Everything I share here was not written by me. Please see highlighted references to dive deeper into the excercise science and ways to make mindful decisions about your body. We all have unique bodies and are affected differently
The Truth of the Fat Burning Zone: What is the Best Heart Rate to Lose Fat?
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The Truth of the Fat Burning Zone: What is the Best Heart Rate to Lose Fat?
Last updated: Thursday, September 3, 2020 | 7 min reading time
Cardiologist
The ‘fat burning zone’ is where you are working out at about 70 – 80% of your maximum heart rate, also known as your fat burning heart rate.
If you're looking to lose weight and keep fit, the general rule of the game is to increase the intensity of your workouts. But what about the 'fat burning zone' theory that says you should exercise at lower intensities instead? What is the idea behind this concept, and is it true?
The link between heart rate and fat loss
Your body requires glucose as fuel for your muscles. The 2 main sources of fuel are glycogen (a substance that stores carbohydrate) and fat, which breaks down to form glucose and ultimately carbon dioxide and water. Oxygen is required to oxidise (break down) either the glycogen or fat stores into glucose to fuel the muscles.
During a workout, your body requires more energy. Thus, your heart pumps faster and harder to send oxygen to your muscle cells to break down more glycogen and fat to fuel your muscles.
While 1 gram of carbohydrate contains 4 calories of energy, 1 gram of fat contains 9 calories. This makes glycogen (carbohydrate) a less dense form of energy storage that is readily broken down into glucose, as compared to fats. As such, glycogen is your body's first source of energy during exercise. Since high-intensity workouts require more energy quickly, you tap on glycogen rather than fat in your body for fuel. Your body only taps onto the next fuel, fat, when you start to run out of glycogen.
The truth of the fat burning zone theory
The fat burning zone theory seeks to help adherents lose weight by tapping on the body's fat storage rather than glycogen. They argue that the body burns a greater percentage of fat with lower-intensity exercises than at higher intensities because the body does not require 'fast energy' from glycogen. As such, this theory promotes longer and lower-intensity cardio workouts that maintain your heart rate within the 'fat burning zone'.
However, that is a bit of a misconception. While it is true that the body burns fat during low-intensity workouts, the fat burning rate remains low and you have to exercise longer to burn the same amount of calories you would at higher intensities.
In a high-intensity workout, although your body uses your glycogen stores first for 'fast energy', it depletes the glycogen stores rapidly enough to force your body to tap on the fat storage. This means that high-intensity workouts are more efficient in burning way more total calories – both glycogen and fat calories. Ultimately, the total number of calories you burn leads to the most weight (and fat) loss.
How to measure exercise intensity using your heart rate
The intensity of your workout can be estimated by your heart rate during the activity. The first step to this is to determine your maximum heart rate, which is the upper limit of what your cardiovascular system can handle during physical activity.
To calculate your maximum heart rate, subtract your age from 220. For example, a 50-year-old will have a maximum heart rate of 170. This means that on average, the maximum number of heartbeats per minute is 170 for this person.
Next, calculate your desired target heart rate zone. This is the level at which your heart is being exercised and conditioned but not overworked. The following target heart rates are generally recommended:
Moderate exercise intensity: 50 – 70% of your maximum heart rate
Vigorous exercise intensity: 70 – 85% of your maximum heart rate
Do remember not to rush into achieving a vigorous exercise intensity. If you're just beginning an exercise routine, aim for the lower end of your target heart rate zone.
Finally, to know whether or not you're in your target heart rate zone, you can either use an activity tracker or measure it yourself using the following steps:
Briefly stop your exercise
Take your pulse for 15 seconds by placing two fingers on your wrist, nearer to the thumb.
Multiply this number by 4 to calculate your heart beats per minute.
The 4 training zones
Working out with a heart rate monitor helps you to gauge the specific zones in which your body is working and how your body benefits from different intensities of exercise. Each of the 4 main training zones can be predicted by your heart rate:
Your warm-up zone is where you prepare your cardio-respiratory system, muscles and joints to exercise harder. Here, you are functioning at 60 – 70% of your maximum heart rate. It is a comfortable pace where you feel as though you can go on for a long time.
Just beyond the warm-up zone is the so-called fat burning zone where you are working out at about 70 – 80% of your maximum heart rate. It is still a comfortable rate but you might sweat more and breathe harder than usual. Although you may burn more fat than glycogen at this zone, the absolute amount of fat burnt is much less than the subsequent stages.
Still in the comfortable zone is the aerobic zone. Your heart rate is at 81 – 93% of your maximum heart rate. You will be able to talk but only in short phrases. The calories you burn here split evenly between your fat stores and glycogen. Although you will not burn more fat calories than glycogen, you will be burning more calories overall. (Plus, the aerobic zone makes your heart pump hard, which is great to keep your heart healthy!)
Finally, you will be at 94 – 100% of your maximum heart rate in the anaerobic territory. You are panting and unable to talk. It is hard work and nearly impossible to spend more than a minute here as your glycogen stores are depleted faster than they can be replenished. Anaerobic intervals widen your fat and aerobic zones and zap tons of calories. This is where the afterburn (temporary increase in metabolism) kicks in. Also known as excess post-exercise oxygen consumption (EPOC), your body continues to burn more calories even after a high-intensity workout, as compared to a low-intensity exercise.
The intensity of your activity determines how much your heart rate increases. For example, a running heart rate should be between 50% and 85% of your maximum heart rate. You can then adjust your pace based on what you're aiming for in your run. If you notice that your heart rate is going below this, you can increase your pace to improve your workout results. Or if your heart rate reaches its maximum, it would be better to slow down so that you are able to finish your run.
A high-intensity workout reaps many benefits of burning total calories efficiently both during and after exercising, and keeping your heart healthy. But if you prefer a low-intensity workout, it would require you to devote a longer amount of time to burn the same amount of calories!
Major fat-burning discovery
June 1, 2012
Harvard researchers discover a hormone released by exercise.
When you're taking a brisk walk on a beautiful day, what are you thinking about? The sun, the breeze, how good it feels to loosen up the stiff parts. The last thing you're thinking about as you pick up the pace is what's happening to your body chemistry.
When you exercise, your body chemistry changes in ways that we only now are coming to understand. Over the past 20 years, scientists have identified natural molecules in all of us that influence our appetite and our metabolism—and, hence, our weight. Now, researchers at Harvard Medical School and elsewhere are identifying the molecules that not only affect our weight, but also cause other health benefits of exercise.
"Our muscle cells need a source of energy when they exercise," says Dr. Anthony Komaroff, a professor at Harvard Medical School. "Muscles get that energy by burning fat and sugar brought to them by the blood. That's been known for nearly a century. However, it's not the whole story. "
The hormone irisin
In January 2012, a research team led by Dr. Bruce Spiegelman, a Harvard Medical School professor, published a new study in the journal Nature. The study was done in mice, but may well apply to humans. The study showed that exercising muscle produces a hormone called irisin.
Irisin travels throughout the body in the blood, and alters fat cells," explains Dr. Komaroff. "Body fat is stored inside fat cells. Most of these fat cells are called white fat cells, and their function is to store fat."
White fat vs. brown fat
Why do we store fat? When we eat more calories than we burn by exercise, the extra calories have to go somewhere. They're stored partly as fat. Our distant ancestors didn't eat as regularly as we do. Forty thousand years ago on the Serengeti, our ancestors were able to get a serious meal only a few times each week. In between meals, they needed some source of energy. A large part of it came from the fat they stored away after a meal.
In 2009, studies from Harvard Medical School and elsewhere discovered that humans have not only white fat cells but also brown fat cells.
"Brown fat cells don't store fat: they burn fat. If your goal is to lose weight, you want to increase the number of your brown fat cells and to decrease your white fat cells," says Dr. Komaroff.
Irisin does that, at least in mice. And those newly-created brown fat cells keep burning calories after exercise is over. But it gets better.
Irisin's other effects
We've known for some time that a regular program of moderate exercise protects us against type 2 diabetes. For example, a lifestyle program that included regular moderate exercise reduced the risk of developing type 2 diabetes by nearly 60%—more than any medicine yet invented. How does that happen? Irisin may be an important part of the answer. In addition to its effect in creating brown fat cells, it also helps prevent or overcome insulin resistance, which leads to type 2 diabetes.
Although Dr. Spiegelman did his studies in mice, he found that humans have irisin, too. While not yet proven, it is very likely that irisin has similar effects in humans.
"Studies like these are just plain interesting, in and of themselves," says Dr. Komaroff. "They help us to understand better how our body works. However, the discovery of irisin also could have some very practical and beneficial applications. Theoretically, irisin could become a treatment to help us maintain a healthy body weight and reduce the risk of diabetes."
Yes, other medicines with a similar promise have come and gone. However, irisin is not an unnatural pharmaceutical. Rather, it's part of our natural body chemistry. That may make it more potent and less likely to have adverse effects. So there is justifiable excitement about the discovery of irisin, and about the speed with which science is discovering the chemistry of exercise, appetite, metabolic rate and body weight.
However, our environment, and its effect on our own behavior, plays a huge role in determining how much we exercise and how much we eat, and therefore how much we weigh.
The body primarily uses fat and carbohydratesfor fuel. The ratio of which fuels are utilized will shift depending on your activity. A small amount of protein is used during exercise, but it's mainly used to repair muscles after exercise.
Higher-intensity exercises such as runningcause the body to rely on carbs for fuel. The metabolic pathways available to break down carbs for energy are more efficient than those for fat breakdown. Fat is used more for energy than carbs for long, slower exercise.
This is a simplified look at energy with a solid take-home message. Burning more calories matters more than using fat for energy. The harder you work, the more calories you will burn overall.
It doesn't matter what type of fuel you use for weight loss. What matters is how many calories you burn.
Think about it this way—when you sit or sleep, you're in your prime fat-burning mode. But you probably don't think of sitting and sleeping more as a pathway to losing body fat. The bottom line is that just because you're using more fat as energy doesn't mean you're burning more calories.
Burn Fat With a Mix of Cardio
You may be confused about exactly how hard to work during cardio. You may even think that high-intensity exercise is the only way to go. After all, you can burn more calories and you don't have to spend as much time doing it.
But variety can help you stimulate your energy systems, protect you from overuse injuries, and help you enjoy your workouts more. You can set up a cardio program with various exercises at different intensities.
High-Intensity Cardio
For our purposes, high-intensity cardio falls between 80% to 90% of your maximum heart rate (MHR). Or, if you're not using heart rate zones, about a six to eight on a 10-point perceived exertion scale. This is exercising at a level that's challenging and leaves you too breathless to talk in complete sentences.
But you're not going all-out, like sprinting as fast as you can. There's no doubt that some high-intensity training can be helpful for weight loss as well as improving endurance and aerobic capacity.
You can get the same benefit from short workouts spread throughout the day as you do with continuous workouts. For example, a 150-pound person would burn about 341 calories after running at 6 mph for 30 minutes.3 If this person walked at 3.5 mph for that same length of time, they would burn 136 calories.
But, the number of calories you can burn isn't the whole story. Too many high-intensity workouts every week can put you at risk in a number of ways.
If you're doing several days of cardio each week, you would probably want only one or two workouts to fall into the high-intensity range.4 You can use other workouts to target different fitness areas (like endurance) and allow your body to recover. Here are some examples of how to incorporate high-intensity workouts.
Exercising at a fast pace for a 20-minute workout keeps you in the high-intensity work zone. Twenty minutes is usually the recommended length, and most people wouldn't want to go much longer.
Moderate-Intensity Cardio
There are a variety of definitions of what moderate-intensity exercise is, but it typically falls between 70% to 80% of your maximum heart rate. That would be a level four to six on a 10-point perceived exertion scale. You are breathing harder than usual but can carry on a conversation without difficulty.5
Schedule your day around exercise instead of trying to squeeze it in. Making your workout a priority increases the chances that you will accomplish your goal. The American College of Sports Medicine (ACSM) often recommends this level of intensity in its exercise guidelines. The lower end of this range usually incorporates the fat-burning zone.
Low-Intensity Activity
Low-intensity exercise is below 60% to 70% of your MHR, or about a level three to five on a 10-point perceived exertion scale. This level of intensity is no doubt one of the most comfortable areas of exercise, keeping you at a pace that isn't too taxing and doesn't pose much of a challenge.
Low-intensity cardio can be everyday activities like taking an extra lap when shopping, taking the stairs, parking farther from the entrance, and doing more physical chores around the house. Exercise such as Pilates and yoga are lower intensity but help develop your core, flexibility, and balance. They can be a part of a well-rounded fitness routine.
Importance of Consistent Exercise
It may seem like a no-brainer that regular exercise is key for how to burn fat. But it's not just about the calories you're burning; it's also about adaptations your body makes when you exercise regularly. Many of those adaptations lead directly to your ability to burn more fat without trying.
Benefits of Consistent Exercise
Here are some benefits of consistent exercise.
Become more efficient: Your body becomes more efficient at delivering and extracting oxygen. Simply put, this helps your cells burn fat more efficiently.
Have better circulation: This allows fatty acids to move more efficiently through the blood and into the muscle. That means fat is more readily available to fuel the body.
Increase the number and size of mitochondria: These are the cellular power plants that provide energy inside each cell of your body.
Lift Weights to Burn Fat
Adding muscle by lifting weights and other resistance exercises can also help burn fat.6While many people focus more on cardio for weight loss, there's no doubt that strength training is a key component in any weight loss routine. Here are some benefits of weight training.
Burn More Calories at Rest
If you lift weights at a higher intensity, you can increase your afterburn, or the calories you burn after your workout. That means you burn calories during workouts—and after your workouts, while your body returns to its resting state.
Keep Metabolism Going
A diet-only approach to weight loss could lower a person's resting metabolic rate by up to 20% a day. Lifting weights and maintaining muscle helps keep your metabolism elevated, even if you're cutting your calories.
Preserve Muscle Mass
If you are restricting calories, you risk losing muscle. Muscle is metabolically active, so when you lose it, you also lose the extra calorie burn muscles produce.
To start, choose a basic total body workout and do that about twice a week, with at least one day in between. As you get stronger, you can do more exercises, increase intensity, or add more days of strength training. It may take a few weeks but you'll eventually see and feel a difference in your body.
Strategies
Here are strategies to burn more fat when strength training.
Incorporate circuit training:Circuit training is a great way to burn more calories by combining high-intensity cardio with strength training exercises. You keep your heart rate elevated by moving from one exercise to another with little or no rest while focusing on cardio and strength in the same workout.
Lift heavy weights: If you're a beginner, work up to heavy weights over time. Once your body is ready for more, lifting heavy weight forces your body to adapt by building lean muscle tissue to handle that extra load.
Use compound movements: Movements that involve more than one muscle group (e.g., squats, lunges, deadlifts, and triceps dips) help you lift more weight and burn more calories while functionally training the body.
If you want a more structured program, try a four-week slow-build program that includes a schedule of cardio and strength workouts to increase your intensity gradually.
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Physiology of Fat Loss
Mike Deyhle, Christine Mermier, Ph.D. and Len Kravitz, Ph.D.
Introduction
Fat serves many important functions in the human body. For example, fat provides a key role for the structure and flexibility of cell membranes and also helps to regulate substance movement through the cell membranes. Special types of fat (known as eicosanoids) can do specialized hormone signaling, exerting intricate control over many bodily systems, mostly in inflammation or for immune function. Perhaps the most well known function of fat is as an energy reserve. Fat serves the role of an efficient energy store because it can hold a lot of energy per gram. In fact, fat yields more than two times the Calories per gram than that of carbohydrate (9 Calories/gram for fat versus 4 Calories/gram for carbohydrate). It has been estimated that lean adult men store about 131,000 Calories in fat (Horowitz & Klein, 2000). That is enough energy to sustain life for the average person for approximately 65 days. Excessive fat storage can be unhealthy and/or unwanted. Reducing body fat, whether for health, sports performance or body image reasons, is often a client's goal when working with a personal trainer, and is the focus of this article.
The Journey of a Fatty Acid to Muscle
The Adipocyte Fat is primarily stored in designated fat storage cells called adipocytes. For the most part, adipocytes are located just under the skin throughout the body as well as in regions surrounding vital organs (for protection) called visceral fat. Most of the fat inside the adipocytes is in the form of a triacylglycerol (TAG or triglyceride). TAGs are composed of a backbone (glycerol) with 3 fatty acid tails.
Depending on energy supply and demand, adipocytes can take up and store fat from the blood or release fat back to the blood. After eating, when energy supply is high, the hormone insulin keeps the fatty acids inside the adipocyte (Duncan et al., 2007). After a few hours of fasting, or especially during exercise, insulin levels tend to drop while other hormones such as epinephrine (otherwise called adrenaline) increase. When epinephrine binds to the adipocyte it causes lipolysis of the TAG stores in the adipocyte (Duncan et al., 2007). Lipolysis is the separation of the fatty acids from the glycerol backbone. After lipolysis, the fatty acids and glycerol can leave the adipocyte and enter the blood.
Fatty Acids In the Blood The blood is an aqueous (water based) environment. Because fat is not water-soluble (i.e., it does not dissolve or mix well in water), a carrier protein is required to keep it evenly suspended in the blood. The primary protein carrier for fat in the blood is albumin (Holloway et. al. 2008). One albumin protein can carry multiple fatty acids through the blood to the muscle cell (Horowitz and Klein, 2000). In the very small blood vessels (capillaries) surrounding the muscle, fatty acids can be removed from albumin and taken into the muscle (Holloway et al., 2008).
Fatty Acids From the Blood into the MuscleIn order for fatty acids to get from the blood into the muscle they must cross two barriers. The first is the cell lining that makes up the capillary (called the endothelium) and the second is the muscle cell membrane (known as the sarcolemma). Fatty acid movement across these barriers was once thought to be extremely rapid and unregulated (Holloway et al., 2008). More recent research shows that this process is not nearly as rapid as once thought and that it requires special binding proteins present at the endothelium and sarcolemma to take in fatty acids (Holloway et al. 2008). Two proteins that are important for fatty acid transport into the muscle cell are FAT/CD36 and FABPpm.
The Two Fates of Fat Inside the MuscleOnce inside the muscle, a molecule called Coenzyme A (CoA) is added to the fatty acid (Holloway et al., 2008). CoA is a transport protein which maintains the inward flow of fatty acids entering into the muscle and prepares the fatty acid for two fates: 1) oxidation (a process in which electrons are removed from a molecule) to produce energy or, 2) storage within the muscle (Holloway et al. 2008, Shaw, Clark & Wagenmakers 2010). The majority (80%) of fatty acids entering the muscle during exercise are oxidized for energy while most fatty acids entering the muscle after a meal are repackaged into TAGs and stored in the muscle in a lipid droplet (Shaw, Clark & Wagenmakers, 2010). Fat that is stored inside the muscle is called intramyocellular triacylglycerol (IMTAG or intramuscular fat). The amount of IMTAG in slow twitch muscles (the slow oxidative fibers) is two to three times greater than the IMTAG stored in fast twitch muscles fibers (Shaw, Clark and Wagenmakers). Shaw and colleagues continue that even though this IMTAG content makes up only a fraction (<1% to 2%) of the total fat stores within the body, it is of great interest to exercise physiologists. This is because it is a metabolically active fatty acid substrate especially used during periods of increased energy expenditure, such as endurance exercise.
Fatty Acids Burned for EnergyFatty acids burned for energy (oxidized) in the muscle can either come directly from the blood or from the IMTAG stores. In order for fatty acids to be oxidized, they must be transported into the cell's mitochondria. The mitochondrion is an organelle that functions like a cellular power plant. The mitochondrion processes fatty acids (and other fuels) to create a readily usable energy currency (ATP) to meet the energy needs of the muscle cell. Most fatty acids are transported into the mitochondria using a shuttle system called the carnitine shuttle (Holloway et al. 2008). The carnitine shuttle works by using two enzymes and carnitine (an amino acid-like molecule) to bring the fatty acids into the mitochondria. One of these enzymes is called carnitine palmitoyl transferase I (CPTI). CPT1 may work with one of the same proteins (FAT/CD36) used to bring fatty acids into the muscle cell from the blood (Holloway et al. 2008). Once inside the mitochondria, fatty acids are broken down through several enzymatic pathways including beta-oxidation, tricarboxylic acid cycle (TCA), and the electron transport chain to produce ATP.
Focus Paragraph: An Overview of Fat Metabolism in the MitochondrionFatty acids are transported into the muscle where they are either stored (as IMTAG) or transported into the mitochondrion, which can be referred to as the fat-burning furnace in a person's body cells (as this is the only place TAG are completely broken down). As the chemical bonds in TAG molecules are broken up in metabolism they begin to lose electrons (a process called oxidation) and are picked up (a process called reduction) by electron transporters (NADH+H+ and FADH2). The electron transporters take the electrons to the electron transport chain for further oxidation, which leads to a liberation of energy that is used to produce adenosine triphosphate (ATP). Unused energy becomes heat energy to sustain the body's core temperature. This ATP synthesizing process depends upon a steady supply of oxygen, which is why this process is aptly nicknamed “aerobic metabolism” or “aerobic respiration.”Adapted from Achten, J., and Jeukendrup, A.E. 2012.
Fatty Aid Oxidation During a Single Bout of ExerciseAt the start of exercise blood flow increases to adipose tissue and muscle (Horowitz and Klein, 2000). This allows for increased fatty acid release from adipose tissue and fatty acid delivery to the muscle. Exercise intensity has a great impact on fat oxidation. Maximal fat oxidation occurs at low to moderate intensity (between 25% and 60% of maximal oxygen consumption (VO2max) (Horowitz & Klein 2000). At lower exercise intensities, most of the fatty acids used during exercise come from the blood (Horowitz & Klein 2000). As exercise increases to moderate intensity (around 60% of VO2max) the majority of fatty acids oxidized appear to come from IMTAG (Horowitz and Klein, 2000). At higher exercise intensities (>70 % VO2max), total fat oxidation is reduced to levels lower than that of moderate intensity (Horowitz and Klein, 2000). This reduced rate of fatty acid oxidation is coupled with an increase in carbohydrate breakdown to meet the energy demands of the exercise (Horowitz & Klein, 2000).
This counterintuitive drop in fat utilization during high intensity exercise is caused by several factors. One factor is related to blood flow to adipose tissue and thus reduced fatty acid supply to the muscle. At high exercise intensity, blood flow is shunted (or directed) away from adipose tissue so that fatty acids released from adipose tissue become “trapped” in the adipose capillary beds, and are not carried to the muscle to be used (Horowitz and Klein, 2000). Another reason for reduced fat usage at high exercise intensities is related to the enzyme CPT1. CPT1 is important in the carnitine shuttle that moves fatty acids into the mitochondria for oxidation. The activity of CPT1 can be reduced under conditions of high intensity exercise. Two mechanisms are thought to reduce CPT1 activity during intense exercise. As stated above, with increasing exercise intensity fatty acid oxidation drops while carbohydrate oxidation increases. The increased usage of carbohydrate leads to increased levels of a molecule called malonyl CoA inside the cell (Horowitz and Klein, 2000). Malonyl CoA can bind to and inhibit the activity of CPT1 (Achten and Jeukendrup, 2012).
Another way intense exercise may reduce CPT1 activity is by changes in cellular pH. The cellular pH is the measure of the acidity in the cell's cytoplasm (fluid) in terms of the activity of hydrogen ions. As exercise intensity increases the muscle becomes more acidic. Increased acidity (which means the pH is lowering) can also inhibit CPT1 (Achten and Jeukendrup, 2012). The reason for the increased acidity during high intensity exercise is not because of lactic acid formation as once thought. Instead, acidosis increases because the muscle is using more ATP at the contracting muscle fibers (just outside of the mitochondria), and the splitting of ATP releases many hydrogen ions into the cellular fluid (sarcoplasm) leading to the acidosis in the cell (Robergs, Ghiasvand and Parker, 2004).
Too much emphasis is often placed on percent of fatty acid contribution of Calories burned during a single bout of exercise. Recovery from a bout of exercise as well as training adaptations to repeated bouts are important to consider when working with clients with fat loss goals.
Focus Paragraph. The Splitting of Adenosine Triphosphate (ATP)ATP is split by water (called hydrolysis) with the aid of the ATPase enzyme. During intense exercise there is a high level of hydrolysis of ATP by the muscles fibers. Each ATP molecule that is split releases a hydrogen ion, which is the cause of acidosis in the cell (Robergs, Ghiasvand and Parker, 2004). This acidosis can slow the carnitine shuttle that moves fatty acids into the mitochondria for oxidation.
Energy/Fat Used During RecoveryAfter exercise an individual burns more energy, which is primarily used for muscle cell recovery and glycogen replacement with the muscle. This elevated metabolic rate is termed excess post exercise oxygen consumption (EPOC). EPOC appears to be greatest when exercise intensity is high (Sedlock, Fissinger and Melby, 1989). For example, EPOC is higher after high intensity interval training (HIIT) compared to exercise for a longer duration at lower intensity (Zuhl and Kravitz, 2012). EPOC is also notably observed after resistance training (Ormsbee et al. 2009), because it disturbs the working muscle cells' homeostasis to a great degree resulting in a larger energy requirement after exercise to restore the contracting muscle cells to pre-exercise levels. EPOC is particularly elevated for a longer period of time after eccentric exercise due to additional cellular repair and protein synthesis needs of the muscle cells (Hackney, Engels, and Gretebeck, 2008). Many studies also show that during the period of EPOC, fat oxidation rates are increased (Achten and Jeukendrup, 2012, Jamurtas et al. 2004, and Ormsbee et al., 2009). Comparatively, fatty acid use during high intensity bouts of exercise such as HIIT and resistance training may be lower as compared to moderate intensity endurance training; however, high intensity exercise and weight training may make up for this deficit with the increased fatty acid oxidation through EPOC.
Focus Paragraph. Comparison of Effect of Light Exercise versus Heavy Exercise on EPOCSome key factors that contribute to the elevated post-exercise oxygen consumption during high intensity exercise include the replenishment of creatine phosphate, the metabolism of lactate, temperature recovery, heart rate recovery, ventilation recovery, and hormones recovery (Sedlock, Fissinger and Melby, 1989).
Adaptations to Exercise that Improve Fat UsageTrained people are able to use more fat at both the same absolute (speed or power output) and relative (% of VO2 Max) exercise intensity than untrained people (Achten and Jeukendrup, 2012). Interestingly, lipolysis (breakdown of fats to release fatty acids) and fat release from adipocytes is not different between untrained and trained people (Horowitz and Klein, 2000). This suggests that the improved ability to burn fat in trained people is attributed to differences in the muscle's ability to take up and use fatty acids and not the adipocyte's ability to release fatty acids. The adaptations that enhance fat usage in trained muscle can be divided into two categories: 1) those that improve fatty acid availability to the muscle and mitochondria and 2) those that improve the ability to oxidize fatty acids.
Fatty acid availabilityOne way exercise can improve fatty acid availability is by increasing fatty acid transport into the muscle and mitochondria. As mentioned above, specific proteins mediate transport of fatty acids into the muscle and mitochondria. Exercise training has been shown to increase the amount of FAT/CD36 on the muscle membrane and mitochondrial membrane (Holloway et al. 2008) and has been shown to increase CPT1 on the mitochondrial membrane (Horowitz and Klein 2000). Together these proteins will improve fat transport into the muscle and mitochondria to be used for energy.
Exercise may also cause changes in the intramuscular lipid droplet (that contains IMTAGs). The intramuscular lipid droplet is mostly found in close proximity to the mitochondria (Shaw, Clark and Wagenmakers, 2010). Having IMTAGs close to the mitochondria makes sense for efficient IMTAG usage so that fatty acids released from the lipid droplet do not have to travel far to reach the mitochondria. Exercise training can further increase IMTAG availability to the mitochondria by causing the lipid droplet to conform more closely to the mitochondria. This increases surface area for more rapid fatty acid transport from the lipid droplet into the mitochondria (Shaw, Clark and Wagenmakers, 2010). Exercise training may also increase the total IMTAG stores (Shaw, Clark and Wagenmakers, 2010).
Another training adaptation that may improve fatty acid availability is increased number of small blood vessels within the muscle (Horowitz and Klein, 2000). Remember, fatty acids can enter the muscle through the very small blood vessels. Increasing the number of capillaries around the muscle will allow for increased fatty acid delivery into the muscle.
Fatty acid breakdownIMTAGs are a readily available substrate for energy during exercise because they are already located in the muscle. Trained athletes have an increased ability to use IMTAG efficiently during exercise (Shaw, Clark and Wagenmakers, 2010). Athletes also tend to have larger IMTAG stores than lean sedentary individuals. Overweight and obese individuals, interestingly, also have high levels of IMTAG but are not able to use IMTAGs during exercise like athletic individuals can (Shaw, Clark and Wagenmakers, 2010).
So what causes the reduced ability to use IMTAGs in obese individuals? A logical guess would be that they have dysfunctional mitochondria that cannot use fatty acid properly. Research has shown however, that the mitochondria from muscles of obese individuals are not dysfunctional (Holloway et al. 2008). Instead, the number of mitochondria per unit of muscle (mitochondrial density) is reduced in an obese population (Holloway et al. 2008). Reduced mitochondrial density is a more likely explanation for reduced ability to use fat for energy in obese individuals. An important adaptation to exercise training is increased mitochondrial density (Horowitz and Klein 2000; Zuhl and Kravitz, 2012). Increasing mitochondrial density would improve the ability to use fat and benefit individuals with fat loss goals.
Endurance exercise training is an effective way to improve the body's fatty acid usage abilities by improving the availability of fatty acids to the muscle and mitochondria and by increasing fatty acid oxidation (Horowitz and Klein, 2000). HIIT training has also been shown to result in similar fat burning adaptations while requiring fewer workouts and less total time commitment (Zuhl and Kravitz, 2012)
Practical application Rather than trying to maximize fat oxidation in a single bout of exercise, it is recommended that the personal trainer design a workout program aimed at causing muscle adaptations described above to improve fatty acid oxidation ability. The exercise professional should include interval and endurance training programs as these have been shown to improve mitochondrial density and fat oxidation (Zuhl and Kravitz, 2012). In addition, regular progressively increasing programs of resistance training are encouraged as this training will enhance EPOC and post-workout fat oxidation. Also, the personal trainer should encourage the client to engage in low to moderate intensity exercise (such as walking and cycling) on “off hard workout days” in order to enhance caloric deficit and support muscle adaptions between training days.
Workout examples
High intensity interval training (HIT) with variable recovery (modified from Seiler and Hetlelid, 2005)High intensity interval training uses exercise intensity that corresponds to the individual's VO2max. Seiler and Hetlelid (2005) exercised subjects at their highest running speeds for 4 minutes with 1, 2 or 4 minutes of recovery and repeated this interval 6 times. The trainer can do HIT with clients with many different modes of exercise, simply having the client maintain his/her maximal sustained exercise effort for the 4 minutes. The idea of a systematic variation of the recovery is a very novel approach to interval training and certainly warrants more research.
The workout
Have the client complete up to 6 sets of 4-minute bouts at a maximal sustained workout effort and vary each recovery period to be 1 min, 2 min or 4 minutes at a light intensity (client's self-selected intensity).
Sprint interval training (SIT) (Modified from Burgomaster et al. 2008) Sprint interval training is repeated all-out (maximum effort) bouts of exercise. The maximal effort generated in SIT necessitates a small work to larger rest ratio. That is, SIT is often done with a 30-second all-out effort followed by a 4.5-minute rest period. The trainer can do SIT with clients using a variety of different modes of exercise including the stationary bike, elliptical cross-trainer and rowing machine. The resistance on the chosen mode of exercise should be relatively challenging during the work bout. During the sprint interval the trainer should verbally encourage the client to maintain maximal effort throughout the bout. During the recovery phase between bouts the client is encouraged to continue “moving” on the exercise machine at a very low self-selected “light” effort.
The workout
Have the client complete 3 to 4 bouts of 30-second all-out bouts bout with 4.5 minutes of active recovery between bouts.
Special Comments
This is a very challenging workout. Modifications may be required to match the individual's fitness level needs.
Resistance Training (RT) (modified form Melby et al. 1993)This workout is a slight modification of others that have been shown to cause EPOC (Melby et al. 1993) and increased fat usage (Jamurtas et al. 1993) in time period after the exercise. This is total body weight lifting workout that uses 10 exercises. The exercises are arranged in 5 pairs so that each pair of exercise is completed before resting and moving on to the next pair. The whole circuit of exercise should be completed up to 6 times. The rest interval between pairs should be no longer than 2 minutes. The resistance used on each exercise should allow the client to lift 8 to 12 repetitions.The Workout-o Pair 1
o Bench press
o Bent over row
o Pair 2
o Split squat (Right leg forward)
o Split squat (Left leg forward)
o Pair 3
o Military press
o Crunches
o Pair 4
o Biceps curls
o Triceps extensions
o Pair 5
o Half squat
o Lateral raises
Special Comments
As with any workout, exercise modifications or substitutions may be necessary to fit individual's fitness needs and abilities.
Tabata-inspired interval training (modified form Tabata et al., 2006) Tabata-style intervals use 20 seconds of high-intensity work followed by 10 seconds of rest, repeated up to eight times. Tabata-style training can use cardiovascular equipment such as the treadmill, rowing machine or stationary bike, or in calisthenics such as burpees, mountain climbers or body-weight squats. During the rest interval, keep the client moving to avoid blood pooling in the lower extremities. This will also help prevent the client from feeling queasy or faint.
The workout
Have the client perform complete three sets of Tabata intervals, resting 3 minutes between sets. Use burpees for the first set, the stationary bike for the second and the rowing machine for the third. Workout should last about 21 minutes.
Comments
This type of exercise has been shown to be effective at improving VO2max. Encourage the client maintain a challenging effort during this workout. The personal trainer should provide verbal encouragement to help the client do this.
Moderate intensity steady-state exercise (MIR)Light-to-moderate exercise should be encouraged on days when the client is recovering from one of the more intense condition workouts provided here. This exercise should be restorative, allowing for the client's body to promote new muscle adaptations they have gaining from the more intense training.
The Workout
"We don't have to wait for a magic potion," says Dr. Komaroff. "We already have a proven treatment that profoundly protects our health: exercise,”
Walking is a great way to implement this workout. Encourage the client to walk around their neighborhood or local park for 30 minutes to 1 hour. The walking pace should be that which the client can sustain a conversation.
Bios:Mike Deyhle, B.S, CSCS, is an Exercise Science masters student at the University of New Mexico, Albuquerque. He is interested in neural and skeletal muscular physiology especially with respect to skeletal muscular damage, metabolism, fatigue, and exercise training/detraining.
Christine Mermier, Ph.D. is an assistant professor and exercise physiology laboratory director in the exercise science Program at UNM. Her research interests include the effect of exercise in clinical patients, women, and aging populations, and high altitude physiology.
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and American Council on Exercise Fitness Educator of the Year.
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