Objective
The objective of the study was to evaluate the effect of a resistance exercise program with an elastic band on insulin requirement and glycemic control in patients with gestational diabetes mellitus (GDM).
Study Design
Sixty-four patients with gestational diabetes mellitus were randomly assigned into 2 groups: an exercise group (EG; n = 32) and a control group not submitted to the exercise program (CG; n = 32).
Results
A significant reduction in the number of patients who required insulin was observed in the EG (7/32) compared with the CG group (18/32) ( P = .005). The percentage of time spent within the proposed target glucose range (of at least 80% of weekly measurements below the limits preestablished for the disease) was significantly higher in EG compared with the CG group (EG = 0.63 ± 0.30; CG = 0.41 ± 0.31; P = .006).
Conclusion
The resistance exercise program was effective in reducing the number of patients with GDM who required insulin and in improving capillary glycemic control in this population.
Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance that first occurs or is first diagnosed during pregnancy. Adequate glycemic control of patients with GDM is necessary to minimize complications resulting from the disease. In this respect, diet therapy is the first intervention, which, if unsuccessful, should be accompanied by insulin treatment. Although effective in reducing the risk of fetal macrosomia, insulin therapy does not act on the origin of the problem (ie, increased peripheral resistance to the action of insulin in the second half of gestation).
Because skeletal muscles represent the main site of insulin resistance observed during pregnancy, both the American College of Sports Medicine and the American College of Obstetricians and Gynecologists recommend exercise as an effective and safe supporting therapy for the treatment of GDM because several lines of evidence have shown the effectiveness of aerobic exercise in reducing the frequency of women using insulin. On the other hand, little is known about the therapeutic application of resistance exercise (RE) to women with GDM. This modality of exercise (RE) consists of the voluntary contraction of skeletal muscle of a certain body segment against some type of external resistance. The scientific literature regarding the use of this type of physical activity as a coadjuvant for the treatment of GDM is scarce. To our knowledge, there is only 1 study on this subject conducted by Brankston et al in 2004.
Because RE might be an important tool for glycemic control in patients with GDM, the objective of the present study was to evaluate the impact of an RE program with elastic band on insulin requirement and on the adequacy of capillary glycemic control in pregnant patients with GDM. We hypothesized that RE would reduce the number of women who require insulin and would improve glycemic control in these patients.
Materials and Methods
A randomized controlled trial was conducted involving patients with GDM who were under prenatal follow-up at the Obstetric Clinic of the University Hospital, University of Sao Paulo School of Medicine, between October 2006 and November 2008 (study period). The study was approved by the Institutional Review Board of the University Hospital, University of Sao Paulo, and written informed consent for participation was obtained from each patient. For data analysis, the patients were randomized into 2 groups: an exercise group (EG), which underwent an RE program until the end of gestation, and a control group (CG), which was not submitted to this program.
Patients with a diagnosis of GDM (made by the 3 hour oral glucose tolerance test [OGTT] after a 100 g glucose overload or by the 2 hour OGTT after a 75 g overload) who fulfilled the following criteria were included in the study: sedentary patients according to the International Physical Activity Questionnaire (IPAQ), nonsmokers, age range 18-45 years, no physical factor or disease limiting exercise, singleton pregnancy and absence of fetal malformation upon ultrasound, gestational age ranging from 24 to 34 weeks, and no risk factors for preterm delivery. Exclusion criteria were the occurrence of clinical or obstetric complications contraindicating exercise during pregnancy and loss to follow-up. All subjects were instructed not to start any new type of physical activity after the randomization.
On the first visit after the diagnosis of GDM, the patients received instructions regarding capillary glucose monitoring through self-monitoring of fingertip capillary blood glucose 4 times per day (after an overnight fast, 2 h after breakfast, 2 h after lunch, and 2 h after dinner). The objective was to maintain fasting glucose levels of 95 mg/dL or less and postprandial levels of 120 mg/dL or less according to American Diabetes Association (ADA) guidelines.
All pregnant women with a diagnosis of GDM were systematically evaluated and received diabetic dietary instructions from a nutritionist. The diet was divided into 7 servings, containing 35 kcal/kg ideal weight –1 /day –1 , and 300 kcal/day were added in the second and third trimesters of gestation.
After the first medical visit, the patient was informed about the opportunity to participate in this study. Women admitted to the study were randomized using a computer-generated random series produced by a person not related to the protocol. The main researcher (M.C.D.B.) received the next on a numbered series of sealed opaque envelopes and was responsible for allocating each patient to 1 of the 2 groups (EG or CG) according to the randomization list and instructed the patients regarding RE. However, this researcher did not participate, at any time, in the decision about the introduction or adjustment of the insulin dose. The obstetricians responsible for clinical and prenatal care and data recording was unaware to which group the patients belonged, and only the main researcher (M.C.D.B.) questioned the patients with respect to the exercise practice.
RE was performed with an elastic band ( Figure 1 ). The patients were advised to start the program about 90 minutes after consuming a meal of their preference (breakfast, lunch, or dinner) and after the measurement of capillary glycemia with an Accu-Chek Advantage glucose meter (Roche Diagnostics, Indianapolis, IN). If capillary glucose levels were between 100 and 250 mg/dL, EG patients started the program with a stretching sequence. If capillary glycemia was below this range, the patients were instructed to do the RE program on the next day to prevent hypoglycemia. If the values were above this range, the patients were instructed not to undergo RE to prevent the occurrence of ketoacidosis and to contact the responsible obstetrician.
The RE program consisted of a circuit type resistance training, elaborated in such a way that the main muscle groups of the patients would be exercised (chest, back, biceps, triceps, deltoid, quadriceps, thigh, and calf muscles). A circuit series was defined as a sequence of these eight exercises (stations). The women performed 15 repetitions of each exercise (station), with a minimum resting period of 30 seconds and a maximum of 1 minute between each one. In the first and second week of follow-up, the women underwent 2 circuit series, followed by 3 circuit series from the third week of inclusion in the study to the end of gestation.
Exercise intensity was controlled by the women themselves using a perceived exertion scale for RE provided to them. The women were advised to maintain an exercise intensity close to 5 or 6, which corresponds to a “somewhat heavy” exercise perception. The use of the elastic band facilitated the adaptation of exercise intensity to the level of conditioning of the patients because only its length needed to be adjusted. The main researcher (M.C.D.B.) was responsible for the adjustments, which were always made on the weekly return visits of the patients to the outpatient clinic.
The patients received written guidelines of how to perform each exercise and were instructed to undergo the program on 3 nonconsecutive days a week (twice a week at home). The participants were contacted by telephone at least once a week to verify adherence to the program. The other session was performed during the weekly return visit, always under the supervision of the main researcher (M.C.D.B.). On that occasion, EG patients were asked whether they had performed any type of physical activity other than RE. In addition, the adequate execution of RE at the correct intensity was verified.
The prenatal routine care of CG patients was kept unchanged. The patients attended weekly return outpatient visits and, on that occasion, were questioned whether they had started some type of physical activity. In addition, the patients again responded to the IPAQ. The research visits and care visits were scheduled weekly at the same day for all patients (CG and EG).
The glycemic profile of each patient was determined weekly, and insulin was introduced when more than 30% of the glucose measurements were above the recommended value or when 20-30% of the measurements indicated hyperglycemia and fetal weight was above the 75th percentile. The estimated fetal weight percentile was determined once a month. The initial insulin dose (NPH) was calculated at 0.4 IU/kg –1 per day –1 , divided into half at breakfast, one-quarter at lunch, and one-quarter at 10:00 pm . Regular insulin was added at meals to improve the glycemic control if the exclusive use of NPH insulin was not sufficient to maintain the glycemias at adequate levels.
Comparison of the percentage of weeks spent within the target glucose range of at least 80% of weekly measurements considered to be normal for gestation according to ADA guidelines was used as a parameter to evaluate the adequacy of glycemic control. Throughout the follow-up period (time between study inclusion and delivery), the weekly mean of all capillary glucose was calculated for both groups. The mean weekly values of fasting and postprandial capillary blood glucose levels were also obtained. The analysis of the mean of means weekly values previously established was performed for comparison between groups.
Statistical analysis
All variables were submitted to comparative analysis using the SPSS for Windows 15.0 program (SPSS, Inc, Chicago, IL). For calculation of the sample size, the objective was to reduce the percentage of patients in EG who required insulin to 20%, with approximately 50% of patients with GDM using insulin according to the databank of the Endocrinopathy and Pregnancy Unit (obstetric clinic’s department responsible for the care of pregnant women affected by endocrine disturbances, such as thyroidopathies and GDM). Assuming a power of the test of 80% and a level of significance of 5%, the calculated sample size in each group was 30 patients.
Variables measured at diagnosis, at inclusion in the study, and during delivery were compared between groups by the Student t test. The type of delivery is reported as absolute and relative frequency for each group, and a possible association of this variable with the groups was subsequently tested by the χ 2 test.
A graph of mean glycemic profiles and their respective standard errors was constructed for the analysis of glucose levels over the weeks of gestation, and the results were submitted to analysis of variance for repeated measures with Huynh-Feldt correction. Mean values of each patient per time of the day (after an overnight fast, 2 h after breakfast, 2 h after lunch, and 2 h after dinner) were used for analysis. Gestational body mass index (BMI) was also compared between groups and periods of gestation using analysis of variance for repeated measures with Huynh-Feldt correction. Bonferroni’s multiple comparisons were performed to determine between which periods glucose levels differed.
The unpaired Student t test was used to compare the mean percentage of time (weeks) spent within the target glucose range during the follow-up period between groups. The existence of an association between groups for the use or not of insulin was evaluated by the χ 2 test. Data were analyzed using the intention-to-treat principle. The level of significance was set at 5% for all tests.
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