Abstract
mbre de 2009 doi:10.5232/ricyde2010.01805
Meléndez-Ortega, A.; Davis, C.; Barbeau, P.; Boyle, C. (2010). Oxygen uptake of overweight and obese children at different stages of a progressive treadmill test. Revista Internacional de Ciencias del Deporte. 18(6), 74-90. http://www.cafyd.com/REVISTA/01805.pdf 75 Introduction he increase in the rates of obesity in all population groups in the last 20 years the world over has been confirmed by a large quantity of data published in the scientific literature. According to the World Health Organization (WHO), in 1995 there were an estimated 200 million obese adults worldwide and another 18 million children of less than 5 years of age classified as overweight. The number of adults had increased to over 300 million by 2000 and at least 400 million adults were obese in 2005 and the WHO further predicts that by 2015 more than 700 million will be obese (WHO, 2004; WHO, 2006). In almost all the developed countries, the prevalence has been increasing in a similar way in children and adolescents. At least 20 million children under the age of 5 years were overweight in 2005 (WHO, 2006). These trends are extremely important as excess weight and obesity in childhood are significant predictors of obesity in adulthood, with experts considering that there is an 80% chance of overweight or obese children carrying this problem into adult life (Whitaker and Wright, 1997). Simultaneously with the appearance of an epidemic increase in obesity including children (Fagot- Capagna, Pettitt et al., 2000; Pinhas-Hamiel, Dolan et al., 1996; Troiano and Flegal, 1998; Straus and Pollack, 2001) there has been an epidemic increase in type-2 diabetes in both children and adults (Mokdad, Serdula et al., 1996; Harrel, Mc Murria et al., 2000) and the WHO (2006) projects that diabetes deaths will increase by more than 50% worldwide in the next ten years. Although many factors are involved, basically the cause of too much fat being deposited depends on the imbalance between energy consumption and expenditure (Swinburn, Jolly et al., 2006) and although its degree of importance can be debated, physical inactivity is considered to play a major role in the development of obesity (Powell and
50% worldwide in the next ten years. Although many factors are involved, basically the cause of too much fat being deposited depends on the imbalance between energy consumption and expenditure (Swinburn, Jolly et al., 2006) and although its degree of importance can be debated, physical inactivity is considered to play a major role in the development of obesity (Powell and Blair, 1994) and some authors think that vigorous activity is necessary to provide the mechanical stimulation that leads stem cells to differentiate into bone and muscle instead of fat (Gutin, 2008; Rosen et al., 2006; Rubin et al., 2007). Maximum oxygen uptake (VO 2 max) is generally considered to be the best measure of cardio respiratory fitness (CRF) (Freedson and Goodman, 1993). Moreover, although VO 2 max has a major genetic component, it is greatly influenced by the subjects’ activity, thereby serving also to assess activity levels (Siconolfi, Lasater et al., 1985). This has meant that the determination of VO 2 max is a routine procedure in research projects to assess the cardiovascular capacity (CVC) of the subjects. Eriksson and Lindgarde (1996) found that Swedish men who developed type-2 diabetes within 6 years of testing had 16% lower VO 2 max values than normal and insulin sensitivity has been positively related with physical fitness in adults (Clausen, Borch-Jonen et al., 1996; Endre, Mattiasson et al. 1994; Nyholm, Mengel, et al., 1996) and lower VO 2 has been linked with a greater concentration of small, dense LDL and an unfavourable HDL profile in healthy young men (Clausen, Borch-Jonen et al., 1996; Endre, Mattiasson et al., 1994; Nyholm, Mengel, et al., 1996). In the same way lower levels of physical and vascular fitness are associated with cardio-metabolic risk in youth as well as elevated body fatness (Andersen et al., 2006; Gutin et al., 2004; Krekoukia et al., 2007) and because of the strong inverse correlation between CRF and fatness it is possible that deleterious consequences ascribed to adiposity may be partially due to the influence of a lack of CRF (Gutin, 2005). T
as elevated body fatness (Andersen et al., 2006; Gutin et al., 2004; Krekoukia et al., 2007) and because of the strong inverse correlation between CRF and fatness it is possible that deleterious consequences ascribed to adiposity may be partially due to the influence of a lack of CRF (Gutin, 2005). T
Meléndez-Ortega, A.; Davis, C.; Barbeau, P.; Boyle, C. (2010). Oxygen uptake of overweight and obese children at different stages of a progressive treadmill test. Revista Internacional de Ciencias del Deporte. 18(6), 74-90. http://www.cafyd.com/REVISTA/01805.pdf 76 In spite of its usefulness, to try to carry out determinations of VO2 max in children and especially in overweight or obese children is not an easy task. The common result is that a more or less significant proportion does not fulfil the requisites to be able to consider that they reached VO 2 max in their tests (Buono, Roby et al., 1991; Rivera-Brown, Rivera et al., 1992; Armstrong and Welsman, 1994; Rivera-Brown, Rivera et al., 1994; Rivera-Brown, Rivera et al., 1995; Duncan and Howley, 1999; Gutin et al., 2002). Apart from the possible lack of physical fitness and motivation, there is a series of problems which make it difficult to generalize the procedures for testing overweight and obese children. Among them we could cite the need for costly equipment, personnel specialized in the administration of the protocols used and having to collect samples of expired air, which independently of the procedure used, make the task of walking or running on a treadmill or pedalling on a cycle ergometer, uncomfortable (Rivera-Brown, Rivera et al., 1992; Armstrong and Welsman, 1994; Rivera-Brown, Rivera et al. 1994; Rivera-Brown, Rivera et al., 1995; Duncan, Mahon et al., 1996). In many situations which do not require the precision of a direct VO 2 determination recourse is made to procedures for estimating uptake based on the relation that exists between the intensity of effort or work load and oxygen uptake. VO 2 consumption estimates can be used to ascertain the energy expenditure, but they must take into account the greater or lesser economy of the work performed (Wasserman, Hansen et al., 1987). These authors indicate how adult obese subjects have a greater oxygen uptake when walking and therefore greater energy expenditure at submaximal intensities. Several authors have also indicated the lower economy of children compared to adults when doing physical activity and consequently the use of adult models to predict energy cost
economy of the work performed (Wasserman, Hansen et al., 1987). These authors indicate how adult obese subjects have a greater oxygen uptake when walking and therefore greater energy expenditure at submaximal intensities. Several authors have also indicated the lower economy of children compared to adults when doing physical activity and consequently the use of adult models to predict energy cost in weight-bearing activities fails to account for the increased energy costs in children (McArdle, Katch et al., 2001; Krahenbulhl and Pangrasi, 1983; Krahenbuhl, Pangrazi, et al., 1989; Ariëns et al., 1998) and especially in obese children (Bar-Or, 1983). There is presently no specific equation to estimate oxygen uptake for obese children, therefore it would be extremely useful to know the actual uptake of these children and provide a specific equation to estimate their oxygen uptake and thus their energy expenditure based on the workload on the treadmill. Due to the relation among oxygen uptake, work load and heart rate, the individual relation between heart rate and work load determined in a progressive stress test will permit the estimation of energy expenditure in these subjects. The purpose of this analysis was to determine relative VO 2 (ml/kg/min) in a group of overweight or obese children at different stages of a treadmill stress test with a modified protocol proposed by Rowland (1993) and the ACSM (2000) to provide a specific equation to estimate relative VO 2 in order to obviate its direct measurement in practical evaluations of overweight children. As the energy expenditure for a given workload is relatively constant, relative VO 2 at a given stage during the treadmill test will not be affected by physical training. An additional purpose of the study was to check the proportion of tests that could be considered maximal.
Meléndez-Ortega, A.; Davis, C.; Barbeau, P.; Boyle, C. (2010). Oxygen uptake of overweight and obese children at different stages of a progressive treadmill test. Revista Internacional de Ciencias del Deporte. 18(6), 74-90. http://www.cafyd.com/REVISTA/01805.pdf 77 Methods Subjects A total of 222 children (age range 7.0 to 11.9; mean = 9.4; SD = 1.1) were selected in the 6 cohorts that participated in the PLAY project carried out at the Georgia Prevention Institute (GPI) at the Medical College of Georgia (MCG). Of the subjects 94 were male and 128 female, 93 white and 129 African American, all of whom were recruited through school flyers from elementary schools in the area. Prior to the tests analyzed below the children and their parents had signed informed assent and consent forms as part of the protocol to participate in the Project. They were chosen if their Body Mass Index (BMI) was above the 85th percentile for their age and gender according to the norms supplied by the CDC (Ogden, Kuczmarski et al., 2002). Children with significant health problems (e.g. orthopaedic limitations, cardiac conditions, etc.) or medication that could affect the results of the study or preclude their safe participation were excluded. The population of obese children was selected because of our interest in amelioration of obesity and the GPI’s background working with this type of subjects. Some of the children did not have adequate data for the pre-stress test (10 children) and data of 2 additional tests were not accurate enough to be used for the analysis due to equipment malfunctioning, so, the data of 210 pre-tests and 193 (17 dropped out) post-tests repeated four months later were used for the analysis. The children participating in the Project were randomly assigned to one of three groups: a control group with 0 minutes of exercise, one with 20 minutes and the other with 40 minutes. The program was carried out over 4 months, 5 days a week in the gym of the GPI. During these training periods the children carried out different activities which raised their heart rate during the session to over 150 beats per
groups: a control group with 0 minutes of exercise, one with 20 minutes and the other with 40 minutes. The program was carried out over 4 months, 5 days a week in the gym of the GPI. During these training periods the children carried out different activities which raised their heart rate during the session to over 150 beats per minute. Measurements Weight (in shorts and t-shirt) was measured on an electronic scale and height on a stadiometer. Body composition was determined by DXA with a Hologic QDR 4500W (Hologic Inc. Bedford MA) that determines body composition in three compartments: fat, bone and fat-free soft tissue. Sexual maturation state was assessed by a paediatrician using the Tanner stages and whether the girls had experienced menarche. The treadmill test consisted of a multi-stage protocol modified from the protocol proposed by Rowland (1993) and the ACSM (2000) for poorly fit children with an additional warm-up period of 2.5 mph (4.02 km/h) and 0% slope for 2 minutes before the warm-up at 3 mph (4.83 km/h) with a 3% slope for 2 minutes proposed in the original protocol. After the warm-up the speed remained at 3 mph but the slope increased by 2% every two minutes until the children decided to stop, or until VO 2 max was reached. Sometimes it was stopped for safety reasons (e.g. gait problems). The criteria used to consider the test as maximal were if the child achieved at least 2 of the 3 following conditions: a) a plateau of VO 2 over the last two work rates, i.e. less than 0.100 L/min (2 mL/kg/min) increase; b) a plateau of the heart rate over the last work rates, i.e. less than a 5 bpm increase; and c) a respiratory exchange ratio (RER) greater than 1.00. Oxygen uptake was measured with a Sensormedic Metabolic System (Vmax 12 l-a) and heart rate was recorded
Meléndez-Ortega, A.; Davis, C.; Barbeau, P.; Boyle, C. (2010). Oxygen uptake of overweight and obese children at different stages of a progressive treadmill test. Revista Internacional de Ciencias del Deporte. 18(6), 74-90. http://www.cafyd.com/REVISTA/01805.pdf 78 with a Polar pulsometer model S610i, which registered values during the last 15 seconds of each minute. Rate of Perceived Exertion (RPE) according to Börg’s 20 points scale (1974) was recorded as an indicator of the intensity of effort. Statistical analyses The data selected on the participating children were analyzed using SPSS 15.0 with descriptive statistics. For the data analysis oxygen uptake values were grouped for the different stages and 1.9% of the warm-up data, and 0.9%, 1.4%, 0.7%, 1.5% for stages 1-4, which were more than 1.5 of the interquartile distance, were considered outliers and eliminated for the typification of the relative VO 2 (mL/kg/min) for the different stages. Difference in economy of effort between children and adults was assessed using a one-sample t- test comparing values obtained with the values calculated using the formula proposed by the ACSM (2000: 303) to estimate oxygen uptake in adults at the different stages. The average values for relative VO 2 (mL/kg/min) at the different stages before and after the intervention, and absolute VO 2 (L/min) were compared using a two-tailed t-test for correlated data in the first case and for independent data in the second one. For the analysis of percentage body fat the values were categorized in two groups using the median as reference (Mdn = 41.4%). The differences for the uptake values for race, gender and categories of % body fat at each stage in the pre and post tests were compared with a two-tailed three-way ANOVA (2 x 2 x 2). While no changes in relative VO 2 were anticipated for a given stage due to intervention, in order to see whether the physical training improved economy of movement, the VO 2 values for the groups with different exercise doses (0, 20 and 40 minutes) were analyzed at post-test using a two-tailed one-way ANOVA at each stage. The results obtained made it unnecessary to
in relative VO 2 were anticipated for a given stage due to intervention, in order to see whether the physical training improved economy of movement, the VO 2 values for the groups with different exercise doses (0, 20 and 40 minutes) were analyzed at post-test using a two-tailed one-way ANOVA at each stage. The results obtained made it unnecessary to carry out an “a posteriori” test. All statistical analyses were performed with the level of significance fixed at α = 0.05. As the ANOVA analysis showed significant differences for % of body fat in stages 4 and 5 and interaction between races in stage 5, a break-down of the relative VO 2 values of categories of % body fat at stages 4 to 5 and for race at stage 5 was done a posteriori to elucidate practical differences among them. The goodness of fit of the data of children that reached stages 4 to 7 at the end of the program was tested by a χ 2 at an α level equal or below .05. Results The physical characteristics of the children are presented in table 1. All the parameter values were similar for African-American and white children of both genders. Table 2 shows maturation stages of the children in the study. Only 5 girls had experienced menarche at the beginning of the program and a total of 7 when the second test was administered at the end of the intervention. The highest stage experienced by boys was 4. Only 4 boys had reached it at the beginning of the program and 8 boys had reached it at the end.