The Impact of Body Composition on Exercise Capacity - Research Paper Example

1.Chapter 1 Introduction The study of human body composition in relation to health and disease is an ancient field. It started from a researcher into human cadavers and has progressed to include the use of advanced technologies within the current era. In an effort to understand the relationship between body composition and the risk to morbidity and mortality, several reference models have been developed. In these models, the body is divided into different compartments and studied through different levels; atomic, molecular, cellular and functional (Wang et al., 1992). In the field of Exercise research , where the focus is on the relation of body measurements to body fitness and performance, the basic 2-compartmental that are most oftentimes used are as follows: fat mass (FM) and fat-free mass (FFM) (Ellis, 2000). Although several techniques are available for estimating body composition, there is no a gold standard to measure body composition in vivo. Body Mass Index (BMI), which is calculated as weight(Kg)/height (m2), is the most common tool that is used to assess body composition .Although BMI is extensively used in clinical practice and epidemiological studies as a surrogate measure of body composition, it does not provide adequate information about body fat because it combines information about FM and FFM(Gómez-Ambrosi et al., 2012; Dulloo et al., 2010). The relationship between BMI and % BF can be confounded by physiologic, pathologic and environmental factors. For example, women have higher %BF than men at any given BMI( Baumgartner et al., 1995). Aging is associated with a decrease in FFM which results in older adults having a higher %BF than the young at any given BMI (Baumgartner, 1993; Mazariegos & Wang, 1994). For example, it was found that Asians have lower BMI than Whites but higher %BF (Wang & Thornton, 1994) .According to (Anjos et al. 2013) , in a study conducted in Brazil, within a normal range of BMI, the %BF ranged from 4.1-27.7% in men while in women it ranged from 21.6 to 41.5%. Moreover, blacks typically have denser FFM than Whites as a result of heavier muscle mass. Patterns of abdominal adiposity were observed to be greater in Black women than in Whites(Baumgartner et al., 1995). Likewise, a San –Antonio heart study reported that Hispanic –American have a higher tendency to adiposity than non-Hispanic Whites in both male and female populations (Haffner, 2000). In Italy, it has reported that women from the Southern regions have higher body fat distribution than women from the North. Several Studies have reported that using BMI alone may lead to misclassification of obesity and underestimation of the metabolic risks that are associated with the elevated levels of body fat (Gómez-Ambrosi et al., 2012). Diet and physical activity are important determinants of body composition. Imbalances between energy intake and energy expenditure results in either an increase or decrease on body mass. Much effort has been devoted during the last decades to such studies. Several epidemiological studies have concerned about the role of increase dietary fat intake and adiposity(Lissner & Heitmann, 1995). In the EPIC study that was conducted in Greece, protein intake was conductive to increased BMI (Trichopoulou et al., 2002). Consumption of refined grains is associated with abdominal adiposity while consumption of fibres from whole grains has beneficial effects on both %BF and fat distribution (McKeown et al., 2009). A comparison between dietary patterns and the effects on body composition has reported that meat and potato consumption is associated with annual increases in BMI; whereas white bread consumption is associated with significant increase in waist circumference (Newby et al., 2003). Physical activity is a key component in the metabolic equation to maintain body composition. A large body of evidence has confirmed the importance of physical activity as a preventive measure against CVD risk factors. Regular physical activity controls lipid metabolic profile, diabetes and obesity. On the other hand, physical inactivity is associated with adiposity as well as a host of other negative health outcomes (Lichtman et al., 1992; Jennings et al., 1989; Braith et al., 1994; Fletcher et al., 1996). Assessing exercise capacity provides better clinical prognostic value than assessing physical activity. It is objectively measured and reflects the patterns of daily life activity as well as detecting the health outcome of sedentary behaviour. While assessing physical activity by questionnaire is prone to recall bias, often overestimated and does not take account the free living activities, objective methods for quantifying energy expenditure such as double-labelled water and accelerometers are limited due to their cost (Hainer et al. 2009; Lichtman et al., 1992). Exercise Capacity represents the cardio-respiratory fitness of an individual; which reflects the overall capacity of cardiovascular and respiratory systems to supply oxygen during a sustained exercise (Taylor & Buskirk, 1955). Cardio-respiratory fitness is defined as the maximal ability of the heart to pump blood (maximal cardiac output) and the ability of the skeletal muscle to extract and use oxygen (Farrell et al., 2002). On the other hand, the peak exercise capacity reflects ‘’the maximum ability of the cardiovascular to deliver and use oxygen to exercising skeletal muscle to extract oxygen from blood’’ (Braunwald, 1992). In most clinical assessments exercise capacity is expressed in terms of Metabolic Equivalents (MET)(Myers et al., 2002). One MET is defined as the energy consumed in setting quietly at rest, which is equivalent to a body consumption of 3.5 ml of O2 per kilogram of body weight per minute .(1 MET=3.5 ml O2∙Kg-1∙min-1) (Jette et al., 1990). It is also defined in terms of energy expenditure as ratio of work metabolic rate to a standard RMR (resting metabolic rate) of 1.0 Kcal per Kg of body weight (Ainsworth et al. 2000). As such, in the exercise field, the MET system is extensively used. The maximum oxygen consumption (VO2 max) is the ‘’gold standard’’ for measuring exercise capacity and it is used as a benchmark criterion of cardiorespiratory fitness (Ross & Murthy, 2010; McArdle et al., 2010). The oxygen consumption in healthy individuals increases as the work load increases until a plateau is reached. This threshold is known as VO2max (Dunford, 2006). VO2max can be expressed in absolute units as (litres per minute) L/min; however, it is often expressed in relative to body weight as (millilitres per minute per kilogram) (Dunford, 2006). Other than body mass, VO2max is also influenced by many other factors. Age, genetics, endurance training and body composition all affects the rate of VO2max (Kenny et al. 2008; Hollenberg 2006; Weiss & Spina, 2006; Ades & Toth, 2005; Stathokostas, 2004; Hawkins & Wiswell, 2003; Ross & Katzmarzyk, 2003’ Lynch, n.d.; Toth et al., 1994). Previous studies have shown that higher levels of exercise capacity have a greater impact in lessening the adverse effects of CHD risk factors; even if the individual has multiple risk factors (Kaminsky et al., 2013). It has also been found that in most circumstances, patients with higher levels of exercise capacity and CHD risk factors have lower rates of mortality in comparison with patients without CHD risk factors with lower levels of exercise capacity (Kaminsky et al., 2013). In addition to the importance of exercise capacity as prognostic value to mortality, low levels of exercise capacity predicts the development of hypercholestermia, hypertension and metabolic syndrome (Kaminsky et al., 2013). Weiss et al. reported also exercise capacity is inversely related to frailty which is known as limitations in the functional reserve in the body, which may be accompanied with reduced muscle strength, decrease in walking ability, fatigue and increased the susceptibility to disease ( Weiss et al. 2010). The two protocols of exercise testing are maximal and sub-maximal. Maximal exercise tests are the gold standard for assessing the maximal exercise capacity. Where VO2 max is directly measured. It is used as diagnostic tool and it is the basis for determining physical fitness. Submaximal tests overcome these limitations, It estimates VO2 indirectly. It is used to predict vo2 max or assess the performance. It is more practical and can be applied in field by walking, running and cycling tests (Dunford, 2006; Noonan & Dean, 2000; Armstrong, 2006). A six- minute walk test is a submaximal exercise test that is used extensively in clinical settings by using established standards. The subject is asked to walk for 6 minutes at a self-paced speed. The total distance covered in a 6-minute period is the main measurement outcome. The individuals exercise capacity is affected by multiple factors. Other than clinical diseases and medications such as beta-blockers, which are known to significantly reduce the exercise tolerance, many other factors have effects on exercise capacity (Kaminsky et al., 2013; Myers et al., 2002).These include age, gender, genetics, environmental factors, physical activity and body composition (Whaley et al., 1992; Kaminsky et al., 2013; Church et al., 2007; Garber et al., 2011). Physical activity levels are an important determinant in exercise capacity. These improve the cardiorespiratory fitness and play crucial preventive measure against CVD risk factors (Morris & Froelicher, 1991; Chandrashekhar & Anand, 1991; Smith & Blair, 1995; Wenger et al., 1995; Paffenbarger et al., 1986). Further, lifestyle and behaviour are important determinants in exercise capacity. In children and adolescents physical activity and sedentary behaviour act as an independent factor in relation to CRF (Santos et al., 2013). Several studies confirmed the role of PA in survival improvement in patients post myocardial infarction (O’Connor et al., 1989; Oldridge et al., 1988). Body composition and exercise capacity are frequently used in association with each other and it is often inferred that these physiological factors are strongly inter-related. Both excess body adiposity and decreased exercise capacity are risk factors for prospect health outcomes. Misperception exists whether these two factors are related to one and another or they are independent. Some studies reported that they are independent (Blair et al., 1996; Farrell & Kampert, 1998; Lee et al.,1998; Cooper & Gibbons, 1989; Blair et al., 1995). Obese people have low physical fitness and exercise capacities. In children, a cross-sectional study has shown a clear inverse relationship between exercise capacity and body fat ratio (Gutin & Manos 1993). Mota et al. (2002) conducted a study on children between the ages 8-16 years to estimate the changes in body composition and exercise capacity across different stages of pubertal maturation. The study reported that, in both sexes exercise capacity was inversely associated with %BF after adjustment for maturation status. In adults, the nature and magnitude of difference of exercise capacity was compared between lean and obese women, the study confirmed that obese women have lower exercise capacity at maximal and submaximal level in comparison with their leaner counterparts (Hulens et al., 2001). Walking abilities shown to be hampered in obese. In addition to slow pace, exhaustion and pain that are common, walking capacity is reduced in obese and VO2 cost is increased (Hulens et al., 2003; Mattsson et al., 1997). In women, BMI alone did not significantly increase all-cause mortality risk in comparing normal, overweight and obese while the level of exercise capacity was associated significantly with all cause-mortality (Farrell et al., 2002). Taken together the available information about body composition, exercise capacity and the lack of local findings, this study will evaluate the impact of %BF on exercise capacity in Saudi females with normal BMI measured by 6MWT.In addition, assess the dietary intake between different groups of %BF and within normal BMI. 1.2 Rationale: Since much effort has been devoted in studying the effect of adiposity on exercise capacity and six-minute walk test in overweight and obese. Current knowledge on the effect of adiposity in subjects with normal BMI on exercise capacity is limited. Hence, it is important to assess the effect of %BF in normal BMI on exercise capacity and quantify the magnitude of difference. 1.3 Aims and objectives: The study aims to determine the impact of dietary intake on body composition and the impact of body composition on exercise capacity in the form of six- minute walk distance in subjects with normal body mass index. 1.3.1 Objectives: 1-To compare the six-minute walk distance among subjects with normal BMI with different percentages of body fat: low %BF, normal %BF and high %BF. 2-To compare the dietary intake (macronutrients intake) among subjects with normal BMI with different percentages of body fat: low %BF, normal %BF and high %BF. 1.4 Hypothesis: The impact of dietary intake on body composition in subjects with normal BMI and the impact on exercise capacity. Research question for the primary outcome: Is the percentage of body fat in subjects with normal body mass index affects the six-minute walk distance? Research question for the secondary outcome: Do the dietary intake affects the percentage of body fat in subjects with normal BMI? Read More