ORCP-441; No. of Pages 11
ARTICLE IN PRESS
Obesity Research & Clinical Practice (2015) xxx, xxx—xxx
ORIGINAL ARTICLE
Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention Megan L. Gow a,b,∗, Nancy van Doorn c,d, Carolyn R. Broderick c,d, Louise L. Hardy e, Mandy Ho a,b, Louise A. Baur a,f, Chris T. Cowell a,b,f, Sarah P. Garnett a,b,f,1 a
The Children’s Hospital at Westmead Clinical School, University of Sydney, Westmead, NSW 2145, Australia b Institute of Endocrinology and Diabetes, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia c School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia d The Children’s Hospital Institute of Sports Medicine, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia e NSW Physical Activity, Nutrition and Obesity Research Group (PANORG), School of Public Health, University of Sydney, NSW 2006, Australia f Kids Research Institute, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia Received 14 January 2015 ; received in revised form 30 March 2015; accepted 2 April 2015
KEYWORDS Aerobic fitness; Anaerobic threshold; Exercise tolerance; Adolescents; RESIST
Summary A 12 week exercise program was evaluated for its effect on aerobic fitness, anaerobic threshold, physical activity and sedentary behavior levels in obese insulin resistant adolescents post intervention and at follow up. 111 obese insulin resistant 10—17 year olds were recruited to a 12 month lifestyle intervention, known as RESIST. From months 4 to 6, adolescents participated in supervised exercise sessions twice per week (45—60 min/session). Aerobic fitness and anaerobic threshold were measured by gas analysis at baseline, 6 months (post intervention) and 12 months (follow up). Self-reported physical activity and sedentary behavior was measured using the CLASS questionnaire. At 6 months aerobic fitness and time to
∗ Corresponding author at: The Children’s Hospital at Westmead, Institute of Endocrinology and Diabetes, Locked Bag 4001, Westmead, NSW 2145, Australia. Tel.: +61 2 9845 3119; fax: +61 2 9845 3170. E-mail address: [email protected] (M.L. Gow). 1 Tel.: +61 2 9845 3152; fax: +61 2 9845 3170.
http://dx.doi.org/10.1016/j.orcp.2015.04.001 1871-403X/© 2015 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
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2
M.L. Gow et al. reach the anaerobic threshold had improved by 5.8% [95% CI: 0.8—11.3] and 19.7% [95% CI: 10.4—29.0], respectively compared with baseline. These improvements were maintained at 12 months. Compared to baseline, 6 month physical activity levels increased by 19 min/day [95% CI: 5—33] and screen time decreased by 49 min/day [95% CI: 23—74] but returned to baseline levels by 12 months. Improved fitness and anaerobic threshold can be sustained up to 6 months following completion of an exercise program possibly enhancing capacity to perform daily functional tasks. © 2015 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Introduction
Methods and procedures
Adolescent obesity is a global public health concern associated with poor aerobic fitness and suboptimal physical activity levels [1,2]. This places obese adolescents at increased risk of cardiometabolic complications, including insulin resistance and type 2 diabetes [3]. Obesity, poor fitness, low physical activity levels and cardiometabolic complications are known to track into adulthood and predict premature death [4,5]. Therefore, effective interventions are necessary to achieve improved long-term health outcomes. Twelve week exercise intervention programs to treat obesity in adolescents have achieved improved aerobic fitness [6—9], weight related outcomes [6,9] and cardiometabolic risk factors [6—8] following the intervention. However, few studies examine the long-term sustainability of physiological improvements associated with an adolescent exercise program [10]. The anaerobic threshold is a useful predictor of aerobic fitness [11] as well as a measure of exercise tolerance [12] and is decreased in obese adolescents [13,14]. Poor exercise tolerance, as indicated by an early anaerobic threshold, is likely to have an effect on an obese adolescent’s ability to perform daily functional tasks. Exercise interventions can lead to improvements in the anaerobic threshold in adults [15]; however, this has not yet been described in adolescents. Hence the aim of this study was to examine the effect and sustainability of a 12 week exercise program on aerobic fitness, anaerobic threshold, physical activity and sedentary behavior in obese insulin resistant adolescents. We hypothesized that aerobic fitness, anaerobic threshold, physical activity and sedentary behavior levels would improve following a 12 week exercise intervention compared with baseline. We also hypothesized that positive effects would be sustained at follow up, 6 months from completion of the exercise intervention.
This paper presents secondary data analyses of a 12 month randomized control trial, known as RESIST, which examined the efficacy of two different diets to improve insulin sensitivity in adolescents with clinical features of insulin resistance and/or pre-diabetes treated with metformin. The study protocol [16] and results reporting weight outcomes at 6 and 12 months [17,18] have been previously published. The study was approved by the Human Research Ethics Committee of The Children’s Hospital at Westmead (07/CHW/12), Sydney South West Area Health, Western Zone (08/LPOOL/195) and Sydney South West Area Health Service, Royal Prince Alfred Hospital (08/RPAH/455). Written informed consent was sought from the parent and assent from the adolescent prior to enrolment in the study.
Participants The RESIST study recruited overweight and obese (International Obesity Task Force age-sex adjusted definitions [19]) 10—17 year olds with pre-diabetes and/or insulin resistance and at least one other clinical feature of insulin resistance [16]. Prediabetes was defined by the American Diabetes Association (impaired fasting glucose >5.6 mmol L−1 and/or impaired glucose tolerance >7.8 mmol L−1 ) [20] and insulin resistance was defined as a fasting insulin (pmol L−1 ) to glucose (mmol L−1 ) ratio greater than 20.
Exercise intervention Fig. 1 outlines the RESIST study exercise intervention timeline conducted at The Children’s Hospital at Westmead, Australia. In phase 1 (0—3 months), adolescents received standard physical activity advice during individual consultations at baseline, 2, 6 and 12 weeks. Advice was consistent with the Australian Government recommendations for children and adolescents which include reducing
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
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Sustained fitness gains in adolescents
3
Figure 1 Timeline of RESIST study exercise intervention and measurement of related outcomes.
recreational screen time (ST) to ≤2 h per day and increasing incidental activity and active transport, with the aim of spending ≥60 min per day in moderate-to-vigorous intensity physical activity (MVPA) [21]. During phase 1, all adolescents underwent a pre-participation assessment by a sports physician (CRB) and identified risk factors for injury were addressed prior to commencement of the exercise program. In phase 2 (4—6 months), adolescents completed a 12 week supervised exercise program, which involved two 45—60 min training sessions per week with a qualified personal trainer at either a certified gym or local park at no cost to the families. Exercise programs were arranged in close proximity to the adolescent’s home in small groups of 2—6 study participants where possible or with siblings or friends. Sessions were aimed at familiarizing the adolescents with different types of exercise, including both aerobic and resistance activities of moderateto-vigorous intensity. A set program for sessions was not prescribed, giving the trainers flexibility to tailor activities to appeal to the group and make the sessions enjoyable for the adolescents. In addition, adolescents were encouraged to complete at least one home-based physical activity session per week. In phase 3 (7—12 months; maintenance phase), adolescents received standard physical activity advice consistent with the Australian Government recommendations [21] as in phase 1 and were encouraged to continue to participate in activities learned during the exercise intervention.
Measurements A medical review of each adolescent was conducted by the study physician at baseline, 3, 6, 9 and 12
months. At baseline, the physician collected demographic information (including ethnicity, parental education and income) and family medical history (including diabetes, overweight, polycystic ovarian syndrome, heart disease and hypertension). The physician also completed pubertal staging at baseline and 12 months by clinical examination or self-reports using Tanner drawings. Weight (kg) and height (cm) were measured by study nurses at baseline, 3, 6 and 12 months using standard procedures as previously described [16]. Body mass index (BMI; kg m−2 ) was calculated from age and sex specific reference values and expressed as a percentage of the 95th centile (BMI % 95th centile) [22]. Change in BMI z-score was not used as >86% of the adolescents had a BMI > 97th centile which is beyond the scope of the CDC 2000 reference data [23]. Body composition was measured using dual energy X-ray absorptiometry (DXA) (Prodigy, LunarGE, Madison, WI) equipped with propriety software version 13.6, at baseline, 3 and 12 months. Scans were analyzed using manufacturer recommended techniques. Fat free mass index (FFMI) was calculated (fat free mass height−2 ) [24]. Blood pressure was measured using an automated blood pressure monitor (Dinamap 1846 SX) with adolescents sitting at rest and z-scores were calculated from age, height and sex specific references [25]. An oral glucose tolerance test was performed after an overnight fast at baseline, 3 and 12 months [26] and whole body insulin sensitivity index (ISI) calculated using the Matsuda equation [27]. Fasting blood drawn at baseline, 3, 6 and 12 months was analyzed using standard techniques for glucose, insulin and blood lipids as previously described [16].
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
ARTICLE IN PRESS
4
M.L. Gow et al.
Aerobic fitness and anaerobic threshold were measured by an accredited exercise physiologist (NvD) using a Bruce treadmill protocol with gas analysis (Medgraphics CPX/D Breath-by-Breath Exchange system [Medical Graphics Corporation, MN] and the BreezeSuite Version 6.4.1 software program [Medical Graphics Corporation, MN]). Baseline fitness was assessed before the exercise intervention commenced (between 0 and 3 months) and reassessed post intervention (6 months) and at follow up (12 months). Aerobic fitness was recorded as VO2peak and time to fatigue. VO2peak was defined as the peak rate of oxygen consumption during the exercise test expressed relative to body weight (mL kg−1 min−1 ). The anaerobic threshold was defined as the point at which a systemic increase in the ventilatory equivalent for oxygen occurred without an increase in the ventilatory equivalent for carbon dioxide [28]. This point was determined independently by two trained exercise physiologists (NvD/MLG). Both time to reach the anaerobic threshold and relative VO2 (mL kg−1 min−1 ) at the anaerobic threshold were recorded. The exercise test was deemed to be maximal if the respiratory exchange ratio exceeded 1.15 [29], predicted maximal heart rate was reached or the adolescent could not continue due to physical exhaustion. Adolescents self-reported their typical time spent in a range of moderate-to-vigorous physical activities and sedentary behaviors, including ST activities, using the Children’s Leisure Activities Study Survey (CLASS) questionnaire [30] at baseline, 3, 6 and 12 months. From the CLASS questionnaire, total time spent in daily MVPA and ST was calculated and data could be categorized according to national recommendations for daily MVPA (≥60 min) and ST (≤2 h) [30].
Statistical analysis Data were assessed for normality and analyzed using IBM® SPSS Statistics Software for Windows, version 20 (SPSS Inc., Chicago, IL). There were no differences between diet groups at any time point during the study for weight, body composition, cardiometabolic, aerobic fitness, anaerobic threshold, physical activity and sedentary behavior outcomes, therefore results for diet groups were pooled for all analysis. Sex differences between continuous data were examined using independent sample t tests for normally distributed data, Mann—Whitney tests for non-parametric data and Chi-squared tests for categorical data. Correlations between variables were assessed by Pearson’s correlation coefficient,
Spearman’s rho or Kendall’s tau for normally distributed and non-parametric data as appropriate. Consistent with an intention-to-treat approach, all available data for participants as randomly assigned, were retained. Continuous data were assessed using linear mixed models with an unstructured covariance structure and Bonferroni adjusted post hoc tests were used to test for the effect of time (baseline, 3, 6, 12 months) for adolescents with at least one outcome measure. Nonparametric data were log or square root transformed as appropriate. Sex and pubertal status were tested in the model but were not significant for aerobic fitness, physical function, physical activity or sedentary behavior outcomes hence results have been reported as unadjusted models and expressed as estimated marginal means with standard error of the mean for normal data or geometric marginal means with 95% confidence intervals for non-parametric data. Binary data were analyzed using generalized estimating equations with an unstructured correlation structure to test for the effect of time (baseline, 3, 6, 12 months) and expressed as estimated marginal means with standard error of the mean. Completer analysis examining adolescents who had both baseline and 12 month fitness test measurements (n = 81) and subgroup analysis examining adolescents who attended the exercise intervention (n = 100) were also conducted. These results were not different from intention-to-treat analysis therefore results from completer analysis and subgroup analysis are not reported.
Results Baseline characteristics Baseline characteristics of the participants are shown in Table 1. There were no significant differences in baseline aerobic fitness and anaerobic threshold between boys and girls. Baseline ST was significantly higher among boys (mean difference [MD] ± SD: 57.3 ± 27.1 min/day), and only one boy met the recommendation for ST compared with 18 girls. There were more pre-pubertal boys than girls (42% versus 23%) at baseline and boys were taller and heavier. Unadjusted values showed that boys had less total body fat % compared with girls (MD: 4.4 ± 1.0%), while the girls had lower blood pressure and higher ISI compared with the boys. Greater aerobic fitness and anaerobic threshold was associated with lower BMI % 95th centile, blood pressure and body composition outcomes (correlations −0.170 to −0.599), Table 2. Additionally, there was a weak, but significant positive
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
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Sustained fitness gains in adolescents Table 1
5
Baseline characteristics of adolescents in the RESIST study. Boys (n = 45)
Girls (n = 66)
All (n = 111)
13.3 (1.7) 19 (42)
13.0 (2.0) 15 (23)
13.1 (1.9) 34 (31)
0.465 0.033
96.9 (20.1) 166.9 (12.6) 34.5 (4.7) 136.8 (21.1)
86.5 (19.0) 159.4 (9.2) 33.8 (5.7) 129.2 (20.6)
90.7 (20.0) 162.4 (11.3) 34.1 (5.3) 132.3 (21.1)
0.006 0.001 0.483 0.063
Body composition measured by DXAa Total body fat (kg) 43.3 (9.6) Total body fat (%) 44.9 (5.1) Total fat free mass (kg) 50.6 (12.7) Fat free mass index 1.8 (0.3)
42.8 (11.7) 48.9 (4.9) 40.7 (8.1) 1.6 (0.2)
43.0 (10.8) 47.6 (5.3) 44.7 (11.3) 1.7 (0.3)
0.816
ARTICLE IN PRESS
Obesity Research & Clinical Practice (2015) xxx, xxx—xxx
ORIGINAL ARTICLE
Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention Megan L. Gow a,b,∗, Nancy van Doorn c,d, Carolyn R. Broderick c,d, Louise L. Hardy e, Mandy Ho a,b, Louise A. Baur a,f, Chris T. Cowell a,b,f, Sarah P. Garnett a,b,f,1 a
The Children’s Hospital at Westmead Clinical School, University of Sydney, Westmead, NSW 2145, Australia b Institute of Endocrinology and Diabetes, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia c School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia d The Children’s Hospital Institute of Sports Medicine, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia e NSW Physical Activity, Nutrition and Obesity Research Group (PANORG), School of Public Health, University of Sydney, NSW 2006, Australia f Kids Research Institute, The Children’s Hospital at Westmead, Westmead, NSW 2145, Australia Received 14 January 2015 ; received in revised form 30 March 2015; accepted 2 April 2015
KEYWORDS Aerobic fitness; Anaerobic threshold; Exercise tolerance; Adolescents; RESIST
Summary A 12 week exercise program was evaluated for its effect on aerobic fitness, anaerobic threshold, physical activity and sedentary behavior levels in obese insulin resistant adolescents post intervention and at follow up. 111 obese insulin resistant 10—17 year olds were recruited to a 12 month lifestyle intervention, known as RESIST. From months 4 to 6, adolescents participated in supervised exercise sessions twice per week (45—60 min/session). Aerobic fitness and anaerobic threshold were measured by gas analysis at baseline, 6 months (post intervention) and 12 months (follow up). Self-reported physical activity and sedentary behavior was measured using the CLASS questionnaire. At 6 months aerobic fitness and time to
∗ Corresponding author at: The Children’s Hospital at Westmead, Institute of Endocrinology and Diabetes, Locked Bag 4001, Westmead, NSW 2145, Australia. Tel.: +61 2 9845 3119; fax: +61 2 9845 3170. E-mail address: [email protected] (M.L. Gow). 1 Tel.: +61 2 9845 3152; fax: +61 2 9845 3170.
http://dx.doi.org/10.1016/j.orcp.2015.04.001 1871-403X/© 2015 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
ARTICLE IN PRESS
2
M.L. Gow et al. reach the anaerobic threshold had improved by 5.8% [95% CI: 0.8—11.3] and 19.7% [95% CI: 10.4—29.0], respectively compared with baseline. These improvements were maintained at 12 months. Compared to baseline, 6 month physical activity levels increased by 19 min/day [95% CI: 5—33] and screen time decreased by 49 min/day [95% CI: 23—74] but returned to baseline levels by 12 months. Improved fitness and anaerobic threshold can be sustained up to 6 months following completion of an exercise program possibly enhancing capacity to perform daily functional tasks. © 2015 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Introduction
Methods and procedures
Adolescent obesity is a global public health concern associated with poor aerobic fitness and suboptimal physical activity levels [1,2]. This places obese adolescents at increased risk of cardiometabolic complications, including insulin resistance and type 2 diabetes [3]. Obesity, poor fitness, low physical activity levels and cardiometabolic complications are known to track into adulthood and predict premature death [4,5]. Therefore, effective interventions are necessary to achieve improved long-term health outcomes. Twelve week exercise intervention programs to treat obesity in adolescents have achieved improved aerobic fitness [6—9], weight related outcomes [6,9] and cardiometabolic risk factors [6—8] following the intervention. However, few studies examine the long-term sustainability of physiological improvements associated with an adolescent exercise program [10]. The anaerobic threshold is a useful predictor of aerobic fitness [11] as well as a measure of exercise tolerance [12] and is decreased in obese adolescents [13,14]. Poor exercise tolerance, as indicated by an early anaerobic threshold, is likely to have an effect on an obese adolescent’s ability to perform daily functional tasks. Exercise interventions can lead to improvements in the anaerobic threshold in adults [15]; however, this has not yet been described in adolescents. Hence the aim of this study was to examine the effect and sustainability of a 12 week exercise program on aerobic fitness, anaerobic threshold, physical activity and sedentary behavior in obese insulin resistant adolescents. We hypothesized that aerobic fitness, anaerobic threshold, physical activity and sedentary behavior levels would improve following a 12 week exercise intervention compared with baseline. We also hypothesized that positive effects would be sustained at follow up, 6 months from completion of the exercise intervention.
This paper presents secondary data analyses of a 12 month randomized control trial, known as RESIST, which examined the efficacy of two different diets to improve insulin sensitivity in adolescents with clinical features of insulin resistance and/or pre-diabetes treated with metformin. The study protocol [16] and results reporting weight outcomes at 6 and 12 months [17,18] have been previously published. The study was approved by the Human Research Ethics Committee of The Children’s Hospital at Westmead (07/CHW/12), Sydney South West Area Health, Western Zone (08/LPOOL/195) and Sydney South West Area Health Service, Royal Prince Alfred Hospital (08/RPAH/455). Written informed consent was sought from the parent and assent from the adolescent prior to enrolment in the study.
Participants The RESIST study recruited overweight and obese (International Obesity Task Force age-sex adjusted definitions [19]) 10—17 year olds with pre-diabetes and/or insulin resistance and at least one other clinical feature of insulin resistance [16]. Prediabetes was defined by the American Diabetes Association (impaired fasting glucose >5.6 mmol L−1 and/or impaired glucose tolerance >7.8 mmol L−1 ) [20] and insulin resistance was defined as a fasting insulin (pmol L−1 ) to glucose (mmol L−1 ) ratio greater than 20.
Exercise intervention Fig. 1 outlines the RESIST study exercise intervention timeline conducted at The Children’s Hospital at Westmead, Australia. In phase 1 (0—3 months), adolescents received standard physical activity advice during individual consultations at baseline, 2, 6 and 12 weeks. Advice was consistent with the Australian Government recommendations for children and adolescents which include reducing
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
ARTICLE IN PRESS
Sustained fitness gains in adolescents
3
Figure 1 Timeline of RESIST study exercise intervention and measurement of related outcomes.
recreational screen time (ST) to ≤2 h per day and increasing incidental activity and active transport, with the aim of spending ≥60 min per day in moderate-to-vigorous intensity physical activity (MVPA) [21]. During phase 1, all adolescents underwent a pre-participation assessment by a sports physician (CRB) and identified risk factors for injury were addressed prior to commencement of the exercise program. In phase 2 (4—6 months), adolescents completed a 12 week supervised exercise program, which involved two 45—60 min training sessions per week with a qualified personal trainer at either a certified gym or local park at no cost to the families. Exercise programs were arranged in close proximity to the adolescent’s home in small groups of 2—6 study participants where possible or with siblings or friends. Sessions were aimed at familiarizing the adolescents with different types of exercise, including both aerobic and resistance activities of moderateto-vigorous intensity. A set program for sessions was not prescribed, giving the trainers flexibility to tailor activities to appeal to the group and make the sessions enjoyable for the adolescents. In addition, adolescents were encouraged to complete at least one home-based physical activity session per week. In phase 3 (7—12 months; maintenance phase), adolescents received standard physical activity advice consistent with the Australian Government recommendations [21] as in phase 1 and were encouraged to continue to participate in activities learned during the exercise intervention.
Measurements A medical review of each adolescent was conducted by the study physician at baseline, 3, 6, 9 and 12
months. At baseline, the physician collected demographic information (including ethnicity, parental education and income) and family medical history (including diabetes, overweight, polycystic ovarian syndrome, heart disease and hypertension). The physician also completed pubertal staging at baseline and 12 months by clinical examination or self-reports using Tanner drawings. Weight (kg) and height (cm) were measured by study nurses at baseline, 3, 6 and 12 months using standard procedures as previously described [16]. Body mass index (BMI; kg m−2 ) was calculated from age and sex specific reference values and expressed as a percentage of the 95th centile (BMI % 95th centile) [22]. Change in BMI z-score was not used as >86% of the adolescents had a BMI > 97th centile which is beyond the scope of the CDC 2000 reference data [23]. Body composition was measured using dual energy X-ray absorptiometry (DXA) (Prodigy, LunarGE, Madison, WI) equipped with propriety software version 13.6, at baseline, 3 and 12 months. Scans were analyzed using manufacturer recommended techniques. Fat free mass index (FFMI) was calculated (fat free mass height−2 ) [24]. Blood pressure was measured using an automated blood pressure monitor (Dinamap 1846 SX) with adolescents sitting at rest and z-scores were calculated from age, height and sex specific references [25]. An oral glucose tolerance test was performed after an overnight fast at baseline, 3 and 12 months [26] and whole body insulin sensitivity index (ISI) calculated using the Matsuda equation [27]. Fasting blood drawn at baseline, 3, 6 and 12 months was analyzed using standard techniques for glucose, insulin and blood lipids as previously described [16].
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
ARTICLE IN PRESS
4
M.L. Gow et al.
Aerobic fitness and anaerobic threshold were measured by an accredited exercise physiologist (NvD) using a Bruce treadmill protocol with gas analysis (Medgraphics CPX/D Breath-by-Breath Exchange system [Medical Graphics Corporation, MN] and the BreezeSuite Version 6.4.1 software program [Medical Graphics Corporation, MN]). Baseline fitness was assessed before the exercise intervention commenced (between 0 and 3 months) and reassessed post intervention (6 months) and at follow up (12 months). Aerobic fitness was recorded as VO2peak and time to fatigue. VO2peak was defined as the peak rate of oxygen consumption during the exercise test expressed relative to body weight (mL kg−1 min−1 ). The anaerobic threshold was defined as the point at which a systemic increase in the ventilatory equivalent for oxygen occurred without an increase in the ventilatory equivalent for carbon dioxide [28]. This point was determined independently by two trained exercise physiologists (NvD/MLG). Both time to reach the anaerobic threshold and relative VO2 (mL kg−1 min−1 ) at the anaerobic threshold were recorded. The exercise test was deemed to be maximal if the respiratory exchange ratio exceeded 1.15 [29], predicted maximal heart rate was reached or the adolescent could not continue due to physical exhaustion. Adolescents self-reported their typical time spent in a range of moderate-to-vigorous physical activities and sedentary behaviors, including ST activities, using the Children’s Leisure Activities Study Survey (CLASS) questionnaire [30] at baseline, 3, 6 and 12 months. From the CLASS questionnaire, total time spent in daily MVPA and ST was calculated and data could be categorized according to national recommendations for daily MVPA (≥60 min) and ST (≤2 h) [30].
Statistical analysis Data were assessed for normality and analyzed using IBM® SPSS Statistics Software for Windows, version 20 (SPSS Inc., Chicago, IL). There were no differences between diet groups at any time point during the study for weight, body composition, cardiometabolic, aerobic fitness, anaerobic threshold, physical activity and sedentary behavior outcomes, therefore results for diet groups were pooled for all analysis. Sex differences between continuous data were examined using independent sample t tests for normally distributed data, Mann—Whitney tests for non-parametric data and Chi-squared tests for categorical data. Correlations between variables were assessed by Pearson’s correlation coefficient,
Spearman’s rho or Kendall’s tau for normally distributed and non-parametric data as appropriate. Consistent with an intention-to-treat approach, all available data for participants as randomly assigned, were retained. Continuous data were assessed using linear mixed models with an unstructured covariance structure and Bonferroni adjusted post hoc tests were used to test for the effect of time (baseline, 3, 6, 12 months) for adolescents with at least one outcome measure. Nonparametric data were log or square root transformed as appropriate. Sex and pubertal status were tested in the model but were not significant for aerobic fitness, physical function, physical activity or sedentary behavior outcomes hence results have been reported as unadjusted models and expressed as estimated marginal means with standard error of the mean for normal data or geometric marginal means with 95% confidence intervals for non-parametric data. Binary data were analyzed using generalized estimating equations with an unstructured correlation structure to test for the effect of time (baseline, 3, 6, 12 months) and expressed as estimated marginal means with standard error of the mean. Completer analysis examining adolescents who had both baseline and 12 month fitness test measurements (n = 81) and subgroup analysis examining adolescents who attended the exercise intervention (n = 100) were also conducted. These results were not different from intention-to-treat analysis therefore results from completer analysis and subgroup analysis are not reported.
Results Baseline characteristics Baseline characteristics of the participants are shown in Table 1. There were no significant differences in baseline aerobic fitness and anaerobic threshold between boys and girls. Baseline ST was significantly higher among boys (mean difference [MD] ± SD: 57.3 ± 27.1 min/day), and only one boy met the recommendation for ST compared with 18 girls. There were more pre-pubertal boys than girls (42% versus 23%) at baseline and boys were taller and heavier. Unadjusted values showed that boys had less total body fat % compared with girls (MD: 4.4 ± 1.0%), while the girls had lower blood pressure and higher ISI compared with the boys. Greater aerobic fitness and anaerobic threshold was associated with lower BMI % 95th centile, blood pressure and body composition outcomes (correlations −0.170 to −0.599), Table 2. Additionally, there was a weak, but significant positive
Please cite this article in press as: Gow ML, et al. Sustained improvements in fitness and exercise tolerance in obese adolescents after a 12 week exercise intervention. Obes Res Clin Pract (2015), http://dx.doi.org/10.1016/j.orcp.2015.04.001
ORCP-441; No. of Pages 11
ARTICLE IN PRESS
Sustained fitness gains in adolescents Table 1
5
Baseline characteristics of adolescents in the RESIST study. Boys (n = 45)
Girls (n = 66)
All (n = 111)
13.3 (1.7) 19 (42)
13.0 (2.0) 15 (23)
13.1 (1.9) 34 (31)
0.465 0.033
96.9 (20.1) 166.9 (12.6) 34.5 (4.7) 136.8 (21.1)
86.5 (19.0) 159.4 (9.2) 33.8 (5.7) 129.2 (20.6)
90.7 (20.0) 162.4 (11.3) 34.1 (5.3) 132.3 (21.1)
0.006 0.001 0.483 0.063
Body composition measured by DXAa Total body fat (kg) 43.3 (9.6) Total body fat (%) 44.9 (5.1) Total fat free mass (kg) 50.6 (12.7) Fat free mass index 1.8 (0.3)
42.8 (11.7) 48.9 (4.9) 40.7 (8.1) 1.6 (0.2)
43.0 (10.8) 47.6 (5.3) 44.7 (11.3) 1.7 (0.3)
0.816
