Impact of Short-Term Training Camp on Aortic Blood Pressure in Collegiate Endurance Runners

Abstract

To investigate the influence of short-term vigorous endurance training on aortic blood pressure (BP), pulse wave analysis was performed in 36 highly trained elite collegiate endurance runners before and after a 7-day intense training camp. Subjects participated three training sessions per day, which mainly consisted of long distance running and sprint training to reach the daily target distance of 26 km. After the camp, they were divided into two groups based on whether the target training was achieved. Aortic systolic BP, pulse pressure, and tension-time index (TTI, a surrogate index of the myocardial oxygen demand) were significantly elevated after the camp in the accomplished group but not in the unaccomplished group, whereas the brachial BP remained unchanged in both groups. The average daily training distance was significantly correlated with the changes in aortic systolic BP (r = 0.608, p = 0.0002), pulse pressure (r = 0.415, p = 0.016), and TTI (r = 0.438, p = 0.011). These results suggest that aortic BP is affected by a short-term vigorous training camp even in highly trained elite endurance athletes presumably due to a greater training volume compared to usual.

Full text

ORIGINAL RESEARCH
published: 28 March 2018
doi: 10.3389/fphys.2018.00290
Frontiers in Physiology | www.frontiersin.org 1March 2018 | Volume 9 | Article 290
Edited by:
Thomas Leonhard Stöggl,
University of Salzburg, Austria
Reviewed by:
Beat Knechtle,
University of Zurich, Switzerland
Naoto Fujii,
University of Tsukuba, Japan
*Correspondence:
Jun Sugawara
jun.sugawara@aist.go.jp
Specialty section:
This article was submitted to
Exercise Physiology,
a section of the journal
Frontiers in Physiology
Received: 31 December 2017
Accepted: 12 March 2018
Published: 28 March 2018
Citation:
Tomoto T, Sugawara J, Hirasawa A,
Imai T, Maeda S and Ogoh S (2018)
Impact of Short-Term Training Camp
on Aortic Blood Pressure in Collegiate
Endurance Runners.
Front. Physiol. 9:290.
doi: 10.3389/fphys.2018.00290
Impact of Short-Term Training Camp
on Aortic Blood Pressure in
Collegiate Endurance Runners
Tsubasa Tomoto 1, Jun Sugawara1
*, Ai Hirasawa 2, Tomoko Imai 3, Seiji Maeda4and
Shigehiko Ogoh5
1Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan,
2Faculty of Health Sciences, Kyorin University, Mitaka, Japan, 3Center for General Education, Aichi Institute of Technology,
Toyota, Japan, 4Faculty of Health and Sports Sciences, University of Tsukuba, Tsukuba, Japan, 5Department of Biomedical
Engineering, Toyo University, Kawagoe, Japan
To investigate the influence of short-term vigorous endurance training on aortic blood
pressure (BP), pulse wave analysis was performed in 36 highly trained elite collegiate
endurance runners before and after a 7-day intense training camp. Subjects participated
three training sessions per day, which mainly consisted of long distance running and
sprint training to reach the daily target distance of 26 km. After the camp, they were
divided into two groups based on whether the target training was achieved. Aortic systolic
BP, pulse pressure, and tension-time index (TTI, a surrogate index of the myocardial
oxygen demand) were significantly elevated after the camp in the accomplished group
but not in the unaccomplished group, whereas the brachial BP remained unchanged in
both groups. The average daily training distance was significantly correlated with the
changes in aortic systolic BP (r=0.608, p=0.0002), pulse pressure (r=0.415,
p=0.016), and TTI (r=0.438, p=0.011). These results suggest that aortic BP is
affected by a short-term vigorous training camp even in highly trained elite endurance
athletes presumably due to a greater training volume compared to usual.
Keywords: aortic blood pressure, pulse wave analysis, endurance training, vigorous training, athletic conditioning
INTRODUCTION
There is a widely held notion that the central arterial pressure waveform is synthesized by the
overlapped reflection waves returning from the periphery (mainly lower body) on the incident wave
in phase; therefore, there are disparities between aortic and peripheral BP waveforms (Nichols and
McDonald, 2011). Importantly, aortic BP is more strongly related to concentric left ventricular
geometry than brachial BP (Roman et al., 2007). Furthermore, systolic BP is strongly related to left
ventricular hypertrophy, and pulse pressure is strongly related to vascular stiffening (Roman et al.,
2007, 2010). Thus, assessment of aortic BP could be an indicator of cardiac and vascular condition.
The beneficial effects of endurance exercise at a moderate intensity on the cardiovascular
system are well recognized (Thompson et al., 2003; Seals et al., 2008; Rowe et al., 2014).
On the other hand, the unfavorable effects of cardiovascular system including higher aortic
stiffness and aortic BP have been confirmed among highly endurance-trained populations
who participate in prolonged intense exercise events, especially marathons running (Scharhag
et al., 2005; Vlachopoulos et al., 2010) and ultramarathons running (Knez et al., 2006; Burr
et al., 2014) compared with age-matched physically active peers. However, the potential genetic

Tomoto et al. Short-Term Training and Aortic Pressure
influences in the aforementioned results cannot be completely
ruled out due to a cross-sectional study design (Scharhag et al.,
2005; Knez et al., 2006; Vlachopoulos et al., 2010; Burr et al.,
2014). Vlachopoulos et al. (2010) and Scharhag et al. (2005)
observed that peripheral and aortic BP and pulse pressure
were significantly reduced 24 h after a marathon running race
(Scharhag et al., 2005; Vlachopoulos et al., 2010), but this
response seems to reflect post-exercise hypotension (Halliwill,
2001). Thus, the effect of high intense exercise training (e.g.,
repetition of intense endurance exercise bouts) on the aortic BP
and pulse pressure is still unknown.
We previously reported that in well-trained male collegiate
endurance runners, systemic arterial stiffness increased after a 7-
day intense endurance training camp (Tomoto et al., 2015). Since
arterial stiffening promotes early return of the reflected wave
from peripheral to the heart and increases aortic BP (Nichols
and McDonald, 2011), we hypothesized that the arterial stiffening
induced by intense endurance training may cause to amplify
the aortic arterial pressure waveform. As a follow-up study, the
purpose of this study was to determine the effect of intense
endurance exercise bouts to aortic BP.
METHODS
We recruited the subjects from national ranked Ekiden relay
race team in Japan. We studied a total of 36 well-trained male
collegiate endurance runners. The average of their official best
times for a 5,000-m race was 14′28′′ ±0′17′′ (mean ±SD). All
of the subjects were healthy, normotensive (<140/90 mmHg),
non-obese (Body mass index, BMI<25 kg/m2), nonsmokers,
who were free of medication as well as overt chronic heart
and lung disease as assessed by their medical histories. None
of the subjects were taking cardiovascular-acting medication.
This study was reviewed and approved by the Institutional
Review Board (Toyo University: 2012-R-04). Additionally, all
procedures conformed to the ethical guidelines of the Helsinki
Declaration. All subjects provided informed written consent
prior to participation.
All measurements were performed at the same time of
the day on the first day of the 7-day training camp and the
day after the camp ended. Each subject fasted overnight
prior to all measurements. Aortic and brachial hemodynamic
parameters were recorded after at least 15 min supine-position
rest in a quiet air-conditioned room (24–25◦C). Subjects
abstained from alcohol for 24 h and caffeine for 12 h prior
to the experiment. Electrocardiogram (ECG), left carotid
arterial pressure waveforms (via applanation tonometry
sensor), and brachial BP (via oscillometric sensors) were
simultaneously measured using a vascular function-screening
device (form PWV/ABI, Omron-Colin, Kyoto, Japan). Carotid
arterial pressure waveforms were transferred into aortic
pressure waveforms by pulse wave analysis software involving a
validated generalized transfer function (SphygmoCor software,
AtCor Medical, Sydney, Australia) (Figure 1). The aortic
hemodynamic parameters including aortic systolic BP, pulse
pressure, augmentation pressure (AP), augmentation index
(Alx), Alx corrected for heart rate at 75 beats per minutes
(AIx75), time to wave reflection (TR), tension time index (TTI),
diastolic time index (DTI), and sub-endocardial viability ratio
(SEVR) were computed as previously reported (Vlachopoulos
et al., 2010).
The 7-day camp was conducted in August (summer season).
Although all subject engaged in regular long distance running,
the target training distance during the 7-day camp was longer
(26 km/day) than the weekly mandatory training distance.
The target running distance the week before the camp was
13 km/day. To accomplish such a long distance, subjects
participated in three practice sessions per day; 1st session
(5:30–7:30), athletes mainly performed long distance running
(group, individual, tempo running); 2nd session (8:30–12:30)
consisted of jogging, basic core, and lower body strength
training; 3rd session (14:00–18:30) consisted mainly of speed
development training such as repetition of 400- and 1,000-
m sprints. During the camp, all subjects were required to
participate all practice sessions, and their schedules were
strictly controlled, especially practice duration, meal times, and
sleep.
To determine the effect of the intervention on the
hemodynamic parameters, repeated measures analysis of
variance was performed. In the case of a significant F-value,
a post hoc test (the Bonferroni method) was performed to
identify significant differences in the mean values of interest.
For simple correlation analysis as well as to identify the
effect of training distance on aortic and brachial BP, three
subjects who did not engage any running practice during
the camp were excluded due to lower leg injuries. These
three subjects trained on the same schedule as others and
performed stationary bike training instead of running. Data
were reported as the mean ±SD. All comparisons were based
on a 95% confidence limit with P<0.05 considered statistically
significant.
RESULTS
After the camp, the athletes were divided into two groups: the
accomplished and unaccomplished group. The accomplished
group (n=24) achieved the daily and overall target, while
the unaccomplished group (n=12) did not complete the
training menu due to deconditioning during the camp. The
accomplished group constantly completed all training menu,
whereas the unaccomplished group mainly engaged to long
distance jogging and basic core and lower body strength training
without speed development training (e.g. repetition of 400- and
1,000-m sprints). During the camp, the accomplished group
completed a longer training distance than the unaccomplished
group (31 ±3 km/day vs. 13 ±10 km/day, P<0.001).
The completed training distance in the accomplished group
was approximately 2.5 times longer than 1 week before
the camp. Table 1 shows the physical characteristics and
hemodynamic parameters before and after the camp. There was
no significant group-difference in either physical characteristics
or hemodynamic parameters prior to the camp. After the
camp, excessive body weight loss, an indicator of dehydration,
was not observed. The heart rate, brachial BP, aortic AP,
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Tomoto et al. Short-Term Training and Aortic Pressure
FIGURE 1 | Aortic pulse wave analysis. Type A waveform: reflecting wave during early systole produces an augmented systolic pressure. Type C waveform: reflecting
wave during late systole produces a longer TRand Pi after Ps. AP, augmentation pressure; DTI, diastolic tension index; Pi, incident pressure from a reflecting pressure
wave; PP, pulse pressure; Ps, systolic pressure; TR, round-trip travel time of the reflecting pressure wave; TTI, tension-time index.
TABLE 1 | Physical characteristics and hemodynamic variables in unaccomplished and accomplished training group before and after the camp.
Unaccomplished group (n=12) Accomplished group (n=24)
Before After Before After
Height, cm 171 ±5 – 171 ±5 –
Weight, kg 58 ±5 58 ±5 58 ±4 58 ±4
Heart Rate, bpm 48 ±5 48 ±7 47 ±5 48 ±5
Brachial systolic BP, mmHg 109 ±4 109 ±4 110 ±8 112 ±8
Brachial Mean BP, mmHg 76 ±3 75 ±3 76 ±6 78 ±6
Brachial diastolic BP, mmHg 60 ±4 58 ±4 59 ±6 60 ±6
Brachial PP, mmHg 49 ±4 50 ±5 51 ±4 52 ±5
Aortic AP, mmHg −2±6 0 ±4 0 ±5 1 ±6
AIx, % −4±12 0 ±9−1±11 3 ±11
AIx75, % −17 ±13 −13 ±9−14 ±11 −11 ±11
TR, msec 173 ±10 175 ±7 172 ±10 167 ±11*
TTI, mmHg*ms 1,399 ±146 1,366 ±159 1,342 ±168 1,434 ±134*
DTI, mmHg*ms 3,096 ±172 3,129 ±215 3,115 ±290 3,186 ±316
SEVR, % 223 ±27 233 ±40 235 ±31 224 ±27
Data are mean ±SD. BP, blood pressure; MAP, mean arterial pressure; PP, pulse pressure; AP, augmentation pressure; AIx, augmentation index; AIx75, Alx corrected for heart rate at
75 beats per minutes; TR, round-trip travel time of the pressure wave from the heart to the peripheral reflected sites; TTI, time tension index; DTI, diastolic tension time integral; SEVR,
subendocarial viability ratio. *P<0.05 vs. before the camp.
AIx, and AIx75 were unchanged in both groups. The aortic
systolic BP and pulse pressure significantly increased after the
camp in the accomplished group (P<0.001) but not in the
unaccomplished group (Figure 2). In the accomplished group,
TRshortened and TTI increased significantly (P<0.01),
whereas DTI and SEVR did not significantly change after the
camp. The average training distance during the camp was not
significantly correlated with the changes in brachial systolic BP
and pulse pressure, whereas changes in aortic hemodynamic
measures were correlated with the average training distance:
aortic systolic BP, pulse pressure, TTI, and SEVR (Figure 3).
Individual changes in TRdid not correlate with corresponding
changes in aortic hemodynamic measures: aortic systolic BP
(r= −0.230, P=0.166); aortic pulse pressure (r= −0.055,
P=0.750); aortic AP (r=0.012, P=0.945), AIx (r= −0.016,
P=0.929), and AIx75 (r= −0.064, P=0.725); TTI (r= −0.203,
P=0.235); DTI (r=0.056, P=0.746); SEVR (r=0.250,
P=0.142).
DISCUSSION
The primary findings from the present study are as flows. First,
aortic systolic BP, pulse pressure, and tension-time index (TTI,
a surrogate index of the myocardial oxygen demand) were
significantly elevated after the camp in the accomplished group
but not in the unaccomplished group, whereas the brachial BP
remained unchanged in both groups. Secondly, the average daily
training distance was significantly correlated with the changes in
aortic systolic BP, pulse pressure, and TTI. These results suggest
that aortic BP is affected by a short-term vigorous training camp
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Tomoto et al. Short-Term Training and Aortic Pressure
FIGURE 2 | Change in aortic systolic blood pressure (A) and pulse pressure
(B) in the unaccomplished and accomplished groups before and after the
camp. *P<0.05 vs. before the camp.
even in highly trained elite endurance athletes partly due to a
greater training volume compared to usual.
To the best of our knowledge, this is the first study
demonstrating the acute elevation of aortic systolic BP and
pulse pressure in elite endurance athletes after short-term
endurance training camp characterized by a greater-than-
normal training volume. Such changes were associated with
a proximally greater than twice longer running distance
compared with 1 week before the camp. In addition, individual
changes in TTI, a surrogate index of oxygen demand, was
positively correlated and SEVR, surrogate indices of myocardial
oxygen consumption (Sarnoff et al., 1958) and sub-endocardial
perfusion (Buckberg et al., 1972), was correlated negatively
with the training distance during the camp. These results
suggest that increased training volume with short-term may
lead imbalance of myocardial oxygen demand and supply
and cause of myocardial fatigue. Our findings could expand
the evidence from the cross-sectional investigation that highly
trained marathon runners have a higher aortic BP compared with
age-matched recreationally active control subjects (Vlachopoulos
et al., 2010). More importantly, the training camp did not
significantly alter the peripheral BP, and individual changes
in peripheral BP were not associated with the training
distance during the camp. These results suggest that aortic
hemodynamic measures are more sensitive than peripheral
BP to acutely increased training volume. To confirm these
findings, prospective data linking aortic BP response to chronic
overtraining are needed.
The aortic pressure wave may be augmented by overlapping
the early return and high amplitude of the reflected wave
from the periphery (mainly from lower body) to the proximal
aorta on the forward traveling wave generated by the LV
ejection in-phase (Nichols and McDonald, 2011). In the present
study, TR(a surrogate index of aortic pulse wave velocity)
significantly correlated with other aortic hemodynamic measures
such as aortic systolic BP and PP. Therefore, increases in aortic
systolic BP and PP could not be explained by the early return
of the reflected wave from peripheral to the heart. In this
context, contrary to the traditional wave theory (Nichols and
McDonald, 2011), recent studies suggest that the reflected wave
component of arterial hemodynamics does not contribute to
augmented central pressure (Schultz et al., 2015; van Mil et al.,
2016). Furthermore, it has been also reported that the reflected
wave might become diminished until in the proximal aorta,
and it no longer possible to identify contributions to central
pressure augmentation (Davies et al., 2012). Growing evidence
suggests that major determinants of central BP waveform may
be the incident waves arising from left ventricular ejection
and proximal aortic compliance rather than the wave reflection
(Sharman et al., 2009; Davies et al., 2010; Schultz et al.,
2014).
The changes in central hemodynamic parameters in this study
were potentially impacted by repeated mechanical stress from
the heart, inflammatory state from muscle damage, and heart
accumulation from prolonged exercise training during summer.
First, repeated and particularly excessive stress imposed on the
elastic elements of the aortic wall may be a cause of their
mechanical fatigue which leads to elevating aortic BP (Nichols
and McDonald, 2011). Secondary, aortic BP is affected by
inflammatory state common observed in marathon runner after
the race (Knez et al., 2006, 2007). It is plausible that the vigorous
training-induced muscle damage and systemic inflammation
may contribute to elevating aortic BP (Jee et al., 2013). In the
present study, the participants of the camp practiced not only on
flat track conditions but also on up-and downhill courses; thus, a
large amount of exercise stress—especially eccentric contractions
during downhill running—was given to the muscle. Furthermore,
the 7-day training camp was conducted on summer, thus, the
prolonged exercise in the heat causes greater hyperthermia that
may yield heat acclimation. Further investigation to clarify the
underlying mechanisms for sustained aortic arterial pressure
elevation following vigorous intensity exercise training, especially
during heat stress, is needed.
Several experimental considerations should be noted. The
primary issue is the lack of recorded training intensity, such
as heart rate during exercise. For example, by multiplying
the duration of a training session by the average heart rate
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Tomoto et al. Short-Term Training and Aortic Pressure
FIGURE 3 | Relationships between the daily training distance and changes in brachial and aortic hemodynamics: brachial and aortic systolic blood pressure (SBP)
(A,C) and pulse pressure (PP) (B,D); aortic tension-time index (TTI) (E); sub-endocardial viability ratio (SEVR) (F).
achieved during a session (i.e., training impulse; Macdougall
et al., 1982), the training stimulus could be quantified in detail.
In addition, we did not evaluate the concomitant changes
in biochemical parameters (i.e., inflammation biomarker) and
autonomic nervous activity. Measuring these parameters may
yield insight on the mechanism of the increased aortic systolic
BP after the training camp.
Training programs for highly trained athletes are planned
with the repetition in the training cycle composed of intense
training periods followed by shorter recovery periods, such as
the repetition of over-reaching and super-compensation. The
imbalance between training volume/intensity and recovery can
lead to an advanced fatigue state (i.e., overtraining syndrome).
Therefore, useful (e.g., sensitive) markers to detect fatigue are
needed to prevent and manage overtraining for not only athletes
but also coaches. Since the strength of this study was a field
study with measured hemodynamics parameters in controlled
condition among well-trained endurance athletes before and
after the camp, the results of this study may provide the
consideration of planning short-term summer training camps.
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Tomoto et al. Short-Term Training and Aortic Pressure
In conclusion, in highly-trained elite endurance athletes, the
aortic systolic BP and pulse pressure increases acutely without
concomitant elevations in brachial BP after a 7-day training camp
characterized by a greater training volume compared with regular
training. These alterations might be associated with a greater
training volume.
AUTHOR CONTRIBUTIONS
TT, JS, AH, TI, and SO: Decided conception and design of
research; performed experiments; analyzed data; TT, JS, SM, and
SO: Interpreted results of experiments; TT and JS: Prepared
figures; TT, JS, and SO: Drafted manuscripts; TT, JS, AH, TI, SM,
and SO: Approved final version of manuscripts.
FUNDING
This study was funded by a Grant-in-Aid for Scientific Research
from the Japanese Ministry of Education, Science, and Culture
(Grant Numbers JP25702045 and JP26670116).
ACKNOWLEDGMENTS
We thank all subjects of this study and their team staffs.
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Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
The reviewer NF declared a shared affiliation, with no collaboration, with
one of the authors, SM, to the handling Editor.
Copyright © 2018 Tomoto, Sugawara, Hirasawa, Imai, Maeda and Ogoh. This is an
open-access article distributed under the terms of the Creative Commons Attribution
License (CC BY). The use, distribution or reproduction in other forums is permitted,
provided the original author(s) and the copyright owner are credited and that the
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practice. No use, distribution or reproduction is permitted which does not comply
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