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The Effect of a 12 Week High Intensity Interval Training Program on Glycosylated
Hemoglobin A1c in Patients with Type II Diabetes
A Thesis Proposal
Presented to
The Faculty of
Western Washington University
In Partial Fulfillment
Of the Requirements for the Degree
Master of Science
XXXXX XXXXXX
December 3, 2013
Chapter I
The Problem and Its Scope
Introduction
Diabetes is the seventh leading cause of death in the United States, killing over 231,400
people annually and costing the United States 174 billion dollars each year. It is estimated that
25.6 million people age 20 and older are affected by diabetes in the United States, with the
highest prevalence among Caucasians. Diabetes may lead to serious complications including
hypertension, blindness and eye problems, kidney disease, nervous system disease, amputations,
dental disease, pregnancy complications, diabetic ketoacidosis, and hyperosmolar (nonketotic)
coma (Centers for Disease Control and Prevention, 2011b). Furthermore, diabetes was identified
as a key risk factor for development of cardiovascular disease (Murphy, Xu, & Kochanek, 2010),
the leading cause of death among both men and women in the United States (Centers for Disease
Control and Prevention, 2011a).
Treatment goals for diabetics include managing blood glucose, blood pressure, and lipid
levels (Centers for Disease Control and Prevention, 2011b). Physical activity has been proposed
as a preventative measure against diabetes, reducing the risk of developing type II diabetes by
30-50% (Bassuk & Manson, 2005; French et al., 2008). One proposed mechanism by which
exercise protects against type II diabetes is by improved glycemic control (Alizadeh, Bijeh, &
Hakak Dokht, 2012; Boulé, Haddad, Kenny, Wells, & Sigal, 2001; Figueira et al., 2013;
Kennedy et al., 1999). It is widely accepted that aerobic and resistance exercises improve
glycemic control in patients with type II diabetes (Alizadeh et al., 2012; Figueira et al., 2013;
Gordon, Bird, MacIsaac, & Benson, 2013).
Despite the health benefits, only 39% of diabetics are physically active (Morrato, Hill,
Wyatt, Ghushchyan, & Sullivan, 2007). Diabetic patients report lack of time and discomfort
during exercise as the top barriers to physical fitness (Egan et al., 2013). Recent studies suggest
that high intensity interval training may provide the same or superior results in glycemic control
compared with traditional aerobic and resistance training (Babraj et al., 2009; Burgomaster et al.,
2007; Gillen et al., 2012; Kjaer et al., 1990; Little et al., 2011; Nybo et al., 2010; Richards et al.,
2010; Sandvei et al., 2012; Whyte, Gill, & Cathcart, 2010). This exercise model may be
appealing to patients with type II diabetes the time commitment and perceived exhaustion are
less (Gillen et al., 2012; Kjaer et al., 1990; Little et al., 2011).
Purpose of the Study
The purpose of this study was to determine if a significant difference existed in
glycosylated hemoglobin A1c (HbA1c) in type II diabetic patients following a 12 week high
intensity interval training program.
Null Hypothesis
There is no significant difference in HbA1c levels in patients with type II diabetes
following a 12 week high intensity interval training program.
Significance
As the prevalence of type II diabetes rises, cost-effective treatment approaches are highly
valuable in a clinical setting. The role of high intensity interval training in improving glycemic
control is not well researched. Specifically, there is little published research on the effect of high
intensity interval training on HbA1c, a diagnostic marker for pre-diabetes and diabetes (Cox &
Edelman, 2009). Results from this study will provide information about the role of high intensity
interval training in protection against type II diabetes. A better understanding of this may provide
novel and practical approaches to prevention and treatment of type II diabetes.
Limitations of the Study
1. Participants were recruited from the PeaceHealth St. Joseph Medical Center Nutrition and
Diabetes Clinic which assists with lifestyle management. The lifestyle management assistance
may have affected the results of this study.
2. Variations in body weight and fat mass may have impacted the results. For example, obese
individuals may have been less metabolically healthy.
3. Health status of each subject may have changed from pre to post test, impacting HbA1c levels.
4. Use of diabetic medication was not controlled for, as individual medical needs differed.
5. Participants entered the study with varying physical fitness levels and diet. Subjects were
asked not to change their exercise or diet habits during the study, but this was difficult to control
in all subjects.
6. It was assumed that maximal effort was utilized by participants during training and testing
sessions.
7. The study was carried out with type II diabetic patients. The results may not be generalizable
to patients with type I or gestational diabetes.
8. The study did not compare HIIT to other modes of exercise. More research is needed to
evaluate HIIT in comparison with other exercise programs.
9. There were not enough bicycle ergometers for all participants to train at the same time.
Participants completed training at different times which may have affected results.
Definition of Terms
Diabetes: A group of disease characterized by high blood glucose levels. Diabetes may result
from defects in insulin production, insulin action, or both (Centers for Disease Control and
Prevention, 2011b).
Glycemic control: physiological regulation of blood glucose (Centers for Disease Control and
Prevention, 2011b).
HbA1c test: a diagnostic blood test that presents information about a patient’s average blood
glucose levels over the last three months. The HbA1c test is used for diabetes management and
research (Gillett, 2009).
High intensity interval training: there is no universal definition of HIIT, but it usually refers to
exercise comprised of short bursts of vigorous exercise (>90% VO2max) separated by short
recovery periods (Gibala & McGee, 2008).
Pre-diabetes: a condition in which patients have elevated blood glucose or HbA1c levels, but the
levels are not elevated enough for a diagnosis of diabetes. Pre-diabetic patients have an increased
risk for type II diabetes and cardiovascular disease (Centers for Disease Control and Prevention,
2011b).
Type II diabetes: typically begins as insulin resistance, a disorder in which insulin is not properly
used by the cells. The need for insulin increases and the pancreas slowly loses the ability to
produce insulin. This type of diabetes is also known as non-insulin-dependent diabetes mellitus
(NIDDM) or adult-onset diabetes and is associated with age, obesity, family history, impaired
glucose metabolism, physical inactivity, and ethnicity (Centers for Disease Control and
Prevention, 2011b).
Chapter II
Review of Literature
Introduction
Type II diabetes typically begins with insulin resistance, a disorder in which insulin is not
properly used by the cells. As the need for insulin increases, the pancreas slowly lose the ability
to produce insulin. This type of diabetes is associated with age, obesity, family history, impaired
glucose metabolism, physical inactivity, and ethnicity (Centers for Disease Control and
Prevention, 2011b; Hu, 2011). The estimated risk for developing diabetes is 32.8% in males and
38.5% in females (Narayan, Boyle, Thompson, Sorensen, & Williamson, 2003).
Management of diabetes is important as serious complications such as cardiovascular
disease, stroke, hypertension, blindness, kidney disease, nervous system disease, amputations,
dental disease, pregnancy complications, diabetic ketoacidosis, and hyperosmolar coma may
occur (Centers for Disease Control and Prevention, 2011a; Centers for Disease Control and
Prevention, 2011b). Treatment goals for diabetics include managing blood glucose, blood
pressure, and lipid levels (Centers for Disease Control and Prevention, 2011b). Physical activity
is used as a preventative measure, reducing the risk of developing type II diabetes by 30-50%
(Bassuk & Manson, 2005).
Aerobic and resistance training help manage type II diabetes by improving glycemic
control (Alizadeh et al., 2012; Figueira et al., 2013; Gordon et al., 2013). Exercise
recommendations for patients with diabetes consist of 150-210 minutes of moderate intensity
combined aerobic and resistance exercise spread between 3-5 sessions a week (Bhattacharyya,
Shah, & Booth, 2008). Despite the benefits of exercise, only 39% of diabetics are physically
active (Morrato et al., 2007).
Lack of time and discomfort during exercise are reported as major barriers to physical
fitness (Egan et al., 2013). High intensity interval training (HIIT) may provide the same or
enhanced glycemic control compared with aerobic and resistance training (Babraj et al., 2009;
Burgomaster et al., 2007; Gillen et al., 2012; Kjaer et al., 1990; Little et al., 2011; Nybo et al.,
2010; Richards et al., 2010; Sandvei et al., 2012; Whyte et al., 2010). HIIT may appeal to type II
diabetics because the time commitment and perceived exhaustion levels are less compared with
traditional aerobic and resistance exercises (Gillen et al., 2012; Kjaer et al., 1990; Little et al.,
2011).
Aerobic and Resistance Exercise
Aerobic and resistance exercise have been shown to improve glycemic control as
effectively as some anti-diabetic medications (Boulé et al., 2001; Snowling & Hopkins, 2006;
Umpierre et al., 2011). Exercise may be an effective treatment for low-income patients, patients
who dislike taking medications, or those who want additional glucose control. Some research
indicates that both duration and intensity affect glycemic control (Umpierre et al., 2011), but
there is considerable evidence that intensity may have more impact than volume on glycemic
control (Babraj et al., 2009; Burgomaster et al., 2007; Gillen et al., 2012; Little et al., 2011;
Mourier et al., 1997; Nybo et al., 2010; Richards et al., 2010; Sandvei et al., 2012; Whyte et al.,
2010). The exact effects and mechanisms of glycemic control during high intensity exercise
remains unknown. Investigation of the roles of aerobic, resistance, and high intensity interval
training in glycemic control is clinically important for new prevention and treatment approaches.
Mechanism of Glucose Regulation during Aerobic and Resistance Exercise
Most of glucose uptake after eating is by skeletal muscle. Transport of glucose into
muscle cells has been identified as a major limiting step in glucose metabolism (Houmard et al.,
1991; Hughes et al., 1993). Much of glucose uptake into the muscle is carried out by glucose
carrier proteins, such as GLUT4. Exercise and insulin promote the transfer of GLUT4 from the
intracellular compartment to the plasma membrane and transverse tubules. At rest and after
eating, glucose uptake is mediated by insulin-dependent pathways to restore muscle glycogen
levels (Colberg et al., 2010).
During exercise, intramuscular glycogenolysis and glucose uptake are increased to meet
metabolic demands for energy. GLUT4 transport is often impaired in type II diabetic patients.
Exercise, however, has been shown to increased GLUT4 levels and translocation of GLUT4 to
the plasma membrane. Therefore, more glucose can be taken into the skeletal muscle by a
pathway which is not insulin dependent (Colberg et al., 2010). The resulting glucose uptake may
be equal to normal glucose uptake in non-diabetics (Colberg et al., 2010; Kennedy et al., 1999).
In people who do not have diabetes, insulin levels are decreased with exercise and this is
sensed by the liver which increases glucose production in response. The increased glucose
uptake by skeletal muscle is balanced by an increase in hepatic production of glucose explaining
unchanged blood glucose levels (Colberg et al., 2010; Marliss & Vranic, 2002). During exercise
for patients with type II diabetes, skeletal muscle glucose uptake is usually higher than hepatic
glucose production (Little, Safdar, Wilkin, Tarnopolsky, & Gibala, 2010), explaining the slight
decrease in blood glucose levels in response to exercise. Despite the drop in blood glucose,
hypoglycemia is not a pertinent concern during exercise because insulin levels decrease. This
helps to balance the increased skeletal muscle glucose uptake (Colberg et al., 2010).
High Intensity Exercise
Models of high intensity interval training. There is no universal definition of HIIT, but
it usually refers to exercise comprised of short bursts of vigorous exercise (>90% VO2max)
separated by short recovery periods (Gibala & McGee, 2008). The wingate test is a common
model of HIIT performed on a cycle ergometer. It is preceded by 3-5 minutes of warm up. The
test usually consists of 4-6 30 second “all-out” maximal effort cycling bouts against a
standardized resistance. The cycling bouts are separated by 4 minute rest intervals. During the
wingate test, a total of 2-3 minutes of maximal exercise is typically performed over 15-30
minutes (Little et al., 2010). The high intensity and short duration of the wingate test elicit
mostly anaerobic power (Smith & Hill, 1991). The wingate test is very stressful and participants
are usually supervised and verbally encouraged as a high level of motivation is needed to
complete the test (Bayati, Farzad, Gharakhanlou, & Agha-Alinejad, 2011).
Altered HIIT programs comprised of longer sessions, more repetitions, and shorter rest
periods may be a better option for studies with diabetic participants (Bayati et al., 2011). Recent
studies have shown that interval training programs using decreased intensity and increased
duration have shown similar benefits compared with more intense programs. The less intense
model of interval training may be more realistic for nonathletic participants. Such programs may
consist of 6-10 cycling bouts of 30 seconds at 125% of power at VO2max separated by 2 minute
rests between each cycling bout (Bayati et al., 2011; Burgomaster, Hughes, Heigenhauser,
Bradwell, & Gibala, 2005).
Glucose metabolism during high intensity interval training. Exercise of >80%
VO2max utilizes glucose as the exclusive muscle fuel, greatly impacting glycemic control
(Marliss & Vranic, 2002). Unlike moderate intensity exercise, research has shown a significant
rise in catecholamine levels during high intensity exercise. This stimulates a 7-8 fold increase in
glucose production and a 3-4 fold increase in glucose uptake. The resulting increase in blood
glucose seen in diabetic patients during HIIT is mediated by increased plasma insulin levels.
This response is only present in patients with type II diabetes, as insulin production is absent in
type I diabetes (Centers for Disease Control and Prevention, 2011b).
High intensity interval training and glycemic control in healthy non-diabetic adults.
Research on the effect of HIIT on glycemic control is more prevalent in healthy non-diabetic
patients. This could be because the musculoskeletal and cardiometabolic risks are lower for non-
diabetic participants. Healthy subjects naturally may also be more physically fit than diabetic
subjects. For the following studies, the cycle ergometer was considered superior to running
interval training. Even though the intensity during running was lower than the cycle ergometer,
obese individuals developed shin splints and dropped out (Nybo et al., 2010).
Four of the following studies used maximal effort during cycle ergometer training and
two of them used submaximal training. Richards et al. (2010) studied young and healthy
sedentary or recreationally active subjects. Subjects were randomly assigned to one of three
groups: 1) 6 sessions of HIIT, 2) 1 session of HIIT, or 3) sedentary control. Insulin sensitivity
was recorded before and 72 hours after treatments. Insulin sensitivity was evaluated by the
euglycemic clamp method (golden standard). Results showed that 2-3 days after a 2-week
exercise program of 6 HIIT sessions, fasting blood glucose was not improved. However, insulin
sensitivity was improved compared to baseline measurements. Insulin sensitivity did not improve
after one session of HIIT or in the sedentary control group.
In contrast to the study of healthy subjects by Richards et al. (2010), Whyte et al. (2010)
studied overweight and obese sedentary men using a HIIT program similar to that used by
Richards et al. and Whyte et al. found no improvement in fasting blood glucose, but insulin
sensitivity was improved at both 24 hours and 72 hours post-intervention compared with baseline
measurements. These results supported the findings of Richards et al.
Babraj et al. (2009) evaluated insulin sensitivity before and 48-72 hours after HIIT
interventions using the oral glucose tolerance test (OGTT) and Cederhold index. In contrast to
the results found by Richards et al. (2010) and Whyte et al. (2010), fasting blood glucose (FBG)
and fasting insulin levels were unchanged. However, both glucose area under the curve (AUC) (-
12%) and insulin AUC (-37%) were significantly reduced during OGTT. HIIT may have
improved insulin action by using up muscle glycogen stores.
Burgomaster et al. (2007) looked at muscle GLUT4 content in response to HIIT. Results
showed that HIIT elevated muscle GLUT4 content by 20% after 1 week of training compared
with baseline. The levels remained increased for the rest of the 5 week training program.
Furthermore, levels remained elevated after 6 weeks of detraining. Burgomaster et al. also
evaluated cytochrome c oxidase subunit 4 (COX4) protein content, an indicator of muscle
oxidative capacity. COX4 protein content increased by 35% after 1 week of HIIT and remained
significantly higher compared with baseline levels after 6 weeks of detraining.
These findings suggest that some physiological benefits of HIIT may remain even if
training is discontinued. This is important for participants who have difficulty adhering to an
exercise program. People who are not willing or able to continually participate in HIIT may still
benefit from physiologically adaptations obtained during training. Future research should
examine how long these physiological benefits last.
Sub maximal models have also been examined and compared with maximal interval
training models in regards to glycemic control. Nybo et al. (2010) found that 20 minutes of near
maximal running (40 minutes of total exercise including rest) per week for 12 weeks was equally
effective as 150 minutes of running at 65% VO2max per week over 12 weeks. Both exercise
programs both improved fasting blood glucose and blood glucose two hours after oral ingestion
of 75 grams of glucose. Sandvei et al. (2012) had similar results to Nybo et al., finding that 7.5-
15 minutes of near maximal running each week was sufficient to improve glucose regulation.
These studies suggest that a submaximal interval training program may produce similar
results to maximal interval training. This is important to consider when working with diabetic
patients as they may not be willing to complete maximal interval training.
High intensity interval training and glycemic control in adults with type II diabetes.
There are few studies on HIIT in people with diabetes. Many studies use a less intense form of
interval training that does not require maximal effort since the diabetic population is largely
sedentary and less willing to complete maximal exercise training.
Little et al. (2011) examined the effects of six HIIT sessions spread over two weeks on
glucose regulation 48-72 hours after the final training day in subjects with type II diabetes. The
majority of subjects completed 60 minutes or less of exercise each week before the study. The
interval training included 30 minutes of high intensity exercise each week with a total of 75
minutes per week including warm up, cool down, and rest periods. Little et al. used a
submaximal training program. Glucose regulation was evaluated using 24 hour continuous
glucose monitoring with standardized dietary regulation. Blood glucose levels were reduced by
13% 24 hours after the last exercise training session. Standard 3 hour postprandial glucose AUC
for breakfast, lunch, and dinner was reduced by 30%. These results may be important to
clinicians as postprandial hyperglycemic control is a goal for type II diabetes management.
Little et al. (2011) also found that GLUT4 protein content was increased by 369% after
two weeks of training. This increase in GLUT4 would greatly increase skeletal muscle glucose
uptake. Glucose uptake by GLUT4 is not insulin-dependent and increased GLUT4 protein
content is highly beneficial to participants with type II diabetes (Colberg et al., 2010).
Little et al. (2011) asked subjects to rate how enjoyable they would consider participating
in HIIT three times a week for a month and found that the mean response was 7.9 on a scale
from 1 (not enjoyable at all) to 9 (very enjoyable). They also evaluated rate of perceived
exhaustion and found a range of 4-8 on a 10 point scale during training. These results suggest
that on average, participants considered HIIT somewhat enjoyable and perceived exhaustion was
variable. This is important when considering the barrier of discomfort for physical activity in
diabetes (Houmard et al., 1991).
Gillen et al. (2012) used the same exercise program as Little et al. (2011). Their results
showed that a single exercise session was sufficient to reduce 3 hour postprandial glucose AUC.
Additionally, they found that the amount of time that glucose was above 10 mmol/L during 24
hours post-exercise period compared to the sedentary control was significantly decreased.
However, after 24 hours, blood glucose reduction was no longer significant (p=0.16). The results
seem to suggest that HIIT improves glycemic control, however Gillen et al. used the same
subjects from the study by Little et al. It is possible that the participants were still exhibiting
benefits from the study by Little et al. and that the benefits found by Gillen et al. were not due to
the exercise treatment in the study. However, the sedentary control did not show significant
increases in glycemic control, suggesting that the interval training may have been effective.
Kjaer et al. (1990) examined the effect of 5 minutes of high intensity interval exercise in
relation to blood glucose control during and up until 3 hours postexercise in type II diabetic
subjects. They found that the rise in glucose levels in type II diabetics compared to controls was
greater and lasted longer. Peak blood glucose levels were seen in type II diabetic subjects at 30
minutes post-exercise, with baseline levels at 147 mg/dL and 30 minutes post-exercise levels at
169 mg/dL. Blood glucose levels began to decrease at one hour post-exercise. For non-diabetic
controls, blood glucose increased from baseline level of 90 mg/dL to a peak of 100 mg/dL at 10
minutes post-exercise. At one hour post-exercise, blood glucose did not differ from baseline
levels in non-diabetic controls. Plasma insulin levels were increased in both groups after exercise
and returned to baseline at 120 minutes post-exercise.
Plasma epinephrine and glucagon were also measured. The increase in these hormones
following exercise was higher in type II diabetic patients compared with non-diabetic controls.
Type II diabetic subjects showed increased insulin effect on glucose uptake by insulin clamp
technique 24 hours after exercise. Other studies have supported this finding that insulin helps to
dispose of glucose after short term HIIT programs (Devlin, Hirshman, Horton, & Horton, 1987;
Devlin & Horton, 1985). Kjaer et al. (1990) attributed post-exercise hyperglycemia and
hyperinsulinemia in type II diabetes to hormonal responses.
These studies demonstrate that HIIT may provide multiple benefits that increase
glycemic control in people with type II diabetes. They also show that the response to HIIT is
highly variable. Blood glucose tests may be affected by factors such as the time of testing, the
last meal, stress levels, hormone responses, and insulin activity (Gillen et al., 2012; Kjaer et al.,
1990; Little et al., 2011). Future considerations for the method of testing glycemic control are
important, especially when working with diabetic patients.
Glycosylated hemoglobin A1c as a measurement of glycemic control in type II
diabetics. Glycosylated hemoglobin A1c, HbA1c, is formed by a reaction of glucose with the α
amino group of the valine residue at the N-terminus of β globin chains. Internal rearrangement of
the resulting aldimine produces a stable ketoamine derivative (Peacock, 1984). HbA1c blood
concentration is a sensitive measure used in the evaluation of glycol-metabolic control in
diabetes and in the diagnosis of diabetes mellitus (Standards of Medical Care in Diabetes, 2012).
HbA1c is considered the golden standard for measuring glucose control (Cox & Edelman, 2009)
and was endorsed by the American Diabetes Association (ADA) as a first-line screening and
diagnostic test in 2009 (Gillett, 2009).
Despite the accuracy of this test, very few studies examining the effect of HIIT on
glycemic control have used HbA1c. HbA1c is an excellent test for research, especially for long
term experiments. HbA1c blood levels represent the average glucose control over the last three
months. For this reason, it is more accurate than a blood glucose test at a single time point (Cox
& Edelman, 2009).
In addition to the accuracy of the HbA1c test, it is easy to obtain and does not require
fasting. HbA1c levels are often monitored by physicians and may be accessed by researchers with
permission from participants. This method of assessment is also more convenient to the
researcher because it only requires one test before and one test after the treatment. Researchers
do not need to control for factors that affect blood glucose variation during a given day. HbA1c is
also a valuable tool because it measures insulin function (Cox & Edelman, 2009). The studies in
this review show that HIIT has a significant impact on insulin (Gillen et al., 2012; Kjaer et al.,
1990; Little et al., 2011), further justifying the use of HbA1c as a measurement of glycemic
control.
Summary
Type II diabetes is a serious condition characterized by impaired glycemic regulation
(Centers for Disease Control and Prevention, 2011b). Aerobic and resistance training provide
improved glycemic control to diabetic patients (Boulé et al., 2001; Snowling & Hopkins, 2006;
Umpierre et al., 2011), but the clinical exercise guidelines for type II diabetic patients may not be
followed due to time constraints and discomfort during exercise (Egan et al., 2013).
HIIT is an alternate form of exercise that may provide equally beneficial improvements
in glucose regulation, insulin sensitivity, GLUT4 content, COX4 content, and VO2max when
compared with aerobic and resistance training (Gillen et al., 2012; Kjaer et al., 1990; Little et al.,
2011). HIIT is less of a time commitment and the perceived exhaustion is less than aerobic or
resistance training (Little et al., 2011). This is important when considering that the major barriers
to physical fitness in diabetics are lack of time and discomfort during exercise (Egan et al.,
2013).
There are few studies that have examined the effect of HIIT in type II diabetic patients.
Specifically, there is very little published research on long term effects of a HIIT program on
glycemic control in patients with type II diabetes. Very few studies have used HbA1c as a
measure of glycemic control (Cox & Edelman, 2009). Future research should utilize this highly
accurate measure to examine the long term effects of HIIT on glycemic control. Future research
is needed to determine these effects and provide information about HIIT as a prevention or
treatment of diabetes.
Chapter III
Methods and Procedures
Introduction
This study was designed to examine the effect of a twelve week high intensity interval
training (HIIT) program on glycosylated hemoglobin A1c (HbA1c) levels in type II diabetic
patients.
Description of Study Population
Twenty male and twenty female participants with type II diabetes [as defined by the
American Diabetes Association (2013)] were recruited from the PeaceHealth St. Joseph Medical
Center Nutrition and Diabetes Clinic in Bellingham, WA, following approval of the study from
the University Human Subjects’ Committee. Participants (mean age 52 ± 3 years, body mass
index 30.5 ± 1.9 kg/m2) exhibited baseline HbA1c values of >6.0% (Rosenzweig, Weinger,
Poirier-Solomon, & Rushton, 2002), and had no exercise training within the past six months.
Exclusion criteria included severe cardiovascular and cerebrovascular disease, diabetic
nephropathy, diabetic retinopathy, and severe diabetic neuropathy. All participants were on
antihyperglycemic medications and did not change the dosage of medication during the study.
Likewise, participants were asked not to alter their diet during the course of the study.
Participants performed an exercise stress test and were not allowed to participate in the study if
abnormalities were seen in the electrocardiogram (ECG) recordings.
Design of the Study
This study utilized a pretest-posttest randomized groups experimental design in which
participants were randomly assigned to either the control or treatment group.
Data Collection Procedures
Instrumentation. High intensity interval training (HIIT) was completed in the Exercise
Physiology Laboratory at Western Washington University on a Monarck bicycle ergometer
(Sweden). Maximal oxygen uptake (VO2max) was obtained using the Parvo Medics metabolic
cart (Sandy, UT). Glycosylated hemoglobin A1c (HbA1c) blood levels were taken before and after
treatment and measured at the PeaceHealth laboratory (Bellingham, WA).
Measurement techniques and procedures. VO2max was obtained prior to training
using the Bruce Treadmill Test (Bruce, 1972). VO2max was used to calculate the individual
work rate for each participant to maintain 80% VO2max during HIIT. The work rate was
calculated using the VO2max metabolic equation (Armstrong, Brubaker, Whaley, & Otto, 2005).
The Monarck bicycle ergometer (Sweden) was set to the calculated work rate in order to
maintain 80% VO2max during HIIT.
Training procedures. Participants were randomly assigned to either the sedentary
control group or the HIIT group. Sedentary control subjects were instructed not to alter their diet
or physical activity during the 12 week study. HIIT subjects participated in a HIIT program five
days a week for 12 weeks. Blood HbA1c levels were measured both sedentary controls and HIIT
subjects prior to treatment. HIIT subjects completed the Bruce Treadmill Test (Bruce, 1972) to
find their V02max. Individual work rate needed to sustain 80% VO2max during HIIT was
calculated (Armstrong et al., 2005) and the bicycle ergometer was set at this work rate. During
training, HIIT participants were instructed to wear comfortable, loose fitting clothes, and athletic
shoes. On training days, subjects completed a 10 minute warm up on the bicycle at 20% of the
determined workload. During HIIT, subjects completed four to six 30 second “all-out” cycling
bouts separated by 4 minute recovery periods. Participants were verbally encouraged during the
“all-out” cycling bouts. Participants completed a 10 minute cool down on the bicycle at 20% of
the determined workload. HIIT participants were instructed not to change their diet during the 12
week training program. At the conclusion of the 12 week experiment, HbA1c levels were
measured.
Data Analysis
Statistical analysis was performed using a mixed factorial ANOVA to determine the
difference in HbA1c levels due to high intensity interval training in type II diabetics.
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