DM: Physical Activity (2007)

Study Design:
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Quality Rating:
Research Purpose:
To examine the acute glucose-lowering effects of aerobic exercise in children and adolescents with type 1 diabetes.
Inclusion Criteria:
  • Children and adolescents with type 1 diabetes of at least 18 months duration 
  • Ages 10 to <18 years
  • Stable insulin regimen involving either the use of an insulin pump or use of insulin glargine and short-acting insulin for at least 1 month (NPH or Lente, if part of regimen, used only in the morning)
  • HbA1c < 10.0%
  • BMI between the 5th and 95th percentile for age and sex
  • No severe hypoglycemia episodes within the past 2 weeks
Exclusion Criteria:
Excluded if not included above.
Description of Study Protocol:


Recruitment methods not described.


Randomized Controlled Trial.

Blinding used (if applicable)

Not used - lab tests.

Intervention (if applicable)

Study consisted of 2 randomized 24-hour clinical research center admissions separated by 1 - 4 weeks.  Subjects studied during a 75-minute exercise session consisting of four 15-minute periods of walking on a treadmill to target heart rate of 140 bpm and three 5-minute rest periods, and studied on a sedentary day.

Statistical Analysis

Exercise versus sedentary day glucose concentrations were compared separately using repeated measures regression.  Logistic regression was used to identify factors associated with hypoglycemia and/or treatment for low glucose during exercise.  Factors considered in these models included baseline glucose, age, sex, insulin route, A1c, BMI, self-reported days with at least 1 hour of exercise during a typical week, and estimated level of cardiovascular fitness.  Repeated measures regression treating time as a linear continuous factor was used to test for changes in the concentration of growth hormone, norepinephrine, cortisol and glucagon.  ANCOVA was used to compare changes between subjects whose glucose did versus did not drop <70 mg/dl during exercise adjusting for the baseline concentrations.  Logarithm transformation was used for norepinephrine and cortisol and a square root transformation for growth hormone to reduce the skewness of the distributions.

Data Collection Summary:

Timing of Measurements

Blood measurements taken before, during and after exercise.

Dependent Variables

  • Blood samples analyzed for blood glucose and plasma glucagon, cortisol, growth hormone, epinephrine and norepinephrine concentrations

Independent Variables

  • Exercise day or sedentary day 

Control Variables

  • Baseline glucose
Description of Actual Data Sample:

Initial N: 50 subjects, 44% female

Attrition (final N):  46 subjects completed full exercise session (92%).  2 subjects had unavailable baseline glucose.

Age:  mean age 14.8 +/- 1.7 years

Ethnicity:  90% Caucasian, 4% African American, 2% Hispanic, 4% Asian   

Other relevant demographics:  duration of diabetes was 7.0 +/- 3.7 years 


Location:  United States 


Summary of Results:

Other Findings

In 83% of subjects, plasma glucose concentration dropped at least 25% from baseline, and 15 (30%) of subjects became hypoglycemic (<60 mg/dl) or were treated for low glucose either during or immediately following the exercise session.

The incidence of hypoglycemia and/or treatment for low glucose varied significantly by baseline glucose, occurring in 86% vs 13% vs 6% of subjects with baseline values <120, 120 - 180, and >180 mg/dl, respectively (P < 0.001).

Exercise-induced increases in growth hormone and norepinephrine concentrations were marginally higher in subjects whose glucose dropped <70 mg/dl.

Treatment of hypoglycemia with 15 g of oral glucose resulted in only about a 20-mg/dl rise in glucose concentrations.  

After controlling for baseline glucose, no other factors were associated with the risk of hypoglycemia including age (P = 0.71), sex (P = 0.64), BMI (P = 0.38), duration of diabetes (P = 0.52), A1c (P = 0.39), insulin route (multiple daily injections versus pump, P = 0.65), treadmill workload required to raise heart rate to 140 bpm (P = 0.49), and self-reported days of exercise in a typical week (P = 0.91).

Author Conclusion:
In youth with type 1 diabetes, prolonged moderate aerobic exercise at the time of day for after school activity and consistent with federal recommendations for physical activity results in a consistent ~40% reduction in plasma glucose and the frequent occurrence of hypoglycemia when preexercise glucose concentrations are <120 mg/dl.  Moreover, treatment with 15 g of oral glucose is often insufficient to reliably treat hypoglycemia during exercise in these youngsters.  Consequently, 30 - 45 g of oral glucose may be a more appropriate amount of carbohydrate to treat hypoglycemia during exercise in children and adolescents with type 1 diabetes.
Funding Source:
Reviewer Comments:
Large sample size.
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? Yes
  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? Yes
  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? 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.) 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? Yes
  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? 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? 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? 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