- ACRONYMS AND DEFINITIONS
- ADA - American Diabetes Association
- DKA - Diabetic ketoacidosis
- EASD - European Association for the Study of Diabetes
- GI - Glycemic index
- ISPAD - International Society for Pediatric and Adolescent Diabetes
- T1DM - Type 1 diabetes mellitus
- TYPES OF EXERCISE
- Aerobic exercise - exercise that involves continuous, repeated movements of large muscle groups. Examples include walking, cycling, jogging, and swimming. During aerobic exercise, muscles utilize energy pathways that require oxygen. If energy requirements exceed oxygen supply, anaerobic pathways are then utilized.
- Anaerobic exercise - exercise that involves alternating between short bursts of vigorous activity and periods of rest. Examples include weightlifting, sprints, and interval training. Anaerobic exercise utilizes energy pathways that do not require oxygen (e.g. muscle phosphagens, muscle glycogen). These pathways can be depleted quickly if activity is prolonged (> 30 seconds), causing aerobic sources of energy to become involved.
- Mixed exercise - exercise that is a combination of aerobic and anaerobic exercise. Examples include team sports like basketball and soccer. [1,2]
- EFFECTS OF EXERCISE ON GLUCOSE AND INSULIN LEVELS
- When estimating the effect of exercise on glucose and insulin levels, a number of variables must be considered, including insulin dose, carbohydrate consumption, exercise type and duration, and individual conditioning. The physiologic responses discussed below are given in general terms and may vary by individual.
- Aerobic exercise
- During aerobic exercise, muscles increase glucose uptake by as much as fifty times, an effect that is independent of insulin. In order to keep blood glucose levels steady (70 - 110 mg/dl), insulin levels decrease, and counter-regulatory hormones (e.g. glucagon, cortisol, growth hormone, norepinephrine) increase. Diabetics who use insulin may have inappropriately high insulin levels because exogenous insulin does not respond to counter-regulatory hormones. To prevent hypoglycemia, carbohydrates must be consumed, and/or insulin doses must be reduced.
- Anaerobic exercise
- During anaerobic exercise, muscles utilize phosphagens and glycogen for energy. Insulin levels decline, but the effect is less than with aerobic exercise, and glucose levels tend to rise secondary to counter-regulatory hormones. These combined effects often cause blood sugars to increase during anaerobic activity.
- Mixed exercise
- During mixed exercise, the effects of anaerobic and aerobic exercise offset each other, and blood glucose levels tend to stay steady
- After exercise, insulin-independent glucose uptake by muscles remains elevated for approximately two hours. Insulin sensitivity also increases and remains high for about 24 hours; prolonged strenuous exercise can increase insulin sensitivity for up to 48 hours. During this time, diabetics who use insulin are at increased risk of hypoglycemia if they do not adjust their doses. The greatest risk is seen during the night following afternoon exercise (nocturnal hypoglycemia). [1,2]
- GLUCOSE/CARBOHYDRATE ADJUSTMENTS FOR EXERCISE
- The table below gives recommendations for carbohydrate consumption based on glucose levels checked before exercise. The recommendations are derived from the ADA position statement on exercise and expert opinion. A number of variables affect glucose response to exercise, so it is important to tailor these recommendations to the individual's needs.
|Carbohydrate adjustments for exercise|
Pre-exercise glucose: < 90 mg/dl (< 5 mmol/L)
Pre-exercise glucose: 90 - 150 mg/dl (5 - 8.3 mmol/L)
Pre-exercise glucose: 150 - 250 mg/dl (8.3 - 13.9 mmol/L)
Pre-exercise glucose: 250 - 350 mg/dl (13.9 - 19.4 mmol/L)
Pre-exercise glucose: > 350 mg/dl (> 19.4 mmol/L)
- INSULIN ADJUSTMENTS FOR EXERCISE
- To avoid hypoglycemia, diabetics may need to adjust their insulin doses around exercise, particularly aerobic exercise. Recommendations from the ADA and other experts are given in the table below. In 2020, the EASD/ISPAD published detailed guidelines for type 1 diabetics with continuous or intermittently-scanned glucose monitoring systems (see EASD/ISPAD recommendations for more).
- When starting or changing an exercise regimen, diabetics should closely monitor their blood sugars before, during, and after exercise
|Suggested reduction in bolus (premeal) insulin if given within 90 minutes prior to exercise|
|30 minutes of exercise||Bolus insulin dose reduction|
|Intense mixed exercise||No dose reduction|
|60 minutes of exercise||Bolus insulin dose reduction|
|Intense mixed exercise||N/A|
|Prevention of nocturnal hypoglycemia
(particularly for exercise performed in afternoon or evening)
For first meal after exercise (within 90 minutes)
|Suggested reductions in basal insulin for prolonged exercise (> 30 minutes)|
Patients using multiple injections a day
Patients using insulin pumps
- EASD/ISPAD recommendations for adjusting insulin
- In 2020, the EASD/ISPAD published detailed recommendations for adjusting insulin before, during, and after exercise in type 1 diabetics with continuous or intermittently-scanned glucose monitoring systems. A link to those guidelines is provided below, along with a list of important pages.
- EASD and ISPAD T1DM Recommendations for Insulin and Exercise [pdf]
- Risk assessment
- Exercise experience and hypoglycemia risk assessments [page 1381, figure 2]
- Pre-exercise recommendations [page 1379]
- During exercise recommendations [page 1380]
- Post-exercise recommendations [page 1381]
- Children and adolescents
- General recommendations [page 1382]
- Pre-exercise recommendations [page 1383]
- During exercise recommendations [page 1384]
- Post-exercise recommendations [page 1385]
- KETONE TESTING
- In diabetics, a lack of insulin causes the liver to secrete ketone bodies (β-hydroxybutyric acid, acetoacetate), which cells use as an alternative to glucose for energy. A buildup of ketone bodies can lead to diabetic ketoacidosis (DKA).
- Diabetics can test for ketone bodies in their blood or urine. Blood testing is available with certain glucose meters, and urine testing can be done with dipsticks. The table below provides a general estimate of ketone body levels and how they compare in blood and urine. Cutoff values for urine can vary by manufacturer.
- Ketone testing is more important in type 1 diabetics because they are at greater risk for DKA. Ketone levels > 1.5 mmol/L should be addressed immediately by checking a blood sugar and administering corrective insulin.
|Blood value (mmol/L)||Urine value|
|0.6 - 1.5||Small to moderate|
|1.6 - 3.0||Moderate to large|
- GLYCEMIC INDEX AND EXERCISE
- The glycemic index (GI) is a measure of how much blood sugar levels tend to rise after ingesting various carbohydrate-containing foods (see glycemic index for a full discussion). Foods are grouped based on their GI using the following categories:
- High GI (> 70) - food causes a quick rise in blood sugar that is shorter in duration
- Low GI (< 55) - food causes a slower rise in blood sugar that is longer in duration
- Medium GI (56 - 69) - the effect is somewhere between high and low foods
- General considerations for consuming carbohydrates based on their GI are given in the table below, along with GI food resources
|Glycemic index (GI) and exercise|
GI food resources
Low GI foods
High GI foods
- 1 - PMID 27926890 - Physical Activity/Exercise and Diabetes: A Position Statement of the American Diabetes Association, Diabetes Care 2016
- 2 - PMID 28126459 - Exercise management in type 1 diabetes: a consensus statement, Lancet Diabetes Endocrinol 2017