Research Design and Methods
Subjects were recruited from the St. Paul's Hospital Diabetes Teaching and Training Center and by newspaper advertisement. Inclusion criteria were as follows: postmenopausal status, type 2 diabetes controlled by diet or oral agents, central obesity (waist circumference >90 cm), and an inactive lifestyle (<20 min of moderately vigorous activity, twice per week, over the last year). Eligible subjects underwent a physical examination and a maximal graded exercise tolerance test with electrocardiogram monitoring to exclude individuals with subjective or objective evidence of coronary artery disease. Subjects were then randomly assigned to one of three groups: usual care, aerobic plus resistance training (Ae+RT), or aerobic only training (Ae only). A total of 28 women completed the study; their descriptive characteristics are outlined in Table 1 . Their initial age, years since diagnosis of diabetes, glycosylated hemoglobin levels, weight, BMI, level of fitness, or computed tomography (CT) measures did not differ between the groups (P > 0.05), although subcutaneous AT areas displayed a trend to statistical difference across groups (P = 0.057). Distribution of diabetic therapy is outlined in Table 1 . All subjects gave their written informed consent to participate in the study, which was conducted according to the ethical guidelines of the University of British Columbia and St. Paul's Hospital.
Ae+RT. A total of 10 women participated in a supervised 16-week structured aerobic and resistance training program, three times per week. Each class consisted of a warm-up, an aerobic phase, a resistance training phase, and a cooldown to total a class time of 75 min. The aerobic phase involved individually prescribed exercise at 60-75% of heart rate reserve (based on the initial maximal graded exercise tolerance test), using treadmills, stationary bicycles, recumbent steppers, elliptical trainers, and rowing machines. The resistance training program consisted of five exercises (leg press, leg curl, hip extension, chest press, and latissimus pull down) for two sets of 12 repetitions using stack weight equipment. Resistive training began with light loads and thereafter progressed as technique permitted. Training loads were monitored during the program, with strength improvements reported from the third week of training (to allow for learning) as compared with the last week.
Ae only. Nine women participated in a supervised aerobic training program lasting 16 weeks, three times per week, with 75-min structured exercise classes. Each class consisted of a warm-up, an aerobic phase, and a cooldown. Aerobic exercise intensity was individually prescribed as for the Ae+RT group, and the equipment used was the same. Low-impact low-intensity dynamic movement replaced the resistance training component of the Ae+RT group; therefore, the warm-up and cooldown phases were somewhat longer than in the combined training group. Published values for low-impact aerobic movement are estimated to be ~0.1 kcal · min-1 · kg,-1[15,16] similar to the estimated energy cost of resistance training.[17,18] These class designs were used to minimize potential differences in energy expenditure between the exercise training groups.
Peak VO2 was determined before entering the study and at the end of the 16 weeks. Respiratory gas analyses were carried out during a progressive Naughton protocol treadmill test to voluntary exhaustion. Oxygen uptake (VO2) was determined using a Beckman metabolic cart (Sensormedics Yorba Linda, CA). The 12-lead electrocardiogram analyses were ongoing throughout the test.
Subjects were asked to continue with their current diet and physical activity patterns outside of the study protocol. Dietary patterns were analyzed by 3-day food records before and after the study and were analyzed with the Nutritionist IV software (First Data Bank, San Bruno, CA).
CT imaging was performed on a General Electric CT/i scanner (General Electric Medical Systems, Milwaukee, WI) before and after the treatment. An initial lateral scout, centered at the level of the iliac crest, allowed accurate positioning of a single non-angled axial image at the L4/L5 vertebral disc space. A 10-mm single-image scan was taken using the parameters of 120 kVp, 300 mA, with 1 s duration, with a 512 by 512 matrix. This image was used to assess cross-sectional areas of subcutaneous and visceral AT. A second anterior-posterior scout covered the iliac crest to just below the knee to allow accurate positioning of a second image at the midpoint of the femur, from the superior rim of the femoral head to the inferior surface of the femoral condyles. A single non-angled axial image was taken at this position, and muscle cross-sectional areas were assessed.
CT images were analyzed using the Slice-O-Matic software (version 4, Montreal, Quebec, Canada). Standard attenuation ranges were used to visualize and quantify AT (-190 to -30 Hounsfield units [HU] and muscle tissue [0-100 HU]). Muscle characteristics were expressed as the cross-sectional area of muscle and were separated into the cross-sectional areas of low-density muscle (0-34 HU) or normal-density muscle (35-100 HU).
Subjects were asked to report to the hospital laboratory after a 12-h overnight fast, as previously described.[19] Subjects in the exercise groups underwent their repeat glucose clamp at 48-72 h after the last exercise class. Four blood samples were taken from -30 min to time 0 to measure basal insulin and glucose. At time 0, the euglycemic clamp study was started and continued to 180 min. Regular human insulin (Humulin R; Eli Lilly, Indianapolis, IN) was infused at a constant rate of 40 mU · m-2 · min-1 via an 18-gauge catheter inserted into an antecubital vein. Glucose levels were allowed to fall from fasting level to ~5.5 mmol/l, thereafter maintained at this level by a variable glucose infusion rate and adjusted according to 5-min interval sampling of arterialized venous blood from a contralateral hand vein. Plasma glucose was analyzed immediately using a YSI Glucose Analyzer (Yellow Springs Instruments, Yellow Springs, OH). Results of the euglycemic clamps are expressed as the glucose infusion rate averaged over the last 60 min of the clamp.
Venous blood samples were analyzed for fasting glucose, glycosylated hemoglobin, total cholesterol, LDL, HDL, triglyceride, and apolipoprotein B. Sampling was done after a 14-h fast, with no alcohol for the preceding 3 days. All measures were conducted in the St. Paul's Hospital, accredited by the Diagnostic Accreditation Program of British Columbia. Serum total cholesterol and HDL cholesterol were assessed by the enzymatic colorimetric test using Boehringer Mannheim Systems reagents in a Hitachi 911 system. Serum triglyceride was measured by the enzymatic colorimetric test using Bayer reagents in a Hitachi 911 system. LDL cholesterol (mmol/l) was calculated using the equation (LDL cholesterol = total cholesterol - HDL cholesterol - triglyceride/2.22).
Results are reported as group means ± SE, unless otherwise indicated. Initial metabolic and body composition results have been analyzed by ANOVA to determine differences between the groups before intervention. The changes in metabolic and body composition variables were compared between groups by ANOVA. Pearson product-moment correlations were used to determine the simple relationship between CT imaging results and euglycemic clamp results. Statistical tests were performed using SPSS software (v. 10). Statistical significance of the change in results, from prestudy to poststudy, are indicated at the P < 0.05 level.
Diabetes Care. 2003;26(11) © 2003 American Diabetes Association, Inc.
Cite this: Effective Exercise Modality to Reduce Insulin Resistance in Women With Type 2 Diabetes - Medscape - Nov 01, 2003.
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