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Abdominal width

Belly fat tends to remain in the same position in your abdomen whether you are standing up or lying down. In contrast, abdominal subcutaneous fat – the fat you can pinch around your tummy – will tend to move sideways and downwards when in a lying position. To test if you have a lot of belly fat, you can compare your abdominal width when you are standing up and lying down.

Stand against a wall, making sure to push your spine against it. Place something flat, such as a plastic ruler, across your abdomen, then use a tape measure or another ruler to measure your abdominal width from the wall to the plastic ruler. Record the distance. Now lie on a flat surface. Place the ruler on your abdomen and measure from floor to ruler with the tape measure. If the measurement does not change much and if you have a large waist circumference (as per the measurements in Table 2), then it is likely you possess a lot of belly fat. If the difference is large – a 2.5cm difference can be considered large – you probably have a significant amount of subcutaneous abdominal fat.

These simple methods will not assess exactly how much belly fat you possess but they will let you know if interval sprinting is reducing your belly fat over time. If you undertake the program described in Chapter 6, measuring abdominal width and waist circumference weekly are good ways of assessing your progress.

Waist skinfold measure

An estimate of total body fat can also be achieved by measuring the thickness of skinfolds in different parts of the body. This is done with a device called a skinfold calliper, which assesses the thickness of the skin together with a layer of subcutaneous fat. Taking skinfolds at different parts of the body can give you an estimate of the amount of subcutaneous fat on your body. Formulas have been developed to estimate the total percentage of body fat from calliper measurements, however the accuracy of these has been questioned. Like bioelectrical impedance, calliper measurements are best used to estimate subcutaneous fat change over time rather than one single estimate of total body fat.

Skinfold assessment does not estimate belly fat, how-ever it can be used to monitor changes in the subcutaneous fat around your belly. A useful place to take a measurement is the waist skinfold, which is illustrated in Figure 2 below. The waist, or suprailiac, skinfold is located just above the protrusion of the hip bone, which is known as the iliac crest. It is more accurate if you get someone else to do the measurement for you. It is important that the skinfold is taken in the same position every time. Taking a picture of the site with a digital camera is recommended.

Figure 2. Assessment of waist subcutaneous fat by skinfold.

The fold is taken almost horizontally. For right-handed people, pinch and hold a fold of skin with its layer of subcutaneous fat with the left forefinger and thumb. Using the right hand, place the calliper jaws about 8mm from the left forefinger. Keep holding the skinfold with the left hand throughout. Release the calliper so all the force of its jaws is on the skinfold alone. The callipers will take a few moments to stabilise; the value should only be recorded when they have stopped changing and before releasing any calliper pressure. Measure the waist site twice and record the readings on the Body Composition Recording Form (see Appendix E).

Figure 3. A computed tomography scan across the waist area. White is the subcutaneous abdominal fat, grey is mostly abdominal muscle and other tissue, and black is the belly, or visceral, fat.

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Now you have 3 abdominal and belly fat measures that can be used to monitor subcutaneous and belly fat change as you proceed with the interval sprinting program:

• waist circumference
  
• abdominal width
  
• waist skinfold
  

In Figure 3 (above), the subcutaneous abdominal fat is shown in white, the abdominal muscle in grey, and the belly or visceral fat in black. If your waist circum-ference gets smaller, then either your subcutaneous abdominal fat (white) or belly fat (black) has been reduced. If your waist circumference gets smaller but the skinfold caliper measure does not change then it is likely that your belly fat has decreased.

How to measure leg circumference

Measuring skeletal muscle mass is best done through clinical techniques such as MRI and DEXA. For individual monitoring, however, the assessment of leg circumferences can provide an indirect guide to possible change in muscle mass after interval sprinting. Leg measurements are obtained in a similar fashion to waist circumference, and are taken at mid-thigh and at the widest point of the calf.

For the mid-thigh measurement, use a tape measure to assess the distance between your groin and the top of your kneecap, and then determine the mid-point of the measurement. You should mark the site with a non-permanent ink pen and take a digital picture to ensure you measure in the same place each time. Stand with your weight evenly distributed on both feet and wrap the tape measure around the mid-point of your thigh. The tape measure should not be pulled too tight. Having someone else take the measurement reduces error, and it is best if 2 measures are recorded and the average value documented. Record the results on the Body Composition Recording Form (see Appendix E).

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The key points to remember about the problems of having too much belly fat are:

• Worldwide, belly fat accumulation is increasing dramatically.
  
• Belly fat increases with a poor diet and physical inactivity.
  
• Belly fat has a number of negative effects on health.
  
• Belly fat is influenced by a variety of factors, including diet, inactivity, ethnicity, gender, age, stress, poor sleep and genes.
  
• Belly fat change can be assessed by measuring waist circumference, abdominal width and waist skinfold, and leg muscle mass change can be assessed by measuring girth circumference.
  

You should now have an understanding of the difference between belly or visceral fat and subcutaneous fat, and of the dangers of carrying high levels of belly fat. You might even have identified factors in your own life that can lead to an increase of belly fat and will be able to estimate how much subcutaneous and belly fat you carry. Read on to learn the best ways to combat belly fat and create a healthier life.

Aerobic exercise can result in a loss in belly fat, however a lot of aerobic exercise has to be performed before results are seen. Similarly, carrying out 3 sessions of resistance exercise per week does not seem to reduce belly fat. In contrast, research has shown regular interval sprinting will reduce belly fat in far less time than other forms of exercise. In this chapter, you’ll find a discussion of the results of published research articles that have examined the effect of aerobic and resistance exercise and interval sprinting on belly fat loss. There is also an examination of the possible mechanisms that are thought to contribute to the belly fat-reducing effect of interval sprinting and its effects on aerobic fitness, skeletal muscle mass and insulin resistance.

Aerobic exercise and belly fat

Traditionally, programs that use exercise to promote fat loss have consisted of participants engaging in a steady-state, moderate-intensity exercise such as walking, jogging or swimming for at least 45 minutes per session. The rationale for this is that individuals burn more fat as a fuel during moderate-intensity exercise and should lose more body fat as a result. Disappointingly, however, many studies have shown that this form of exercise leads to little total body fat loss unless the individual does very high volumes of aerobic exercise.
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And while belly fat loss can occur after regular aerobic exercise, a lot of aerobic exercise has to be performed. For example, researchers at Duke University compared sedentary adults with adults who exercised at light or hard intensity. Results showed that the sedentary people gained about 9% of belly fat in 6 months, whereas adults who walked or jogged about 20 kilometres a week put on no belly fat. Those who jogged about 30 kilometres a week lost both belly and subcutaneous fat but their muscle mass was unchanged. A greater amount of belly fat (18%) was lost by overweight men and women who carried out a 14-week aerobic exercise program that involved exercising for 60-minute sessions 5 days per week. Again, their muscle mass remained unchanged.

A summary of results of the aerobic exercise studies in this area found that, to reduce belly fat, at least 30 minutes per day – and preferably up to 60 minutes per day – was needed for at least 14 weeks.
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Thus, there is evidence to suggest that aerobic exercise for at least 45 minutes per day, 5 days per week, for 14 weeks can result in about an 18% decrease in belly fat without a change in muscle mass. As most people do not have the time or the motivation to engage in over 5 hours of exercise a week, there is need to find a form of exercise that results in a significant decrease in belly fat while maintaining or increasing muscle mass, and yet be time-efficient. Interval sprinting appears to be a form of exercise that meets these time constraints.

Resistance exercise and belly fat

Strength or resistance training – that is, exercising with weights – may also help reduce belly fat accumulation in some individuals. Researchers from the University of Pennsylvania monitored overweight and obese premenopausal women over a 2-year period. In comparison to women who performed no exercise, those women performing an hour of weight training twice a week decreased their total body fat by about 4%; however, while they did not record an increase in belly fat, the amount of belly fat was not reduced. Another 2 studies conducted with older men and women showed that 3 moderately hard weekly weight training bouts for 12 weeks resulted in little change in total body fat but a significant decrease in belly fat. A significant number of other studies, however, did not find any effect of resistance exercise on belly fat. A 2012 meta-analysis by one group of researchers reviewed the results of 35 well-controlled studies examining the effect of resistance exercise on belly fat and concluded that resistance training failed to induce significant reductions in belly fat.
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The weight training protocols used in these studies typically involved around 8 different exercises, with 8–10 repetitions, repeated 3 times each exercise. The individual exercises included upper arm, abdominals and leg muscles. This type of protocol was typically performed 2–3 times per week. During a typical 60-minute weight training session, the actual time spent lifting weights is about 8–10 minutes. Thus, it is likely that lifting weights at a moderate intensity for 8 minutes, 3 times per week will not result in significant decreases in body or belly fat.

What is interval sprinting?

Interval sprinting protocols typically involve repeated sprinting or hard exercise at near all-out intensity, followed by low-intensity exercise or rest. The length of the sprint period has varied from 6 seconds to 2 minutes, and the recovery period has ranged from 12 seconds to 4 minutes. Most researchers in this area have examined interval sprinting on a stationary cycle ergometer and have examined adolescents, young people, older individuals and patient groups consisting of cardiac rehabilitation, intermittent claudication, type 2 diabetes and obese children and adults. One of the most utilised protocols has been the Wingate test, which consists of 30 seconds of all-out sprint with a hard resistance. Subjects typically perform the Wingate test 4–6 times, with each sprint being separated by 4 minutes of recovery. Knowledge about changes to skeletal muscle from interval sprinting has been achieved mainly by using this protocol. However, the Wingate test is extremely hard and people have to be highly motivated to tolerate a lot of pain and discomfort. Consequently, the Wingate test is unsuitable for most overweight, sedentary individuals interested in losing belly fat.

Other, less intense interval sprinting protocols have also been applied. For example, we have used an 8-second cycle sprint followed by 12 seconds of low-intensity cycling for a period of 20 minutes. Thus, instead of 4–6 sprints per session, as used in Wingate studies, subjects using the 8-second/12-second protocol sprint 60 times at a lower exercise intensity for a total sprint of 8 minutes, with 12 minutes of low-intensity cycling. For this method, the total exercise time is 20 minutes, plus a 4-minute warm-up and 4-minute cool-down. Thus, one of the features of interval sprinting is it takes far less time than traditional aerobic exercise protocols, making it a time-efficient strategy by which to accrue health benefits.

Interval sprinting and belly fat

Direct measures, like magnetic resonance imaging (MRI), and indirect measures, like waist circumference, have been used to assess the effects of interval sprinting on belly fat. Mourier and colleagues showed a 48% decrease in belly fat, measured by MRI, after steady-state aerobic exercise 2 days per week and interval training 1 day a week for 8 weeks in middle-aged men and women.
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Another study with older men, also using MRI, found that 8 weeks of aerobic interval training, which also involved hard exercise for 2 minutes and resting for 4 minutes, resulted in a 14% loss of belly fat.

Our research has used a shorter interval sprinting protocol with younger overweight people. In our first 2 studies with women, we used DEXA and waist circumference to assess belly fat change. DEXA does not directly assess belly fat but does measure a variable called central abdominal fat, which is highly related to belly fat. The first study we conducted lasted 15 weeks and our candidates did 20 minutes of interval sprinting at an 8-second/12-second ratio, 3 times per week.
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They lost 2.6kg of total body fat (11%), which was accompanied by a significant decrease in central abdominal fat. In a second study, overweight women exercised for only 12 weeks using the same protocol.
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They lost 9% of total body fat (2.5kg) and experienced a 6% decrease in central abdominal fat. In this study, waist circumference was reduced by 3.5cm after 6 weeks of interval sprinting. Waist circumference is highly related to central abdominal fat, which suggests that belly fat was significantly reduced after 6 weeks, or 6 hours, of interval sprinting. Women in this study also changed their diet in favour of a Mediterranean eating plan, which resulted in a 13% decrease in daily caloric intake.

In a third study, we examined a 12-week interval sprinting program on the belly fat of young overweight men.
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In this study, we measured belly fat with a technique called computed tomography, which uses ionising radiation to locate the belly fat deep inside the abdomen. Males lost 9% of total body fat (2kg) and 17% of belly fat. They also lost 5% of subcutaneous abdominal fat. Similar to our studies with women, waist circumference was reduced by 3.5cm after 6 weeks of interval sprinting. In the male study, waist circumference was highly correlated with belly fat, suggesting that belly fat was significantly reduced after 6 weeks, or 6 hours, of interval sprinting. A summary of the results of studies examining the effects of aerobic exercise, resistance exercise and interval sprinting on belly fat reduction is shown in Table 3 (below).

Because interval sprinting has only been studied relatively recently with subjects who are not athletes, there are fewer published research studies in this area. But it already looks like interval sprinting has resulted in far greater reductions of total body and belly fat than the other 2 exercise modalities in significantly less exercise time. It takes just 6 weeks of interval sprinting exercise to see a significant reduction in waist circumference, so we can conclude that the most effective form of exercise for reducing belly fat is interval sprinting.

Table 3. A summary of the results of randomised controlled studies examining the effects of aerobic exercise, resistance exercise and interval sprinting on total and belly fat reduction.

Adapted from information found in studies by Boutcher et al., Ohkawara et al., and Ismail et al.
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Possible reasons interval sprinting leads to belly fat loss

The mechanisms underlying the interval sprinting-induced belly fat loss include increased exercise and post-exercise fat burning, increased muscle mass, decreased appetite after exercise, and reduced postprandial lipemia, which is when triglyceride levels in blood rise after eating. These levels can stay elevated for up to 18 hours.

Increased fat burning

Towards the end of an interval sprinting session that involves many repeat sprints, the exercising muscles start to run out of sugar, which, in the form of glucose and glycogen, is needed to create a high-energy compound called adenosine triphosphate (ATP), which provides the energy for muscular contraction. Towards the end of an interval sprinting session, it is thought that the ATP is mainly derived from intramuscular fat stores, the fat stored within the skeletal muscles. Together with subcutaneous and belly fat, these depots are an important source of fat. If we don’t regularly burn up the fat accumulated inside our muscles, then the result is usually the development of insulin resistance and type 2 diabetes. When we deplete the fat stores inside the muscle by interval sprinting, however, the body is forced to replace them with fat stored elsewhere, such as in the belly and under the skin. This shuttling of fat from the belly to the skeletal muscle may also happen after exercise has stopped, as some of the hormones generated during interval sprinting appear to continue burning fat long after exercise. Because the fat stored in belly fat cells is more responsive to interval sprinting, we think that this shuttling of fat from the belly to the skeletal muscles contributes to long-term reduction of belly fat stores.

The ability of aerobic exercise to burn up extra energy after aerobic exercise has been extensively studied. A review of these studies concluded that a session of aerobic exercise lasting 40 minutes or more typically generated an increase in energy of about 13%. This is a negligible effect and is likely to make only a small contribution to overall fat loss. The fat-burning response after interval sprinting, however, has not been extensively examined. It is possible that the high blood catecholamine levels occurring during interval sprinting (see Figure 10) could induce fat burning long after exercise has stopped. This elevation may also happen because of the necessity to lower blood and muscle lactate – a chemical that accumulates during hard exercise – and to re-synthesise the depleted glycogen in the exercising muscles. The elevated growth hormone levels documented after a session of interval sprinting may also contribute to enhanced energy expenditure and fat burning.

Increased muscle mass

It has been estimated that an increase of 1kg of skeletal muscle has the capability to burn up about an extra 21 calories per day. In theory, this could amount to just under 3kg of body fat usage per year. Thus, retaining or increasing muscle mass is very important for health. Unfortunately, it is well documented that participating in aerobic exercise does not change muscle mass, while moderately hard resistance exercise may result in increased muscle mass in some people. A recent review concluded that weight-training programs carried out by middle-aged people resulted in an average increase of muscle mass of 1.2kg.
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As can be seen in Table 5, our 3 interval sprinting studies resulted in significant increases of leg and trunk muscle mass of 0.2kg and 0.3kg for women and 0.5kg and 0.7kg for men.
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Another research group found a large increase in leg muscle mass of older women after they had carried out interval training for 16 weeks. These results are important, as muscle mass affects health and is typically reduced by ageing and when people go on a severe diet.