Keywords
reporting quality - clinical practice - CERT checklist - interval training - high
blood pressure
Introduction
Hypertension is a major public health problem that affects millions of people
worldwide. This can lead to a variety of serious health problems, including heart
disease, stroke, and kidney disease [1].
Risk factors for hypertension include obesity, lack of physical activity, high salt
intake, smoking, and high alcohol consumption. In addition, genetic factors and age
can also play a role in the development of hypertension [2]
[3]
[4].
Hypertension is treated with lifestyle changes such as diet, exercise, and weight
management, as well as medication. While medications can effectively lower blood
pressure [5], they come with a risk of side
effects [6]. Lifestyle changes, on the
other hand, can not only lower blood pressure but also improve overall health [7]
[8]
[9].
Physical exercise, including regular exercise, is known to be one of the most
effective lifestyle interventions for the management of hypertension. Exercise,
particularly aerobic exercise, has been shown to be effective in reducing both
systolic and diastolic blood pressure [10]
[11]. The American Heart
Association (ACC/AHA) and other professional societies recommend regular
moderate-intensity aerobic exercise, such as brisk walking or cycling, for at least
150 minutes per week, or 30 minutes per day, five days a week, as a strategy for
preventing hypertension and controlling blood pressure in those with hypertension
[12]
[13]
[14]
[15].
More recently, research has begun to focus on the effects of other exercise modes
such as high-intensity interval training (HIIT) on hypertension. HIIT in a variety
of forms, involves repeated short to long bouts of rather high intensity exercise
interspersed with active or passive recovery periods [16]. HIIT has recently generated research
interest as it is more time-efficient while showing similar blood pressure reducing
effects than traditional endurance training in the general and hypertensive
population [17]
[18]
[19]. Surprisingly, HIIT is not included in most routine exercise programs
for hypertension, and even the latest guideline recommendations of the European
Society of Cardiology [13] and the European
Society of Hypertension as well as the ACC/AHA [12] are largely based on older data without mentioning high-intensity
training protocols for patients with hypertension.
A distinctive feature of interval training is the possibility to manipulate the
different training variables making this training approach infinitely variable.
Thus, studies using HIIT as a novel exercise mode should be very precise in
describing the intervention. The primary objective of this study is to assess the
quality of studies on HIIT for hypertensive treatment.
Notably, compared with similar trials of medicines, the reporting of interventions
in
exercise trials is often poor [20]. Only
high-quality reporting will ensure replicability in clinical practice and reduction
of possible risks of the HIIT intervention [21]
[22]
[23]. As HIIT can have potential side effects
in individuals with cardiovascular disease, it is particularly crucial to provide
clear and detailed reports of the exercise intervention for individuals with
hypertension. Previous research by our group and other authors has revealed a lack
of quality in reporting exercise interventions for hypertension [24] and other trials in health and disease
[25]
[26]
[27]
[28].
Therefore, the present study aimed to investigate the reporting quality of HIIT on
hypertension. It was hypothesized that shortcomings of the quality of reporting HIIT
interventions might be similar to moderate endurance interventions previously
demonstrated by our group [24].
Material and Methods
This study followed the Preferred Reporting Items for Systematic Reviews and
Meta-Analyses (PRISMA) reporting guidelines [29].
Eligibility criteria
We included individually randomised parallel group-controlled trials. We excluded
cluster-randomised studies due to the risk of contamination and we did not
include cross-over trials due to possible carry-over effects of the
intervention. All randomised controlled trials involving adults (18 years of
age) with a blood pressure that was at least high normal according to ESH
guideline (systolic blood pressure [SBP]≥130 mmHg and/or diastolic blood
pressure [DBP]≥85 mmHg [15]) treated
with HIIT. Exercise therapy interventions were defined as those involving any
HIIT intervention with a minimum duration intervention of 6 weeks.
The comparison was non-exercising or non-intervention controls or other exercise
interventions. Only studies with data on the long-term effect on systolic and
diastolic blood pressure measured by any standard devices were included. Studies
showing information in the acute post-intervention blood pressure only were
excluded. Studies published in languages other than English or German were not
eligible for study inclusion.
Search strategy
The studies included in this analysis were retrieved by a systematic search
strategy as shown in [Fig. 1]. In
contrast to previous studies investigating the quality of reporting of exercise
interventions, we did not use meta-analyses found in the guidelines of the
hypertension or cardiology societies as a data source because currently here are
no uniform recommendations for HIIT in hypertension. Thus, we looked for newer
studies using HIIT in patients with hypertension. We searched PubMed up to July
2022, using the search terms “hypertension AND high intensity interval
training”. Intentionally, we did not restrict the study search by year
of publication, publication status, or language.
Fig. 1 Flow chart of study selection.
We checked the bibliographies of included studies and any relevant systematic
reviews identified for further references to relevant trials. Where necessary,
we contacted authors of key papers and abstracts to request additional
information about their trials.
Data extraction
Primary studies with hypertensive patients were evaluated using the Consensus on
Exercise Reporting Template (CERT) [26]. The CERT template was used to investigate the quality of reporting
of HIIT interventions in the selected studies as this checklist was specifically
designed to improve the reporting of exercise interventions. The completeness of
reporting is expressed as the percentage of studies that reported each item in
sufficient detail. CERT was published in 2016 as an extension of the Template
for Intervention Description and Replication (TIDieR) [30] to give guidance to authors for
structured and detailed reporting of exercise-based interventions. This will
lead to subsequently facilitate research replication and increase the clinical
uptake of an intervention, which turned out to be effective in research. In
addition, authors, editors, and reviewers can use both templates to ensure
completeness and quality of exercise intervention description.
The CERT template was applied to the selected studies by checking every item
(Supplemental Table 1). Completely described items were marked with
“1” and incomplete or missing descriptions were marked with “0”, while not
applicable items were “NA”. The assessment of every item was performed by two
different experienced researchers (blinded for peer review). In case of a
discrepancy, differences were discussed based on the explanation and elaboration
statements of the CERT guideline [31].
The checklists items for every RCT were extracted into Excel and results were
analysed descriptively.
Data analyses
Individual study ratings were described as counts and proportions and the sum of
“1” assessments as means and SD or 95% confidence intervals (95% CI). Analyses
were based on the number of “1” assessments compared with “0”. “Not applicable”
was treated as a given item. The following study details were extracted: author,
year, journal, country, population, intervention and control data, blood
pressure inclusion criteria.
Results
At the time of the literature search (July 2022), we found 92 studies at the initial
screening. Studies without an intervention were excluded (n=11). Animal studies were
not included in the present review (n=15). Two studies had to be eliminated because
they were not published either in English or German and one study had to be excluded
as no full-text article was found (n=1). Studies not using HIIT were omitted (n=6)
as were papers originally excluding hypertensive as well as including normotensive
subjects or underage persons (n=27). Investigations with no information on the
long-term effect on blood pressure or only data on the acute effect post training
session were excluded (n=9). The minimum duration intervention was defined at 6
weeks (9 studies excluded). Interestingly, two of the remaining 10 studies were
identical with the same dataset but only one study reported pre- and post-test blood
pressure data. Therefore, one of the duplicates or double publications was excluded
[32].
Finally, we assessed HIIT intervention reporting of nine RCTs [33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41] comprising 718 patients
(HIIT intervention group: 334, control group: 384; mean age 51.84 years). The nine
trials were published between 2010 and 2020 and reported data from six countries.
In
total, 19 interventions were performed, whereas 12 were HIIT protocols (n=334) and
7
were moderate intensity endurance training protocols (n=194). All studies except one
had a non-exercising control group (n=190). On average, interventions ranged from
6
weeks to 16 weeks, involved two to three sessions per week, lasting 15–80 minutes
per session. CERT ratings of the included studies are presented in Supplementary
Table 1 and a detailed exercise dose description with blood pressure inclusion
criteria of each trial is shown in Supplementary Table 2.
The quality of description of the HIIT interventions is shown in [Fig. 2]. Completeness of CERT item
reporting ranged from 42.1 to 73.7% among the studies. On average, 12 items out of
19 items of the CERT template were described in detail in every study, resulting in
an average reporting quality of 62.6% (95% CI: 55.4–69.7). Following the CERT
checklist, the type of exercise equipment (item 1, 89%) and description of each
exercise (item 8, 89%) as well as the mode of delivery (item 4, 100%) and intended
method of exercise tailoring/progression (item 14a and 14b, 100%) were also
addressed in almost all studies. The least reported items belong to motivation
strategies und instructor’s adherence (none of the studies). Only one study reported
information on adverse events.
Fig. 2 Percentage of studies which adequately reported the CERT item
(n=9).
However, there was a good quality of reporting of item 13 – exercise dosage (reported
in 8 (89%) of the studies). A complete description of the essential components of
the exercise dose intervention could be found for type, time and frequency, whereas
the intensity of exercise prescribed was missing in one study (Supplementary
Table 2).
Discussion
The goal of the present study was to evaluate for the first time the quality of
intervention reporting of HIIT studies for arterial hypertension. Our study provides
evidence that there is still an urgent need of improvement in the reporting quality
of HIIT interventions for patients with hypertension. Overall, maintaining a good
quality of reporting is important in order to promote clinical translation, evidence
synthesis, and study appraisal. Only explicit reported interventions can be
replicated for research and, more importantly, for clinical practice [22]
[23]. Poor reporting of interventions is a general issue across a range of
medical interventions [42], but exercise
interventions were found to be less well described [20]. We did not find a single intervention
with all items of CERT completely described. However, the overall quality of
reporting is better in HIIT interventions than in moderate endurance training
interventions for hypertension (62% vs. 49%) as previously described by our group
[24]. Particularly, the reporting of
the exercise dose is remarkably better than the description for aerobic endurance
training intervention [24] or other health
conditions (e. g. cardiovascular, musculoskeletal, neurological) [27].
To date, aerobic (endurance) interventions of moderate intensity were generally
recommended in hypertension [43]. There
still is a widespread perception that HIIT may be associated with greater safety
concerns than moderate intensity exercises [18]. This might trigger doubts about using HIIT for clinical practice.
However, according to the blood pressure reduction effects that could be
demonstrated in recent studies by Edwards et al. [17] and Li et al. [18], exercise
of higher intensity and in intervals lower blood pressure in hypertensive subjects
to a very similar degree compared with moderate endurance training or other exercise
training modes. In addition, HIIT might have other advantages over low intensities.
It is more time-efficient and more effective in improving associated risk factors
and physical fitness, which is an important protective factor in cardiovascular
disease [44]
[45]
[46]. However, the shortcomings of the reporting quality especially found
for items of delivery mode, progression, adherence, and adverse events in the
present study are a further problem for a general prescription of HIIT interventions
in common recommendations despite their importance. As a result, clinicians may not
be able to replicate and recommend HIIT programs for their hypertension patients.
Our findings should therefore be considered in future exercise recommendations for
the prevention and treatment of arterial hypertension using HIIT protocols as
replicability is limited to a certain extent.
An item that is also indispensable for the replicability not only of exercise studies
in hypertension is certainly the reporting of adverse events. HIIT is associated
with greater safety concerns than traditional moderate intensity endurance training;
however, no significant adverse events were found in HIIT versus moderate endurance
training [47]. In our analysis, adverse
events (item 11) were sufficiently reported in only one out of nine studies. In
clinical practice, hypertensive patients might have concomitant diseases such as
coronary artery disease or heart failure. Although these conditions are not always
contraindications for HIIT, there is a need to closely monitor adverse events. The
lack of reporting of adverse events or the absence of adverse effects in almost all
studies might seriously prevent the use of HIIT in clinical practice. Only one study
reported a myocardial infarction at home in the comparator moderate intensity group
but stated that the numbers of patients was too small to estimate the issue of
safety. While we rated this description as adequate, we did not consider it
sufficient to report that the intervention was well tolerated. Since HIIT is a
popular alternative for patients with hypertension, a detailed description of
possible adverse events would be all the more important.
Despite the clinical utility of exercise modes with high intensities [48], recent studies have demonstrated
greater ratings of perceived enjoyment than moderate endurance exercise
interventions [49] but revealed conflicting
results regarding completion rates and attendance at exercise training sessions
[47]
[50]. There was only insufficient information in the studies on adherence
parameters (56%), which is in line with the quality of adherence reporting for
moderate intensity exercise interventions [24]. We are convinced that in the majority of interventions, motivation
strategies are used to reduce dropout rates and increase adherence. Again, there was
no detailed information on if and how such strategies were used in the
interventions. By contrast, we found a good quality of reporting (89%) of items that
are crucial for the dosage of HIIT for hypertension. This finding is even better
than the quality of reporting of dosage information in moderate intensity training
interventions for hypertension (78%) [24].
However, it should be noted that a low level of reporting of details about an
exercise intervention may not reflect a low quality of the intervention per se.
Abell et al. contacted authors of interventions about unreported details and found
that many aspects were considered in the exercise protocols but not adequately
reported [51]. Moreover, although journals
with higher impact factors are more likely to endorse and enforce reporting quality
guidelines [52]
[53]
[54], we demonstrated no correlation between the quality of exercise
reporting and the impact factor of the journals in which the studies were published
[24]
[25]. One could have hypothesized finding a much better and more complete
description of the exercise programs, as HIIT is an innovative tool and investigated
in more recent studies. In this study, the oldest study from 2010 has the lowest
quality of reporting (47%) [33]. However,
despite the advent of checklists, research show that the quality of reporting of
exercise interventions does not appear to have improved over time [27]. Full compliance with reporting
guidelines can be difficult given the strict word limits of many journals. We
therefore suggest authors provide all relevant information required for CERT as
supplemental material. Notably, no single study reported to follow the Consolidated
Standards of Reporting Trials (CONSORT) guideline [55], which is used worldwide to improve the
reporting and transparency of trials. Journals should encourage and require
submission of a completed CERT checklist when exercise interventions are submitted.
Based on the findings of this study, if HIIT is comparable to traditional moderate
intensity training modes with regard to blood pressure reduction, then how it is
prescribed and delivered is mainly unclear, potentially limiting its translation
from research to practice. In a previous publication, we proposed the CORE-CERT
template with the most important items necessary for the replicability of exercise
interventions in clinical practice [26]. In
addition, disease-specific checklists would further improve the intervention
description of exercise studies for hypertension including blood pressure values
during HIIT. For hypertension interventions, items relating to patients’
antihypertensive medication directly before and during the intervention or
monitoring time and method could usefully be integrated into such “CERT plus”
hypertension-specific checklist.
Strength and limitations
This study revealed the quality of reporting of RCTs with HIIT in patients with
at least high normal blood pressure. However, this study has several
limitations. In previous studies investigating reporting quality we used the
best available evidence according to meta-analyses quoted by the most recent
recommendations of international scientific societies. The RCTs in these
meta-analyses were presumed to the most relevant evidence. In the case of HIIT
for hypertension, there is no widespread recommendation by national and
international hypertension societies. Thus, we did a study search on our own and
found a low number of RCTs with small sample sizes as compared to our previous
analysis of moderate intensity endurance exercise and hypertension. Although,
the number of RCTs on the subject is ever increasing of late, we have no
indication that the studies used in our study have a lower quality than more
recent publications. Additionally, we have included and analysed far fewer
primary studies than those of a recent meta-analysis by Li et al. [18] on HIIT for hypertension. In
contrast to our study, this meta-analysis included studies of any intervention
duration and with adult patients diagnosed at least with prehypertension
(SBP≥120 mmHg / DBP≥80 mmHg) according to Chinese guidelines. Different
international guidelines classify certain blood pressure levels differently,
with some categorizing a blood pressure of≥130/85 mmHg as primary hypertension.
However, in our study, we followed the ESH guidelines, which classify a blood
pressure of SBP≥130/ DBP≥85 mmHg as ‘high normal’.
Although the CERT template is increasingly being used to assess the reporting
quality of exercise interventions, it paid little attention to the question on
what is essential for simple replication of study setting as proposed in a
recent study by our group [26]. A
greater focus on key components could produce findings that account more for the
ability to perform and replicate an exercise therapy intervention in practice
and therefore are prerequisite for subsequent physical exercise recommendations.
Therefore, we basically refined the original CERT tool as a future step in the
initiative to improve the quality of reporting and developed the CORE-CERT
checklist as a more focused version of a guideline to report key items of
exercise studies, which are necessary for study replication. Although we propose
the use of the CORE-CERT checklist as a reporting tool across all types of
exercise interventions and conditions, we used the original CERT version here in
order to compare our results with our previous findings on endurance exercise
intervention for hypertension. In the future, researchers, journal editors, and
reviewers should insist on the use of reporting guidelines if exercise
interventions are described.
Practical Implications
Numerous analyses have stressed the importance of good reporting quality in studies
on exercise and different diseases. Recently, a comparable pressure-lowering effect
of HIIT with common exercise training modes was shown; however, the low quality of
reporting in studies of HIIT interventions for high blood pressure is a
disappointing result. Given the high variability of HIIT protocols, it would be very
difficult to replicate the interventions to reduce blood pressure in clinical
practice. To improve quality appraisal, evidence synthesis, replication and
translation of exercise interventions in practice, reporting of exercise
interventions must improve. In particular, the absence of references to adverse
effects is not suited to create confidence in clinicians considering the use of HIIT
in patients with hypertension. Therefore, we propose that authors be strongly
encouraged to use CORE-CERT for planning, carrying out, and publishing exercise
interventions. This would help to capture elements of the intervention that are
thought influential in determining effectiveness.
Bibliographical Record
Claudia Bünzen, Kaija Oberbeck, Sascha Ketelhut, Burkhard Weisser. High Intensity
Interval Training and Arterial Hypertension: Quality
of Reporting. Sports Med Int Open 2025; 09: a24939466.
DOI: 10.1055/a-2493-9466
