Download Training prescription in patients on beta-blockers

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SO CIETY O F
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Original scientific paper
Training prescription in patients on
beta-blockers: percentage peak
exercise methods or self-regulation?
European Journal of Preventive
Cardiology
19(2) 205–212
! The European Society of
Cardiology 2011
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DOI: 10.1177/1741826711398823
ejpc.sagepub.com
Renzo Zanettini, Paola Centeleghe, Fosco Ratti,
Stefania Benna, Laura Di Tullio and Nadia Sorlini
Abstract
Background: Exercise prescription based on percentage of peak exercise variables has many limitations in patients
taking beta-blockers. The aim of this study was to evaluate efficacy and safety of a training protocol based on the rating of
perceived exercise (RPE) in patients taking beta-blockers after cardiac surgical revascularization.
Design and methods: 71 patients treated with beta-blockers after recent coronary artery bypass grafting were
randomly allocated to two different programmes with training intensity adjusted to keep heart rate close to first
ventilatory threshold (36 subjects, AeT group) or RPE between grades 4 and 5 of 10-point category-ratio BORG
scale (35 subjects, RPE group).
Results: In the RPE group, mean training workloads and heart rate values were significantly higher than in the AeT
group; during the last week of the programme, six RPE patients were training very close to anaerobic threshold. Aerobic
peak capacity increased similarly in the two groups. Considering the potential effects on training intensity of prescriptions
based on percentages of peak exercise variables, we found that only percentage heart rate reserve and peak workload
methods were reliable in defining a safe upper limit of training intensity, with values of 50% and 65% respectively.
Conclusions: Self-regulation of exercise training intensity between grades 4 and 5 of the 10-point category-ratio BORG
scale is effective but may promote overtraining in some patients without significant functional advantages. For these
reasons, RPE method should be integrated with objective indices based on percentage of heart rate reserve or of peak
workload.
Keywords
Anaerobic threshold, beta-blocker therapy, exercise intensity prescription, percentage peak exercise methods, rating of
perceived exercise
Received 13 January 2010; accepted 10 April 2010
Introduction
In cardiac rehabilitation the use of heart rate (HR) as
an estimate of exercise intensity is the common standard. The range of HR considered optimal for aerobic
conditioning, with maximal gain and minimal risk, is
generally established as a percentage of maximum HR
(HRpeak) or heart rate reserve (HRR): training intensities recommended by these two methods are 40–80% of
HRR or 70–85% of HRpeak.1,2 The rationale supporting
this
practice
is
the
relatively
linear
relationship existing between HR and oxygen uptake
(VO2) which enables the use of HR as an index of training intensity.
However, aging, disease, medications, and motor
skills can displace the HR/VO2 relationship so that
the use of standard HR intensity guidelines can result
in very different levels of metabolic stress across
subjects.3–6 This problem is amplified in patients on
Cardiac Rehabilitation Centre, Istituti Clinici di Perfezionamento
Hospital, Milan, Italy.
Corresponding author:
Renzo Zanettini, Cardiac Rehabilitation Centre, Istituti Clinici di
Perfezionamento, via Bignami 1, 20126, Milan, Italy
Email: [email protected]
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206
European Journal of Preventive Cardiology 19(2)
beta-blockers: the blunting of HR response observed in
these patients reduces the reliability of HR methods
since small HR changes can account for large differences in workload. The findings of recent studies
addressing this issue are interesting, but operative
recommendations for clinical use are inconsistent.7–9
Furthermore, these studies were conducted in healthy
volunteers or patients after myocardial infarction; no
data exist, to our knowledge, about patients taking
beta-blockers after coronary artery bypass grafting
(CABG) who often suffer from marked deconditioning
as well.
Ideally, training intensity should be adjusted according to metabolic markers such as aerobic and anaerobic
threshold,10,11 but systematic cardiopulmonary exercise
testing (CPET) for training prescription cannot be
recommended to all cardiac patients because it is not
feasible and probably unnecessary, at least for low-risk
patients.
In an editorial addressing this issue, Schmid12
suggested starting training at 65% of HRpeak with
adjustments of training intensity based on rating of
perceived exercise (RPE) for low-risk patients taking
beta-blockers. This approach is supported by the
strong relationship between RPE and both VO2 and
lactate concentration;13–15 moreover, the RPE/power
output relationship seems to be unaffected by betablockade.16–18 The reliability of perceived exertion
ratings in exercise prescription has been evaluated in
normal subjects and in some clinical settings.19–22 but
no specific data are available about the effects of betablockers on RPE regulation of exercise intensity in
cardiac rehabilitation.
The aim of the present study was to evaluate the
efficacy and safety of a training protocol based on
RPE in patients on beta-blockers after CABG.
Methods
Patients
Consecutive male patients (from 1 September 2007 to
30 June 2008) referred to the Cardiac Rehabilitation
Centre of Istituti Clinici di Perfezionamento in Milan
for a phase-II rehabilitation programme were enrolled
into this study if the following eligibility criteria were
met: recent CABG (<60 days) and beta-blocker therapy. Exclusion criteria were: atrial fibrillation, left
ventricular ejection fraction <35%, haemoglobin
<10 g/dl, cerebrovascular or musculoskeletal disease
preventing exercise testing or training, peripheral arterial occlusive disease limiting exercise, severe respiratory limitations (FEV1 or VC <60% of predicted),
residual myocardial ischaemia or exercise induced
arrhythmias, and unmeasurable aerobic threshold
(AeT) during baseline cardiopulmonary exercise testing
(CPET). This study was approved by the institution’s
research Ethics Committee and all patients gave written
informed consent.
Study design
After an initial assessment (clinical evaluation, cardiopulmonary exercise test, standard echocardiogram, and
routine laboratory tests) patients were randomly
allocated to one of two different programmes of endurance exercise training: (1) AeT group: intensity of training adjusted to keep HR at the aerobic threshold (AeT)
2 bpm; and (2) RPE group: training intensity adjusted
to keep RPE between grades 4 and 5 of 10-point category-ratio (CR-10) BORG scale.23–24 AeT group
patients were used as controls since exercise intensity
prescription based on AeT determination may be
considered a reference method, in view of its capacity
to elicit uniform metabolic responses across subjects
during aerobic training.5,6,25
We considered the range of workload (WL) between
the individual AeT and anaerobic threshold (AnT) as
the optimal training zone. In the RPE group, an exercise intensity persistently lower than workload at AeT
or higher than individual workload at AnT were
considered indicative of undertraining or overtraining,
respectively. Initial training data were compared with
the results of the first CPET and final training data with
the results of the last CPET. Physiotherapists were
blinded to CPET results.
Rating of perceived exertion
Subjective regulation of training intensity in the RPE
group was based on the CR-10 BORG scale, currently
used for training monitoring at our centre: grades 4 and
5 correspond to effort levels perceived as ‘somewhat
hard’ and ‘hard’ respectively and are equivalent to
13–15 of 6–20 on the Borg scale. The reliability of the
Borg scale as a means of regulating high levels of exercise intensity in repeated trials has been previously
confirmed.19
Standardized instructions about correct usage of
CR-10 scale1 were given to every patient before starting
the rehabilitation programme; in addition the first two
training sessions were ‘learning’ sessions during
which the patients were taught to exercise using a
self-regulated intensity between a rating of 4 and 5.
In the following sessions each subject of the RPE
group continued to exercise at this intensity and was
provided with no other feedback regarding HR or WL;
thus, RPE work demand was used as an independent
variable to control work intensity.
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Zanettini et al.
207
p-value <0.05 was considered to indicate statistical
significance.
Training programme
Patients trained in hospital as out-patients, three times
a week for 5 weeks. Every training session consisted of
flexibility and stretching exercises (20 min), dynamic
resistance training on multifunctional fitness equipment
(UNICA, Technogym) at 30% of one repetition maximum (10 min) and cycling: 5 min of warming-up,
30 min of endurance training, and 5 min of cooldown. Training sessions were supervised by experienced
physiotherapists; ECG and workload during bicycle
training were centrally monitored by an automatized
system (CUSTO-MED).
Besides exercise training, patients underwent an
educational programme based on individual and
group sessions with medical staff, a dietician, and a
psychologist.
At the end of the training programme, patients
underwent a final CPET.
Cardiopulmonary exercise test
Symptom-limited cardiopulmonary exercise test was
performed on a bicycle ergometer (Ergoselect 200P;
Ergoline), under medication, with 10–15 W/min increments until exhaustion. Twelve-lead ECG and heart
rate were recorded continuously (Cardiosoft; GE
Medical Systems); blood pressure was measured every
2 min, at peak exercise, and during recovery.
Respiratory gas exchange measurement involved use
of the VMAX 29C Sensor Medics system. VO2,
VCO2, and VE were measured breath by breath and
data were averaged every 15 s; peak oxygen consumption (VO2peak) was expressed as the highest attained
VO2 during the final 30 s of exercise. The AeT (first
ventilatory threshold) was measured using the V-slope
method and, if necessary, ventilatory equivalent and
end-tidal gas concentration curves for O2.26 Only
patients in whom AeT was clearly determined were
included in the study. The AnT (second ventilatory
threshold), corresponding to maximal lactate steady
state, was assessed using one of the following methods:
inflection of VE vs. VCO2, nadir or nonlinear increase
of VE/VCO2 vs. workload or deflection point of the
PETCO2.27 Unmeasurable AnT was not considered
an exclusion criterion. All measurements were reviewed
by the same experienced investigator.
Statistical analysis
Data are reported as mean SD. Differences between
groups or between pre- and post-training values for
continuous variables were tested with unpaired or
paired Student’s t-test. For all statistical analyses, a
Results
Study population
Between September 2007 and June 2008 we screened
90 consecutive male patients with recent CABG treated
with beta-blockers. Sixteen were excluded for: left
ventricular ejection fraction <35% (n ¼ 6), atrial fibrillation (n ¼ 4), unmeasurable AeT (n ¼ 3), Hb <10 g/dl
(n ¼ 2), and lower extremity arterial disease (n ¼ 1). Out
of the remaining patients, three completed <12 training
sessions and were excluded a posteriori. The data of 71
patients are reported in the present study; the betablockers used were: atenolol (n ¼ 27, mean daily dose
52 26 mg), bisoprolol (n ¼ 33, mean daily dose
3.2 1.3 mg), and metoprolol (n ¼ 11, mean daily dose
98 49 mg). The mean interval between heart surgery
and first CPET was 37 10 days; in 11 patients CABG
was associated with valve surgery and 22 patients had a
history of myocardial infarction (inferior or infero-lateral n ¼ 9, anterior or antero-lateral n ¼ 8, no Q wave
n ¼ 5).
Main anthropometric and baseline functional data
of patients are shown in Table 1: parameters measured
in basal conditions and at maximal exercise capacity
are reported for all patients and separately for the
two different training groups. No significant differences
were found between the two groups; only a trend
towards higher HRresting and HRpeak in the AeT
group was observed. AnT was detected in 65 subjects
during CPET1 and in 66 during CPET2.
In Table 2, HR and WL values at AeT and AnT
found in the two groups are reported both as absolute
values and as percentage of peak exercise values. The
only difference between the two groups was found for
HR, which at AnT was significantly higher in the AeT
group than in the RPE group (p ¼ 0.046), but the
relative percentage values of the two groups were very
similar (AeT 90 5% vs. 89 6%).
Effects on training intensity and functional outcome
of the two different training protocols
In Table 3, training parameters of the two groups are
compared at the beginning and at the end of the training programme. Mean training WL and corresponding
mean RPE values in the RPE group were significantly
higher than in the AeT group. In addition, we observed
a significant increase of training intensity in both
groups as programme went on.
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208
European Journal of Preventive Cardiology 19(2)
Table 1. Main clinical and functional characteristics of patients
Characteristic
All patients (n ¼ 71)
RPE group (n ¼ 35)
AeT group (n ¼ 36)
p-value
Age (years)
Body mass index (kg/m2)
Ejection fraction (%)
Peak systolic BP (mmHg)
Peak diastolic BP (mmHg)
HRresting (bpm)
HRpeak (bpm)
Maximal workload (watt)
VO2peak (ml/kg/min)
%VO2max predicted
RERmax (VCO2/VO2)
62.3 8.8
26.5 3.2
53.7 8.7
152.5 23.8
85 10.5
64.7 11.8
106 19.6
92.2 20.6
17.3 3,7
70.6 17.7
1.1 0,09
60.5 9
26.6 3.3
52.9 8.2
148.6 23.8
82.9 10.6
62.1 10
101.7 18.7
93.8 20
16.9 3,7
69.8 16.9
1.09 0.09
63.9 8.5
26.4 3.2
54.5 9.1
156.1 23.7
86.9 10.1
67.1 12.9
110 19.7
90.7 17.6
17.6 3,6
72.3 17.9
1,11 0.09
0.107
0.711
0.423
0.187
0.112
0.076
0.076
0.532
0.377
0.412
0.505
Values are mean SD. Functional parameters refer to the first cardiopulmonary exercise test. T test for comparison between RPE and AeT groups.
AeT, aerobic threshold; BP, blood pressure; HR, heart rate; RER, respiratory exchange ratio; RPE, rating of perceived exercise.
Table 2. Absolute and relative values of heart rate and workload at AeT and AnT
Characteristic
All patients (n ¼ 71)
RPE group (n ¼ 35)
AeT group (n ¼ 36)
p-value
HRAeT (bpm)
%HRpeak at AeT
%HRR at AeT
HRAnT (bpm)
%HRpeak at AnT
%HRR at AnT
Workload at AeT (watt)
% maximum workload at AeT
Workload at AnT (watt)
% maximum workload at AnT
82.6 12.6
79 8
43 14
95.1 30.7
89 5
73 11
46.8 10.4
52 10
74 25,2
79 8
80.7 13.1
80 8
47 14
91.1 26.8
89 6
73 10
48.8 12.2
52 10
75 23,4
79 9
84.3 12
77 8
40 13
98.9 34
90 5
73 12
45 8.1
51 10
73 26,7
78 8
0.220
0.219
0.051
0.046
0.922
0.972
0.116
0.491
0.521
0.875
Values are mean SD. Functional parameters refer to the first cardiopulmonary exercise test. T test for comparison between RPE and AeT groups.
AeT, aerobic threshold; AnT, anaerobic threshold; HR, heart rate; RPE, rating of perceived exercise.
Table 3. Training parameters and functional outcomes of the two groups
AeT group (n ¼ 36)
Parameter
Training intensity (watt)
HRAeT (bpm) CPET
Training HR (bpm)
Mean RPE score
Watt/kg CPET
VO2peak (ml/kg/min) CPET
Initial
RPE group (n ¼ 35)
Final
42.9 12.5
84.3 12
85.6 10.2
Initial
55 11.8
83.5 9.8
86.5 12
a
50.5 12.7
80.7 13b
81.8 11.2
65.6 19a,c
78.3 10.1b
87.3 12a
4.1 0.3b
3.8 0.4
1.2 0.3
17.4 3.6
Final
b
d
1.38 0.3
19.4 4.7d
1.22 0.3
16.8 3.7
1.4 0.3d
19.2 4.6d
Values are mean SD. AeT, aerobic threshold; CPET, cardiopulmonary exercise test; HR, heart rate; RPE, rating of perceived exercise. a<0.01 t-test for
initial vs. final mean values. b<0.05 t-test for AeT group vs. RPE group mean values. c<0.01 t-test for AeT group vs. RPE group mean values. d<0.05
t-test for initial vs. final mean values.
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Zanettini et al.
209
In the initial phase, mean training HR values in both
groups were slightly higher than HRAeT but while in the
AeT group training HR increased minimally during the
programme, in RPE patients a significant increase of
this parameter was found between the initial and final
phase of the training programme.
Working and aerobic peak capacity increased significantly after training and the magnitude of the improvement was similar in the two groups: VO2peak
11.5 16% in the AeT group vs. 14.3 14% in the
RPE group (p ¼ 0.46). This finding is clinically remarkable considering the short period of time elapsed
between first and final CPET: 32.4 4.4 days in the
RPE group and 33.4 5.5 days in the AeT group.
Regarding individual data of RPE patients, their
training intensity expressed as difference in watts
between actual training WL and AeT and AnT workloads is reported in Figure 1. Considering the area
between AeT and AnT (dotted lines of the figure) as
ideal training zone, in the initial phase of the training
programme 11 subjects were training below the AeT,
while the others were in the optimal training zone. Four
exercised at a load very close to AnT, without exceeding it.
During the last week of the rehabilitation
programme most patients (87%) exercised in the optimal zone; two of the remaining patients exercised just
below AeT and another two were slightly above AnT.
No adverse events were reported in either group during
the rehabilitation programme.
Comparison with percentage peak exercise methods
In Table 4, the effects on training prescription of different percentages of peak exercise variables are examined
with reference to individual AeT and AnT values. The
numbers of patients training below AeT, between AeT
and AnT, and above AnT are reported for different
percentages of these parameters.
Regarding %HRpeak method, training at the habitually used upper limit (85%) made 12 patients (18%)
exercise above AnT; with lower percentages of HRpeak
the number of these subjects diminished but the
proportion of undertrained patients rose sharply: at
75% of HRpeak about two-thirds of subjects exercised
below AeT.
The %HRR method seemed to work better, since
training intensity eliciting HRR values of about 50%
made almost 77% of subjects exercise between AeT and
AnT; at this percentage value, none exceeded AnT.
Concerning %WLpeak, exercise training around 60%
of maximum workload placed 85% of patients between
AeT and AnT.
Figure 2 shows the distribution of individual
percentage values of peak exercise variables at AeT
and AnT; for each variable the optimal cut-off percentage value corresponding to the maximum number of
subjects training between AeT and AnT is reported.
As far as %HRpeak values are concerned, we
observed significant overlapping between individual
data at AeT and AnT. Consequently, to avoid the
AnT
10
Overtraining
0
AeT
–20
–10
0
10
20
30
40
–10
Undertraining
–20
–30
–40
–50
Figure 1. Training intensity of RPE group patients expressed as absolute difference in watt between actual training workload and
individual AeT and AnT workloads. «, first week; ^, fifth week; dotted lines, optimal training zone. AeT, aerobic threshold; AnT,
anaerobic threshold; RPE, rating of perceived exercise.
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European Journal of Preventive Cardiology 19(2)
Table 4. Training intensity at different percentages of peak
exercise variables
Variable
<AeT
between AeT
and AnT
>AnT
HRpeak
70%
75%
80%
85%
90%
52
44
28
16
4
13
19
33
37
31
0
2
4
12
30
HRR
40%
50%
60%
70%
80%
38
15
1
0
0
27
50
57
38
20
0
0
7
27
45
WLpeak
50%
55%
60%
65%
70%
29
26
10
6
5
36
39
55
58
48
0
0
0
1
12
Discussion
Values are n. Data relative to 65 patients with AnT detectable at first
cardiopulmonary exercise test. AeT, aerobic threshold; AnT, anaerobic
threshold; HR, heart rate; HRR, heart rate reserve; WL, workload.
%HRpeak
risk of overtraining, patients should work at very low
%HRpeak values.
The distribution of individual %HRR and WLmax
values is more favourable, since the overlapping of data
at AeT and AnT is small; this enables the detection of
acceptable cut-off values for effective and safe management of most patients as reported in Figure 2.
In low-risk cardiac patients, the option of training
prescription based on RPE regulation of effort intensity
is very attractive for several reasons. First of all, after
CABG many patients undergo cardiac rehabilitation
without a true maximal exercise test owing to their
low fitness, which would prevent the achievement of a
true peak heart rate. Furthermore, even if we could
base our prescription on the results of a preliminary
exercise test, in patients on beta-blockers with very
low chronotropic reserve, the definition of a training
zone based on percentage HR methods is of limited
utility, because very small HR changes correspond to
large differences in workload: in 14% of our patients
the HR difference between AeT and AnT was 5 bpm.
Finally, learning to self-regulate training intensity properly may favour long-term patient compliance and is
%HRR
%WLmax
100
100
100
85
75
75
70
50
50
55
25
25
40
0
AeT
AnT
0
AeT
Peak exercise variable
HRpeak
HRR
WLmax
Cut-off value
72%
51%
64%
AnT
AeT
AnT
Subjects between AeT and AnT
25%
78%
89%
Figure 2. Dot-plot distribution of pre-training individual percentage values of peak exercise variables at AeT and AnT.
AeT, aerobic threshold; AnT, anaerobic threshold; HR, heart rate; HRR, heart rate reserve; WL, workload; Cut-off value, percentage
value of the variable corresponding to maximum number of subjects exercising between AeT and AnT without any subject above AnT.
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Zanettini et al.
211
essential for those participating in home rehabilitation
programmes or when monitoring facilities are not
available.
The present study demonstrated that, in patients on
beta-blockers after CABG, self-regulation of exercise
intensity between grades 4 and 5 of the CR-10 BORG
scale makes most patients train between AeT and AnT.
During the first week of the programme, 65% of
subjects exercised in the optimal training zone, while
less fit patients set their training WL below AeT.
As rehabilitation proceeded, patients increased their
training intensity progressively, so that during the last
week of the programme about 90% of them were
exercising between AeT and AnT; worthy of note, six
of them trained very close to AnT.
Since training WL for AeT patients was adjusted to
keep training HR close to HR at AeT, mean training
HR and WL in the RPE group were significantly higher
than in the AeT group.
Aerobic capacity improvement of RPE subjects was
a little higher, but the difference vs. AeT patients was
not statistically significant. This finding was probably
due to the small sample size and to the short duration
of the programme.
On the other hand, the significant improvement in
VO2peak observed in the AeT group confirms the effectiveness of training WL close to AeT. Since every
patient of the RPE group was able to reach this level
of training intensity in the course of the programme,
the choice of AeT as lower limit of the optimal training
zone seems reasonable, as it is effective and can be
proposed even to less fit patients.
Comparing these results with those of a prescription
based on percentage peak exercise variables we
found that:
. In our clinical setting the %HRpeak method is
absolutely inadequate owing to the broad
overlapping between individual AeT and AnT
values, which prevents the definition of acceptable
upper and lower limits for exercise intensity
optimization.
. The %HRR method works better, but the upper
limit should be reset to 50% to avoid overtraining
of a significant proportion of patients.
. Even better, the use of %WLpeak method with a
cut-off value of 64% enables effective and safe treatment of about 90% of subjects.
A few considerations should be borne in mind for
the assessment of differences between our data and
conclusions of previous studies addressing this issue.
Exercise training intensity is usually evaluated with reference to the concept of anaerobic threshold. However,
this term has been used very often as synonym of the
first and second ventilatory threshold: this is a source of
growing conceptual and methodological confusion and
can make comparisons among different studies very difficult, as recently outlined by Binder et al.27
Chaloupka et al.8 and Tabet et al.9 proposed values
between 70 and 80% of HRR as upper limits for training intensity in patients on beta-blockers. These values
are notably higher than our cut-off value for this
parameter. However, our data arise from direct
measurement of the true AnT, whereas their optimal
criterion was a training intensity corresponding to
HR at first ventilatory threshold10%. Limitations
and potential pitfalls of such a methodological
approach have already been pointed out: in some
patients the lower limit may be considerably below
AeT, while the upper limit may correspond to the
peak WL. Very different conclusions were drawn by
Wonisch et al.,7 who studied the influence of betablockers on percentage HR prescription methods in
healthy males. Using AnT as upper limit for safe exercise training this author demonstrated that the usual
upper values that are considered safe for %HRpeak
and %HRR are too high for patients on beta-blockers.
This is consistent with our findings.
Finally, we used the direct measurement of training
WL to evaluate training intensity instead of a ‘surrogate’ load indicator, as HR has many limitations in
patients taking beta-blockers.
In conclusion, our findings suggest that self-regulation of exercise training intensity between grades 4 and
5 of the 10-point category-ratio BORG scale is effective
and safe in the initial phase of the rehabilitation
programme in patients on beta-blockers after CABG.
As some patients tend to increase effort intensity as the
programme continues and reach training WL very close
to AnT, we think that after the initial phase subjective
methods should be integrated with objective indices.
According to our data, the %HRR or %WLpeak
method with upper limits of 50% and 65%, respectively, can prevent the subject from exceeding AnT
during exercise training.
Funding
As mentioned previously, when chronotropic reserve
is very reduced, among the objective methods of exercise prescription we think that the %WLpeak method
should be preferred to %HRR method in view of the
very low reliability of HR as indicator of effort intensity
in these patients.
This research received no specific grant from any funding
agency in the public, commercial, or not-for-profit sectors.
Conflict of interest
None.
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European Journal of Preventive Cardiology 19(2)
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