DM: Physical Activity (2007)

Study Design:
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Quality Rating:
Research Purpose:

To systematically review and quantify the effect of exercise on glycosylated hemoglobin and body mass in patients with type 2 diabetes.

Inclusion Criteria:
  • Interventions lasting > 8 weeks
  • Defined exercise intervention as a predetermined program of physical activity described in terms of type, frequency, intensity and duration
  • Compliance to physical activity intervention verified by direction supervision or through exercise diaries
  • Non-English studies
Exclusion Criteria:
  • Drug co-intervention studies
Description of Study Protocol:


Literature searches of computer databases were performed for the period including December 2000 (MEDLINE 1966-2000, EMBASE 1980-2000, Sports Discuss 1949-2000, Health Star 1975-2000, Dissertation Abstracts 1861-2000, and the Cochrane Controlled Trials Register).  2 of the authors independently performed the literature search and data analysis.  When there was disagreement, a discussion was held with the third author. 

Design:  Meta-analysis.

Blinding Used (if applicable):  Not applicable

Intervention (if applicable)

Sample sizes, baseline and post-intervention means and SDs for the intervention and control groups were examined.  Authors of studies were contacted directly to verify some information.  Postintervention SDs imputed when not available.  Characteristics of the exercise interventions were extracted, including the type, frequency, duration, intensity and energy cost.

Statistical Analysis

The weighted mean difference and the standard mean difference were calculated and pooled separately using the fixed-effects model.  The Chi-square test for heterogeneity was performed and when significant heterogeneity was found, the analysis was redone with a random-effects model.  The funnel plot technique was used to detect publication bias.

Data Collection Summary:

Timing of Measurements:  not applicable


Dependent Variables: 

  • HbA1c
  • BMI

Independent Variables:

  • Exercise interventions

Control Variables


Description of Actual Data Sample:

Initial N:  2700 potential articles identified for review

Attrition (Final N):  After application of the filter for clinical control trials, the number of studies was reduced to 1487.  14 trials met all inclusion criteria with a total of 504 participants in the studies.

Age:  Mean age of participants in studies:  55.0 +/- 7.2 years

Ethnicity:  not mentioned

Other relevant demographics:  Mean duration of diabetes 4.3 +/- 4.6 years, 50% were women


Location:  Worldwide studies

Summary of Results:

Other Findings:

Quality of trials was low (1.6 +/- 0.5) out of a possible score of 5.  Of the 14 trials, 11 were RCT and 3 were clinical control trials.

Compliance to exercise interventions was high.  In 9 studies, the mean participation rate was >80%, 2 articles indicated that compliance was good, and 2 studies did not comment on compliance.

Effect of exercise on body mass:

1.  In the BMI comparisons for the 13 exercise groups vs non-exercise control groups, no significant post intervention differences were found (SMD, 0.06; P = 0.60).

2.  Abdominal obesity was represented by waist circumference in 4 studies.  The post intervention WMD was -4.53 cm (P < 0.001).

3.  One study reported changes in abdominal obesity using magnetic resonance imaging.  The subjects participated in an aerobic training program for 55 minutes, 3 x week for 10 weeks.  There was a significant decrease in abdominal subcutaneous adipose tissue (227.3 cm2 to 186.7 cm2, P < 0.05) and visceral adipose tissue (156.1 cm2 to 80.4 cm2, P < 0.05) with no significant differences in waist circumference or waist to hip ratio.

Effect of exercise on glycemic control:

1.  Baseline and post intervention HbA1c were described in 12 studies (14 comparisons).  When the post intervention results were pooled, HbA1c was significantly decreased in the exercise group (7.65% vs 8.31%, WMD, -0.66%, P < 0.001).

There was one study in which participation was limited to participants with diabetes who were older than 65 years of age - the mean age was 69.4 +/- 4.7, compared to 55.0 +/- 7.2 in the remaining subjects.  When this study was excluded from the analysis, the overall WMD for HbA1c would have been -0.74% (95% CI: -1.09% to 0.39%).

Author Conclusion:

Although individual trials on the effects of exercise in patients with type 2 diabetes have had partially conflicting results, the current meta-analysis suggests that exercise training decreases HbA1c by ~0.66%, an amount that would be expected to decrease the risk of diabetic complications significantly.

The studies reviewed in this meta-analysis did not find significantly greater weight loss in the exercise groups compared with the control groups.  Therefore, exercise should be viewed as beneficial on its own, not just a way to lose weight.

Future studies should include longer interventions with better quantification of body composition changes.  In the interim, our analysis using an evidence-based approach adds support to the idea that exercise is a cornerstone of diabetes therapy.

This review shows the importance of evaluating body composition in exercise intervention studies; even though there was no weight change, there was a decrease in waist circumference in 4 studies in which it was measured and a decrease in abdominal fat as measured by magnetic resonance imaging.

The study period needs to be extended with follow-up to demonstrate long-term benefits of exercise intervention.

Funding Source:
Government: Onterio Ministry of Health and Long Term Care (Canada), Canadian Institute of Health Research, Natural Sciences and Engineering Research Council of Canada
Reviewer Comments:
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes