Journal of Physical Activity and Health, 2015, 12, 74 -79 http://dx.doi.org/10.1123/jpah.2013-0284 © 2015 Human Kinetics, Inc.
Official Journal of ISPAH www.JPAH-Journal.com ORIGINAL RESEARCH
Home-Based Exercise May Not Decrease the Insulin Resistance in Individuals With Metabolic Syndrome Chiao-Nan Chen, Lee-Ming Chuang, Mallikarjuna Korivi, and Ying-Tai Wu Background: This study investigated the differences in exercise self-efficacy, compliance, and effectiveness of home-based exercise in individuals with and without metabolic syndrome (MetS). Methods: One hundred and ten individuals at risk for diabetes participated in this study. Subjects were categorized into individuals with MetS and individuals without MetS. Metabolic risk factors and exercise self-efficacy were evaluated for all subjects before and after 3 months of home-based exercise. Univariate analysis of variance was used to compare the effectiveness of a home-based exercise program between individuals with and without MetS. Results: The home-based exercise program improved body mass index and lipid profile in individuals at risk for diabetes, regardless of MetS status at baseline. Individuals without MetS had higher exercise self-efficacy at baseline and performed greater exercise volume compared with individuals with MetS during the intervention. The increased exercise volume in individuals without MetS may contribute to their better control of insulin resistance than individuals with MetS. Furthermore, baseline exercise self-efficacy was correlated with exercise volume executed by subjects at home. Conclusions: We conclude that home-based exercise programs are beneficial for individuals at risk for diabetes. However, more intensive and/or supervised exercise intervention may be needed for those with MetS. Keywords: self-efficacy, compliance, metabolic parameters Metabolic syndrome (MetS) and its associated diseases, including coronary artery disease, stroke, and type 2 diabetes (T2DM) are progressively increasing around the world.1,2 MetS, a cluster of diseases, is a major concern in the modern medicine and is causing additional financial burden to many countries. Lifestyle modifications that include physical exercise are the first line of defense in the prevention of MetS and T2DM.3–5 The beneficial outcomes of exercise on diabetes prevention are related to improvements in metabolic risk factors such as body composition, blood pressure (BP), blood lipid levels, and glucose metabolism.6–8 However, most previous studies that investigated the benefits of exercise used supervised, center-based exercise programs that may not be affordable or convenient for many individuals, especially for those who work full time. In addition, home-based exercise is less expensive and can be easily incorporated into daily activities. Home-based exercise has been found to improve exercise volume, physical fitness, and quality of life in cancer survivors, patients with chronic heart failure, and patients with ankylosing spondylitis.9–11 The effectiveness of exercise depends on whether individuals participate in the exercise program. Specifically, exercise selfefficacy, a psychological factor defined by confidence in the ability to perform exercise even under unfavorable conditions (eg, poor weather or bad mood), was found to be a predictor of the initiation and continuation of exercise behavior. A positive relationship
between exercise self-efficacy and exercise adherence has been reported in individuals with impaired glucose tolerance, cancer survivors, and older women after hip fracture.12–15 Concisely, exercise self-efficacy could predict the exercise adherence of an individual. Because there is no supervision from researchers or clinicians in home-based exercise, individuals need greater self-efficacy to initiate and maintain it compared with supervised, center-based exercise programs. Thus, the effectiveness of home-based exercise programs may be population-specific and dependent on individuals’ self-efficacy levels. Previous studies have shown that exercise selfefficacy is associated with body composition; individuals with better body composition showed greater exercise self-efficacy.16–18 To date, it is unclear whether exercise self-efficacy is different between individuals with and without MetS. It is also unknown whether the compliance with a prescribed home-based exercise program depends on the MetS status. The aims of this study were to (1) understand the differences in the baseline psychological character and exercise program adherence between individuals with and without MetS and (2) evaluate the effectiveness of a home-based exercise program on metabolic risk factors in individuals with and without MetS. We hypothesized that individuals without MetS would have higher levels of exercise self-efficacy, better adherence to a homebased exercise program, and achieve greater improvements or control in metabolic risk factors compared with individuals with MetS.
Methods Chen ([email protected]) is with the Dept of Physical Therapy and the Healthy Aging Research Center, Chang Gung University, Tao-Yuan, Taiwan. Chuang is with the Dept of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan. Korivi is with the Dept of Occupational Therapy, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan. Wu is with the Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan. 74
Subjects Subjects were included if they had at least one of the following risk factors for diabetes: body mass index (BMI) ≥ 24 kg/m2 (criteria of the Taiwanese national nutrition survey), hypertension (BP ≥ 130/85 mm Hg), dyslipidemia [triglycerides (TG) ≥ 1.7 mmol/L, or high-density lipoprotein (HDL) < 1.04 mmol/L in men and < 1.29
Home-Based Exercise and Metabolic Syndrome 75
mmol/L in women], first-degree relatives or parents with T2DM, impaired glucose tolerance, gestational diabetes, or having delivered a baby weighing ≥ 4.0 kg. The inclusion criteria were generated based on Helmrich et al19 and National Cholesterol Education Program Adult Treatment Panel III.20 Exclusion criteria included already performing regular exercise, a confirmed diagnosis of diabetes, and treatment with insulin or oral hypoglycemic agents. Finally, 110 Chinese individuals (42 men and 68 women) from the metropolitan area of northern Taiwan participated in the home-based exercise program and were included in this study. Participants were divided into 2 groups: MetS and non-MetS. Individuals in the MetS group had 3 or more of the following characteristics at baseline: fasting blood glucose ≥ 5.5 mmol/L, serum TG ≥ 1.7 mmol/L, HDL < 1.04 mmol/L in men or < 1.29 mmol/L in women, BP ≥ 130/85 mm Hg or use of antihypertensive medication, and a waist circumference ≥ 90 cm in men or ≥ 80 cm in women.20 Evaluative data before and after a 3-month home-based exercise program were analyzed. The study was approved by our institutional Committee of Ethics, and informed consent was obtained from each participant.
Assessments Anthropometric and Metabolic Measurements. Waist circumference, BMI, BP, fasting blood glucose level, serum TG level, HDL level, and insulin resistance (IR) were measured after 8 hours of fasting and refraining from exercise. BMI was calculated by dividing weight (kg) by height squared (m2). Waist circumference was measured at the end of expiration while the subject was standing, using a flexible steel tape, at the midpoint between the lowest rib and the iliac crest. The average of 2 measurements was recorded. BP was obtained at rest from the right arm by auscultation using a mercury sphygmomanometer.21 The serum concentrations of HDL and TG were measured using enzymatic assays (DRI-CHEM 3000; Fuji, Tokyo, Japan). Blood glucose levels were determined by the glucose oxidase membrane/hydrogen peroxide electrode method using Antisense II (Bayer-Sankyo Co., Tokyo, Japan). Plasma insulin levels were measured with a microparticle enzyme immunoassay using an AxSYM system analyzer (Abbott Laboratories, Dainabot Co. Ltd., Tokyo, Japan). Standard samples of known concentrations were included for quality control. IR was evaluated by homeostasis model assessment (HOMA), a good surrogate of IR in adults.22 Homeostasis model of IR (HOMA-IR) is the product of fasting plasma insulin level (mU/mL) and fasting plasma glucose level (mmol/L) divided by 22.5.
Homeostasis model of IR ( HOMA − IR ) =
fasting plasma insulin level ( U / mL) * fasting plasma glucose level (mmol / L) 22.5
Exercise Volume. Exercise volume was determined by reviewing a daily exercise log in which subjects recorded the mode, intensity,
and duration of their exercise. Specifically, the intensity of exercise was determined by each subject based on the Borg rating of perceived exertion (RPE) scale, a valid tool for monitoring exercise intensity subjectively.23 Subjects were asked to complete the exercise log daily with many details about exercise parameters. The daily report on the exercise parameters in the diabetes prevention brochure was reinforced and reminded via phone calls every 2 weeks. The completion rate of the exercise log was 94% in the non-MetS group and 87% in the MetS group; there were no significant differences in the basic characteristics of individuals who did and did not complete the exercise logs. Exercise volume was calculated as the product of exercise intensity (metabolic equivalent; METs), duration (hours per session), and frequency (sessions per week), expressed in units of MET × hours per week. Moderate exercise (RPE between 12 and 14) was defined as 3 to 5 METs, vigorous exercise (RPE between 15 to 17) was defined as 5.1 to 6.9 METs, and very vigorous exercise (RPE between 18 to 20) was defined as > 7 METs.24 One MET represents 3.5 mL O2/min/kg of body weight (or 1 kcal/h/kg of body weight).
Exercise Self-Efficacy. Exercise self-efficacy was determined using a validated method in which individuals were asked to rate their confidence levels for performing regular exercise for each of the following 5 conditions: “I am tired,” “I am in a bad mood,” “I feel I do not have the time,” “I am on vacation,” and “It is raining or snowing.” Each condition was assessed on a 7-point scale (1 indicated no confidence at all and 7 indicated very high confidence). The test-retest reliability for this self-efficacy measurement was 0.9, and the total score was found to be associated with exercise behavior.25
Home-Based Exercise After baseline assessment, each subject received a diabetes prevention brochure that was designed based on the health belief model. The health belief model proposes that an individual changes his/her behavior to improve health when he/she knows that they are susceptible to a disease and can decrease morbidity. The brochure contained topics including “What is type 2 diabetes?” “What are the negative effects and complications of type 2 diabetes?” “Who is at risk for type 2 diabetes?” “Is type 2 diabetes preventable?” and “What are the strategies to prevent type 2 diabetes?” Using the brochure as a guide, each participant was interviewed to learn about T2DM and the importance of exercise in the prevention of T2DM. Exercise was promoted at this interview through goal setting, attempting to remove barriers to exercise, and designing the individualized home-based exercise plan. The selection of the exercise mode was based on the preference and accessibility of the participant. For individuals who did not have a preferred mode, 2 indoor exercise options, stepping (a stepper; Takasuma, Taipei, Taiwan) and cardio-dance, were provided. Stepping exercise was prescribed as 2400 steps in 30 minutes. Participants were allowed to adjust the exercise intensity on the basis of their physical condition. Cardio-dance involved a 50-min exercise video consisting of a 5-min warm-up period, 30 min of cardio-dance, 10 min of muscle strengthening, and 5 min of stretching. All the exercise plans were designed to be of moderate intensity; therefore, participants were instructed to exercise at an intensity at which mild-to-moderate dyspnea was experienced. The duration of all planned exercise sessions was at least 30 min and the frequency was at least 3 sessions per week. In addition to the initial interview in which the exercise program was set up, subjects received phone calls every 1 to 2 weeks encouraging them to keep exercising during the 3-month period of the program. Participants were asked to maintain a daily exercise log and record their body weight daily in our diabetes prevention brochure to facilitate exercise behavior via self-monitoring.
76 Chen et al
Statistical Analysis All data were analyzed using SPSS (version 10.0 for Windows; SPSS Inc., Chicago, IL) and were presented as either mean ± SEM or count (percentage). Listwise deletion (complete case analysis) was used for missing data. HOMA-IR, TG, and HDL were logarithmically transformed for analyses because of the skewed distribution of the data. Independent t tests and c2 tests were used for continuous and categorical variables, respectively, to compare the baseline differences between the MetS and non-MetS groups. If the significant between-group differences were noted at baseline, the differential effects of home-based exercise were examined by univariate analysis of variance with 3-month data as dependent variables and baseline data as covariates. Pearson product-moment correlation coefficient was performed to evaluate the correlation between exercise selfefficacy and exercise volume. P < .005 was used to define statistical significance for the adjustment of multiple comparisons in testing the effectiveness of the home-based exercise.
Results Baseline Characteristics The study population was characterized by a mean age of 48.6 ± 1.1 years, BMI of 25.9 ± 0.4 kg/m2, and waist circumference of 87.5 ± 0.7 cm for men and 78.0 ± 0.6 cm for women. Furthermore, 69% of subjects were overweight or obese, 36% had central obesity, and 53% had hypertension. In addition, 31% of subjects had fasting TG levels ≥ 1.7 mmol/L, 35% had HDL levels < 1.04 mmol/L (men) or < 1.29 mmol/L (women), and only 1% had fasting blood glucose levels ≥ 5.5 mmol/L. The MetS criteria were fulfilled by 21% of subjects, and no significant differences were found in age
or percentage of smokers between the MetS and non-MetS groups (Table 1). The MetS group had a greater prevalence of overweight subjects, central obesity, hypertension, hypertriglyceridemia, hypoHDL, and impaired glucose tolerance. In addition, the MetS group had significantly lower exercise self-efficacy than the non-MetS group at baseline (Table 1).
Response to the Home-Based Exercise Program Exercise Self-Efficacy. Exercise self-efficacy was found to improve in the non-MetS group after 3 months of homebased exercise. Individuals with MetS did not show significant improvement in exercise self-efficacy. Exercise self-efficacy of the MetS group remained lower than that of the non-MetS group after 3 months of home-based exercise (Table 2). Exercise Adherence and Exercise Volume. The non-MetS group showed better adherence to the prescribed exercise plan than the MetS group. Specifically, 72% of the non-MetS group and 39% of the MetS group met the minimum exercise prescription of at least 3 sessions of 30 minutes of moderate exercise per week. In addition, exercise volume for the non-MetS group was 2-fold higher than that of the MetS group (15.5 ± 1.4 and 7.8 ± 2.4 MET × h/wk, respectively; P = .02). E ffe c t o f H o m e - Ba s e d E xe rc i s e o n M e t a b o l i c R i s k Factors. Home-based exercise significantly improved (P < .005)
metabolic risk factors, including BMI and blood lipid levels in both groups (Table 2). The improvements in BP and waist circumference after home-based exercise were significant in the non-MetS group (P < .005) and approached significance in the MetS group (P values for systolic BP and WC were .005 and .008, respectively). Another key finding of this study was that the effect of home-based exercise
Table 1 Characteristics of the Study Subjects at Baseline Age (y) Women, n (%) Height (cm) Weight (kg) Smokers, n (%) Diabetic risk factors, n (%) Overweight (BMI ≥ 24 kg/m2) Central obesity (WC ≥ 90 cm [men] or ≥ 80 cm [women]) HTN (BP ≥ 130/85 mm Hg; use of anti-HTN medication) Hypertriglyceridemia (≥ 1.7 mmol/L) Hypo-HDL (< 1.04 mmol/L [men] or < 1.29 mmol/L [women]) Impaired glucose tolerance (≥ 5.5 mmol/L) Family history of DM Delivering a baby weighing ≥ 4.0 kg Number of diabetic risk factors, median (interquartile range) Exercise self-efficacy Exercise volume (METs × h/wk)
Non-MetS
MetS
P
48.8 ± 1.2 53 (60.9) 161.9 ± 1.0 65.2 ± 1.3 10 (11.5)
47.9 ± 2.9 15 (65.2) 162.6 ± 1.8 80.3 ± 3.7 2 (8.7)
.76 .71 .78 .001 .80
54 (62.1) 18 (20.7) 39 (44.8) 14 (16.1) 19 (21.8) 3 (3.4) 54 (62.1) 2 (2.3) 2 (2) 21.1 ± 0.1 15.5 ± 1.4
22 (95.7) 21 (91.3) 19 (82.6) 20 (87.0) 19 (82.6) 5 (21.7) 7 (30.4) 2 (8.7) 5 (1) 16.5 ± 0.3 7.8 ± 2.4
.002 < .001 .002 < .001 < .001 .01 .01 .20 < .001 .03 .02
Note. Values are mean ± SEM or n (%). Abbreviations: BMI, body mass index; WC, waist circumference; BP, blood pressure; HTN, hypertension; HDL, high density lipoprotein; DM, type 2 diabetes mellitus; MetS, metabolic syndrome.
Home-Based Exercise and Metabolic Syndrome 77
Table 2 Effects of the Home-Based Exercise Program on Individuals With and Without Metabolic Syndrome (MetS) Effects of home-based exercise
Baseline
3 Months
P (between-groups comparison of changes from baseline to 3 months)
16.5 ± 0.3* 30.2 ± 1.2* 129.9 ± 2.8* 82.4 ± 2.1 91.8 ± 2.3* 1.09 ± 0.09* 2.87 ± 0.4* 4.93 ± 0.15* 3.6 ± 0.6*
18.4 ± 0.3 29.5 ± 1.3† 121.7 ± 2.5 79.7 ± 2.0 90.0 ± 2.7 1.22 ± 0.08† 2.06 ± 0.3† 4.90 ± 0.14 4.3 ± 0.7
.02 .80 .58 .19 .42 .52 .46 .94 < .001
Non-MetS Baseline Exercise self-efficacy BMI (kg/m2) SBP (mm Hg) DBP (mm Hg) Waist circumference (cm) HDL (mmol/L) Triglycerides (mmol/L) Fasting blood glucose (mmol/L) HOMA-IR
21.1 ± 0.1 24.7 ± 0.4 120.8 ± 1.8 77.6 ± 1.3 79.0 ± 1.1 1.44 ± 0.05 1.25 ± 0.06 4.50 ± 0.06 1.8 ± 0.1
MetS
3 Months 0.1†
24.2 ± 24.3 ± 0.3† 115.2 ± 1.5† 74.7 ± 1.1† 77.7 ± 1.0† 1.52 ± 0.05† 1.27 ± 0.05 4.66 ± 0.06 1.9 ± 0.1
Note. Values are mean ± SEM. Abbreviations: MetS, metabolic syndrome; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL, high-density lipoprotein; HOMA-IR, homeostasis model of insulin resistance. * P < .05 compared with the baseline values of the non-MetS group. †P
< .005 compared with the baseline values within groups.
on the changes in HOMA-IR was different in the non-MetS and MetS groups (P < .001). HOMA-IR in the MetS group had a trend to increase even after the home-based exercise (P = .08). However, home-based exercise could maintain the HOMA-IR of the non-MetS group at a normal level (Table 2). Correlation Between Exercise Self-Efficacy and Exercise Volume. We found that exercise volume was significantly
correlated with exercise self-efficacy at baseline (P < .0001). Greater exercise self-efficacy was correlated with greater exercise volume that individuals performed at home (r = .41) (Figure 1).
Figure 1 — Correlation between exercise-self-efficacy and exercise volume in individuals at risk for type 2 diabetes.
Discussion This study showed that a home-based exercise program has benefits for body composition and lipid profile in individuals with and without MetS. More particularly, individuals without MetS scored higher on exercise self-efficacy, were more adherent to the homebased program, and had higher exercise volume than individuals with MetS. In addition, the non-MetS group showed better control of IR, which may be due to the greater exercise volume, whereas in the MetS group, exercise was unable to control the progression of IR. Our study showed for the first time that individuals without MetS had higher exercise self-efficacy than those with MetS. The link between psychological characteristics and health condition has been reported in children, women, and overweight adults with impaired glucose tolerance, where lower exercise self-efficacy was found to correlate with poor body composition.16–18 Another key finding is that exercise self-efficacy was positively correlated with exercise volume. The positive relationship between exercise self-efficacy and exercise adherence has been reported previously. For example, Delahanty et al13 found that exercise self-efficacy independently predicted exercise duration and whether subjects in the Diabetes Prevention Program achieved the 150 min/wk physical activity goal. Exercise self-efficacy was also found to be a significant determinant of exercise adherence in cancer survivors and older women after hip fracture.12,15 Collectively, our findings suggest there are differences in psychological characteristics and exercise behavior between individuals with and without MetS. Because exercise self-efficacy is not a routine assessment, unlike blood glucose and BP, it is hard to predict individuals’ adherence to the exercise prescription. Based on our finding that exercise selfefficacy is different between individuals with and without MetS, the metabolic status can be a key consideration when developing or designing exercise prescriptions and supervision modes. Concerning the effects of home-based exercise on metabolic risk factors, we found that both groups exhibited improvements
78 Chen et al
in BMI and blood lipid levels after the 3-month program. Several clinical trials have shown that the development and progression of T2DM could be prevented or delayed through lifestyle modification, including supervised center-based exercise.3–5 In contrast, the home-based exercise program in our study did not reverse the elevated IR in individuals with MetS but did effectively control the IR of individuals without MetS. Our findings indicated that individuals without MetS had greater benefits from the homebased exercise program than individuals with MetS. This finding is similar to those in previous studies. Joseph et al26 reported that individuals without MetS, but not those with MetS, showed improved blood lipid profile after 6 months of weight loss and low-intensity exercise. Likewise, Lien et al27 found that individuals without MetS had greater reductions in SBP as a result of regular aerobic physical activity compared with individuals with MetS. Taken together, our results suggest that the extent of benefits from home-based exercise is related to an individual’s metabolic characteristics. Our findings emphasized that HOMA-IR was under control in individuals without MetS but not in those with MetS after homebased exercise. The lower exercise volume performed by individuals with MetS compared with individuals without MetS may explain the uncontrolled IR in the MetS group. A previous study found IR to be unchanged in postmenopausal women participating in a low-intensity exercise program.26 In contrast, IR was improved in individuals with prehypertension or stage-1 hypertension after an intensive exercise intervention that included at least 180 min/wk of moderate-intensity exercise.27 Another possible reason for the lack of improvement in IR is the relatively short duration (3 months) of the exercise program. In line with this, Dunstan et al28,29 found that 9 months of resistance training, but not 3 or 6 months, improved IR in older individuals with T2DM. The findings of lower exercise self-efficacy in individuals with MetS and the positive correlation between exercise self-efficacy and exercise adherence imply that integrating techniques that increase exercise self-efficacy may improve the effectiveness of exercise program in individuals with MetS. Techniques that have been found to significantly improve exercise self-efficacy include detailed planning about when, how, and where to perform the exercise; giving feedback about past performance; and providing feedback about the performance of the individual compared with other people.30,31 There are some caveats in the data interpretation of the current study. First, the cross-sectional design of the study limits causal inferences. Nevertheless, our finding of lower exercise selfefficacy and poorer exercise adherence in individuals with MetS suggested that individuals with MetS may need more intensive and/or supervised exercise intervention. Second, self-reported exercise behavior is commonly used yet has been reported to have limitations. Although we found a significant association between the self-reported exercise volume and changes in HOMA-IR (not shown in the results) that supports the soundness of the use, it is important to be aware of the limitations. In conclusion, the home-based exercise program improved BMI and blood lipid levels in individuals at risk for diabetes. Importantly, we found that individuals with MetS had lower levels of baseline exercise self-efficacy, poorer adherence to the prescribed homebased exercise program, and poorer control of insulin resistance compared with individuals without MetS. Therefore, individuals with MetS may need exercise supervision to increase their exercise volume and reverse their elevated IR levels. This study provides additional information to the current understanding of the homebased exercise program benefits in individuals at risk for diabetes
and also helps to determine the group that benefits the most from such exercise. Acknowledgments This project was funded by the Bureau of Health Promotion, Department of Health (DOH94-HP-1105) in Taiwan. The authors thank the additional support from Healthy Aging Research Center, Chang Gung University (EMRPD1E1651) and the statistical assistance provided by the National Translational Medicine and Clinical Trial Resource Center and the Department of Medical Research in National Taiwan University Hospital. This study is registered at www.clinicaltrials.gov (No. NCT01136096).
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22. Muniyappa R, Lee S, Chen H, Quon MJ. Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage. Am J Physiol Endocrinol Metab. 2008;294:E15–E26. PubMed doi:10.1152/ajpendo.00645.2007 23. Scherr J, Wolfarth B, Christle JW, Pressler A, Wagenpfeil S, Halle M. Associations between Borg’s rating of perceived exertion and physiological measures of exercise intensity. Eur J Appl Physiol. 2013;113:147–155. PubMed doi:10.1007/s00421-012-2421-x 24. Sallis JF, Haskell WL, Wood PD, et al. Physical activity assessment methodology in the Five-City Project. Am J Epidemiol. 1985;121:91– 106. PubMed 25. Marcus BH, Selby VC, Niaura RS, Rossi JS. Self-efficacy and the stages of exercise behavior change. Res Q Exerc Sport. 1992;63:60–66. PubMed doi:10.1080/02701367.1992.10607557 26. Joseph LJ, Prigeon RL, Blumenthal JB, Ryan AS, Goldberg AP. Weight loss and low-intensity exercise for the treatment of metabolic syndrome in obese postmenopausal women. J Gerontol A Biol Sci Med Sci. 2011;66:1022–1029. PubMed doi:10.1093/gerona/glr093 27. Lien LF, Brown AJ, Ard JD, et al. Effects of PREMIER lifestyle modifications on participants with and without the metabolic syndrome. Hypertension. 2007;50:609–616. PubMed doi:10.1161/HYPERTENSIONAHA.107.089458 28. Dunstan DW, Daly RM, Owen N, et al. High-intensity resistance training improves glycemic control in older patients with type 2 diabetes. Diabetes Care. 2002;25:1729–1736. PubMed doi:10.2337/ diacare.25.10.1729 29. Dunstan DW, Daly RM, Owen N, et al. Home-based resistance training is not sufficient to maintain improved glycemic control following supervised training in older individuals with type 2 diabetes. Diabetes Care. 2005;28:3–9. PubMed doi:10.2337/diacare.28.1.3 30. Ashford S, Edmunds J, French DP. What is the best way to change self-efficacy to promote lifestyle and recreational physical activity? A systematic review with meta-analysis. Br J Health Psychol. 2010;15:265–288. PubMed doi:10.1348/135910709X461752 31. Williams SL, French DP. What are the most effective intervention techniques for changing physical activity self-efficacy and physical activity behaviour–and are they the same? Health Educ Res. 2011;26:308–322. PubMed doi:10.1093/her/cyr005
Official Journal of ISPAH www.JPAH-Journal.com ORIGINAL RESEARCH
Home-Based Exercise May Not Decrease the Insulin Resistance in Individuals With Metabolic Syndrome Chiao-Nan Chen, Lee-Ming Chuang, Mallikarjuna Korivi, and Ying-Tai Wu Background: This study investigated the differences in exercise self-efficacy, compliance, and effectiveness of home-based exercise in individuals with and without metabolic syndrome (MetS). Methods: One hundred and ten individuals at risk for diabetes participated in this study. Subjects were categorized into individuals with MetS and individuals without MetS. Metabolic risk factors and exercise self-efficacy were evaluated for all subjects before and after 3 months of home-based exercise. Univariate analysis of variance was used to compare the effectiveness of a home-based exercise program between individuals with and without MetS. Results: The home-based exercise program improved body mass index and lipid profile in individuals at risk for diabetes, regardless of MetS status at baseline. Individuals without MetS had higher exercise self-efficacy at baseline and performed greater exercise volume compared with individuals with MetS during the intervention. The increased exercise volume in individuals without MetS may contribute to their better control of insulin resistance than individuals with MetS. Furthermore, baseline exercise self-efficacy was correlated with exercise volume executed by subjects at home. Conclusions: We conclude that home-based exercise programs are beneficial for individuals at risk for diabetes. However, more intensive and/or supervised exercise intervention may be needed for those with MetS. Keywords: self-efficacy, compliance, metabolic parameters Metabolic syndrome (MetS) and its associated diseases, including coronary artery disease, stroke, and type 2 diabetes (T2DM) are progressively increasing around the world.1,2 MetS, a cluster of diseases, is a major concern in the modern medicine and is causing additional financial burden to many countries. Lifestyle modifications that include physical exercise are the first line of defense in the prevention of MetS and T2DM.3–5 The beneficial outcomes of exercise on diabetes prevention are related to improvements in metabolic risk factors such as body composition, blood pressure (BP), blood lipid levels, and glucose metabolism.6–8 However, most previous studies that investigated the benefits of exercise used supervised, center-based exercise programs that may not be affordable or convenient for many individuals, especially for those who work full time. In addition, home-based exercise is less expensive and can be easily incorporated into daily activities. Home-based exercise has been found to improve exercise volume, physical fitness, and quality of life in cancer survivors, patients with chronic heart failure, and patients with ankylosing spondylitis.9–11 The effectiveness of exercise depends on whether individuals participate in the exercise program. Specifically, exercise selfefficacy, a psychological factor defined by confidence in the ability to perform exercise even under unfavorable conditions (eg, poor weather or bad mood), was found to be a predictor of the initiation and continuation of exercise behavior. A positive relationship
between exercise self-efficacy and exercise adherence has been reported in individuals with impaired glucose tolerance, cancer survivors, and older women after hip fracture.12–15 Concisely, exercise self-efficacy could predict the exercise adherence of an individual. Because there is no supervision from researchers or clinicians in home-based exercise, individuals need greater self-efficacy to initiate and maintain it compared with supervised, center-based exercise programs. Thus, the effectiveness of home-based exercise programs may be population-specific and dependent on individuals’ self-efficacy levels. Previous studies have shown that exercise selfefficacy is associated with body composition; individuals with better body composition showed greater exercise self-efficacy.16–18 To date, it is unclear whether exercise self-efficacy is different between individuals with and without MetS. It is also unknown whether the compliance with a prescribed home-based exercise program depends on the MetS status. The aims of this study were to (1) understand the differences in the baseline psychological character and exercise program adherence between individuals with and without MetS and (2) evaluate the effectiveness of a home-based exercise program on metabolic risk factors in individuals with and without MetS. We hypothesized that individuals without MetS would have higher levels of exercise self-efficacy, better adherence to a homebased exercise program, and achieve greater improvements or control in metabolic risk factors compared with individuals with MetS.
Methods Chen ([email protected]) is with the Dept of Physical Therapy and the Healthy Aging Research Center, Chang Gung University, Tao-Yuan, Taiwan. Chuang is with the Dept of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan. Korivi is with the Dept of Occupational Therapy, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan. Wu is with the Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan. 74
Subjects Subjects were included if they had at least one of the following risk factors for diabetes: body mass index (BMI) ≥ 24 kg/m2 (criteria of the Taiwanese national nutrition survey), hypertension (BP ≥ 130/85 mm Hg), dyslipidemia [triglycerides (TG) ≥ 1.7 mmol/L, or high-density lipoprotein (HDL) < 1.04 mmol/L in men and < 1.29
Home-Based Exercise and Metabolic Syndrome 75
mmol/L in women], first-degree relatives or parents with T2DM, impaired glucose tolerance, gestational diabetes, or having delivered a baby weighing ≥ 4.0 kg. The inclusion criteria were generated based on Helmrich et al19 and National Cholesterol Education Program Adult Treatment Panel III.20 Exclusion criteria included already performing regular exercise, a confirmed diagnosis of diabetes, and treatment with insulin or oral hypoglycemic agents. Finally, 110 Chinese individuals (42 men and 68 women) from the metropolitan area of northern Taiwan participated in the home-based exercise program and were included in this study. Participants were divided into 2 groups: MetS and non-MetS. Individuals in the MetS group had 3 or more of the following characteristics at baseline: fasting blood glucose ≥ 5.5 mmol/L, serum TG ≥ 1.7 mmol/L, HDL < 1.04 mmol/L in men or < 1.29 mmol/L in women, BP ≥ 130/85 mm Hg or use of antihypertensive medication, and a waist circumference ≥ 90 cm in men or ≥ 80 cm in women.20 Evaluative data before and after a 3-month home-based exercise program were analyzed. The study was approved by our institutional Committee of Ethics, and informed consent was obtained from each participant.
Assessments Anthropometric and Metabolic Measurements. Waist circumference, BMI, BP, fasting blood glucose level, serum TG level, HDL level, and insulin resistance (IR) were measured after 8 hours of fasting and refraining from exercise. BMI was calculated by dividing weight (kg) by height squared (m2). Waist circumference was measured at the end of expiration while the subject was standing, using a flexible steel tape, at the midpoint between the lowest rib and the iliac crest. The average of 2 measurements was recorded. BP was obtained at rest from the right arm by auscultation using a mercury sphygmomanometer.21 The serum concentrations of HDL and TG were measured using enzymatic assays (DRI-CHEM 3000; Fuji, Tokyo, Japan). Blood glucose levels were determined by the glucose oxidase membrane/hydrogen peroxide electrode method using Antisense II (Bayer-Sankyo Co., Tokyo, Japan). Plasma insulin levels were measured with a microparticle enzyme immunoassay using an AxSYM system analyzer (Abbott Laboratories, Dainabot Co. Ltd., Tokyo, Japan). Standard samples of known concentrations were included for quality control. IR was evaluated by homeostasis model assessment (HOMA), a good surrogate of IR in adults.22 Homeostasis model of IR (HOMA-IR) is the product of fasting plasma insulin level (mU/mL) and fasting plasma glucose level (mmol/L) divided by 22.5.
Homeostasis model of IR ( HOMA − IR ) =
fasting plasma insulin level ( U / mL) * fasting plasma glucose level (mmol / L) 22.5
Exercise Volume. Exercise volume was determined by reviewing a daily exercise log in which subjects recorded the mode, intensity,
and duration of their exercise. Specifically, the intensity of exercise was determined by each subject based on the Borg rating of perceived exertion (RPE) scale, a valid tool for monitoring exercise intensity subjectively.23 Subjects were asked to complete the exercise log daily with many details about exercise parameters. The daily report on the exercise parameters in the diabetes prevention brochure was reinforced and reminded via phone calls every 2 weeks. The completion rate of the exercise log was 94% in the non-MetS group and 87% in the MetS group; there were no significant differences in the basic characteristics of individuals who did and did not complete the exercise logs. Exercise volume was calculated as the product of exercise intensity (metabolic equivalent; METs), duration (hours per session), and frequency (sessions per week), expressed in units of MET × hours per week. Moderate exercise (RPE between 12 and 14) was defined as 3 to 5 METs, vigorous exercise (RPE between 15 to 17) was defined as 5.1 to 6.9 METs, and very vigorous exercise (RPE between 18 to 20) was defined as > 7 METs.24 One MET represents 3.5 mL O2/min/kg of body weight (or 1 kcal/h/kg of body weight).
Exercise Self-Efficacy. Exercise self-efficacy was determined using a validated method in which individuals were asked to rate their confidence levels for performing regular exercise for each of the following 5 conditions: “I am tired,” “I am in a bad mood,” “I feel I do not have the time,” “I am on vacation,” and “It is raining or snowing.” Each condition was assessed on a 7-point scale (1 indicated no confidence at all and 7 indicated very high confidence). The test-retest reliability for this self-efficacy measurement was 0.9, and the total score was found to be associated with exercise behavior.25
Home-Based Exercise After baseline assessment, each subject received a diabetes prevention brochure that was designed based on the health belief model. The health belief model proposes that an individual changes his/her behavior to improve health when he/she knows that they are susceptible to a disease and can decrease morbidity. The brochure contained topics including “What is type 2 diabetes?” “What are the negative effects and complications of type 2 diabetes?” “Who is at risk for type 2 diabetes?” “Is type 2 diabetes preventable?” and “What are the strategies to prevent type 2 diabetes?” Using the brochure as a guide, each participant was interviewed to learn about T2DM and the importance of exercise in the prevention of T2DM. Exercise was promoted at this interview through goal setting, attempting to remove barriers to exercise, and designing the individualized home-based exercise plan. The selection of the exercise mode was based on the preference and accessibility of the participant. For individuals who did not have a preferred mode, 2 indoor exercise options, stepping (a stepper; Takasuma, Taipei, Taiwan) and cardio-dance, were provided. Stepping exercise was prescribed as 2400 steps in 30 minutes. Participants were allowed to adjust the exercise intensity on the basis of their physical condition. Cardio-dance involved a 50-min exercise video consisting of a 5-min warm-up period, 30 min of cardio-dance, 10 min of muscle strengthening, and 5 min of stretching. All the exercise plans were designed to be of moderate intensity; therefore, participants were instructed to exercise at an intensity at which mild-to-moderate dyspnea was experienced. The duration of all planned exercise sessions was at least 30 min and the frequency was at least 3 sessions per week. In addition to the initial interview in which the exercise program was set up, subjects received phone calls every 1 to 2 weeks encouraging them to keep exercising during the 3-month period of the program. Participants were asked to maintain a daily exercise log and record their body weight daily in our diabetes prevention brochure to facilitate exercise behavior via self-monitoring.
76 Chen et al
Statistical Analysis All data were analyzed using SPSS (version 10.0 for Windows; SPSS Inc., Chicago, IL) and were presented as either mean ± SEM or count (percentage). Listwise deletion (complete case analysis) was used for missing data. HOMA-IR, TG, and HDL were logarithmically transformed for analyses because of the skewed distribution of the data. Independent t tests and c2 tests were used for continuous and categorical variables, respectively, to compare the baseline differences between the MetS and non-MetS groups. If the significant between-group differences were noted at baseline, the differential effects of home-based exercise were examined by univariate analysis of variance with 3-month data as dependent variables and baseline data as covariates. Pearson product-moment correlation coefficient was performed to evaluate the correlation between exercise selfefficacy and exercise volume. P < .005 was used to define statistical significance for the adjustment of multiple comparisons in testing the effectiveness of the home-based exercise.
Results Baseline Characteristics The study population was characterized by a mean age of 48.6 ± 1.1 years, BMI of 25.9 ± 0.4 kg/m2, and waist circumference of 87.5 ± 0.7 cm for men and 78.0 ± 0.6 cm for women. Furthermore, 69% of subjects were overweight or obese, 36% had central obesity, and 53% had hypertension. In addition, 31% of subjects had fasting TG levels ≥ 1.7 mmol/L, 35% had HDL levels < 1.04 mmol/L (men) or < 1.29 mmol/L (women), and only 1% had fasting blood glucose levels ≥ 5.5 mmol/L. The MetS criteria were fulfilled by 21% of subjects, and no significant differences were found in age
or percentage of smokers between the MetS and non-MetS groups (Table 1). The MetS group had a greater prevalence of overweight subjects, central obesity, hypertension, hypertriglyceridemia, hypoHDL, and impaired glucose tolerance. In addition, the MetS group had significantly lower exercise self-efficacy than the non-MetS group at baseline (Table 1).
Response to the Home-Based Exercise Program Exercise Self-Efficacy. Exercise self-efficacy was found to improve in the non-MetS group after 3 months of homebased exercise. Individuals with MetS did not show significant improvement in exercise self-efficacy. Exercise self-efficacy of the MetS group remained lower than that of the non-MetS group after 3 months of home-based exercise (Table 2). Exercise Adherence and Exercise Volume. The non-MetS group showed better adherence to the prescribed exercise plan than the MetS group. Specifically, 72% of the non-MetS group and 39% of the MetS group met the minimum exercise prescription of at least 3 sessions of 30 minutes of moderate exercise per week. In addition, exercise volume for the non-MetS group was 2-fold higher than that of the MetS group (15.5 ± 1.4 and 7.8 ± 2.4 MET × h/wk, respectively; P = .02). E ffe c t o f H o m e - Ba s e d E xe rc i s e o n M e t a b o l i c R i s k Factors. Home-based exercise significantly improved (P < .005)
metabolic risk factors, including BMI and blood lipid levels in both groups (Table 2). The improvements in BP and waist circumference after home-based exercise were significant in the non-MetS group (P < .005) and approached significance in the MetS group (P values for systolic BP and WC were .005 and .008, respectively). Another key finding of this study was that the effect of home-based exercise
Table 1 Characteristics of the Study Subjects at Baseline Age (y) Women, n (%) Height (cm) Weight (kg) Smokers, n (%) Diabetic risk factors, n (%) Overweight (BMI ≥ 24 kg/m2) Central obesity (WC ≥ 90 cm [men] or ≥ 80 cm [women]) HTN (BP ≥ 130/85 mm Hg; use of anti-HTN medication) Hypertriglyceridemia (≥ 1.7 mmol/L) Hypo-HDL (< 1.04 mmol/L [men] or < 1.29 mmol/L [women]) Impaired glucose tolerance (≥ 5.5 mmol/L) Family history of DM Delivering a baby weighing ≥ 4.0 kg Number of diabetic risk factors, median (interquartile range) Exercise self-efficacy Exercise volume (METs × h/wk)
Non-MetS
MetS
P
48.8 ± 1.2 53 (60.9) 161.9 ± 1.0 65.2 ± 1.3 10 (11.5)
47.9 ± 2.9 15 (65.2) 162.6 ± 1.8 80.3 ± 3.7 2 (8.7)
.76 .71 .78 .001 .80
54 (62.1) 18 (20.7) 39 (44.8) 14 (16.1) 19 (21.8) 3 (3.4) 54 (62.1) 2 (2.3) 2 (2) 21.1 ± 0.1 15.5 ± 1.4
22 (95.7) 21 (91.3) 19 (82.6) 20 (87.0) 19 (82.6) 5 (21.7) 7 (30.4) 2 (8.7) 5 (1) 16.5 ± 0.3 7.8 ± 2.4
.002 < .001 .002 < .001 < .001 .01 .01 .20 < .001 .03 .02
Note. Values are mean ± SEM or n (%). Abbreviations: BMI, body mass index; WC, waist circumference; BP, blood pressure; HTN, hypertension; HDL, high density lipoprotein; DM, type 2 diabetes mellitus; MetS, metabolic syndrome.
Home-Based Exercise and Metabolic Syndrome 77
Table 2 Effects of the Home-Based Exercise Program on Individuals With and Without Metabolic Syndrome (MetS) Effects of home-based exercise
Baseline
3 Months
P (between-groups comparison of changes from baseline to 3 months)
16.5 ± 0.3* 30.2 ± 1.2* 129.9 ± 2.8* 82.4 ± 2.1 91.8 ± 2.3* 1.09 ± 0.09* 2.87 ± 0.4* 4.93 ± 0.15* 3.6 ± 0.6*
18.4 ± 0.3 29.5 ± 1.3† 121.7 ± 2.5 79.7 ± 2.0 90.0 ± 2.7 1.22 ± 0.08† 2.06 ± 0.3† 4.90 ± 0.14 4.3 ± 0.7
.02 .80 .58 .19 .42 .52 .46 .94 < .001
Non-MetS Baseline Exercise self-efficacy BMI (kg/m2) SBP (mm Hg) DBP (mm Hg) Waist circumference (cm) HDL (mmol/L) Triglycerides (mmol/L) Fasting blood glucose (mmol/L) HOMA-IR
21.1 ± 0.1 24.7 ± 0.4 120.8 ± 1.8 77.6 ± 1.3 79.0 ± 1.1 1.44 ± 0.05 1.25 ± 0.06 4.50 ± 0.06 1.8 ± 0.1
MetS
3 Months 0.1†
24.2 ± 24.3 ± 0.3† 115.2 ± 1.5† 74.7 ± 1.1† 77.7 ± 1.0† 1.52 ± 0.05† 1.27 ± 0.05 4.66 ± 0.06 1.9 ± 0.1
Note. Values are mean ± SEM. Abbreviations: MetS, metabolic syndrome; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL, high-density lipoprotein; HOMA-IR, homeostasis model of insulin resistance. * P < .05 compared with the baseline values of the non-MetS group. †P
< .005 compared with the baseline values within groups.
on the changes in HOMA-IR was different in the non-MetS and MetS groups (P < .001). HOMA-IR in the MetS group had a trend to increase even after the home-based exercise (P = .08). However, home-based exercise could maintain the HOMA-IR of the non-MetS group at a normal level (Table 2). Correlation Between Exercise Self-Efficacy and Exercise Volume. We found that exercise volume was significantly
correlated with exercise self-efficacy at baseline (P < .0001). Greater exercise self-efficacy was correlated with greater exercise volume that individuals performed at home (r = .41) (Figure 1).
Figure 1 — Correlation between exercise-self-efficacy and exercise volume in individuals at risk for type 2 diabetes.
Discussion This study showed that a home-based exercise program has benefits for body composition and lipid profile in individuals with and without MetS. More particularly, individuals without MetS scored higher on exercise self-efficacy, were more adherent to the homebased program, and had higher exercise volume than individuals with MetS. In addition, the non-MetS group showed better control of IR, which may be due to the greater exercise volume, whereas in the MetS group, exercise was unable to control the progression of IR. Our study showed for the first time that individuals without MetS had higher exercise self-efficacy than those with MetS. The link between psychological characteristics and health condition has been reported in children, women, and overweight adults with impaired glucose tolerance, where lower exercise self-efficacy was found to correlate with poor body composition.16–18 Another key finding is that exercise self-efficacy was positively correlated with exercise volume. The positive relationship between exercise self-efficacy and exercise adherence has been reported previously. For example, Delahanty et al13 found that exercise self-efficacy independently predicted exercise duration and whether subjects in the Diabetes Prevention Program achieved the 150 min/wk physical activity goal. Exercise self-efficacy was also found to be a significant determinant of exercise adherence in cancer survivors and older women after hip fracture.12,15 Collectively, our findings suggest there are differences in psychological characteristics and exercise behavior between individuals with and without MetS. Because exercise self-efficacy is not a routine assessment, unlike blood glucose and BP, it is hard to predict individuals’ adherence to the exercise prescription. Based on our finding that exercise selfefficacy is different between individuals with and without MetS, the metabolic status can be a key consideration when developing or designing exercise prescriptions and supervision modes. Concerning the effects of home-based exercise on metabolic risk factors, we found that both groups exhibited improvements
78 Chen et al
in BMI and blood lipid levels after the 3-month program. Several clinical trials have shown that the development and progression of T2DM could be prevented or delayed through lifestyle modification, including supervised center-based exercise.3–5 In contrast, the home-based exercise program in our study did not reverse the elevated IR in individuals with MetS but did effectively control the IR of individuals without MetS. Our findings indicated that individuals without MetS had greater benefits from the homebased exercise program than individuals with MetS. This finding is similar to those in previous studies. Joseph et al26 reported that individuals without MetS, but not those with MetS, showed improved blood lipid profile after 6 months of weight loss and low-intensity exercise. Likewise, Lien et al27 found that individuals without MetS had greater reductions in SBP as a result of regular aerobic physical activity compared with individuals with MetS. Taken together, our results suggest that the extent of benefits from home-based exercise is related to an individual’s metabolic characteristics. Our findings emphasized that HOMA-IR was under control in individuals without MetS but not in those with MetS after homebased exercise. The lower exercise volume performed by individuals with MetS compared with individuals without MetS may explain the uncontrolled IR in the MetS group. A previous study found IR to be unchanged in postmenopausal women participating in a low-intensity exercise program.26 In contrast, IR was improved in individuals with prehypertension or stage-1 hypertension after an intensive exercise intervention that included at least 180 min/wk of moderate-intensity exercise.27 Another possible reason for the lack of improvement in IR is the relatively short duration (3 months) of the exercise program. In line with this, Dunstan et al28,29 found that 9 months of resistance training, but not 3 or 6 months, improved IR in older individuals with T2DM. The findings of lower exercise self-efficacy in individuals with MetS and the positive correlation between exercise self-efficacy and exercise adherence imply that integrating techniques that increase exercise self-efficacy may improve the effectiveness of exercise program in individuals with MetS. Techniques that have been found to significantly improve exercise self-efficacy include detailed planning about when, how, and where to perform the exercise; giving feedback about past performance; and providing feedback about the performance of the individual compared with other people.30,31 There are some caveats in the data interpretation of the current study. First, the cross-sectional design of the study limits causal inferences. Nevertheless, our finding of lower exercise selfefficacy and poorer exercise adherence in individuals with MetS suggested that individuals with MetS may need more intensive and/or supervised exercise intervention. Second, self-reported exercise behavior is commonly used yet has been reported to have limitations. Although we found a significant association between the self-reported exercise volume and changes in HOMA-IR (not shown in the results) that supports the soundness of the use, it is important to be aware of the limitations. In conclusion, the home-based exercise program improved BMI and blood lipid levels in individuals at risk for diabetes. Importantly, we found that individuals with MetS had lower levels of baseline exercise self-efficacy, poorer adherence to the prescribed homebased exercise program, and poorer control of insulin resistance compared with individuals without MetS. Therefore, individuals with MetS may need exercise supervision to increase their exercise volume and reverse their elevated IR levels. This study provides additional information to the current understanding of the homebased exercise program benefits in individuals at risk for diabetes
and also helps to determine the group that benefits the most from such exercise. Acknowledgments This project was funded by the Bureau of Health Promotion, Department of Health (DOH94-HP-1105) in Taiwan. The authors thank the additional support from Healthy Aging Research Center, Chang Gung University (EMRPD1E1651) and the statistical assistance provided by the National Translational Medicine and Clinical Trial Resource Center and the Department of Medical Research in National Taiwan University Hospital. This study is registered at www.clinicaltrials.gov (No. NCT01136096).
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