
perceived exertion during a 3-km running time-trial, respectively. C and D panels show the drop jump and sit-and-reach tests performed prior to and
immediately after static stretching treatment. * Significantly different from control situation (p#0.05). #Significant difference over time in each
condition (p#0.05).
doi:10.1371/journal.pone.0099238.g002
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This is consistent with the idea that the effects of SS were
overcome during the event. Ryan et al. [43] showed that two 30-
second bouts of SS were sufficient to induce a significant decrease
in the passive musculotendinous stiffness of the plantar flexor
muscles. However, these authors reported that although stiffness
decreased immediately after 2 min, 4 min, and 8 min of SS, the
effects of stretching disappeared within 10 min. In turn, Mizuno et
al. [44] showed that SS for 5 minutes at maximal dorsiflexion
resulted in significantly increased range of motion that persisted
for 30 min, but significant decreases in musculotendinous stiffness
returned to baseline levels within 10 min. Taking into consider-
ation the fact that the 3-km running was performed with an
average time of 11 min, it can be suggested that the negative
effects of SS on overall exercise performance was negligible. Thus,
the negative effect of the SS in running performance might be
restricted to the initial phase of a middle-distance event when the
metabolic cues are less important for the running pacing strategy
[42].
The current study does have some limitations. It is important to
note that our SS treatment was composed of seven different
exercises for the lower limbs, performed three times in a serial
fashion at ‘‘high-intensity’’, which was defined as scores of 8–9 on
the Borg CR10 scale. This SS treatment may have resulted in a
higher volume and intensity stretching protocol than those often
used in the ‘‘real world’’. In addition, our sample was composed by
recreational runners, which have a lower endurance training
volume and did not perform other training routines (i.e. strength
or stretching training). In this manner, the effects of static
stretching on the neuromuscular variables and pacing strategy in
highly-trained subjects could be distinct from those observed in the
present study. Thus, caution should be exercised in extrapolating
these findings to runners with a higher training level.
In conclusion, the present study provides novel findings
concerning the impact of stretching-induced impairment on
neuromuscular function and pacing strategy. It was detected that
SS resulted in a reduced capacity of the skeletal muscle to produce
explosive force and a reduction in running speed during the
acceleration phase of a time-trial. These results clearly show that,
independent of the intention of the athletes to finish a race as
quickly as possible, the neuromuscular system has a primary
function in contributing to the chosen speed during the initial
phase of the race, where the highest running speeds were reached.
Acknowledgments
The authors thank each of the individuals for their participation.
Author Contributions
Conceived and designed the experiments: MVD LAP AEL-S BRM RB.
Performed the experiments: MVD LAP. Analyzed the data: MVD MD
LAP RB. Contributed reagents/materials/analysis tools: MD AEL-S BRM
RB. Wrote the paper: MVD MD LAP AEL-S BRM RB.
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Static stretching alters neuromuscular function and pacing strategy, but not performance during a 3-km running time-trial.
Damasceno, Mayara V,Duarte, Marcos,Pasqua, Leonardo A,Lima-Silva, Adriano E,MacIntosh, Brian R,Bertuzzi, Rômulo