What Blood Glucose Levels Should You Exercise Safely At?

Whether you have Type 1 or 2 Diabetes, exercise is very much core to the lifestyle management of diabetes. In fact whether you have diabetes or not, exercise is essential for health & well being.

Managing blood glucose during exercise can be a real challenge. Hypoglycemia occurs often during exercise. This is the greatest risk of exercise for people who have diabetes, especially for those who take insulin.

Understanding Exerciseimage of a woman running, exercise is one of the best forms of controlling your diabetes from Diabetes Insight, Cork, Ireland

To understand the effect of exercise on blood sugar levels, you need to understand exercise. During exercise, the demand for fuel increases and the body responds accordingly.

  • Glucose stored in the muscle is burned very quickly.
  • At about the same time, glucose stored in the liver is released into the bloodstream (like fast fuel injection).
  • Fat is released from special cells called adipocytes. This fat along with glucose makes its way through the bloodstream to the muscles to be used for fuel.

Blood Glucose Levels & Exerciseimage of a man swimming, exercise is one of the best forms of controlling your diabetes from Diabetes Insight, Cork, Ireland

Because of these factors, a person with Type 1 Diabetes must consider the following:

Hypoglycaemia (low blood glucose) is more likely to occur with exercise because:

  • The blood stream, liver and muscles ‘burn up’ glucose to release energy
  • The cells of the muscles become more sensitive to insulin for up to 12-16 hours after exercise, particularly after very intense exercise and or prolonged exercise. Some people may hypo during or immediately after exercise or can even hypo many hours later, overnight or the next morning
  • Muscles that are exercised can continue to take up glucose without insulin
  • Extra glucose is moved from the bloodstream to replace liver and muscle stores

Hyperglycaemia (high blood glucose) can occur:

  • After brief, very intense exercise such as competitive sports, there is an increase in the level of the hormone adrenaline.  Adrenaline  stimulates the release of glucose from the liver. Blood glucose may later fall.
  • When blood glucose levels are high (15mmol/L) the body may start producing ketones, indicating that there is not enough insulin in the body.  In this situation, exercise will not help to reduce glucose levels, but rather may cause them to increase further. Usually, extra insulin is needed. Hence the reason why we would not recommend anyone to exercise with blood glucose levels of 15mmol/l or over.

Why Do Blood Glucose Levels Go Up After Exercise? family cycling, keeping fit

When you exercise your muscles need more glucose to supply energy. In response, your liver increases the amount of glucose it releases into your bloodstream. Remember, however, that the glucose needs insulin in order to be used by your muscles. So if you do not have enough insulin available, your blood glucose levels can actually increase right after exercise. Basically, stimulated by the demand from your exercising muscles, your body is pouring glucose into your bloodstream. If you do not have enough insulin available to “unlock the door” to your muscles, the glucose cannot get into your muscles to provide needed energy. The end result is that glucose backs-up in your bloodstream, causing higher blood glucose readings.

Monitor, Monitor, Monitor!

Monitoring blood glucose levels pre, during and post exercise can feed back information for you to make the necessary insulin adjustments, look at food intake and see how the body responds to exercise. Each type of exercise produces a different outcome, so it is important before you embark on any type of exercise regime that you consult with your diabetes team first.

Factors such as the duration and intensity of your exercise and your current blood glucose level can help you work out how much extra carbohydrate to eat and if you need to reduce your insulin dose.

Avoiding Hypoglycemia during exercisedietary_tips

  • You may need to reduce your insulin dose before or after exercise or at bedtime. Speak to your doctor or diabetes educator about how to do this safely
  • Check your blood glucose before, during and after exercise
  • Carry glucose such as jelly beans or Lucozade or sports drink to treat a hypo
  • Make sure your BGL is above 6mmol/L before starting exercise
  • Avoid injecting into the arms or legs as your insulin may work more quickly and increase the risk of a hypo The rate of absorption is more consistent when injecting into the abdomen or buttocks
  • Replenish your liver glucose stores by eating extra carbohydrates after exercising
  • Prevent delayed hypoglycaemia overnight or on waking by having a carbohydrate snack before bed

Dos and don’ts of exercise

  • Never completely omit insulin or hyperglycaemia and ketones could develop. If your blood glucose is high (over 15 mmol/L) and ketones are present or blood glucose is over 20 mmol/L do not exercise. Take extra insulin and delay exercise. You may need to implement the sick day rules given to you by your diabetes team and to contact them also.
  • If you have diabetes complications you need to take some precautions as your ability to tolerate exercise may be reduced or some complications could be worsened by some types of exercise. Speak to your doctor about any exercise you should avoid or modify. For example, avoid straining and jarring exercises if you have retinopathy.
  • If you have had type 1 diabetes for 15 years or more, are aged over 35, have risk factors for heart disease, or have diabetes complications, you should have a check up with your doctor before starting any new exercise. This should include ECG, blood pressure, feet, kidney, eye checks, autonomic nerve function. These checks are also part of your annual diabetes check.
  • Warm up and cool down
  • Wear well fitting sports shoes, that have adequate shock absorption
  • Drink plenty of fluid to keep hydrated

Exercise Services Available at Diabetes Insight

Diabetes Insight has a specialist interest in sports and exercise in people with diabetes, whether it be at beginners, amateur &/or professional level.

We work closely with gyms across Ireland and offer training programmes, support & guidance when dealing with people with diabetes.

Diabetes Insight has a 12 week fitness programme for people with all types of diabetes, in affiliation with Studio Fitness in Marina Commercial Park, Cork. For further information, please click here

We also provide 1-2-1 consultations with a personal fitness trainer and specialist nurse from our centre in Cork and our West Cork offices also.

Contact Us

To contact us on any of the above, please email us on diabetesinsightireland@gmail.com &/or ring us on (086) 1739287.