There are different sorts of muscle in the body and they have different functions. Skeletal muscles are the muscles that, for example, are used for movement in your arms and legs.
Skeletal muscles store glucose as glycogen (Figure 4) and are able to use glucose as a fuel. Insulin stimulates muscles to take up glucose, and while exercising, as muscles are active, the glucose is released from endogenous glycogen and also taken up from the blood. Thus exercise is important for maintaining healthy levels of blood glucose.
Question: People with diabetes who exercise can find that their blood glucose levels can fall too low. How does this happen?
Exercise lowers blood glucose levels as muscles use glucose as a fuel. Insulin circulating in the body also lowers blood glucose levels by making the liver take it up. The two factors together can lower blood glucose levels below levels required to support other tissues, e.g. the brain.
In people without diabetes the body regulates the amount of insulin produced by the pancreas, and production decreases when exercise takes place to stop the blood glucose level from going too low. When tablets are taken for diabetes to stimulate the pancreas to produce insulin, or insulin itself is taken as an injection, then adjustments to therapy may be required when exercise is undertaken. This may not be possible at short notice. If too much insulin is available and insufficient food is eaten when exercise takes place, then the blood glucose level will fall too low and hypoglycaemia results.
Occasionally exercise can result in a high blood glucose level (hyperglycaemia) in people with diabetes. This happens if too little insulin is available when exercise takes place. The various hormones that are released on exercising, such as adrenalin, can act to increase the blood glucose level.
Case study 2 shows how difficult it can be to make appropriate adjustments to insulin and food intake when exercising.
Case study 2
Yusuf Idris is aged 18 years. He was diagnosed with diabetes and started on insulin two months ago. He has been a keen badminton player since the age of 10. His uncle was in the Malaysian national team. Last week he played a match for the first time since his diagnosis. He took his usual insulin at lunch time but ate a large portion of apple pie to try and stop his glucose going too low while playing badminton that afternoon. At the end of the first game he began to feel tired and started to miss shots. He was not sure if it was because he had not played for a while but he checked his blood glucose level and found it to be only 2 mmol/l. For this week's match he has come determined to make sure his blood glucose does not go low again. He has cut his lunchtime insulin dose, eaten extra carbohydrate and brought along a snack to eat at the end of each game. He has also decided to check his glucose level at the start of playing and between games so he can have a better idea about what is happening.