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The Comparison Between High Intensity Interval Training (HIIT)

and Steady-State Cardio Training for Reducing Cardiometabolic

Risks and Obesity Rates in the U.S.

By

Stanley Wu

This thesis is submitted to the Department of Health Education and

Behavior of the University of Florida in fulfillment of the

requirements for the Bachelor of Science degree with Summa Cum

Laude distinction

University of Florida

August 2019

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Abstract

As obesity rates in the United States continue to rise or stay unchanged, many individuals

are looking for better ways to exercise and eat. Individuals know that good exercise and eating

habits lead to a reduction in fat, which ultimately improves one’s quality of life. Previously, most

exercise regimens consisted of steady-state cardio training, however, recently a new type of

training, called High Intensity Interval Training (HIIT) has gained popularity. Many people

including researchers are wondering which type of training is most effective. This paper focuses

on which training style, HIIT or steady-state, is better for reducing cardiometabolic risks and

obesity rates among Americans. Cardiometabolic risk is a person’s risk for heart disease,

diabetes, or stroke (New York State Office of Mental Health, 2009). Diabetes, heart disease, and

stroke are chronic diseases that are among the most common illnesses for death in the United

States (Weatherspoon, 2018). Furthermore, the assumption of decreasing obesity rates will be

determined according to which training style is most effective for decreasing body fat. This

systematic literature examines nine research studies, two systematic reviews, and two meta-

analyses on topics related to HIIT vs Steady-State Cardio for fat loss and cardiometabolic health.

Findings indicate that HIIT is shown to be more time-efficient and effective when compared to

steady-state cardio in reducing fat. In addition, HIIT is more effective for reducing

cardiometabolic risk factors such as decreasing blood pressure, increasing VO2 max, and

increasing insulin sensitivity. However, steady-state cardio is still able to reduce fat and

cardiometabolic risks factors. Specifically, it is that steady-state cardio is better for reducing

abdominal visceral fat, the fat that is linked to diabetes and other cardiovascular diseases.

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Statement of the Problem

The obesity epidemic.

The United States has become a nation known for eating burgers and fries. People from

other countries such as France stereotype Americans as lazy, who eat a lot, and are consequently

overweight (Roux et al., 2007). In fact, one of my friends from Ireland, Gerry Quinn, mentioned

to me that when he and his mother came to the U.S., they noticed the bread in America tasted

different because of all the extra sugar put into the bread. The combination of excessive added

sugars, processed foods, large portion sizes, and lack of exercise has led to the obesity epidemic

in the U.S. In addition, fewer than 25% of Americans reach the goal of the government’s

recommendation of an hour of moderate to vigorous exercise each day (Harvard Health

Publishing, 2017).

There are also a greater number of children with childhood obesity growing up in the

U.S. There are many factors that led to this including what parents feed their kids, where kids

live, and social economic status of the family. Children who are obese are more likely to stay

obese throughout their life because the choices they make when they are young are likely to turn

into lifelong habits (CDC, 2016). This means that it is very important to educate Americans of all

ages about obesity and how to prevent it. More emphasis needs to be placed on children because

if a child develops health habits early on, they will most likely continue with these healthy habits

throughout their lives (Bhadoria, 2015). For example, a child who is active for most of his or her

childhood will be more likely be active the rest of their life.

With obesity being a problem in the U.S., it leads to many other health complications

including heart disease, type 2 diabetes, stroke, and high blood pressure (NIH, 2015). In addition

to the rise in chronic diseases among Americans because of obesity, patients may be spending a

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lot of money to receive treatment for their illnesses (Hruby et al., 2015). This obesity epidemic

should lead to more emphasis on preventative care in which health education materials may be

used to help patients gain the knowledge, skills, and motivation to maintain a healthy lifestyle.

Cardiometabolic risks and fat.

Cardiometabolic risk refers to the “chances of having diabetes, heart disease, or stroke”

(New York State Office of Mental Health, 2009). Diabetes, heart disease, and stroke are among

the leading causes of death in the U.S. (NIH, 2015). Americans need to know if they are at risk

for any illnesses, especially those that may cause death. With prior knowledge of the factors that

contribute to cardiometabolic risks, adequate steps to reduce the chances of an illness can be

applied.

Excessive fat is a huge problem in the U.S. as over 1/3 of the U.S. adult population is

obese (CDC, 2016). Excessive fat is a huge contributor and a major risk factor to chronic

illnesses including cancer (Stöppler, 2007). Having excessive fat may also cause the inability to

move or function well.

Combating effects of obesity.

While many Americans know that the right diet and exercise could lead to a healthier life,

there are many other factors that get in the way of eating right and working out consistently. One

big factor is lack of time. Americans are always looking for quick, easy approach to solving

problems. While exercising takes time, there are many different forms of exercise that can help

improve a person’s quality of life. For instance, strength training and cardio training are just two

of the many types of exercise. In terms of cardio training, there has been recent popularity

around HIIT (High-Intensity Interval Training) and how it may be time-efficient for those

looking to improve their health and fitness.

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HIIT versus Steady-State Cardio

HIIT and steady-state cardio training are two different types of training techniques for

individuals who want to improve their overall health and fitness. Innovative approaches to

exercise always excite people and that is what HIIT training is all about. HIIT training is a new

approach to the traditional steady-state cardio training. HIIT training uses intervals in which a

person raises intensity for a certain amount of time, and then lowers intensity for a certain

amount of time (Zuhl, 2012). For example, this can be repeated sets of going all out on a

stationary bike for 15-20 seconds, then relaxing and biking slowly for about 30 seconds. Steady-

state cardio training is the traditional way of cardio, such as running on a treadmill at a consistent

pace for 30 minutes (Zuhl, 2012). While any form of exercise is beneficial, knowing different

ways to train and exercise could make it more exciting. Some individuals may not want to

exercise the same way every day as it could become repetitive and boring.

In order to educate more Americans about the different types of exercise and which one

could better suit them, there needs to be plenty of health education materials readily available to

the public and to individuals with chronic diseases because exercising is such an important part

of life. Since many individuals already know that exercising has many psychological and

physiological benefits, individuals are now more curious about what exercise technique would

work more efficiently in terms of reducing the risk of cardio metabolic risk and reducing body

fat.

Research Questions

The research that is being reviewed is the comparison between HIIT and steady-state

cardio training on reducing cardiometabolic risks and obesity rates. What style of exercise is best

for longevity and health? I hypothesize that a combination of both types of cardio training is

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needed for maximum benefits of reducing cardiometabolic risks and obesity rates. A

combination may be most beneficial due to the variation of exercising a body goes through, the

more results will happen because the body is not used to different variations and would not know

what to expect when exercising. Using different variations of exercises can stimulate different

muscles and prevent boredom (NIH, 2019).

Significance of the Research Project

A systematic literature review will be conducted on HIIT and steady-state cardio training

on its effectiveness for reducing cardiometabolic risks and obesity rates. There are a lot of

sources covering how effective HIIT is to cardiometabolic risks and fat loss. However, there

seems to be no clear answer as to which training method is best. I am reviewing the latest

literature within the past 10 years to update all the information on HIIT when compared to

steady-state cardio training. That way, health education materials can be developed so that

patients with chronic illnesses could learn more about if HIIT is right for them. Having more

information about the different types of exercises for patients who need to change their lifestyle

habits could encourage them to do the exercises, as they will learn about the benefits of each one.

Research Methodology

Recent popularity surrounding better training styles has made Americans curious. This

leads to many researchers studying about the effects of HIIT versus steady-state cardio. This

systematic literature review is composed of existing literature found from 2010 to 2019. Since

there are numerous studies on HIIT versus steady-state cardio, the focus of this literature review

is on how HIIT and steady-state cardio may reduce cardiometabolic risks and fat. The primary

population studied were men and women ages 6-50.

Search methods.

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A number of methods were used to find literature on HIIT versus steady-state cardio and

its effects of reducing cardiometabolic risks and fat. Searchers were conducted using Google

Scholar or PubMed. The following search words were used: HIIT versus Steady State Cardio,

HIIT versus Steady State Cardio for reducing cardiometabolic risks, HIIT versus Steady State

Cardio for reducing fat loss, HIIT versus Steady State Cardio effects on weight, HIIT versus

Steady State Cardio effectiveness. In addition, primary literature, systematic reviews, and meta-

analysis were reviewed. A total of nine primary literature, two meta-analyses, and two systematic

reviews were examined. Furthermore, some sources where pulled from original literature.

Further Explanation of Exercise and Medical Terminology

Throughout the literature, there have been numerous exercise and medical terminology

that the general public would need to know before understanding the research. This review

below streamlines the process and answers any common questions readers may have before

reading the findings of my systematic literature review.

High Intensity Interval Training (HIIT).

High Intensity Interval Training (HIIT) is a form of exercise that is fairly new to the

public. Many people have heard of aerobic exercise, strength training, or stretching. However,

HIIT is a form of exercise that has gained popularity over the years because researchers are

finding it to be effective in short amounts of time. In addition, the general public loves new

things such as new fitness programs to try and new tools to workout with. For example, the TRX

training system has gained huge popularity over the years, providing people with exercises that

also help them stabilize their core and improve their overall balance.

The HIIT method of training “pairs quick bouts of high-energy exercise with low-effort

rest intervals” (Zuhl, 2012). This is different compared to just running on a treadmill at a

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consistent moderate pace for a long period of time. If a person were to do a HIIT workout on a

treadmill, it would be something like this: running close to max speed for 30 seconds, followed

by jogging at a slower pace than normal for 30 seconds and then you repeat the cycle for 10

times for a total of ten minutes. This kind of workout sounds a lot different than what the

majority of Americans do today because it involves training at high intensity, which pushes the

body to work harder and pump more blood out of the heart.

Steady-State cardio training.

Steady-state cardio training is the way most people workout at the gym. This type of

training “is performed at a steady, low to moderate pace, which utilizes slow-twitch muscle

fibers, and is great for cardiovascular conditioning and improving muscular endurance”

(Pletcher, 2016). This type of training is commonly seen at the gym. An example of a steady-

state cardio training session would be running on the treadmill for 30 minutes at a moderate

pace.

Steady-state cardio training is also known as many other terms, which are used

interchangeably and mean the same thing. For instance, MICT (moderate intensity cardio

training), CME (continuous moderate exercise), and aerobic exercise all mean exercising at a

consistent pace for a long time. There is also moderate to vigorous continuous training (MVCT),

which means going at a faster pace for a long time. MVCT is especially important for trained

athletes who want to push their pace a little more so that they can improve. However, even

MVCT is considered steady-state cardio training because they are still running or cycling at a

consistent pace for a period of time.

VO2 Max or Peak.

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VO2 Max or Peak “refers to the maximum amount of oxygen that an individual can

utilize during intense or maximal exercise. This measurement is generally considered the best

indicator of cardiovascular fitness and aerobic endurance” (UVA Exercise Physiology Core

Laboratory, 2019). This is because, without oxygen, we as humans would not be able to survive

and thus we wouldn’t be able to exercise. If we have more oxygen available to us during intense

exercise, we are more likely to push through it and produce more energy. Furthermore, the VO2

max test is “the gold standard for determining cardiorespiratory fitness because the muscles need

oxygen for prolonged aerobic exercise, and the heart must pump adequate amounts of blood

through the circulation to meet the demands of aerobic exercise” (UVA Exercise Physiology

Core Laboratory, 2019). This is very important to know because for reducing cardiometabolic

risk and improving overall fitness in obese patients, VO2 max testing before and after

interventions allows the patient to know if their cardiorespiratory fitness improved. With

improved cardiorespiratory fitness comes improved health and thus reducing cardiometabolic

risks. VO2 testing is usually done while cycling until exhaustion with a mask hooked up to a

machine.

Cardiometabolic risk.

Cardiometabolic risk “refers to your chances of having diabetes, heart disease or stroke”

(New York State Office of Mental Health, 2009). Knowing your cardiometabolic risk is

extremely important because many Americans today are dying because of heart disease. There

are many factors to look at to determine if your cardiometabolic risks are high enough that you

need to make lifestyle changes. This includes checking you blood pressure, blood cholesterol,

waist circumference, and blood sugar levels. Blood pressure “shows how hard your heart has to

pump to circulate blood” (New York State Office of Mental Health, 2009). Blood cholesterol “is

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the fat that circulates in your blood” and with too much of the “bad cholesterol” (LDL), it may

cause plaque in your arteries (New York State Office of Mental Health, 2009). Waist

circumference is the distance measured around your waist at your hipbone. “People who gain

weight around the waist are more likely to develop diabetes and heart disease than people who

put on weight in other areas of the body” (New York State Office of Mental Health, 2009).

Blood sugar is sugar that circulates in the blood. While there needs to be some sugar in the

blood, having too much is harmful and can increase the risk for diabetes (New York State Office

of Mental Health, 2009). It is important to know the factors associated with cardiometabolic risks

as many of the factors are related to common illnesses in the U.S. and related to obesity rates in

the U.S.

DEXA Scanner.

The dual-energy X-ray absorptiometry (DEXA) scan is an important test used to

accurately measure body fat percentage of an individual (Pietro, 2019). The DEXA scan is for

patient who might have osteoporosis or for patients interested in finding an accurate

measurement of their body fat percentage. The DEXA scan is done with a patient lying

underneath a scanner and the scanner slowly goes from head to toe (Pietro, 2019). The DEXA

scan allows patients to accurately know whether their body fat percentage decreased after

interventions. This is important because body fat percentage is a good measurement to know

when trying to lose weight.

Insulin Sensitivity.

Insulin sensitivity “refers to how responsive your cells are to insulin” (Raman, 2017). To

better understand this term, you need to know what insulin is. Insulin is “an essential hormone

that controls your blood sugar levels” (Raman, 2017). This means that you want your insulin

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sensitivity to be high so that it can move sugar from your blood to cells for storage. If your

insulin sensitivity is low, it will cause more sugar in your blood, which leads to diabetes. This

directly refers to cardiometabolic risks as diabetes is a common illness in the U.S. There are

many ways to increase insulin sensitivity such as getting more sleep, eating a healthy diet with

no processed foods, reducing stress, and losing extra fat (Raman, 2017).

Review of the Literature and Findings

HIIT vs. Steady-State Cardio Training for Fat Loss

HIIT and steady-state cardio training are two very different types of training. HIIT is

done at a high intensity with certain intervals for rest and active periods. Steady-state cardio is

done at a moderate intensity and it is continuous for a long time. With different types of training

comes the curiosity of which type of training is better for losing weight. Losing excess weight is

a goal among many people who are overweight or obese and burning off fat by exercise is one

way to do that. In this systematic review, we are assuming that fat loss will directly impact

obesity rates.

HIIT is more time-efficient than Steady-State Cardio for reducing fat.

There are many studies about HIIT being a new exercise technique to weight loss, which

lead to an increase in research about HIIT and fat loss. A meta-analysis study conducted by the

University of New South Wales in Sydney, Australia examined the effectiveness of HIIT and

steady-state cardio on overweight and obese adults aged 18-45 (Wewege et al., 2017). The study

examined 63 studies and found evidence showing that HIIT and steady-state cardio training did

not differ based on the results. The main finding was that “approximately 10 weeks of HIIT or

steady state cardio training can reduce body fat by about 2 kg and a waist circumference of about

3 cm” (Wewege et al., 2017). However, it is important to note that although HIIT and steady-

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state cardio showed similar results, HIIT was about 40% less time commitment (Wewege et al.,

2017). In other words, the amount of time steady-state cardio trainers had to exercise to achieve

the same results as HIIT exercisers did was almost twice as long. Since lack of time is a strong

barrier for many people to exercise, HIIT may be the best option in terms of time-efficiency

(Wewege et al., 2017).

To further understand how HIIT compares to steady-state cardio in terms of body fat and

which one is more time-efficient, a study by Airin et al. (2014) investigated the comparative

effect between HIIT and steady-state cardio training on improvement of body weight and body

composition among 32 overweight females. Participants were a median age of 20.5 and were

recruited from members of the Contours Express Gymnasium in Singapore (Airin et al., 2014).

Each group (HIIT training vs. steady-state cardio) performed the exercise three times a week for

six weeks. The HIIT training required 8 seconds of sprint at the cadence range (120-130 rpm)

within 80-95% of heart rate maximum. Then there was a 12 second recovery period (40 rpm) and

the cycle was repeated for 20 minutes (Airin et al., 2014). For the steady-state cardio group, the

exercise was performed at 60-70% of max heart rate continuously for 30 minutes (Airin et al.,

2014). “The HIIT group showed significant improvement in body fat percentage (2.2 % vs.

0.3 %), lean body mass (−0.5 kg vs. 0.8 kg) and waist-to-hip ratio” (Airin et al., 2014). In

addition, “the HIIT group showed greater decrease in body fat percentage as well as the

improvement of overall anthropometric indices in overweight females” (Airin et al., 2014). This

suggests that HIIT is ultimately more time-efficient for decreasing body fat since just 20-minute

HIIT exercise sessions show more improvements than 30-minute steady-state cardio sessions.

MICT may be more effective in reducing abdominal visceral fat than HIIT.

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A study by Zhang et al. (2017) compared HIIT to MICT (moderate intensity cardio

training) in terms of reducing abdominal visceral fat. Abdominal visceral fat is linked to a greater

chance of diabetes and cardiovascular diseases much more so than subcutaneous fat, the fat that

is known as “love handles” (Harvard Health Publishing, 2015). Abdominal visceral fat is located

in the abdominal cavity and it is better known as “belly fat”. The study examined 43 female

participants aged 18-22 from University Students in China who received either HIIT, steady-

state, or no training for 12 weeks (Zhang et al., 2017). It is important to note that the participants

in both groups performed HIIT or MCIT equaling at 300kJ per exercise session, even though the

HIIT group took less amount of time to reach the 300kJ each session. The participants were

measure before and after the 12 weeks using a DEXA scanner. It was found that both HIIT and

MICT lead to similar decreases in total body mass after the 12 weeks of training (Zhang et al.,

2017). However, “enhancement in visceral fat reduction with a higher training volume was found

in MICT, but not in HIIT” (Zhang et al., 2017). This suggests that the “inclusion of high training

volumes is essential in MICT to eliminate excess visceral fat in obese females and indirectly

verifies previous proposals that HIIT, rather than MICT, is the more practicable program for

development into a habitual strategic exercise for combatting central obesity” (Zhang et al.,

2017). This study suggests that HIIT may be more time-efficient in terms of burning energy

however, it raises questions on whether it is the best option for reducing visceral fat, which is

important in cardiometabolic risk.

HIIT is effective for reducing fat among males.

Although the previous literature showed how HIIT was more effective in reducing fat,

most of the literature I presented was composed of female participants as those where the

majority of studies found through Google Scholar. However, there was one study that examined

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young males and the effectiveness of HIIT in a similar way. A study by Heydari et al. (2012)

examined the effects of 12 weeks of HIIT among 46 inactive young males around the age of 25.

The DEXA scanner was used to measure body fat. There was an exercise group that performed

20-minute sessions for three times a week and then there was a control group that did not

exercise. The main finding was that “twelve weeks of HIIT resulted in significant reductions in

total, abdominal, trunk, and visceral fat and significant increases in fat free mass and aerobic

power” (Heydari et al., 2012). The one twist to this study is that the HIIT sessions were

performed the morning after a 10-hour overnight fast in which participants did not eat anything

for 10 hours. This could mean that since HIIT was done at a fasted state, it may have more

improvements as the body is using fat stores to exercise when it is at a fasted state. This thought

“has been hypothesized that performing aerobic exercise after an overnight fast accelerates the

loss of body fat” (Shoenfield et al., 2014). However, a study done by Shoenfield et al. (2014)

compared fat loss on participants who exercised at a fasted state compared to participants who

ate before exercise. The findings of that study indicated that there were no significant differences

in body fat loss between the two groups, however both groups did lose weight after the four

weeks (Shoenfield et al., 2014).

Ideal intervals of HIIT for reducing fat.

Since High Intensity Interval Training is a broad term and there are many different ways

people define HIIT and how it is supposed to be done, there have been studies that show what

intervals may be best for reducing body fat. One big question is which HIIT strategy is best for

reducing fat: taking longer active rest periods so that the body may be stronger during the high

intensity interval or taking shorter active rest period so that the body will suffer more? A study

by Mirghani et al. (2018) examined recovery time during HIIT to see which one was more

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beneficial to reducing fat. The study was conducted among 24 overweight women with an

average age of 35 years old. There were three groups: HIIT with 60/60 seconds activity to rest

ratio, HIIT with 60/30 seconds activity to rest ratio, and a control group. The HIIT groups

exercised three times per week for four weeks. The main finding of the study was that the HIIT

with 60/30 seconds activity to rest ratio was more efficient in reducing body fat than the control

group and the HIIT 60/60 seconds activity to rest ratio group (Mirghani et al., 2018). This is

interesting because one may think that allowing yourself to rest a little more will allow yourself

to push your body harder. The study also examined BMI, blood pressure, insulin sensitivity,

blood lipids, thyroid, cortisol, growth hormones, fasting blood glucose, and blood insulin with

the same population of 24 overweight women (Mirghani et al., 2018). There were no significant

results of all those different measurements and it may be due to the short amount of time

exercising (4 weeks).

HIIT vs. Steady-State Cardio for Cardiometabolic Health

One of the biggest factors of mortality in the U.S. is cardiometabolic risk.

Cardiometabolic risk refers to the “chances of having diabetes, heart disease, or stroke” (New

York State Office of Mental Health, 2009). Since heart disease, diabetes, and stroke are all very

common illnesses in the U.S. with many people dying from these conditions, we should know

what cardiometabolic risks are by looking at blood pressure, lifestyle factors, genetics, blood

sugar, etc. If a person has a higher cardiometabolic risk, it is important to exercise. In fact, it is

important that everyone exercises on a consistent basis since exercising comes with many

benefits such as reducing stress, sleeping better, and improving concentration and memory

(Semeco, 2017). With exercising comes many forms of exercising. Americans are always tight

on time as they list time as one of the biggest barriers to exercise (Wewege et al., 2017). There

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have been numerous studies comparing HIIT and steady-state cardio to reducing cardiometabolic

risks as HIIT is an exercise that has been said to take little amount of time. However, is HIITT or

steady-state cardio better for reducing cardiometabolic risk? This is a very important topic to

consider as reducing cardiometabolic risks are detrimental to living a healthy lifestyle and

improving quality of life.

HIIT and steady-state cardio are both effective in reducing cardiometabolic risks.

A study by Fisher et al. (2015) compared effects of HIIT vs. continuous moderate

intensity training (CMT) for “improving body composition, insulin sensitivity (SI), blood

pressure, blood lipids, and cardiovascular fitness in a cohort of sedentary overweight or obese

young men” (Fisher et al., 2015). The HIIT group exercised for 1 hour a week while the CMT

group exercised for 5 hours per week (Fisher et al., 2015). Twenty-eight young overweight or

obese men around the age of 20 participated in this study (Fisher et al., 2015). A greater VO2

peak was observed in the CMT group when compared to the HIIT group, however, the CME

group exercised four hours more than the HIIT group each week (Fisher et al., 2015). The main

findings were that “both exercise conditions were associated with temporal improvements in %

body fat, total cholesterol, medium VLDL, medium HDL, triglycerides, SI, and VO2peak (P <

0.05)” (Fisher et al., 2015). This tells us that both exercise groups are effective in reducing

cardiometabolic risk with no clear advantage between the two exercise groups.

A systematic review by Cassidy et al. (2017) examined HIIT on glucose control and its

ability to affect cardiovascular function. The systematic review found that “for optimal clinical

benefit (improved glycemic control and cardiovascular function), the value of HIIT appears

likely to be adjunct to energy restriction, allowing HIIT to certainly make a hit” (Cassidy et al.,

2017). The review also suggests that one considers the safety aspect of HIIT as patients with

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chronic heart failure, cardiac stress, and chest pain should have a screening before trying HIIT.

On the contrary, “mounting clinical evidence supports HIIT as a safe therapy for the majority of

individuals with elevated cardiometabolic risk” (Cassidy et al., 2017). The systematic review

found that “in circumstances where HIIT is not feasible, considered potentially unsafe or not

well tolerated by an individual , MICT is effective at eliciting important health benefits”

(Cassidy et al., 2017). This means that both HIIT and MICT are effective in improving

cardiometabolic risks and there is no big difference between the two.

HIIT is more effective than steady-state cardio For reducing blood pressure.

Since blood pressure is a huge indicator of cardiometabolic risks, there have been studies

that examined if systolic blood pressure decreases more after HIIT or steady-state cardio. A

meta-analysis by Garcia-Hermoso et al. (2016) examined HIIT interventions on cardio-metabolic

risk factors. Cardiometabolic risk factors include blood pressure since higher blood pressure is

linked to poor cardiometabolic health. The meta-analysis used a computerized search of seven

databases and it found 9 studies (Garcia-Hermoso et al., 2016). The studies only pertained to

pediatric patients ages 6-17 years old (Garcia-Hermoso et al., 2016). However, the studies

showed that “HIIT interventions (4-12 week duration) produced a larger decrease in systolic

blood pressure and greater increases in maximum oxygen uptake than any other forms of

exercise” (Garcia-Hermoso et al., 2016). This means that HIIT training is very effective and time

efficient for youth who are obese. In addition, it is important to target youth when trying to

reduce obesity rates in the U.S. Developing healthy habits early in life will help people have

healthy habits throughout their life.

HIIT is more effective than steady-state cardio for increasing insulin sensitivity.

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Insulin sensitivity is a topic that should not be overlooked as low insulin sensitivity

causes diabetes, a common illness in the U.S. A study by Sun et al. (2018) compared 12-week

sprint interval training, high intensity training, and moderate intensity continuous training on

cardiorespiratory fitness (VO2 Max), body mass, and insulin sensitivity among overweight

females around the age of 22 (Sun et al., 2018). Training interventions were performed three

days a week for twelve weeks (Sun et al., 2018). The results showed that “the three training

strategies are equally effective in improving VO2 peak and reducing body mass, however, the

SIT is time-efficient” (Sun et al., 2018). Insulin sensitivity and fasting insulin levels were also

improved significantly on post-training measures in SIT and HIIT (26% and 39% respectively)

(Sun et al., 2018). However, insulin sensitivity and fasting insulin levels remained unchanged in

MICT (Sun et al., 2018). Higher insulin sensitivity is good because insulin is essential to control

your blood sugar levels (Raman, 2017). When insulin cells are resistant, they cannot use insulin

effectively and that leave your blood sugar high, which causes diabetes (Raman, 2017).

However, fasting glucose levels were only reduced with MICT (Sun et al., 2018). Fasting

glucose levels are also important as high fasting glucose levels leads to diabetes. While it seems

both HIIT and MICT are beneficial to reducing cardiometabolic risks, High Intensity Interval

training (SIT and HIIT) was the most time-efficient and more beneficial than MICT in improving

insulin sensitivity (Sun et al., 2018).

HIIT is more effective than steady-state cardio after 8-12 weeks.

A systematic review study by Kesseler et al. (2012) examined the comparison between

HIIT and continuous moderate exercise (CME). They found 17 studies that measured aerobic

fitness and all 7 studies that measured insulin sensitivity showed significant improvements in

responses to HIIT training (Kesseler et al., 2012). However, the changes did not always exceed

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responses to the CME comparison groups as “a minimum duration of 12 weeks was necessary to

demonstrate improvement in fasting glucose in four of seven studies (57%)” (Kesseler et al.,

2012). “HIT appears to promote superior improvements in aerobic fitness and similar

improvements in some cardiometabolic risk factors in comparison to CME, when performed by

healthy subjects or clinical patients for at least 8–12 weeks” (Kesseler et al., 2012). This means

that in order for HIIT to surpass steady-state cardio in terms of reducing cardiometabolic risks,

HIIT needs to be done consistently for about 8-12 weeks.

HIIT is more time-efficient than steady-state cardio in improving VO2 Max/Peak.

A study by Kong et al. (2016) compared HIIT to moderate to vigorous continuous

training (MVCT). The study was conducted over 5 weeks and included 31 obese female

participants ages 18-30 (Kong et al., 2016). “Participants in HIIT condition performed 20 min of

repeated 8 s cycling interspersed with 12 s rest intervals, and those in MVCT condition cycled

continuously for 40 min at 60–80% of peak oxygen consumption (VO2peak), both for four days

in a week” (Kong et al., 2016). This means that the participants in HIIT spent half the amount of

the time that the steady-state exercisers did. However, there were not significant changes in

results between the two groups as both groups showed improvement in VO2 max. The main

finding of the study was “both HIIT and MVCT are effective in improving cardiorespiratory

fitness and in reducing sexual hormones in obese young women; however, HIIT is a more

enjoyable and time-efficient strategy” (Kong et al., 2016). This tells us that both kinds of

exercises work well for reducing cardiometabolic risks, however, HIIT allows a person to get the

same results with less time.

A study by Lanzi et al. (2015) compared the effects of 2-week exercise interventions

between HIIT and FatMax training group. Nineteen men with a BMI over 35 participated in this

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study and both exercise groups performed cycling sessions (Lanzi et al., 2015). The FatMax

training session consisted of 40-50 minutes of continuous exercise so it is similar to steady-state

cardio training (Lanzi et al., 2015). The HIIT group consisted of 10X60 seconds cycling intervals

at about 90% max heart rate, and it took around 30 minutes per session including 5 minutes of

warm up and cool down and 60 seconds of recovery between sets (Lanzi et al., 2015). It was

found that both methods were effective in producing better aerobic capacity among the men. It is

important to note that even though both groups were able to produce better aerobic capacity in

just two weeks, the magnitude of increase of the HIIT group’s VO2 peak was 8%, whereas the

FatMax training group was 4% (Lanzi et al., 2015). This suggests that in just a short amount of

time HIIT exercise is superior to steady-state cardio for improving VO2 peak which is in direct

correlation to cardiometabolic risks since fitness is related to your chances for heart diseases.

Limitations of the Review

Even though the literature provided a lot of insight to determine whether HIIT or steady-

state cardio was better in terms of reducing fat and cardiometabolic risks, there are some

limitations to the studies that need to be considered.

The majority of studies had a young female adult sample.

While the studies seem to favor HIIT as more time-efficient in reducing fat-loss, the

majority of the studies summarized in this review had participants that were young female adults.

For instance, the research by Airin et al. (2014) had a sample of 32 young female participants

with a median age of 20.5 years. In addition, all of the female participants were between the ages

of 18.5 and 23 and recruited from members of the Contours Express Gymnasium in Singapore

(Airin et al, 2014). HIIT was more effective that steady-state cardio in terms of reducing body fat

percentage, lean body mass, and waist to hip ratio (Airin et al., 2014). Even though the results of

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the study showed that HIIT was more effective for reducing fat, given the fact that the

participants were only females, the diversity of the population was not great enough to conclude

HIIT is more effective at reducing fat for everyone.

Furthermore, the study by Zhang et al. (2017), compared HIIT to Moderate Intensity

Continuous Training (MICT) in terms of visceral fat reduction and body mass. The study found

that both HIIT and MICT led to similar decreases in body mass for participants, even though

HIIT spent less time exercising than MICT (Zhang et al., 2017). However, it also found that

MICT may be more effective in reducing abdominal visceral fat (Zhang et al., 2017). The study

consisted of young females participants ages 18-22 recruited from a University in China (Zhang

et al., 2017). Knowing the participant pool for both the Airin et al. (2014) study and the Zhang et

al. (2017) study, it is difficult to conclude the findings are the same for everyone since these

studies only included young, female participants.

In terms of reducing cardiometabolic risks, specifically referring to increasing insulin

sensitivity, the study by Sun et al. (2018) found that HIIT was more time-efficient and more

beneficial than MICT in improving insulin sensitivity (Sun et al., 2018). However, this study also

included young female participants around the age of 22 (Sun et al., 2018). Just based off this

study, it would be a stretch to say that HIIT is more beneficial than MICT in improving insulin

sensitivity for everyone.

The studies for fat loss were done outside the U.S.

I am assuming that the effectiveness of fat loss between HIIT and steady-state Cardio will

help people know which is more suitable for them, therefore, allowing them to hopefully engage

in that type of exercise, leading to a decrease in obesity rate in the U.S. Since the obesity rate in

the U.S. is abnormally high compared to other countries, research should be focused on

22

participants from the U.S. However, there were only a few recent studies comparing HIIT and

steady-state cardio with participants from the U.S. For instance, the two main studies that

showed that HIIT is more effective and time-efficient than steady-state cardio in terms of

reducing body fat was done by Zhang et al. (2017) and Airin et al. (2014) and those studies had

participants from Singapore and China. Those two studies are the sole studies showing which

exercise technique may help decrease obesity rates in the U.S. since they focused on which

exercise technique reduces fat. However, since those studies were done with participants outside

the U.S., there are some factors to consider. For example, cultural factors in terms of what they

eat and how they live their lives need to be considered. One instance that shows cultural

differences is that in Asian countries studies have shown they have the lowest prevalence of

insufficient physical activity when compared to other parts of the world (WHO, 2018). In

addition, their food is a lot different with less processed foods and smaller portion sizes

(Margolin, 2014). Furthermore, their barriers to exercise may be different from Americans.

Having only participants from China and Singapore, it is hard to say that HIIT will help decrease

obesity rates in the U.S.

Additional limitations.

Other limitations include a need for larger participant sizes, more studies done with equal

training time between HIIT and steady-state cardio, more studies done with people who are of

different ethnic backgrounds, and comparing psychological effects between HIIT and steady-

state cardio. The need for larger participant sizes is definitely needed as many studies were only

composed of about 30 participants such as in the Kong et al. (2016) study and in the Airin et al.

(2014) study. Thirty participants are not enough to conclude that the effects of HIIT may be

more effective than steady-state cardio. In addition, many of the participants in each study are of

23

the same ethnic background such as in the Zhang et al. (2017) and the Airin et al. (2014) studies

as both studies were composed of participants from Asian countries. Lastly, the need for

studying the psychological effects of HIIT and steady-state cardio is needed as the mind is one

reason people choose to exercise or not. It is possible that HIIT increases mood as it is time-

efficient and results may be seen quicker. If an individual has a good mood about certain kinds of

exercise, they may be more likely to engage in that exercise and put forth a good effort so that

their results can show not just mentally but also physically.

Discussion and Future Recommendations

Given the amount of overweight and obese people in the U.S. today and the increasing

number of cardiovascular diseases, examining different types of exercise techniques can allow

people to learn what may be best for them in reducing fat and cardiometabolic risks. In studying

High Intensity Interval Training (HIIT) and steady-state cardio, these two very different

exercises that are both very beneficial for reducing fat and cardiometabolic risks. For instance, in

the study by Wewege et al. (2017) it was found that “approximately 10 weeks of HIIT or steady

state cardio training can reduce body fat by about 2 kg and a waist circumference of about 3 cm.”

Now you must think that two very different exercise techniques cannot produce the same results.

It is important to note that the study by Wewege et al. (2017), the HIIT group spent about 40%

less time exercising than the steady-state cardio group. This shows that HIIT is more time-

efficient than steady-state cardio in terms of reducing fat. In the study by Airin et al. (2014), in

which the HIIT group did 20 minutes of exercise and the steady-state cardio group did 30

minutes of exercise per session, HIIT led to a bigger reduction in body fat (2.2 % vs. 0.3 %) than

the steady-state cardio group. This shows once again that HIIT is more effective and time-

efficient at reducing fat.

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However, there was one study that found that the “enhancement in visceral fat reduction

with a higher training volume was found in MICT, but not in HIIT” (Zhang et al., 2017). MICT

is moderate intensity continuous training and that is essentially the same as steady-state cardio.

The study by Zhang et al. (2017) shows that steady-state cardio can still be effective in reducing

fat, however, the study had participants work out until they burned 300kJ and the HIIT group

took less time to burn 300kJ when compared to the steady-state cardio.

In terms of what interval types are better for reducing fat loss, the study by Mirghani et

al. (2018) found that it was more effective doing HIIT with 60 seconds on and 30 seconds off,

rather than HIIT with 60 seconds on and off cycles. This tells us that HIIT can be furthered

studied and be broken down and compared with the variety of different intervals. This also tells

us that HIIT is best when there is shorter time of active rest between rounds.

For comparing HIIT to steady-state cardio in terms of reducing cardiometabolic risks, it

is important to note that both exercise techniques greatly reduces cardiometabolic risks. That is

very important because many people get chronic diseases such as heart disease and diabetes and

reducing their risks for these long term chronic diseases can greatly improves a person’s life. The

study by Fisher et al. (2015) concluded that “both exercise conditions were associated with

temporal improvements in % body fat, total cholesterol, medium VLDL, medium HDL,

triglycerides, SI, and VO2peak (P < 0.05).” These improvements will greatly reduce the risk for

cardiometabolic risk.

Even though there was research for both HIIT and steady-state cardio to reduce

cardiometabolic risks, HIIT seemed to be the favorite for reducing many of the cardiometabolic

risk factors, which included decreasing blood pressure, improving VO2 max, and increasing

insulin sensitivity. In the study by Garcia-Hermoso et al. (2016) it was found that “HIIT

25

interventions (4-12 week duration) produced a larger decrease in systolic blood pressure and

greater increases in maximum oxygen uptake than any other forms of exercise”. In the study by

Sun et al. (2018) insulin sensitivity and fasting insulin levels were also improved significantly on

post-training measures in SIT and HIIT (26% and 39% respectively), while there were no

improvements in MICT. In the study by Kong et al. (2016), “both HIIT and MVCT are effective

in improving cardiorespiratory fitness and in reducing sexual hormones in obese young women;

however, HIIT is a more enjoyable and time-efficient strategy”. All of these studies show that

HIIT has the best outcomes in terms of reducing cardiometabolic risks.

The need for exercise is found to be a huge component of fitness and health. The studies

between HIIT and steady-state cardio both show that they are very beneficial to one’s health.

However, one must also consider the reasons why an individual chooses to workout. For

instance, there has been research about the many ways to exercise. One of the most common

barrier to exercise is the lack of time (Wewege et al., 2017). As our findings indicate, HIIT is

much more time-efficient in terms of reducing fat and cardiometabolic risks when compared to

steady-state cardio. Considering the busy schedules of individuals who lack exercise, HIIT

allows an individual to get the beneficial results from exercise in a shorter amount of time. This

is crucial for decreasing obesity rates. Now we need to educate more Americans on HIIT and the

beneficial elements of that type of exercise.

Implications to the Health Education Field

With the findings in this systematic literature review, health educators are a crucial

component to getting the word out about High Intensity Interval Training (HIIT). Many people

who are into fitness have long heard of HIIT and the benefits of it in fitness magazines, fitness

pages, or other fitness related media. However, a majority of Americans do not know about HIIT

26

and how time-efficient it can be. Health educators who are specifically dealing with dieting and

obesity can create and implement health education materials for their patients to have. For

example, having a pamphlet explaining what HIIT is, the best way to do it, and the benefits of

training with high intensity would allow patients to have better knowledge about how to exercise

when going to the gym or even working out at home. Including examples of 20-minute HIIT

workouts in the pamphlets that patients can incorporate into their everyday lives would also be

very valuable to the patients.

Conclusion

The comparison between HIIT and steady-state cardio on reducing obesity rates and

cardiometabolic risks in the U.S. brings curiosity among many Americans who are looking for

new, exciting, and efficient ways to exercise. While HIIT is the winner in terms of decreasing fat

levels and cardiometabolic risk factors in a short amount of time, steady-state cardio is still

beneficial, especially for reducing abdominal visceral fat which is linked to diabetes and other

cardiovascular diseases. In addition, we cannot conclude that having the knowledge of High

Intensity Interval Training will decrease obesity rates in the U.S. because we have to consider the

barriers to exercise and the many other factors that contribute to obesity in the U.S. For future

research, studies needs to contain larger U.S. populations with diverse ethnic backgrounds and

study the psychological effects between HIIT and steady-state cardio. This will allow us to see

what exercise technique really provides the most benefit in terms of psychological and physical

benefits.

27

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