Acute Changes in Autonomic Nerve Activity during Passive Static Stretching

Abstract

This study aimed to investigate the acute change of static stretching (SS) on autonomic nerve activity and to clarify the effect of SS on systemic circulation. Twenty healthy young, male volunteers performed a 1-min SS motion of the right triceps surae muscle, repeated five times. The autonomic nerve activity balance was obtained using second derivatives of the photoplethysmogram readings before (pre), during, and after (post) SS. Heart rate and blood pressure (BP) were also measured. The autonomic nerve activity significantly changed to parasympathetic dominance by SS as compared with pre. In addition, for SS, the autonomic nerve activity slowly changed to sympathetic dominance after completion of all sets of stretching, but these value did not return to pre during the 5 minutes after the completion of all sets of stretching, with parasympathetic dominance continuing by 4 minutes after SS. The BP and HR transiently increased during SS and decreased after SS. In addition, HR significantly decreased after completion of all sets of SS.The possibility that the response during SS may differ from the response during active static stretching is shown.

Full text

American Journal of Sports Science and Medicine, 2014, Vol. 2, No. 4, 166-170
Available online at http://pubs.sciepub.com/ajssm/2/4/9
© Science and Education Publishing
DOI:10.12691/ajssm-2-4-9
Acute Changes in Autonomic Nerve Activity during
Passive Static Stretching
Takayuki Inami1,*, Takuya Shimizu2, Reizo Baba3, Akemi Nakagaki4
1School of Exercise and Health Sciences, Edith Cowan University, Joondalup Drive, Joondalup, WA, Australia
2Graduate School of Health and Sports Sciences, Chukyo University, Tokodachi, Toyota, Aichi, Japan
3Department of Pediatric Cardiology, Aichi Children’s Health and Medical Center, Osakada, Obu, Aichi, Japan
4Reproductive Health Nursing/Midwifery, Graduate School of Nursing, Nagoya City University, Japan
*Corresponding author: inami0919@gmail.com
Received June 06, 2014; Revised July 12, 2014; Accepted July 16, 2014
Abstract This study aimed to investigate the acute change of static stretching (SS) on autonomic nerve activity
and to clarify the effect of SS on systemic circulation. Twenty healthy young, male volunteers performed a 1-min SS
motion of the right triceps surae muscle, repeated five times. The autonomic nerve activity balance was obtained
using second derivatives of the photoplethysmogram readings before (pre), during, and after (post) SS. Heart rate
and blood pressure (BP) were also measured. The autonomic nerve activity significantly changed to parasympathetic
dominance by SS as compared with pre. In addition, for SS, the autonomic nerve activity slowly changed to
sympathetic dominance after completion of all sets of stretching, but these value did not return to pre during the 5
minutes after the completion of all sets of stretching, with parasympathetic dominance continuing by 4 minutes after
SS. The BP and HR transiently increased during SS and decreased after SS. In addition, HR significantly decreased
after completion of all sets of SS.The possibility that the response during SS may differ from the response during
active static stretching is shown.
Keywords: sympathetic nerve activity, parasympathetic nerve activity, triceps surae muscle, static stretching,
blood pressure, heart rate
Cite This Article: Takayuki Inami, Takuya Shimizu, Reizo Baba, and Akemi Nakagaki, “Acute Changes in
Autonomic Nerve Activity during Passive Static Stretching.” American Journal of Sports Science and Medicine,
vol. 2, no. 4 (2014): 166-170. doi: 10.12691/ajssm-2-4-9.
1. Introduction
Static stretching (SS) is a form of physical exercise in
which a specific skeletal muscle (or muscle group) is
deliberately stretched and reflects the mechanical
characteristics of skeletal muscle. It is widely used to
increase articular range of motion (ROM) by favorably
affecting the flexibility of muscles and tendons [1,2]. In
addition, it is reported that SS can provide “relaxation”
like the techniques employed in the field of psychology
[3,4].These reports have indicated that extension stimuli
on the muscles may induce advantageous changes in the
balance of autonomic nerve activity; however, only a
small number of studies focusing on SS and autonomic
nerve activity have been conducted.
We could find three studies in which SS was evaluated
by analyzing the changes in autonomic nerve activity
based on the changes in heart rate variability (HRV) in
human subjects. Saito, et al. [5] conducted SS (trunk
flexion) on healthy volunteers and showed that
parasympathetic nerve activity was significantly higher
after SS than it was before SS.Farinatti, et al. [6] applied
SS (trunk flexion) to subjects with a low level of
flexibility and showed that parasympathetic nerve activity
decreased remarkably during SS and was significantly
higher after SS than it was before SS. Mueck-Weymann,
et al. [7] conducted SS on the large muscles of body-
building athletes for 28 days and confirmed a significant
increase in parasympathetic nerve activity and a
significant decrease in sympathetic nerve activity after the
completion. Based on these findings, it can be understood
that the balance of autonomic nerve activity shifts to the
sympathetic nerve activity-dominant state during SS and
the parasympathetic nerve activity-dominant state after SS.
All of these reports involve the response to active SS;
however, there is no report on autonomic nerve activity
relating to passive SS. According to Mohr, et al. [8],SS
has to be conducted first in order to achieve the maximum
effect of SS, and Alter [2] stated that the tension caused by
muscle contraction must be suppressed to the minimum in
order to minimize active resistance. These precedent
studies have a problem in that there is an extremely high
possibility that the muscles other than the target muscle
are under tension, because the trunk flexion was
conducted actively. Actually, the influence of SS on the
nervous system is known to be transmitted to the sites to
which SS is not conducted [9,10]. It is thus assumed that
active SS and passive SS have different influences on the
autonomic nerve activity, although the term “SS” is used
collectively.

American Journal of Sports Science and Medicine 167
We hypothesizes that the changes in autonomic nerve
activity upon passive SS are different from the response
following active SS. This study aims at investigating the
acute effect on autonomic nerve activity when SS is
conducted passively.
2. Materials and Methods
2.1. Participants
This study was approved by the local ethics committee
and conducted in accordance with the Declaration of
Helsinki. The purpose, procedures, and risks of the study
were informed, and a written informed consent was
obtained from each participant. Twenty non-smoking,
healthy male adults (aged 18 to 20 years, 19.3 years on
average) without cardiovascular, orthopedic, or
neurological diseases were recruited as study subjects. SS
was conducted for the right triceps surae muscle. They had
not been involved in any resistance training or stretching
program before the study. The sample size was calculated
on the basis of an α level of 0.05 and a power (1-β) of 0.8,
with an estimated 20% difference in ROM before and
after of SS using data from a previous study [11]. Their
height was 175.0±6.4cm(mean ± standard error: the same
below) and body weight was 68. 9±8.2kg.
2.2. Study Design
Figure 1. Protocol and measurement system
The study participants visited the laboratory on three
occasions at the same time of day, with at least 48 h
between visits; all experimental trials were completed
within 3weeks. A full familiarization with the SS protocol
and test procedures was provided during the first session,
whereas the subsequent two visits were used to complete
the following experimental protocol, in a randomized
order: 1) control session (no stretching); 2) five sets of 1-
min passive plantar flexor SS, as described previously
[11,12]. Data were collected during a period of 30-min
including these stretching sessions, a period of resting in
the sitting position (the knee fully extended) for 15-min
before stretching (referred to as “pre” below), and a 5-min
period after stretching (referred to as “post” below). The
temperature in the experimental room was set at 25°C.
The subjects were asked not to consume any alcohol on
the day before measurement and not eat breakfast on the
day of measurement. The experiment was conducted while
external environmental factors that could affect
measurement were minimized, and care was taken to
ensure subject silence and comfort. The protocol and
measurement system are shown in Figure 1.
2.3. Static Stretching Protocol
Two techniques, SS and a control with no stretching
were used, and SS was conducted passively to minimize
active resistance. In SS, the knee joint was in the extended
position and the ankle joint in the maximally dorsiflexed
position in a sitting position (the knee fully extended) [13].
For control the subjects rested in sitting position (the knee
fully extended). The load with which a subject himself felt
to have an “appropriate stretched feeling” or “slightly taut
feeling” [14] was measured in advance with a hand-held
dynamometer (Loadcell LU-100KSB34D of Kyowa
Electronic Instruments Co., Ltd.; Strain amplifier: F-420
of Uniplus Corporation), and the passive external force
during repeated stretching was controlled to impose the
same load in the respective sets of the respective
stretching. This position was then held at a constant angle
for 1 min, and this stretching procedure was repeated 5
times with a 1-min interval between sets (total 10-min). In
addition, the maximum ROM of the ankle joint was
measured with a goniometer of Tokyo University [13].
2.4. Measurement of Autonomic Nerve Activity,
Blood Pressure (BP) and Heart Rate (HR)
A large number of attempts of evaluating the balance of
autonomic nerve activity by analyzing the waveform of an
electrocardiogram and pulse wave have been reported as
evaluation of autonomic nerve activity. The method
involving frequency analysis of an electrocardiogram or
second derivative of photoplethysmogram (SDPTG)
quantifies sympathetic nerve activity and parasympathetic
nerve activity separately and is clinically applied. In
particular, SDPTG performs measurements using an
optical sensor noninvasively at the fingertips and reflects
changes in the absorbance of hemoglobin independently
from skin tension or properties of the subcutaneous fat,
and thus involves more noninvasive characteristics than
electrocardiography in which electrodes are attached. The
waveform of SDPTG is composed of five components, a
through e. It is reported that the a-a interval of SDPTG
and the R-R interval of electrocardiogram are highly
correlated with a correlation coefficient of 0.992 from
young to middle-aged to elderly individuals; this is
reportedly higher than the 0.977 correlation coefficient
between the R-R interval of electrocardiogram and finger
photoplethysmogram [15]. Further, it is shown in the
report that the spectrum power values obtained from the
SDPTG a-a interval correspond to the spectrum power
values obtained from electrocardiogram from the low-
frequency band to the high-frequency band [15].
Accordingly, analysis of autonomic nerve activity using
SDPTG has physiological significance equivalent to that
obtained using electrocardiogram.
A SDPTG (Artett C of U-Medica Inc., Osaka, Japan)
was used for the measurement of autonomic nerve activity.
The pulse waveforms (a to e waves: Figure 1) output on a
personal computer were used for frequency analysis for

168 American Journal of Sports Science and Medicine
the a-a interval using software for autonomic function
evaluation and analysis exclusively used for Artett. Based
on the results of the frequency analysis, the low-frequency
component (LF) was set at 0.04 to 0.15Hz and the high
frequency component (HF) at 0.15 to 0.4Hz [16]. The
power spectral densities at the respective frequency zones
were calculated, and the LF and HF (mainly
parasympathetic nerve activity) and their ratio LF/HF
(mainly sympathetic nerve activity), and HR were
obtained every 1-min. Since HF and LF/HF differ greatly
among individuals, normalization was performed so that
the means of HF and LF/HF were 0 and the standard
deviation was 1 during the continuous measurement
period for each subject, and the HF and LF/HF converted
into normal distribution are expressed as nHF and
n(LF/HF), respectively. Because the balance of the
autonomic nerve activity have a reciprocal relationship, in
the estimation of the balance of the autonomic nerve
activity, when
( )
nHF n LF/ HF 0−>
it was considered to be parasympathetic nerve activity-
dominant, and when
( )
nHF n LF/ HF 0
−<
it was considered to be sympathetic nerve activity-
dominant [17].
An average blood pressure (BP) also measured over a
1-min period, and included measuring the systolic (SBP)
and diastolic blood pressures (DBP) with an automatic
digital BP meter (HEM-7020, OMRON, Tokyo, Japan).
The subjects were requested to perform respiration at a
rate of 10 times (exhalation for 3 seconds and inhalation
for 3 seconds) per minute in rhythm with an electronic
metronome (Digital metronome: DM-70, Seiko Watch
Corporation, Tokyo, Japan)during the measurement so
that the value evaluated as HF from the relationship
between the frequency and respiration rate did not overlap
LF [18]. Respiration training was conducted for 10
minutes under monitoring before each measurement and
respiration was confirmed visually also during
measurement, since the measurement was conducted
under regulated respiration.
2.5. Statistical Analysis
The values for each parameter before SS (pre) were
averaged over the 5-min period immediately before SS.
One-way analysis of variance (ANOVA) using repeated
measurements and two-way ANOVA were conducted for
each numerical data set; Bonferroni’s tests were used for
post hoc analyses. SPSS, version 12.0 for Windows (SPSS,
Chicago, IL, USA) was used for statistical analyses, and
the statistically significant level was set at less than 5%.
Figure 2. Changes in each parameter
It is shown that changes in a) ROM, b) autonomic nerve activity, c) SBP, d) DBP, and e) HR. The yellow makers indicate the SS phase.
*: p< 0.05; **: p < 0.01, significantly different from baseline.

American Journal of Sports Science and Medicine 169
3. Results
The changes in each parameter are shown in Figure 2-a
to e. The ROM increased significantly until 5-min post SS
(Figure 2-a). The autonomic nerve activity significantly
changed to parasympathetic dominance by SS as
compared with pre. In addition, for SS, the autonomic
nerve activity slowly changed to sympathetic dominance
after completion of all sets of stretching, but these value
did not return to pre during the 5-min after the completion
of all sets of stretching, with parasympathetic dominance
continuing by 4-min after SS(Figure 2-b). The values
obtained for control showed no large change during
measurement(Figure 2-b). No extrasystole was observed
in any subjects by diagnosis with the analysis software for
exclusive use. The changes in SBP, DBP and HR are
shown in Figure 2-c, d and e. These parameters transiently
increased during SS and decreased after SS. In addition,
HR significantly decreased after completion of all sets of
SS (3-min).
4. Discussion
The major results of this study are as follows: 1) The
balance of autonomic nerve activity shifts to a
parasympathetic nerve-dominant state during passive SS;
and2) the parasympathetic nerve-dominant state continues
even after the completion of SS (for at least 5 minutes
after completion). The study on the autonomic nerve
activity upon passive SS in humans is valuable and the
results of this study can be said to be a new fact which can
be added to the findings concerning SS and relaxation.
Considering the precedent studies all together [5,6,7],
when SS is conducted actively, the autonomic nerve
activity shifts to a sympathetic nerve-dominant state
during SS and a parasympathetic nerve-dominant state
after the completion of SS. Also in this study, the balance
of autonomic nerve activity shifts to a parasympathetic
nerve-dominant state after SS, which supports the results
of the precedent studies. However, unlike active SS, the
response during SS shifted to a parasympathetic nerve-
dominant state. This result indicates the possibility that the
process differs between active SS and passive SS,
although the response after the completion of SS is similar
for both. Murata et al. [19] investigated autonomic nerve
activity following passive SS in decerebrate cats as a
precedent study of an animal experiment level. According
to Murata et al. [19], cardiac sympathetic nerve activity
increased only at the time of start of SS (where analysis
was carried out in the condition in which parts of the
cardiac vagal nerve and the stellate ganglion were cut),
and this response has been confirmed muscle sympathetic
nerve activity in human [20]. Since analysis was
conducted for one minute in this study, not only cardiac
sympathetic nerve activity that increases only at the start
of SS, but also stimulation of the suppression system that
subsequently occurs might be analyzed, and as a result,
the balance of autonomic nerve activity is considered to
shift to a parasympathetic nerve-dominant state. In
addition,transient increases in SBP,DBP and HR have
been reported in response to local SS of the triceps surae
muscle [20,21,22], and our results support these
previously described findings. Although the SS method
was different in the previous studies, the transient changes
in hemodynamic properties can be associated with
mechanical stress and modulations of the baroreflex
sensitivity and vagal tone during SS [20,21,22]. It is
difficult to identify the mechanism from the results of this
study; however, it is considered that the reduction in HR
due to SS is mainly due to suppression of sympathetic
nerve activity [2], and the reduction in HR plays a role in
continuation of a parasympathetic nerve-dominant state by
SS.
Limb position is considered to be one of the causes for
the difference in autonomic nerve activity between active
SS and passive SS. There are a large number of muscle
spindles and proprioceptors in the diaphragm and the
intercostals, which involve in up-and-down movements of
the ribs [23]. In the trunk flexion which was conducted in
the precedent studies, SS was conducted with the hip joint
bent maximally so that a large pressure was applied to the
thoracoabdominal part and muscle extension stimuli
would occur at the muscles other than the hamstring
muscle (for example, external oblique muscle and internal
oblique muscle). As mentioned above, the influence of SS
on the nervous system is known to be transmitted to the
sites to which SS is not conducted [9,10]. Further, it is
assumed that respiratory load (load compensation reflex)
due to the position at which the trunk was anteverted
might prevent respiration by an ordinary respiration
method (with relaxation) to affect the balance of
autonomic nerve activity.
There are two main limitations associated with the
present study. The first limitaionsis that HRV analysis
using SDPTG conducted. We used SDPTG to minimize
invasion that included attachment of electrodes as much as
possible. The usability of investigation of autonomic
nerve activity using SDPTG has already been evidenced
by Yamaguchi, et al.; however, influence of changes in
body motion during SS, that is, due to dorsiflexion of the
ankle joint, on measurements is unclear. This point should
be sufficiently considered in further studies.The second
limitation is that all the parameters were calculated as an
average over 1-min intervals. According to Cui et al. [20],
the HR increased between one and three beats during SS.
This suggests that a hyper-acute effect of SS may occur,
and future studies should employ a better temporal
analysis, with times up to 1 min. However, because Cui et
al. [20] employed a different SS paradigm (5-s × 25 sets),
there is also a possibility that the SS performance time had
an effect. The precise effect of SS time should be
investigated in future studies.
In summary, autonomic nerve activity shifts to a
parasympathetic nerve-dominant state by passive static
stretching, and the effect continues for at least five
minutes after the completion. The possibility that the
response during SS may differ from the response during
active static stretching is shown.
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