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The effect of exercise training at different intensities on blood
glucose regulation and cardiorespiratory fitness in patients
with Type 2 Diabetes: a randomized controlled trial
Shimal H. Hamad Chomani
Ph.D, lecturer and researcher at Department of Physical Education, Soran University, Soran, Erbil, Kurdistan Region, Iraq.
https://orcid.org/0000-0001-7050-3680 shamal.hamza@soran.edu.iq
Abstract
Diabetes mellitus is a major global health concern affecting nearly 382 million people worldwide.
Physical activity has long been regarded as the "gold standard" in treating type 2 diabetes.
Nonetheless, the diabetes population has a low prevalence of physical activity. Aim: the present
study aims to investigate the effects of low and high-intensity interval training on blood glucose
levels and cardiorespiratory fitness in patients with type 2 diabetes. Methodology: a prospective
randomized controlled trial with two intervention groups was applied. Participants (n=100; age,
height, weight) with type 2 diabetes were recruited and randomly divided into two intervention
groups: high-intensity interval training (HIIT) or low-intensity interval training (LIIT). HIIT and LIIT
pre and post-test assessments. The study was a follow-up clinic at a regional medical Centre in
Soran City\ Erbil, Iraq. They were aged between 50 and 55 years and had been diagnosed with type
2 diabetes. Results: HIIT and LIIT seems to have a more significant impact on blood sugar and the
cardiorespiratory system. Conclusion: HIIT and LIIT benefit heart rate and FEV1 for type 2 diabetic
patients.
Keywords: blood glucose, training intensity, cardiorespiratory fitness, type 2 diabetes.
Introduction
There is a growing awareness of the function of physical activity in improving both physical and
body health. The majority of studies to date indicate that exercise can significantly enhance
physiological variables such as blood sugar and cardiovascular fitness (Rosenbaum et al., 2014;
Scheewe et al., 2013).
High and low-intensity interval training (HIIT, LIIT) is a type of physical activity in which brief bursts
of vigorous activity are combined with rest periods or low-intensity exercise. HIIT and LIIT are
infinitely changeable, with the physiological adaptations caused by this type of training governed
by many variables, including the precise nature of the exercise stimulus (Hurst et al., 2019).
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However, when compared to regular endurance training on a matched-work basis or when
estimated energy expenditure is identical, HIIT can induce equal or even better improvements in
various physiological, performance, and health-related variables for futsal players (Gibala et al.,
2012).
Low-volume, HIIT is becoming a time-efficient exercise for general population health and fitness
improvement. According to the researchers, HIIT increases oxygen absorption, muscle
deoxygenation, and improved exercise performance compared to low-intensity continuous
endurance training (Jacobs et al., 2013; McKay et al., 2009). In addition, HIIT has been shown to
help increase cardiorespiratory fitness, blood sugar management, fat reduction, and blood
pressure management (Byrd et al., 2019; Finn, 1996).
Several studies have noticed that interval training may pose physical and physiological hazards,
eliciting an avoidant reaction and retreat. Additionally, HIIT requires participants to exercise self-
discipline and self-regulation to achieve the appropriate degree of intensity (Hardcastle et al.,
2014; Viana et al., 2018). Therefore, the study aims to compare between HIIT and LIIT, which
affects blood glucose regulation levels. The researcher's decision to study, understand, and
compare both types of interval training on the impact of blood glucose regulation levels and
cardiorespiratory in type 2 diabetes was due to the knowledge that the training types are essential
for the physiological variables.
Methods and procedures
Participants
One hundred patients presenting a follow-up clinic at a regional medical Centre in Soran City\ Erbil-
Iraq, were referred by medical professionals and volunteered to participate in this study. They were
aged 50-55 years and had been diagnosed with type 2 diabetes (blood glucose level 180ml.mol)
for over a year with a specialist doctor. Patients were included if they met the global initiative for
diabetes guidelines for type 2 diabetes, such as classification based on medical history, diagnosis,
and physical examination (Clinical Guidelines Task Force Global Guideline for Type 2 Diabetes,
2012). Participants were only accepted into the study if they were in a clinically stable condition,
had no history of infections or worsening diabetes symptoms, and had made no medication
changes in the two months preceding the study's start date. The study was approved by the
Institutional Review Board (IRB) of the Soran University in Iraq (date of approval on the third of
November, 2021). All experimental procedures regarding testing, lower and upper torso training
by devices were carefully explained to the participants, and written informed consent from
participants who met the inclusion criteria was obtained before the beginning of the experiment.
Table 1 shows the baseline characteristics of the study population.
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Table 1. Baseline characteristics of the study population.
Variables
Mean
SD
Age, yr
53.2
6.1
Weight, kg
68.1
8.2
High, cm
175.3
11.6
Blood sugar test
185.4
12.8
FEV1, % of predicted
80.2
9.3
Heart rate at rest
80.5
9.4
Experimental design
The researchers used an experimental research design. The study was a prospective randomized
controlled trial with two groups that compared the high and low interval intensity training. The
study sample was recruited and randomly divided into two intervention groups (HIIT n=50, LIIT
n=50). Pre- and post-test assessments were all conducted by the researchers, who had a special
training certificate. Thus, the researcher is familiar with the physiology of cardiorespiratory,
respiratory muscle work, and blood sugar tests.
Measurement Procedures
Outcome Measures
1. Blood Sugar Test
Normal blood sugar levels are less than 120 mg/dL (7.8 mmol/L). After two hours, a blood sugar
level of more than 200 mg/dL (11.1 mmol/L) indicates diabetes. A blood sugar level of 130 to 199
mg/dL (7.8 mmol/L to 11.0 mmol/L) indicates prediabetes. Our participants have done the
measurement after effort.
2. Lung function measurements
Forced expiratory volume in one second (FEV1) was used to assess lung function. A spirometer (as
used by Burt et al., 1995). After the three acceptable Forced vital capacity (FVC) manoeuvres, all
values of FVC, FEV1, and the ratio of FEV1 to FVC was measured. The spirometer is a basic test that
is used to diagnose airway blockage. However, the variability of spirometry measures is greater
than that of most other clinical laboratory tests since the outcome is greatly dependent on the
consistency of patient and technician efforts (Crapo, 1994). In addition, each subject will be tested
according to the criteria of the American Thoracic Society, which recommends the use of FEV1 to
diagnose the severity of airway obstruction to detect lung function (Balmes et al., 2003).
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3. Heart Rate Measurement
Resting heart rate (HR) is frequently used to assess cardiorespiratory fitness. Cardiorespiratory
fitness is inversely associated with resting heart rate in adults, according to cross-sectional
research. Aerobic training lowered resting heart rate in untrained men and women regardless of
age (41 or 41-60 years) or duration of the intervention (3, 4-6, or > 6 months). Although this link
may be ascribed to increased resting cardiac vagal activity, electrophysiologic alterations intrinsic
to the sinus node may also occur in many physically conditioned individuals.
A heart rate monitor (HRM) is a personal monitoring device that allows you to measure and display
your heart rate in real-time and record it for later analysis. It is mostly used to collect resting heart
rate data (Quintana et al., 2012).
Low and High-intensity interval training procedure
Participants attended a 1-h familiarization session where the specific training protocol was
instructed and the necessary training equipment and exercise adherence diary distributed.
Exercise training is performed on an outpatient basis. All sessions started with ergometer cycling.
In the LIIT experimental group, the target training intensity was 50-70% HRmax, whereas in the
HIIT experimental group, the target training intensity was 75-85% HRmax. The intervals in LIIT were
5 min, while 3 min. Total cycle time was 40 min, each session allowed for five "uphills", separated
by four "downhills" and warming up before and cooling down afterwards. Exercise load kept as
high as tolerated at all times, above the target values when possible.
Moreover, training programs used different exercises for upper and lower limb, i.e. jumping,
running, jogging, arm and leg movements, flexibility exercises for thorax, neck, shoulders, arms,
and legs, as well as the abdominal muscles (20 repetitions, 3 sets, at about 50-70% of 1 RM), (8
repeats, 4 sets, at about 75-85% of 1 RM) sessions. All patients scored their measurements before
and after an intervention. After cycling, the session proceeded twice a week with callisthenics and
relaxation and once a week with resistance training.
Statistical Analysis
Data was entered in the SPSS software, and the results were analyzed using an independent and
dependent sample test (T-test).
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Results and discussion
Table 2. Mean, SD, T-test, signal, and Significant of Pre and post-tests for Group 1.
Variables
Pre-test
Post-test
T-test
Significant
Mean
SD
Mean
SD
Accountable
Signal
Blood sugar test
183.17
11.33
145.21
8.45
4.03
50.00
S
FEV1, % of predicted
80.00
6.05
90.52
7.71
3.13
0.000
S
Heart rate at rest
83.2
6.16
73.24
5.81
3.07
0.000
S
Size of the study population (49), and significant level (0.05).
Table 2 shows there is a significant difference between the two tests, pre and post, at the error
rate (5%) and the degree of freedom (49) in measuring blood sugar test, FEV1, and heart rate at
rest, where the value of calculated T in all tests is (4.03, 3.13, 3.07) which is bigger than the value
of T tabular (2.05) and this means there is improvement in all study tests for the group 1.
Table 3. Mean, SD, T-test, signal, and Significant of Pre and post-tests for Group 2
Variables
Pre-test
Post-test
T-test
Significant
Mean
SD
Mean
SD
Accountable
Signal
Blood sugar test
182.23
10.12
144.67
8.67
3.63
00.00
S
FEV1, % of predicted
82.13
6.85
89.44
7.83
3.68
0.000
S
Heart rate at rest
82.86
6.90
74.35
5.95
3.81
0.000
S
Size of the study population (49), and significant level (0.05).
Table 3 shows there is a significant difference between the two tests pre and post at the error rate
(5%) and the degree of freedom (49) in measuring blood sugar test, FEV1, and heart rate at rest,
where the value of calculated T in all tests is (3.63, 3.68, 3.81) which is bigger than the value of T
tabular (2.05) and this means there is improvement in all study tests for the group 2.
Table 4. shows the mean, SD, T-test, signal, and significance of post-tests for both groups.
Variables
Group 1
Group 2
T-test
Significant
Mean
SD
Mean
SD
Accountable
Signal
Blood sugar test
145.21
8.45
144.67
8.67
1.68
0.07
No S
FEV1, % of predicted
90.52
7.71
89.44
7.83
1.70
0.09
No S
Heart rate at rest
73.24
5.81
74.35
5.95
1.73
0.08
No S
Size of the study population (98), and significant level (0.01).
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Table 4 shows there is no significant difference between the two groups in post-tests at the error
rate (1%) and the degree of freedom (98) in measuring blood sugar test, FEV1, and heart rate at
rest, where the value of calculated T in all tests is (1.68, 1.70, 173) which is bigger than the value
of T tabular (1.57) and this means there is no significant between two groups in all study tests.
Endurance and strength exercise performance has been reduced with diabetes type 2 (O'Connor
et al., 2012; Wilkerson et al., 2011). Furthermore, in type 2 diabetes patients, a higher resting heart
rate is associated with an increased risk of cardiorespiratory problems and early mortality (Hillis et
al., 2012). Furthermore, according to a recent study published in Diabetes Care, people with type
2 diabetes are 54% more likely to have pulmonary fibrosis, 22% more likely to have a chronic
obstructive pulmonary disease, 8% more likely to have asthma, and nearly twice as likely to be
hospitalized for pneumonia (Ottaviano et al., 2020). However, exercises with low and high-intensity
interval training (aerobic and anaerobic training) can be used to treat patients with diabetes type
2.
Diabetic individuals can safely do aerobic and anaerobic training involving large muscle groups with
low and high-intensity intervals. As a result, this training group commonly includes low-intensity
interval training aerobic exercises such as walking, jogging, and cycling (Thent et al., 2013; Zhang
et al., 2013). Anaerobic exercises that use high-intensity interval training develop muscle strength
and power by adjusting resistance intensity from 75% to 90% of 1-repetition maximum (Adams,
2013).
The current study found that both groups improved on all tests (blood sugar, FEV1, per cent of
predicted, and heart rate at rest). However, both high and low-intensity interval training resulted
in similar gains. A new study found that high-intensity interval training can enhance blood sugar
and cardiorespiratory health in type 2 diabetic patients (Francois & Little, 2015). On the other hand,
other studies found that low cardiorespiratory fitness is a well-known risk factor for chronic
diseases such as type 2 diabetes and a key predictor of mortality in diabetes patients (Church et
al., 2004; Paffenarger & Lee, 1996; Wei et al., 2000).
According to Terada et al. (2013), HIIT also provided superior acute blood sugar reductions
compared to low-intensity interval exercise, as measured by arm vein samples obtained before
and after each training session throughout a 12-week training program. According to Roberts et al.
(2013), HIIT boosts blood sugar levels, which leads to the recruitment of more muscle fibers and
the rapid depletion of muscle glycogen stores. Thus, high and low-intensity interval training may
be an effective strategy for significantly improving sugar control over the long term by stimulating
a more significant increase in post-exercise muscle insulin sensitivity, which lasts for 24-48 hours
after a single bout of exercise. Furthermore, high and low-intensity interval training may be an
effective strategy for significantly improving sugar control over the long term. In addition, HIIT and
LIIT performed over a more extended period (e.g., 12–16 weeks) may enhance lower-body muscle
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mass (Gillen et al., 2013) and have the added benefit of decreasing abdominal adipose tissue
(Boutcher, 2011).
Heart rate and FEV1 have improved following high and low-intensity interval training; Andrade et
al. (2020) confirmed that HIIT and LIIT improve heart rate and pulmonary function, whereas Parpa
et al. (2009) discovered that training with HIIT and LIIT for 12 weeks leads to significant
improvements in resting heart rate and fasting glucose values.
Conclusion
High-intensity interval training and low-intensity interval training both improve heart rate and FEV1
in type 2 diabetics. The type of activity chosen to treat diabetes should be suited to the patient's
clinical profile. Further studies are needed to assess continued exercises on blood sugar levels in
type 1 diabetes.
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