EURO PEAN
SO CIETY O F
CARDIOLOGY ®
Original scientific paper
Heart rate response to exercise and
cardiorespiratory fitness of young women
at high familial risk for hypertension:
effects of interval vs continuous training
European Journal of Cardiovascular
Prevention & Rehabilitation
0(00) 1–7
! The European Society of
Cardiology 2011
Reprints and permissions:
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DOI: 10.1177/1741826711398426
ejcpr.sagepub.com
Emmanuel G Ciolac1,2, Edimar A Bocchi3, Julia MD Greve1 and
Guilherme V Guimarães2,3
Abstract
Exercise training is an effective intervention for treating and preventing hypertension, but its effects on heart rate (HR)
response to exercise and cardiorespiratory fitness (CRF) of non-hypertensive offspring of hypertensive parents (FHþ)
has not been studied. We compared the effects of three times per week equal-volume high-intensity aerobic interval
(AIT) and continuous moderate-intensity exercise (CME) on HR response to exercise and CRF of FHþ. Forty-four
young FHþ women (25.0 4.4 years) randomized to control (CON; n ¼ 12), AIT (80–90% of VO2MAX; n ¼ 16), or CME
(50–60% of VO2MAX; n ¼ 16) performed a graded exercise test (GXT) before and after 16 weeks of follow-up to evaluate
HR response to exercise and several parameters of CRF. Resting, maximal, and reserve HR did not change after the
follow-up in all groups. HR recovery (difference between HRMAX and HR at 1 minute of GXT recovery phase) improved
only after AIT (11.8 4.9 vs. 20.6 5.8 bpm, p < 0.01). Both exercise programmes were effective for improving CRF
parameters, but AIT was more effective than CME for improving oxygen consumption at the respiratory compensation
point (VO2RCP; 22.1% vs. 8.8%, p ¼ 0.008) and maximal effort (VO2MAX; 15.8% vs. 8.0%, p ¼ 0.036), as well as tolerance
time (TT) to reach anaerobic threshold (TTAT; 62.0 vs. 37.7, p ¼ 0.048), TTRCP (49.3 vs. 32.9, p ¼ 0.032), and TTMAX
(38.9 vs. 29.2, p ¼ 0.042). Exercise intensity was an important factor in improving HR recovery and CRF of FHþwomen.
These findings may have important implications for designing exercise-training programmes for the prevention of an
inherited hypertensive disorder.
Keywords
Cardiorespiratory fitness, exercise, heart rate, hypertension, prevention
Received 29 June 2010; accepted 6 January 2011
Introduction
Essential arterial hypertension is the most common risk
factor for cardiovascular morbidity and mortality,
and is associated with substantial healthcare expenditure.1 Family history of hypertension represents a
major risk factor for future hypertension in non-hypertensive offspring.2 Moreover, non-hypertensive offspring of hypertensive parents (FHþ) have shown
several haemodynamic, metabolic, and neuro-humoral
abnormalities.3 Poor cardiac autonomic control of the
nervous system, evaluated by the heart rate response
during a graded exercise test (GXT), and cardiorespiratory fitness (CRF) are independent risk factors for
hypertension, cardiovascular disease and mortality,
and all-cause mortality.4–6 However, the heart rate
response to GXT and several parameters of CRF has
not been studied in FHþ.
1
Institute of Orthopedics and Traumatology do Hospital das Clı́nicas da
Faculdade de Medicina da Universidade de São Paulo, Laboratory of
Kinesiology, São Paulo, Brazil.
2
Centro de Práticas Esportivas da Universidade de São Paulo, Laboratory
of Physical Activity and Health, São Paulo, Brazil.
3
Heart Institute do Hospital das Clı́nicas da Faculdade de Medicina da
Universidade de São Paulo, São Paulo, Brazil.
Corresponding author:
EG Ciolac, Instituto de Ortopedia e Traumatologia do HCFMUSP,
Laboratório de Estudos do Movimento, Rua Dr. Ovı́dio Pires de
Campos, 333, Sao Paulo 05403-010, Brazil
Email: [email protected]
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2
European Journal of Cardiovascular Prevention & Rehabilitation 0(00)
Physical activity and exercise has shown to reduce
the incidence of hypertension,7,8 to reduce blood pressure (BP) in hypertensive9–11 and normotensive subjects,12 and to improve several factors involved in
the pathophysiology of hypertension.11–14 A small
number of cross-sectional studies are suggestive of
exercise-induced reduction in the cardiovascular
response to stress15,16 and sympathetic activity17,18
in FHþ. Recently, when comparing the effects of
high-intensity interval training (AIT) versus continuous moderate-intensity exercise (CME) on haemodynamic, metabolic, and neuro-humoral abnormalities of
young FHþ women, we have shown that both exercise
programmes were effective, but AIT was superior to
CME in reversing several haemodynamic, metabolic,
and hormonal alterations involved in the pathophysiology of hypertension.12 However, the effects of
exercise training on heart rate response to GXT
and several parameters of CRF have not been studied
in FHþ.
The aim of the present study was therefore to assess
the effects of AIT versus CME on heart rate response to
GXT and CRF of young FHþ women. We hypothesized that AIT is superior to CME for improving these
variables in FHþ women.
Methods
Population and study design
We studied 44 healthy young college women FHþ,
randomly assigned to AIT (n¼16), CME (n ¼ 16), or
control group (CON; n ¼ 12). All women were 20–30
years, had BP below 130/80 mmHg (measurements on
two different occasions on triplicate at 2-minute intervals), and had regular menstrual cycle confirmed by
questionnaire. Positive family history of hypertension
was defined as treatment for essential hypertension
for at least 2 years confirmed by records of the parents’ physicians. Exclusion criteria included use of
medication or oral contraceptive, presence of any
kind of disease (based on history, medical examination, and exercise stress testing), and smoking.
Pregnancy or lactation, and involvement in regular
physical activity or exercise programme during
the previous 12 month were also exclusion criteria.
A maximal GXT was performed at morning (between
9:00 and 12:00 a.m.), before and after 16 weeks of
follow-up, for analyses of CRF and heart rate
response to exercise. After a detailed explanation of
the study design and protocol, written informed consent was obtained from each subject before participation as approved by the ethics committee at our
institution. Subjects’ characteristics at inclusion are
summarized at Table 1.
Table 1. Subject characteristics
Variable
History of hypertension
Father
Mother
Both
Age (years)
Weight (kg)
BMI (kg/m2)
Waist circumference (cm)
Waist-to-hip ratio
Office BP (mmHg)
Systolic
Diastolic
AIT
(n ¼ 16)
CME
(n ¼ 16)
CON
(n ¼ 12)
2
9
5
24.4 3.8
62.1 12.5
23.5 4.8
80.6 10.8
0.85 0.04
5
3
8
26.6 4.9
63.5 12.6
24.3 4.6
81.4 11.2
0.86 0.04
4
4
4
25.3 3.7
61.4 11.0
23.8 3.9
79.6 12.0
0.84 0.07
106.1 9.9 105.3 9.3 105.9 8.3
65.1 9.5 64.9 6.8 62.3 8.0
AIT, aerobic interval training; BMI, body mass index; BP, blood pressure;
CME, continuous moderate exercise; CON, control group.
Graded exercise test
Volunteers were asked to refrain from strenuous physical activities and caffeine or alcohol content beverages
for 24 hours prior to the GXT. Testing was carried
before and after 16 weeks of follow-up, at morning
(between 9:00 and 12:00 a.m.), during the follicular
phase of volunteers’ menstrual cycle, 4 hours after the
last meal and after 1 hour of rest in the supine position.
GXT was performed on a programmable treadmill
(TMX425 Stress Treadmill; TrackMaster, Newton,
KS, USA) in a temperature-controlled room
(21–23 C) using a ramp protocol until exhaustion as
previously described.3 Cardiac rhythm was continuously monitored by electrocardiogram of 12 derivations
(CardioSoft 6.5; GE Medical Systems IT, Milwaukee,
WI, USA), and was recorded for 10 seconds at end of
rest, end of each warm-up and exercise stage, and each
1 minute of recovery. BP was measured at end of rest,
end of each exercise stage, and each 1 minute of recovery (Tango Stress BP; SunTech Medical, Morrisville,
NC, USA). Ventilation (VE), oxygen uptake (VO2),
and carbon dioxide output (VCO2) were measured
breath-by-breath by a computerized system (Vmax
Encore29; SensorMedics, Yorba Linda, CA, USA).
The respiratory exchange ratios (RER) were recorded
as the averaged samples obtained during each stage of
the protocol. The highest VO2 level was considered the
maximal value (VO2MAX). Anaerobic threshold (AT)
was determined by the V-slope method, and respiratory
compensation point (RCP) was determined as the point
at which a rapid rise in VE/VCO2 and a fall in partial
pressure of CO2 were observed.19 AT and RCP were
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Ciolac et al.
3
identified by two experienced observers, blinded for the
subjects’ group, and were used for exercise prescription.
When there was divergence between the two, a third
observer was consulted in order to reach a consensus.
Heart rate resting (HRRESTING), maximal (HRMAX),
reserve (HRRESERVE), and recovery (HRRECOVERY; difference between HRMAX and heart rate at 1 minute of
GXT recovery phase) were compared among groups.
The VO2 at the AT (VO2AT), RCT (VO2RCP), and
VO2MAX, the tolerance time to reach AT (TTAT), the
tolerance time to reach RCP (TTRCP), and the total
tolerance time (TTMAX) at the GXT were also compared among groups.
Exercise-training protocol
Both AIT and CME groups performed a three-timesa-week endurance training programme (walking/running on a treadmill) for 16 weeks, under supervision
of an exercise specialist. CON group did not have any
exercise intervention and subjects were instructed
to maintain their habitual activities during follow-up.
All subjects were instructed not to add any leisure exercise during the study period. Exercise session consisted
of 5 minutes of warm-up, 40 minutes of endurance exercise (AIT or CME), and 15 minutes of calisthenics.
Endurance exercise intensity was determined according
to the workload reached during the GXT and was prescribed to promote the same cardiovascular workload
for both AIT and CME. AIT consisted of 2 minutes
walking at a speed corresponding to AT heart rate
(50–60% of VO2MAX) alternating with 1 minute of running at a speed corresponding to CRP heart rate (80–
90% of VO2MAX) for 40 minutes. CME consisted of
40 minutes walking at a speed corresponding to 60–
70% of VO2MAX, representing the same total training
load as the AIT. All subjects exercised using a heart rate
monitoring device during every training session, to
ensure that the subjects were training on their corresponding heart rate relative to VO2MAX. The speed of
the treadmill was continually adjusted along as training
adaptations occurred, to ensure that all training sessions
were carried out at the desired heart rate throughout the
16-week training period. An exercise-training compliance of 70% was set as criteria for completing the study.
Statistical analyses
All data are reported as mean standard deviation.
The statistical program SPSS 12.0 for Windows
(SPSS, Chicago, IL, USA) was used to perform the
statistical analysis. The Kolmogorov–Smirnov test
was applied to ensure a Gaussian distribution of the
data. One-way ANOVA was used to indicate inter
group differences in the baseline subjects’
characteristics and in the CRF changes during followup. Inter and intra-group comparisons of the variables
were made by two-way ANOVA (group vs. time) with
repeated measurements. Bonferroni post-hoc analysis
was used to identify significant group differences that
were indicated by one-way and two-way ANOVA. The
significance level was set at p < 0.05.
To obtain an estimate of the effect size we might
expect for the variables in our sample, we relied on
the results of exercise-training studies similar to
ours.14,20,21 Considering that the results of those studies
produced a 5.5–35% increase in VO2MAX, with the
lower increases being promoted by continuous moderate exercise (5.5–16%), we estimated that an overall
sample of 12 subjects for each group would be required
to provide a power of 85% to detect a VO2MAX change
of 10% with a two-sided alpha of <0.05.
Results
During the experimental period, 10 volunteers were
unable to complete the study: seven were unable to
complete the exercise programme for personal reasons
(four AIT and three CME group) and three did not
have the minimal exercise-training compliance of 70%
(one AIT and two CME group). There were no significant differences for the baseline characteristics between
the subjects that complete and do not complete the
study (data not shown).
The mean training heart rate was 128 11 (AT
workload) and 161 13 (RCP workload) to AIT and
143 13 bpm to CME. The AIT training speed
increased from 5.3 0.5 to 6.1 0.5 km/h (AT workload) and 8.3 1.2 to 10.3 1.7 km/h (RCP workload),
and CME training speed increased from 6.4 0.4 to
7.2 0.5 km/h, which resulted in a greater mean workload increase in ATI than CME (19.7 9.6% vs.
12.4 5.5%, p ¼ 0.009).
GXT parameters are displayed in Table 2. There
were no significant changes in HRRESTING (p ¼ 0.246),
HRRESERVE (p ¼ 0.297), and HRMAX (p ¼ 0.663)
during the follow-up in all groups. However,
HRRECOVERY improved only in the AIT (p < 0.01).
Both AIT and CME were effective for improving
VO2MAX, VO2AT, and VO2RCP, but AIT were more
effective than CME for improving VO2MAX and
VO2RCP (Figure 1). AIT were also more effective
for improving TTAT (AIT ¼ 62.0 17.6%; CME ¼
37.7 18.7%; p ¼ 0.048), TTRCP (AIT ¼ 49.3 16.5%;
CME ¼ 32.9 16.8%;
p ¼ 0.032),
and
TTMAX (AIT ¼ 38.9 14.2%; CME ¼ 29.2 11.4%;
p ¼ 0.042). With these improvements, AIT group displayed higher post-exercise TTMAX (p < 0.008), TTAT
(p < 0.008), and TTRCP (p < 0.001) when compared to
both CME and CON group. All variables analysed did
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4
European Journal of Cardiovascular Prevention & Rehabilitation 0(00)
Table 2. Graded exercise test parameters before and after the experimental protocol
AIT (n ¼ 11)
CME (n ¼ 11)
CON (n ¼ 12)
Variable
Before
After
Before
After
Before
After
HRRESTING (bpm)
HRRESERVE (bpm)
HRMAX (bpm)
HRRECOVERY (bpm)
VO2AT (ml/kg/min)
VO2RCP (ml/kg/min)
VO2MAX (ml/kg/min)
RER
TTAT (min)
TTRCP (min)
TTMAX (min)
80 11
103 16
182 11
12 6
17.3 2.9
24.4 4.4
29.3 3.6
1.13 0.07
4.5 1.2
8.5 1.2
11.3 1.3
77 11
109 13
186 6
21 8a
19.9 2.9a
29.8 5.0a
33.9 4.6a
1.12 0.07
6.7 0.8a
12.5 0.9a
15.5 1.6a
78 9
105 11
183 11
15 7
17.4 4.0
25.1 4.4
29.9 4.0
1.12 0.08
3.8 1.1
7.7 1.8
10.4 1.8
77 11
112 10
186 7
15 4
19.1 3.7a
27.3 5.2a
32.3 5.6a
1.12 0.05
5.3 1.3a,b
10.1 1.9a,b
13.3 1.7a,b
79 11
105 16
185 12
11 6
18.2 3.7
25.1 4.0
29.8 3.5
1.12 0.08
4.3 1.2
8.4 1.3
11.0 1.9
79 11
105 16
185 12
11 6b
18.2 3.7
25.1 4.0
29.8 3.7
1.12 0.08
4.1 1.0b
8.3 1.0b,c
11.1 1.3b,c
a
Different from before follow-up at same group (p < 0.01). bDifferent from AIT at same period (p < 0.05). cDifferent from CME at same period
(p < 0.05). AIT, aerobic interval training; CME, continuous moderate exercise; CON, control group; HR, heart rate; TT, tolerance time; VO2,
oxygen uptake.
AIT
CME
Percentage of increase (%)
3
2
a
a
1
0
VO2MAX
VO2RCP
Figure 1. Exercise-induced increase in VO2MAX and VO2RCP
after 16 weeks of exercise training aDifferent from AIT
(p < 0.05). AIT, aerobic interval training; CME, continuous
moderate exercise.
not change significantly in the CON group after the
follow-up.
Discussion
The primary finding of the present study is that exercise
intensity was an important factor for improving CRF
and HRRECOVERY of non-hypertensive young women
offspring of hypertensive parents. To the best of our
knowledge, this is the first prospective study that evaluates the effects of exercise training on HRRECOVERY
and submaximal markers of CRF in non-hypertensive
FHþ women.
The higher increase in VO2MAX after AIT
(15.8 6.3%) than CME (8.0 6.1%) observed in the
present study is in line with previous studies that have
showed greater efficiency of high-intensity interval
training over moderate-intensity exercise in improving
VO2MAX of different populations.12,14,20,21 Greater
VO2MAX increase after AIT than CME (35% versus
16%) was observed in subjects with metabolic syndrome following a three-times-a-week exercise programme for 16 weeks.14 In endurance-trained young
men, two different high-intensity AIT (15/15 seconds
or 4/3 minutes of running/active resting at 90–95% or
70% of HRMAX, respectively) were more effective than
two different moderate-intensity steady state exercise
(running at 70% or 85% of HRMAX) for improving
VO2MAX after 8 weeks of follow-up.20 The present
study adds important information showing that AIT
is also superior to CME for improving several markers
of submaximal aerobic capacity, including VO2RCP,
TTAT, and TTRCP. The superiority of AIT for improving VO2RCP and TTRCP may have important implications for the leisure time and daily living activities, since
that physical activity intensity above the VO2RCP is
often accompanied by dyspnoea and early fatigue.19
Moreover, because reduced tolerance to submaximal
exercise has shown to be an independent predictor of
all-cause mortality,22 the greater improvement in submaximal markers of CRF following AIT may also have
important implications for long-term prognosis.
Although it has been suggested that stroke volume is
the main factor that limits CRF, and that the reason for
the superiority of AIT for improving CRF is based on
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Ciolac et al.
5
its greater challenge for the pumping ability of the heart
during the short work periods at higher intensities,14
the greater increase of submaximal aerobic capacity
(VO2RCP and TTRCP) observed after 16 weeks of AIT
also suggests its superiority for improving peripheral O2
uptake. The reason for these peripheral adaptations
is not fully understood but probably reflects a
greater improvement on Ca2þ cycling and mitochondrial capacity.14
Abnormal autonomic nervous system activity is an
independent risk factor for hypertension, cardiovascular disease and mortality, and all-cause mortality that is
presented in FHþ.3,12 On the other hand, a previous
study has demonstrated that exercise training improves
autonomic nervous system response to exercise, measured by norepinephrine response to GXT, of young
non-hypertensive FHþ women, and that better
improvements were observed after AIT than CME.12
In the present study, we used the heart rate response
to GXT to evaluate the autonomic nervous system
activity, an easy and inexpensive tool that provides a
wealth of information for the interaction of the autonomic nervous system and cardiovascular system at various phases of rest, exercise, and recovery,4,5 and found
a reduced HRRECOVERY after 16 weeks of AIT, but not
CME, confirming the greater benefits of AIT for the
autonomic nervous system of FHþ subjects previously
shown.12 HRRESTING, HRRESERVE, and HRMAX did
not change significantly during follow-up in all
groups. Since that the initial increase in heart rate
during exercise is caused by a withdrawal in parasympathetic activation followed by an increase in sympathetic tone, which further increases during exercise,
and HRRECOVERY is mainly related to an increase in
vagal tone which occurs immediately after exercise cessation,23 the improvement in HRRECOVERY observed
only after AIT suggests a greater exercise-induced
improvement in parasympathetic reaction of FHþ
women following AIT than CME. One must argue
that the lack of change in HRRESTING after both AIT
and CME may suggests absence of improvements in
autonomic nervous system reaction at rest. However,
different from the heart rate response to exercise, the
simply measure of HRRESTING may be influenced by
numerous extraneous factors.24 The day-to-day variation in HRRESTING under controlled conditions has
shown to be about 5–8 bpm.25,26 Even when heart rate
was measured during the sleep hours (where the influence of extraneous factors is reduced) the intra-subject
day-to-day variation of the minimum heart rate during
sleeping was about 5 bpm.27 Accordingly, changes in
HRRESTING after training have been varied from no significant differences to a 10 bpm reduction,28,29 which is
in accordance with the no significant differences in
HRRESTING observed in the present study.
The present AIT associated improvement in
HRRECOVERY to GXT of young FHþ may have important implications. Several studies have shown that the
simple application of HR provides powerful risk stratification for cardiovascular disease and mortality from
the exercise test in different populations.4,5,30,31
Accordingly, reduced HRRECOVERY to exercise has
shown to be an independent risk factor for coronary
heart disease, cardiovascular disease, and cardiovascular mortality.30,31 Moreover, reduced HRRECOVERY to
exercise has been associated with several abnormalities
found in young FHþ women,3 including endothelial
dysfunction,31 arterial stiffness,32 and insulin resistance.33 Although the prognostic value of improving
HRRECOVERY is not known, the observed improvement
in HRRECOVERY to exercise following AIT may imply
in an increased ability of the cardiovascular system to
recover from an acute stress, which could improve
prognosis of this high-risk population.
The mechanism by which AIT is more effective than
CME to improve HRRECOVERY is out of the scope of
the present study. However, because the initial heart
rate decrease following GXT is mediated primarily by
vagal reactivation and is independent of sympathetic
withdrawal and exercise workload,23 it is reasonable
to speculate that the low- and high-intensity training
exercise programmes affect the mechanism regulating
parasympathetic reaction differently, thus resulting
in the greater AIT associate improvement in
HRRECOVERY.
The indirect estimation of autonomic nervous
system by the measure of heart rate response to exercise
is a limitation of the present study. However, changes
in heart rate response to exercise following an exercise
programme as the observed in the present study has
been parallel changes in baroreflex sensitivity, a wellknown and widely accepted marker of the vagal control
of the sinoatrial node.34 We also do not know whether
the greater improvements in CRF and HRRECOVERY
caused by AIT actually affect the outcome in terms of
prognosis of FHþ subjects. However, the present study
was not designed for this purpose; rather, it was
focused to assess the effects of AIT versus CME on
heart rate response to GXT and CRF, markers whose
impairments have poor prognosis in healthy and cardiovascular disease subjects.4–6 The results showing
greater benefits of AIT in these markers suggest that
it would be associated with a better outcome in FHþ
women, although a large, prospective, multicentre trial
is required to confirm this suggestion.
In summary, AIT was more effective than CME for
improving HRRECOVERY and several parameters of
CRF of healthy young women offspring of essential
hypertensive parents. These findings may have important implications for designing exercise-training
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6
European Journal of Cardiovascular Prevention & Rehabilitation 0(00)
programmes for the prevention of an inherited hypertensive disorder.
Funding
This work was supported by the Fundação de Amparo à
Pesquisa do Estado de São Paulo (FAPESP 2004/00568-8).
Emmanuel G Ciolac was supported by the Sociedade de
Cardiologia do Estado de São Paulo, and Guilherme V
Guimarães was supported by the Conselho Nacional de
Pesquisa (CNP 304733/2008-3).
Conflict of interest
No conflicts to declare.
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