DM: Physical Activity (2007)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To examine the effect of late afternoon exercise on the frequency of overnight hypoglycemia in children with type 1 diabetes by comparing glucose data collected on a day of exercise with that collected on a sedentary day in an inpatient clinical research center setting.
Inclusion Criteria:
  • Age 10 to 18 years
  • Clinical diagnosis of type 1 diabetes of > 18 months duration
  • On a stable insulin regimen for at least 1 month, involving either use of an insulin pump or multiple daily injections of Glargine or Lispro insulin or Aspart insulin 
  • HbA1c level <10%
  • BMI between 5th and 95th percentile for age and gender
  • Body weight > 36 kg
  • Normal hematocrit level
  • Normal thyroid function
Exclusion Criteria:
  • Had asthma that was medically treated in the previous year
  • Were currently using glucocorticoids or beta blockers
  • Had used pseudoephedrine within 48 hours
  • Had experienced severe hypoglycemia (seizure or loss of consciousness) within the previous 2 weeks
  • Had an active infection
  • Anticipated a significant change in exercise regimen between admissions
  • Had another medical condition or were using a medication that in the judgment of the investigator could affect completion of the exercise protocol
Description of Study Protocol:


Methods not specified.


Randomized Crossover Trial.

Blinding used (if applicable)

Not used - lab tests.

Intervention (if applicable)

Study consisted of 2 inpatient stays lasting 24 hours and separated by 1 -4 weeks.  1 stay with the 75 minute exercise session on treadmill or sedentary day.  Order of exercise and sedentary days were determined at random.

Statistical Analysis

Proportions of subjects developing hypoglycemia overnight on the exercise and sedentary nights were compared using generalized estimating equations, controlling for possible period effect and repeated measures from same subject.  Mean overnight glucose values were compared using repeated-measures regression.  Multivariate analysis for overnight hypoglycemia included a term for exercise versus sedentary visits and used a stepwise procedure to select among the following factors:  gender, age, HbA1c level, insulin route, total daily insulin dose, average bolus dose, BMI and self-reported frequency of at-home exercise.  Sample size was estimated at 50 subjects to have 90% power.

Data Collection Summary:

Timing of Measurements

Blood samples checked before, during and after exercise, as well as before bed and overnight.

Dependent Variables

  • Blood glucose measured through blood samples analyzed using hexokinase enzymatic methods and One-Touch Ultra Meter

Independent Variables

  • Exercise session day or sedentary day
  • Meals and bedtime snacks of similar caloric and carbohydrate content were consumed on both days

Control Variables

  • First or second visit (period effect)
Description of Actual Data Sample:

Initial N: 50 subjects, 44% female

Attrition (final N):  46 completed full exercise session (92%).

Age:  mean age 14.8 +/- 1.7 years

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

Other relevant demographics:  mean duration of diabetes 7.0 +/- 3.7 years, mean HbA1c 7.8 +/- 0.8%


Location:  5 clinical sites in the United States


Summary of Results:


  Development of Hypoglycemia, n (%) P value = 0.009
Exercise Night Only 13 (26%)  

Sedentary Night Only

3 (6%)


Neither Night 23 (46%)  

Both Nights

11 (22%)


  Hypoglycemia Index, mean +/- SD P value = 0.07
Exercise Night 2.3 +/- 3.0  

Sedentary Night

1.5 +/- 3.2


Intrasubject Difference 0.8 +/- 3.2  

  Development of Hyperglycemia, n (%) P value = 0.008
Exercise Night Only 1 (2%)  

Sedentary Night Only

9 (18%)


Neither Night 24 (48%)  

Both Nights

16 (32%)


  Hourly-half hour blood glucose levels, mean +/- SD P value = 0.003
Exercise Night 131 +/- 58  

Sedentary Night

154 +/- 69


Intrasubject difference -23 +/- 52  

Other Findings

During exercise, plasma glucose levels fell in almost all subjects; 11 (22%) developed hypoglycemia.

Mean glucose level from 10 pm to 6 am was lower on the exercise day than on the sedentary day (131 vs 154 mg/dl; P = 0.003).

Hypoglycemia developed overnight more often on the exercise nights than on the sedentary nights (P = 0.009), occurring on the exercise night only in 13 (26%), on the sedentary night only in 3 (6%), on both nights in 11 (22%) and on neither night in 23 (46%).

Hypoglycemia was unusual on the sedentary night if the pre-bedtime snack glucose level was > 130 mg/dl. 

Author Conclusion:

The findings of this study support the well-recognized clinical observation that exercise has benefit in lowering plasma glucose levels both during and after exercise in children with type 1 diabetes.  Hyperglycemia was more common during the sedentary night, and lower glucose levels were sustained for many hours after exercise on the exercise day compared with the sedentary day.  Our findings also support the use of flexible diabetes management regimens that attempt to adjust food intake and insulin dosing on evenings after exercise to reduce the risk of overnight hypoglycemia.  The current FDA-approved CGMS are not practical for day-to-day use in children and lack sufficient accuracy in the low glucose range to serve as effective guides to overnight glucose control.  Consequently, frequent meter glucose testing at bedtime and in the middle of the night remains the only currently effective means of adjusting treatment regimens to minimize the risk of exercise-induced nocturnal hypoglycemia.

Funding Source:
University/Hospital: DirecNet Study Group
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? 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? 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