DM: Physical Activity (2007)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the prospective association of cardiorespiratory fitness and physical inactivity with mortality in men who have type 2 diabetes.
Inclusion Criteria:
  • Baseline medical exam
  • Diagnosis of type 2 diabetes mellitus:  FBG > 126 mg/dl or self-reported hisotry of physician diagnosed diabetes
Exclusion Criteria:
  • Taking insulin
  • Diagnosis of cancer at baseline
Description of Study Protocol:


Subjects were in the Aerobics Center Longitudinal Study (ACLS) who completed a baseline medical exam between 1970 and 1993 at The Cooper Clinic in Dallas, TX.

Design:  Prospective Cohort Study. 

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

Medical exam, self-administered questionnaire, cardiorespiratory fitness evaluation.  Followed for a mean of 12 years or until December 1994 for mortality data.

Statistical Analysis

Survival curves used to estimate survival function against time and log to check the proportional hazards model assumption.  Log estimates were approximately parallel across exposure groups and nonexposure groups.  Cox proportional hazard models were used to determine the association between mortality and estimated exposures after adjustment for potential confounders.  Interaction terms between estimated exposures and other independent variables were entered to evaluate possible interaction.  For adjusted relative risks, all results were from models that included all listed variables without interaction terms.

Data Collection Summary:

Timing of Measurements

Medical exam after overnight fast and self-administered questionnaire at baseline.  Subjects also completed a cardiorespiratory fitness evaluation.

Dependent Variables

  • Death determined by National Death Index

Independent Variables

  • Self-administered questionnaire determining health habits such as smoking, diet, physical activity and personal and family history of disease, leisure time activities and subjects checked all those in which they had participated in the previous 3 months
  • Cardiorespiratory fitness evaluated by subjects walking on a horizontal treadmill at 88 meters/minutes, after the first minute, the elevation increased to 2%, and it further increased 1%/minute up to 25 minutes and the speed increased to 5.4 meters/minute until the subject reached volitional fatigue.
  • Fitness categorized into age groups by decade (30s, 40s, 50s, >60 years).  The least fit 20% in each age category were considered as low fit, the next 40% as moderately fit, and the next 40% as high fit.

Control Variables

  • Medical exam:  physical exam, FBG, serum lipids, uric acid, blood pressure, family and medical history of CVD, anthropometrics
  • Age
  • Baseline cardiovascular disease
  • Fasting plasma glucose
  • High cholesterol
  • Overweight
  • Current smoking
  • High blood pressure
  • Parental history of cardiovascular disease
Description of Actual Data Sample:

Initial N: 1263  men

Attrition (final N):  180 died (14.2%) during 11.8 years of follow up

Age:  50 +/- 10 years

Ethnicity: not mentioned

Other relevant demographics:


Location:  Dallas, TX


Summary of Results:

Other Findings

Causes of death included diabetes, CVD, cancer, digestive disease and injury.

42% of men were identified as less fit and 58% as fit.

Physical inactivity was reported by 50% of men with diabetes and 33% of men without diabetes.

After adjustment for age, baseline cardiovascular disease, fasting plasma glucose, high cholesterol, overweight, current smoking, high blood pressure, and parental history of cardiovascular disease:

1.  Men in the low fitness group had an adjusted risk for all-cause mortality of 2.1 (95% CI: 1.5 to 2.9) compared with fit men (P < 0.001).

2.  Men who reported being physically inactive had an adjusted risk for mortality that was 1.7 fold (95% CI: 1.2 to 2.3 fold) higher than that of men who reported being physically active (P < 0.002).

Author Conclusion:

Decreased cardiorespiratory fitness and physical inactivity are independent predictors of all-cause mortality in men with type 2 diabetes.

Physicians should encourage patients with type 2 diabetes to participate in regular physical activity and improve cardiorespiratory fitness.

Funding Source:
Reviewer Comments:

Questionnaires were not shown to be valid or reliable.  A limitation of this study was that the authors did not report repeated data collection after baseline data was collected.

This study clearly shows an association between physical inactivity and decreased cardiorespiratory fitness and an increased risk for death.  However, poor health could contribute to physical inactivity and poor fitness.

Most men with type 2 diabetes could participate in some type of physical activity on a regular basis - walking, swimming and bicycling.

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) N/A
  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) N/A
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? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? Yes
  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? N/A
  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? N/A
  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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? ???
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  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? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? N/A
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  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? No
  7.5. Was the measurement of effect at an appropriate level of precision? N/A
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  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? N/A
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