DM: Physical Activity (2007)

Study Design:
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Quality Rating:
Research Purpose:

To investigate the efficacy of an exercise intervention program compared to relaxation exercises to decrease HbA1c over a period of 12 weeks, in type 2 DM female subjects.

Inclusion Criteria:
  • Black women
  • age 40-65 years
  • with type 2 DM for > 1 year
Exclusion Criteria:
  • chest pain on effort
  • possible previous myocardial infarction, intermittent claudication, CVA, arthritis, and retinopathy
Description of Study Protocol:

Recruitment all consecutive eligible patients attending the diabetes clinic over a period of 6 months were invited to take part in the study

Design subjects were randomized into the exercise group or the relaxation group.  Groups met on different days of the week to prevent patients from either group adopting the program of the other. 

Blinding used (if applicable)

  • allocation concealment ensured by means of sequentially numbered, sealed, opaque envelopes.
  • a computer-generated list was used
  • subjects were randomized in 17 blocks of 10 each
  • allocation was done telephonically from a central site and was concealed until interventions were assigned.
  • to ensure that the research assistant and laboratory staff were blind to the randomization of the participants, the only form of identification on the questionnaires, EDTA-tubes, and clinical data forms were the names, hopsital file numbers and the study numbers of the subjects.

Intervention (if applicable)

Exercise Group

  • patients were encouraged to form small groups and exercise together
  • subjects instructed to increase walking at home from 10-45 minutes over the 12 weeks of training
  • subjects instructed to walk twice a day, starting at 5 minutes per session and to increase total daily walking time by 10 min every 2 weeks, up to 45 minutes per day.
  • subjects were told to walk briskly, swinging their arms, and to work up a slight sweat, at a REP of 12-14 or "somewhat hard" according to the Borg Scale
  • subjects attending aerobic exercise classes at the hospital every two weeks where they worked for 45 minutes at 55-69% of maximal heart rate.

Relaxation Group

  • required to visit the hospital group every 2 weeks for relaxation exercises
  • exercises involved tensing and then relaxing alternating muscle groups for 20 minutes 


  • Both groups were given the same education consisting of
    • management of type 2 diabetes
    • role of exercise in the management of the disease. 

Statistical Analysis

  • paired t test used to calculate a P value for the comparison of means within the experimental and relaxation groups, respectively
  • ANCOVA was used to compare the experimental and relaxation groups with respect to changes in HbA1c, BMI, and 6-min walking distance using the baseline values as a covariate.


Data Collection Summary:

Timing of Measurements

  • baseline and 12-week post study:  demographic data, non-fasting HbA1c, BMI, blood pressure, 6-min walk test on a 33m course (used to prescribe the intensity of the home training, if applicable)

Dependent Variables

  • HbA1c
  • BMI
  • Blood pressure
  • Results of 6-min walk test
  • Rating of Perceived Exertion (RPE), using Borg Perceived Exertion Scale

Independent Variables

  • Physical activity
    • subjects in the exercise group were given a physical actitivy log with illustrations fo some of the most used phycial activities at home
    • these subjects were instructed to keep a daily record of the time they spent on each of the activities in the diary and hand it in at exercise sessions held at the hospital every two weeks
    • METs were calculated

Control Variables


Description of Actual Data Sample:

Initial N: 85 in exercise group; 80 in relaxation group

Final N:  75 in exercise group, 74 in relaxation group

Age: 54 years

Ethnicity: black

Other relevant demographics:

  • only 2 of the subjects had more than 10 years of schooling
  • unknown whether the groups were significantly different regarding schooling, marital status, income, treatment for DM, or other medical conditions, as only frequency distribution was given 

Anthropometrics none given

Location: South Africa


Summary of Results:

Subjects in the exercise group did not complete the physical activity record correctly, so the MET values of daily physical activity could not be computed.

91% of the participants in the exercise group attended the hospital exercise sessions.


Exercise Group

Mean (SD)

and confidence intervals

P value

Relaxation Group

Measures and confidence intervals


HbA1c, %

-0.63 (0.31)















6-min walk, (meters)








*the paired t-test was used to calculate a P value for the comparison of means within the exercise and relaxation groups respectively.

Other Findings

  • The adjusted baseline mean HbA1c change in the exercise gorup after the 12-week trial was -0.39%, and the difference from the mean for the relaxation group -0.97% was just outside statistical significance (P=0.052).
  • The adjusted baseline mean BMI change in the exercise group was -0.07 kg/m2 and was not significantly different (P=0.29) from the mean change for the relaxation group.
  • The difference in the adjusted baseline mean walking distance change in the exercise groups of 46.76 m was significantly better (P<0.01) than the change from adjusted baseline mean in the relaxation group of 22.7 m.


Author Conclusion:

Both interventions improved HbA1c levels, but it is most likely that these improvements were due to a study effect.

The walking distance improved in both groups, but was significantly better in the exercise group.  However this improvement did not translate into the expected improvement in glycemic control.

Funding Source:
Reviewer Comments:

The authors report their randomization process in detail.

Demographic differences between groups were not analyzed statistically.

Without measures of daily physical activity, apart from the intervention exercise, makes it impossible to control for usual amounts of physical activity.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes