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Research Article
High-Intensity Intermittent Swimming Improves Cardiovascular
Health Status for Women with Mild Hypertension
Magni Mohr,1,2 Nikolai Baastrup Nordsborg,3Annika Lindenskov,4Hildigunn Steinholm,5
Hans Petur Nielsen,6Jann Mortensen,7,8 Pal Weihe,9and Peter Krustrup1,3
1Sport and Health Sciences, College of Life and Environmental Sciences, St. Luke’s Campus, University of Exeter, Exeter EX12LU, UK
2Department of Food and Nutrition, and Sport Sciences, University of Gothenburg, 405 30 Gothenburg, Sweden
3Department of Nutrition, Exercise and Sports, Copenhagen Centre for Team Sport and Health, University of Copenhagen,
2100 Copenhagen, Denmark
4e Faroese Confederation of Sports and Olympic Committee, 100 Torshavn, Faroe Islands
5Department of Nursing, Faculty of Natural and Health Sciences, University of the Faroe Islands, 100 Torshavn, Faroe Islands
6Southern Hospital, e Faroese Hospital System, Faroe Islands
7Department of Medicine, e Faroese National Hospital, 100 Torshavn, Faroe Islands
8Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, Copenhagen University Hospital,
2100 Copenhagen, Denmark
9Department of Occupational Medicine and Public Health, e Faroese Hospital System, 100 Torshavn, Faroe Islands
Correspondence should be addressed to Magni Mohr; m.mohr@exeter.ac.uk
Received January ; Revised March ; Accepted March ; Published April
Academic Editor: David G. Behm
Copyright © Magni Mohr et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
To test the hypothesis that high-intensity swim training improves cardiovascular health status in sedentary premenopausal women
with mild hypertension, sixty-two women were randomized into high-intensity (𝑛=21; HIT), moderate-intensity (𝑛=21;MOD),
and control groups (𝑛=20; CON). HIT performed – × s all-out swimming interspersed by min recovery and MOD swam
continuously for h at moderate intensity for a -week period completing in total 44±1and 43±1 sessions, respectively. In CON, all
measured variables were similar before and aer the intervention period. Systolic BP decreased (𝑃 < 0.05)by6±1and 4±1mmHg
in HIT and MOD; respectively. Resting heart rate declined (𝑃 < 0.05)by5±1bpmbothinHITandMOD,fatmassdecreased
(𝑃 < 0.05)by1.1 ± 0.2 and 2.2 ± 0.3 kg, respectively, while the blood lipid prole was unaltered. In HIT and MOD, performance
improved (𝑃 < 0.05) for a maximal min swim (13 ± 3%and22 ± 3%), interval swimming (23 ± 3%and8±3%), and Yo-Yo IE
running performance (58 ± 5%and45 ± 4%). In conclusion, high-intensity intermittent swimming is an eective training strategy
to improve cardiovascular health and physical performance in sedentary women with mild hypertension. Adaptations are similar
with high- and moderate-intensity training, despite markedly less total time spent and distance covered in the high-intensity group.
1. Introduction
Arterial hypertension is associated with cardiovascular mor-
bidity and mortality, and it is well known that the risk of
arterial hypertension is markedly elevated by obesity and an
inactive lifestyle [,]. Additionally, there is strong evidence
that exercise training lowers arterial blood pressure, improves
aerobic tness, and counteracts several other cardiovascular
risk factors related to increased morbidity in patients with
mild to moderate hypertension [,], but it is still debated
whether the magnitude of training response is related to
exercise mode and the type of training performed.
e vast majority of studies investigating the relation-
ship between exercise training and cardiovascular health
responses have applied running, cycling, or team sports
participation as the training intervention [–], whereas
few have examined the eects of dierent aquatic exercise
regimes [–]. Swimming may be considered a good choice
Hindawi Publishing Corporation
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Volume 2014, Article ID 728289, 9 pages
http://dx.doi.org/10.1155/2014/728289
BioMed Research International
of training especially for obese middle-aged and elderly
individuals because it involves minimum weight-bearing
stress, which may reduce the risk of injury. In addition,
swimming engages the upper body musculature where the
potential for metabolic adaptation can be hypothesized to
be larger than in the postural musculature. However, little
information is available concerning the eects of regular
swimming exercise training on the cardiovascular health pro-
le. Nualnim and coworkers [] demonstrated that wks of
regular – min continuous moderate-intensity swimming
lowered systolic blood pressure (SBP) by mmHg in adults
older than yrs with mild hypertension. e swimming
exercise training also resulted in a % increase in carotid
artery compliance, as well as improvement in ow-mediated
dilation and cardiovagal baroreex sensitivity []. However,
no studies have compared dierent swim training regimes in
sedentary women suering from mild to moderate arterial
hypertension.
Lack of time is a common explanation why people fail
to participate continuously in traditional exercise regimes
based on prolonged session of moderate-intensity training.
erefore, it is of interest to explore the health eects of
short-duration exercise training protocols. Numerous nd-
ings indicate that brief high-intensity training appears to be
ecient in improving aerobic tness and other physiological
adaptations of importance for the cardiovascular health status
in untrained individuals [,,]. Moreover, short-term
sprint training apparently provoked similar muscle metabolic
and exercise performance adaptations as prolonged submax-
imal training protocols [,]. ese studies challenge the
pronouncement by sports medicine authorities that –
min of moderate-intensity exercise per week is required
to maintain a healthy lifestyle [,]andsupporttheidea
that min of vigorous exercise may be sucient []. For
example, Nybo et al. [] found dierences in the adaptive
response within several indicators of cardiovascular health
to short-duration high-intensity intermittent running com-
pared to prolonged submaximal continuous running, includ-
ing more pronounced eects on maximal oxygen uptake for
the high-intensity training group. is study was performed
on sedentary men, while Metcalfe et al. [] demonstrated
marked improvements in aerobic capacity and metabolic
health aer intensied cycling in sedentary participants of
both genders. However, it is currently unclear to what extent
women respond to submaximal prolonged versus short-
term high-intensity swim training. Gender dierences have
beenshowntobepresentwithinarangeofphysiological
adaptations to exercise training [,]. For example, women
appear to display smaller reductions in blood pressure aer
exercise training interventions in comparison to their male
counterparts [,,]. It is therefore of importance to inves-
tigate the eect of two types of swimming exercise training
on the cardiovascular disease risk prole in sedentary women
with mild to moderate hypertension.
us, the objective of the present study was to test the
hypothesis that high-intensity swim training is an ecient
strategy to reduce blood pressure and improve the cardiovas-
cular health prole in sedentary premenopausal women with
mild to moderate hypertension.
2. Materials and Methods
Sixty-two sedentary premenopausal women with mild to
moderate arterial hypertension were recruited for the study.
e subjects were selected among volunteers based on
training history, medication, blood pressure, and body mass
index. A total of participants were recruited. took part in
the present study and were randomly assigned to a football
group being part of another study []. In addition, the
control group ( participants) in the present study was also
thecontrolsintheabove-mentionedstudybyMohretal.[].
e study was approved by the ethical committee of the Faroe
IslandsaswellastheSportandHealthSciencesResearch
Ethics Committee at the University of Exeter, Exeter, UK, and
conducted in accordance with the Declaration of Helsinki
(). Aer being informed verbally and in writing of the
experimental procedures and associated risks, all participants
gave their written consent to take part in the study.
2.1. Experiment Design. e study was designed as a random-
ized controlled trial. Aer initial testing of the volunteers,
participants were enrolled in the present study based
on selection criteria being a sedentary lifestyle for the last
two years, mild hypertension (mean arterial pressure –
mmHg), and a body mass index >. Participants treated
with adrenergic beta-antagonists were excluded. Participants
using diuretics and ACE inhibitors (𝑛=4) were not excluded
from the study, but none of the four subjects changed their
medication during the intervention period. e participants
were randomized into a high-intensity intermittent swim-
ming training group (HIT: age 44 ± 2 (–) ±SEM (range)
yrs; height 164 ± 1cm; weight 76.5 ± 1.9 kg; 𝑛=21), a
moderate-intensity continuous swimming group (MOD: age
46 ± 2 (–) yrs, height 165 ± 1 cm, weight 83.8 ± 4.3kg;
𝑛=21), and a control group (CON: age 45 ± 2 (–) yrs,
height 166 ± 1 cm, weight 76.4 ± 2.6kg; 𝑛=20). e training
groups took part in two types of swimming training with
training sessions per week for wks, while CON had no
training or lifestyle changes in the same period. ere were
nodropoutsfromthestudy,butonesubjectintheMOD
group suered from aquatic phobia and was therefore moved
to CON. All subjects performed an intermittent swimming
sprint test and an endurance swimming test, as well as an
intermittent running test with heart rate recordings, and
had their blood pressure, resting heart rate (RHR), body fat
content, and blood cholesterol measured before and aer the
intervention. Finally, basic anthropometrical measurements
were performed. e pre- and posttests were conducted in
the same order. e posttness tests were conducted – h
aer the last training session. e training was continued
until the last measurement was obtained. e dietary intake
was not controlled during the training period and the testing
periodswerenottimedinrelationtothemenstrualcycle.
2.2. Training Intervention. e HIT participants completed
in total 44 ± 1 (–) training sessions over the -week
intervention period corresponding to 2.9 ± 0.1 (.–.)
sessions per week. Every session lasted ∼– min (– min
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of eective swimming) and consisted of – s all-out
free-style swimming (front crawl) intervals interspersed by
min of passive recovery aer training principles previously
described [,]. In the rst wks of training the partici-
pants completed intervals, the following wks included
intervals, and the nal wks consisted of all-out swimming
intervals. e MOD group completed a total of 43 ±1 (–)
training sessions over wks corresponding to 2.9 ± 0.1 (.–
.) training sessions per week. All MOD training sessions
lasted h and consisted of continuous front crawl swimming
where the participants were encouraged to swim as far as
possible in every session. Five trained swimming coaches
were present during all training sessions in order to give
technical advice and control the intensity and duration of
the training and to secure a safe training environment. Heart
rate was measured during one training session in week and
one session in week of the training intervention, and the
swimming distance was noted in every session.
2.3. Blood Pressure and RHR Measurements. e participants
reported to the hospital at : a.m. aer an overnight
fast and rested in a supine position for h. Systolic blood
pressure (SBP) and diastolic blood pressure (DBP) were
measured according to standard procedures []usingan
automatic BP monitor (HEM-; OMRON, IL, USA) once
every min over the h resting period. e average of the
four measurements was used as the test result. Mean arterial
pressure (MAP) was calculated as / SBP + / DBP. Resting
HR was measured during the same time intervals as the BP
recordings.
2.4. Resting Blood Sampling. A resting blood sample was
collected under standardized conditions from an antecu-
bital vein between : and : a.m. aer an overnight
fast using venipuncture technique. e blood was rapidly
centrifuged for s and analyzed by an automatic analyzer
(Cobas Fara, Roche, France) using enzymatic kits (Roche
Diagnostics, Germany) for determination of total cholesterol,
LDL-cholesterol, HDL-cholesterol, and triglyceride levels.
2.5. DXA Scanning. Whole-body body fat and lean body
mass were evaluated by total body DXA scanning (Norland
XR-, Norland Corporation, Norway). e body was seg-
mented in accordance with standard procedures to evaluate
regional fat distribution [], and all analyses were performed
using Illuminatus DXA soware (Norland Corporation, Nor-
way).eeectiveradiationdosewas<. mSv per scan.
2.6. Exercise Performance Testing. e participants in HIT
and MOD performed two front crawl swimming tests before
and aer intervention. To evaluate if the high-intensity
training improved the ability to repeatedly perform high-
intensity swimming more than moderate-intensity training,
a repeated swimming sprint test (RSST) composed of 4×25m
sprinting starting every s was performed. e participants
were instructed to swim each m as fast as possible. To
evaluate if continuous training was more ecient in improv-
ing continuous swimming performance, a min continuous
swimming test was performed. Swimmers were instructed
to complete the largest possible swimming distance during
the min. Swim testing was performed in a m pool at a
water temperature of ∘C. To evaluate if the swim-training
intervention improved exercise capacity in a land-based
activity, all participants additionally completed a shuttle-run
test. e Yo-Yo Intermittent Endurance test, level (Yo-Yo
IE), was completed before and aer the training period. e
Yo - Yo I E t e s t c o n s i s t s o f 2×20m shuttle runs interspersed
by a s recovery period consisting of 2×2.5mjogging(see
[]). ere is a gradual speed progression during the test,
whichiscontrolledbyaCDplayer[]. e participants
run until the point of exhaustion dened as the second
timetheyareunabletocompletethe2×20mrunsat
therequiredpace[]. Maximum heart rate (HRmax)was
determined during the test as previously described []. e
preintervention test was performed within ten days of the
rst training and the postintervention test four days aer
the last training session. e tests were conducted indoor
on a wooden surface at environmental temperatures between
and ∘C. e tests were preceded by a short warm-
up period consisting of the rst three of the 2×20m
shuttle runs, followed by a min recovery period before
the exhaustive test. Heart rate was measured continuously
during the tests using Polar Vantage NV chest belt monitor
weighing ∼ g (Polar Electro Oy, Kempele, Finland), and
HRmax was determined as previously described []. e pre-
and postintervention tests were conducted at the same time
of day. All participants were familiarized to all test procedures
prior to the experiment according to guidelines presented in
Bradley et al. []. e participants were instructed to avoid
exercise training and intake of alcohol the day prior to the
testing and nutritional items rich in caeine on the day of
testing. In addition, the participants were also instructed to
notethefoodintakeandfollowsimilarnutritionalguidelines
during the last h before both test periods.
2.7. Hip and Waist Circumference and Body Weight. Hip and
waist circumference was assessed as described by Kharal et al.
[]. Body mass was assessed by weighing the participant. e
weighing was performed in the morning aer an overnight
fast using a platform scale (Ohaus, Germany).
2.8. Statistical Analyses. Data are presented as means ±SEM.
Between- and within-group data were evaluated both by two-
factor mixed ANOVA design and with one-way ANOVA on
repeated measurements. When a signicant interaction was
detected, data were subsequently analyzed using a Newman-
Keuls post hoctest. Signicance level was 𝑃 < 0.05.
3. Results
3.1. Heart Rate and Distance Covered during Training. Aver-
age mean and peak HR during HIT training in the rst and
last weeks of the intervention was 158 ± 5 and 176 ± 2bpm,
respectively, corresponding to 85.5 ± 1.1 and 95.3 ± 1.1%
HRmax, respectively, which was higher (𝑃 < 0.05)than
average values in MOD (132 ± 4 and 144 ± 3 bpm equivalent
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to 72.5 ± 0.9 and 79.1 ± 1.0%HR
max). No dierences in
heart rate between the rst and last weeks of training were
detectable within either training group. In HIT the average
swim distance per session during the rst week was 131±7 m
and increased (𝑃 < 0.05)to269 ± 10mduringthelast
training week. Average swim distance per swimming interval
increased (𝑃 < 0.05)by28 ± 6%fromthersttothelast
training week. In MOD the average swim distance per session
was 1177 ± 41m during the rst training week and was
increased (𝑃 < 0.05)to1787 ± 35 m(52.8 ± 3.2%) during
the last training week.
3.2. Blood Pressure and Resting Heart Rate. Prior to the
intervention period, SBP and DBP were 138 ± 4 and 86 ±
3mmHg in HIT, 142 ± 4 and 87 ± 2mmHg in MOD, and
134 ± 4 and 82 ± 2mmHg in CON, respectively, with no
dierences between groups. In HIT, SBP decreased (𝑃<
0.05)by6±1mmHg (4±1%) during the wk intervention
period (Figure ), while the MOD group displayed a decrease
(𝑃 < 0.05)of4±1mmHg (3±1%) in SBP. DBP was similar
before and aer intervention for HIT and MOD (Figure ).
No signicant changes took place in neither SBP nor DBP in
CON (0±0and 0±0mmHg, Figure ). MAP was 103± 4 and
99 ± 2 mmHg before training in HIT and CON, respectively,
and tended (𝑃 = 0.06)todecrease(3±1mmHg, 3±1%) aer
intervention in HIT, with no changes in MOD or CON (−1±0
and 0±0mmHg, Figure ). Sixteen of the twenty-one subjects
in HIT experienced a decline in MAP during the intervention
period, with corresponding numbers in MOD being thirteen
out of twenty-one and eleven out of twenty in CON.
Resting HR decreased (𝑃 < 0.05)by5±1bpmoverwks
both in HIT (76 ± 2 to 71 ± 2 bpm) and MOD (78 ± 3 to 73 ±
2bpm), whereas it was not signicantly altered in CON (77±2
and 74 ± 2 bpm).
3.3. Body Fat, Lean Body Mass, and Anthropometry. Tot a l
body fat percentage was 43.1± 1.1,44.1±1.2,and41.0 ±1.2%
before training in HIT, MOD, and CON, respectively, and
decreased (𝑃 < 0.05)byasimilarmagnitudeto41.4± 1.2 and
42.1±1.0%inHITandMOD,respectively,withnochangein
CON (41.5± 1.1%). Total fat mass decreased by 1.1± 0.2 and
2.2± 0.3kg (𝑃 < 0.05) in HIT and MOD, respectively, during
thewksbutremainedsimilarinCON(Figure ). Lean
body mass increased (𝑃 < 0.05)by1.7 ± 0.3 and 1.3 ± 0.3 kg
in HIT and MOD, respectively, with no signicant changes in
CON (Figure ). Hip circumference was lowered (𝑃 < 0.05)
in MOD (108 ± 2 to 105 ± 2cm) but not in HIT (104 ± 1
to 103 ± 2cm) and CON (104 ± 1 to 103 ± 1cm). Waist
circumference declined (𝑃 < 0.05)inHIT(86±2 to 83±2 cm)
and MOD (94 ±3 to 89± 3cm) but was stable in CON (84±2
and 82±2 cm). Total body mass was lowered (𝑃 < 0.05)over
wks in HIT (76.5±1.9 to 75.9±2.1 kg) and MOD (83.8±4.3
to 82.4±4.0 kg), but remained similar in CON (76.4± 2.6 and
77.3 ± 2.2 kg) (Figure ).
3.4. Plasma Cholesterol and Triglycerides. To t a l p l a s ma
cholesterol was 5.6 ± 0.2,6.0 ± 0.2,and5.3 ± 0.2 mmol⋅L−1
before the training intervention in HIT, MOD, and CON,
CON MOD HIT
Systolic blood pressure (mmHg)
0
130
135
140
145
150
∗
∗
(a)
0wks
15 wks
Diastolic blood pressure (mmHg)
0
70
75
80
85
90
95
CON MOD HIT
(b)
F : Systolic and diastolic blood pressure before and aer
wks with thrice-weekly training sessions of hig h-intensity swim-
ming (HIT) and moderate-intensity swimming (MOD) in com-
parisontoaninactivecontrolgroup(CON).Dataarepresented
as means ±SEM. # denotes signicant within-group dierences.
∗denotes signicant dierence between the training groups and
CON.
respectively, and was similar aer the intervention period
(Table ). HDL and LDL cholesterol was 1.4±0.1and 3.7±0.2,
1.4 ± 0.1 and 3.9 ± 0.2,and1.4 ± 0.1 and 3.5 ± 0.2 mmol⋅L−1
before training in HIT, MOD, and CON, respectively, and was
unchanged aer the intervention period (Ta b l e ). Plasma
triglyceride was 1.1 ± 0.1,1.4 ± 0.1,and1.0 ± 0.1 mmol⋅L−1
in HIT, MOD, and CON before training, but was unchanged
aer the training intervention (1.0 ± 0.1,1.3 ± 0.2,and1.3 ±
0.2mmol⋅L−1).
3.5. Performance Testing. Before the training period, HIT
and MOD covered 306 ± 15 and 305 ± 16 m, respectively,
during the min maximal swim. Aer the training period,
performance was increased (𝑃 < 0.05)inHITandMOD
by 13 ± 3%and22 ± 3%, respectively, resulting in a
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T : Plasma total, HDL, and LDL cholesterol (mmol⋅L−1) before and aer a wks intervention period in HIT, MOD, and CON.
Total cho l e s t e r o l HDL LDL
Before Aer Before Aer Before Aer
HIT 5.6 ± 0.2 5.5 ± 0.2 1.4 ± 0.1 1.4 ± 0.1 3.7 ± 0.2 3.6 ± 0.2
MOD 6.0 ± 0.2 5.8 ± 0.3 1.4 ± 0.1 1.5 ± 0.1 3.9 ± 0.2 3.8 ± 0.3
CON 5.3 ± 0.2 5.4 ± 0.2 1.4 ± 0.1 1.3 ± 0.1 3.5 ± 0.2 3.4 ± 0.2
Data are expressed as means ±SEM.
Fat mass (kg)
0
28
30
32
34
36
38
40
42
CON MOD HIT
∗
∗
(a)
Lean body mass (kg)
0
36
38
40
42
44
46
48
50
0wks
15 wks
CON MOD HIT
∗
∗
(b)
F : Changes in body composition, including fat mass, lean
body mass, and total body weight aer wks with thrice-weekly
training sessions of high-intensity swimming (HIT) and moderate-
intensity swimming (MOD) in comparison to an inactive control
group (CON). Data are presented as means ±SEM. ∗denotes
signicant dierence between the training groups and CON.
total distance of 342 ± 14mand368 ± 15 m(Figure (a)).
e improvement in MOD tended (𝑃 = 0.07)tobehigher
than in HIT. Mean accumulated swimming time in the 4×
25m repeated sprint test was 153 ±9 and 141±5sinHITand
MOD, respectively, before the intervention. Aer training,
accumulated swimming time was reduced (𝑃 < 0.05)inboth
groups by 23 ± 3 and 8±3%, respectively, reaching 116 ± 7
and 129±6 s. HIT reduced their accumulated swimming time
more (𝑃 < 0.05)thanMOD(Figure (b)).
Yo-Yo IE performance before intervention was –
m in the three groups (𝑃 > 0.05)andincreased(𝑃 < 0.05)
similarly by 58 ± 5 and 45 ± 4% aer training in HIT and
MOD, respectively, with no changes in CON (Figure (a)).
HR aer the initial ve 2×20mrunswas92.5 ± 1.1,
94.1 ± 1.0,and92.3 ± 1.0%HR
max before training in HIT,
MOD, and CON, respectively, but was reduced (𝑃 < 0.05)
similarly by 4.5± 0.5 and 3.5±0.4% aer intervention in HIT
and MOD, respectively (88.0 ± 1.4 and 90.6 ± 1.2%HR
max,
resp.) whilst HR remained similar in CON (93.2 ± 0.7%
HRmax;Figure (b)). No dierence was detected in shuttle-
run performance or heart rate response between HIT and
MOD.
4. Discussion
e present study is the rst to examine if two dierent
types of swim training can improve the cardiovascular health
prole and land-based exercise capacity in sedentary pre-
menopausal women with mild to moderate hypertension. e
principal ndings reveal that both short-term intermittent
high-intensity and prolonged moderate-intensity swim train-
ing reduced systolic blood pressure and improved both water
andland-basedexercisecapacities.BecausetheHIgrouponly
covered ∼–% of the total mileage and spent one-third of
time on training compared to the moderate-intensity training
group, high-intensity intermittent training appears to be a
time-ecient alternative to traditional recreational training
regimes in untrained individuals.
e present ndings support that swim training appears
to have a high potential in the treatment of patients with
arterial hypertension, which is supported by others applying
aquatic training protocols [–,]. For example, similar
decreases in blood pressure were reported by Tanaka et al.
[] and Nualnim and coworkers [] demonstrated that
wks of regular swim training lowered SBP by mmHg in
adults older than yrs with mild hypertension. In addition,
the swim exercise training also produced a % increase
in carotid artery compliance, as well as improvements in
ow-mediated dilation and cardiovagal baroreex sensitivity
[]. In addition, in a cross-sectional study, middle-aged
swimmers had a lower carotid systolic blood pressure and
carotid pulse pressure than sedentary controls. Moreover,
carotid arterial compliance was higher and 𝛽-stiness index
was reported to be lower in the swimmers in comparison
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CON MOD HIT
Yo-Yo IE1performance (m)
0
100
200
300
400
500
600
700
800
900
∗
∗
(a)
0wks
15 wks
CON MOD HIT
0
86
88
90
92
94
96
98
100
∗
∗
Submax. Yo-Yo IE1HR (%HRmax)
(b)
F : Yo-Yo Intermittent Endurance level performance (a) as
well as heart rate aer controlled intermittent submaximal exercise
(%HRmax, (b)) before and aer wks with thrice-weekly training
sessions of high-intensity swimming (HIT) and moderate-intensity
swimming (MOD) in comparison to an inactive control group
(CON). Data are presented as means ±SEM. ∗denotes signicant
dierence between the training groups and CON.
to the controls []. us, both intermittent high-intensity
and continuousmoderate-intensity swimming can be recom-
mended for adults with mild hypertension.
In some review articles it is suggested that low-to-
moderate-intensity exercise regimes are more ecient than
protocols encompassing high-intensity exercise []. How-
ever, in the present study both training groups’ SBP was
lowered by -%, which conrms ndings in untrained men
in their midthirties performing intense intermittent and con-
tinuous moderate-intensity running []. In the study by Nybo
et al. [], SBP was lowered in both training groups, but only
DBP declined in the continuous moderate-intensity group,
while mean arterial pressure (MAP) declined aer both types
of training. In the present study DBP was unchanged in both
swim training groups, and MAP tended (𝑃 = 0.06)todecline
Endurance swimming performance (s)
0
240
260
280
300
320
340
360
380
400
MOD HIT
∗
∗
(a)
Repeated swimming sprint test (s)
0
90
100
110
120
130
140
150
160
170
180
0wks
15 wks
MOD HIT
∗
#
∗
(b)
F : Endurance swimming performance (a) and repeated
swimming sprint time (b) before and aer wks with thrice-
weekly training sessions with high-intensity swimming (HIT) and
moderate-intensity swimming (MOD) in comparison to an inactive
control group (CON). Data are presented as means ±SEM. ∗
denotes signicant dierence between the training groups and
CON. # denotes signicant dierences between HIT and MOD.
only in the high-intensity training group with % of the par-
ticipants demonstrating a reduction. us, the discrepancy
between ndings by Nybo et al. []andthepresentstudymay
relate to the dierences in training mode, since exercise in
a supine position may provide a dierent training stimulus
to cardiovascular parameters compared to upright exercise
modes such as running due to the dierences in ventricular
volumes []. Moreover, gender dierences have been shown
to be present within a range of physiological adaptations to
exercise training [,]. Nybo et al. []usedmaleparticipants
and women seem to display smaller reductions in blood
pressure aer exercise training interventions in comparison
to their male counterparts [,,]. In contrast Ishikawa
et al. [] demonstrated that the gender did not inuence
the ecacy of physical activity for lowering elevated blood
pressure.
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In a recent study by Rocha et al. []isogenicrats
were exposed to swim training at low, moderate, and high
intensities and large morphological alterations in the cardiac
myocytes occurred aer high-intensity training in compar-
ison to low and moderate intensities. ese ndings are in
line with several recent review papers supporting that high-
intensity training markedly reduced arterial blood pressure
[,,]. In addition, supportive of this notion are several
studies on cardiovascular eects of recreational football
training from our laboratory on sedentary men [,,]
and women [,]. us, the rapid acceleration of heart rate
andstrokevolumeduringsquare-wavetransitionsfromlow-
to high-intensity exercise as performed in the high-intensity
traininggroupinthepresentstudymaybeanimportant
stimulus to blood pressure reduction. is suggestion is
backedupbythesimilarresponsesobservedinthetwo
training interventions despite large dierences in training
volume.
In the present study total fat mass was reduced and
lean body mass increased in both training groups. In the
aforementioned study by Nybo et al. [] with untrained
men high-intensity running did not change fat mass or
fat oxidation during submaximal exercise. In contrast, the
moderate-intensity running group displayed a reduction in
fat mass as in the present study. Studies by Tjønna et al.
[,] and Schjerve et al. [] compared “isocaloric” high-
intensity and moderate-intensity training and found major
advantages of the high-intensity training regimes. However,
in these studies the overall energy turnover was matched in
contrast to the present study. erefore, it may be surprising
that the reduction in fat mass was not dierent between the
HIT and MOD interventions despite the large dierence in
total energy turnover. e caloric intake was not controlled
in the present study, which may have aected the body fat
adaptations. For example, it has recently been demonstrated
that appetite regulating variables such as leptin are aected
by high-intensity training []. Additionally, the ndings in
the present study are supported by others showing marked
decreases in body fat content aer high-intensity training
[–].
No changes were observed in blood lipid prole in the
present study, which is in contrast to ndings by others
demonstrating that prolonged moderate-intensity running
reduces total/HDL-cholesterol ratio and elevates fat oxidation
during exercise in contrast to brief intense interval training
[]. It is suggested that changes in blood lipid prole relates
to changes in fat mass [], and in the present study no
statistical dierences were evident between the reduction in
body fat between the two interventions, which may partly
explain the similar blood lipid responses. One explanation
for the above-mentioned discrepancy might be that some
of the participants in the present study had normal plasma
cholesterol levels prior to the intervention. If the participants
who had total cholesterol levels lower than . mmol⋅L−1 were
excluded from the statistical analysis, there was a signicant
reduction in total cholesterol in the MOD training group and
a tendency (𝑃 < 0.06)toareductioninHIT(datanotshown),
indicating that women with high plasma cholesterol levels are
more likely to respond to exercise.
e improved performance aer high-intensity as well
as moderate-intensity swimming conducted in the present
studymayberelatedtoanimprovedphysiologicalcapacity,
improved swimming technique, or both. e rather large
∼% improvement in land-based shuttle-run performance
observed in the two swim-training groups, but not in the
control group, strongly indicates that physiological adapta-
tions are a major contributor for the augmented exercise
capacity observed during both shuttle runs and swim tests.
is is further supported by the ∼% heart rate reduction
observed aer the initial ve 2×20m runs indicating
improved aerobic capacity. Previously, the possible transfer
eect between swim training and land-based activity has
been neglected. is is largely because increases in maximal
oxygen uptake aer swim training appear to be specic for
that exercise modality as observed in monozygotic twins
[] and an observation of unchanged running VO2max,
despite increased swimming VO2max in elite swimmers aer
monthsofintensetraining[,]. However, shuttle-run
performance is not strongly correlated to VO2max [,]
and the current observation suggests that possible benecial
health adaptations obtained aer swim training also translate
into improved land-based exercise capacity. However, it
also appears likely that a technical improvement may have
occurred during the swim training. It can be speculated
that the much higher total distance covered by the MOD
group caused greater technical improvements than in the
HITgroupandthatthisisthereasonforthetendency
to a larger performance gain in the min swim test of
the MOD group. e larger improvement observed for the
HIT than MOD group in repeated sprint swimming ability
could be related to more specic motor learning leading to
larger improvements in sprint technique in this group but
could also be due to metabolic and physiological adaptations
specic to sprinting. For example, high-intensity training is
known to recruit more fast type II muscle bres [,]
which could have yielded greater muscle hypertrophy and
more pronounced enzymatic adaptations in type II bres
for the high-intensity group compared to the moderate-
intensity training group []. Physiological adaptations that
would favor improvements in intense short-duration exercise
performance such as in the interval sprint test may be part of
the explanation for the greater eect on sprint performance in
the high-intensity swimming group ( versus %). However,
these suggestions remain speculative and warrant further
investigation.
In conclusion, high-intensity intermittent swimming is
a time-ecient and eective training method and improves
cardiovascular health and physical performance in sedentary,
premenopausal women with mild hypertension. Adaptations
are similar with high- and moderate-intensity training,
despite less total time spent and distance covered in the high-
intensity group.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
BioMed Research International
Acknowledgments
e great eort and positive attitude by the participants
are highly acknowledged. In addition, the technical assis-
tance of Remi Lamhauge, Brynhild Klein, Pauli Øssursson
Mohr, Heini Rasmussen, Olua a Høvdanum, Jakup Mohr,
Ivy Hansen, GunnriðJ´
oannesarson, GuðriðAnd´
orsd´
ottir,
HergerðJoensen, Ann Østerø, Ebba Andreassen, Maud av
Fløtum, Liljan a Fløtum Petersen, Marjun omsen, David
Childs, Sarah Jackman, and Jens Jung Nielsen is greatly
appreciated. e study was supported by a grant from the
Faroese Research Council, e Faroese Confederation of
Sports and Olympic Committee (Itrottarsamband Foroya),
and the Danish Sports Confederation (Danmarks Idrætsfor-
bund). In addition, nancial support was obtained from Eik
Bank.
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