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Author: Dr Matthew Campbell | PhD ACSM-CEP MIFST RNutr FHEA BSc hons.
Read time: 5 minutes
The objective of adjusting insulin doses before exercise is to prevent hypoglycaemia during a match whilst minimising hyperglycaemia during the run up to kick off. Important factors to consider are the insulin dose, where insulin is administered, the blood glucose level before exercise, the type, amount, and timing of the last meal or snack eaten, the intensity and duration of the match (difficult opposition? Will you play a full 90 minutes?), as well as recent hypos1.
What is the best blood glucose level to have during football?
Blood glucose levels are individual; some people feel (and perform) worse with higher glucose levels before exercise, whereas others don’t. The consensus amongst the medical research community is that a reasonable starting range for most footballers would be between 5-10 mmol/L depending on whether blood glucose levels usually decrease, stay stable, or increase as well as the expected difficulty of the match and the likely duration of play (are you a super-sub?). This range generally balances performance considerations against the risk of hypoglycaemia, although achieving and maintaining glucose levels in this range can be very challenging. If starting exercise below 5 mmol/L it is recommended that you eat 10-20 grams of glucose beforehand and delay (if possible) the start of exercise until glucose levels are more than 5 mmol/L. If glucose levels are between 5-10 mmol/L then most people will be ok to start playing football, although some people may see a rise in glucose levels during the match. If glucose levels are above target (10-15 mmol/L) most people will expect a further rise in glucose during a game. Importantly, if glucose levels are above 15 mmol/L it is recommended to check blood ketone levels; if ketones are elevated up to 1.4 mmol/L then a small correction dose might be needed; if ketones are elevated over 1.4 mmol/L then exercise should be suspended and glucose management should be initiated rapidly.
What should I do if I struggle to avoid a hypo during a game?
People who tend to develop hypoglycaemia during exercise will usually turn to eating carbohydrates as a technique to avoid it. There is an issue with this, however. Firstly, if you find yourself eating lots of carbohydrate to prevent glucose lows the extra calories eaten might contribute to unwanted weight gain in the long-term. Secondly, eating carbohydrates does not necessarily tackle the underlying cause of a hypo.
The reason for the fall in glucose during exercise is at least partly due to high insulin levels. Whereas insulin levels fall in people without type 1 diabetes (in order to preserve blood glucose), in people with type 1 diabetes insulin levels are the result of the previously administered insulin dose or the rate of insulin being infused by an insulin pump. Irrespective of the method of insulin delivery, once insulin is in the body, it is unregulated and does not decrease in response to exercise; this results in excessive glucose removal from the blood. Even if individuals with insulin pumps half their basal insulin rates up to an hour before exercise, circulating insulin in the body does not decrease sufficiently before the start of exercise. Moreover, insulin levels tend to increase during exercise even when insulin pump rates are reduced because of changes in blood flow2. Although aggressively lowering insulin levels through reducing insulin administration or skipping an insulin dose can prevent hypoglycaemia during exercise3,4, this often causes hyperglycaemia and raises ketone levels before and during exercise5. For people using insulin pumps, a basal rate reduction, rather than a suspension can be attempted 60-90 minutes before the start of a game. An 80% basal reduction at the onset of exercise helps to mitigate hyperglycaemia after exercise more effectively than basal insulin suspension and appears to reduce the risk of hypoglycaemia both during and after the activity. For individuals treated with insulin pens, mealtime insulin dose can be reduced by about 50% when taken with a carbohydrate-based meal around 1 hour before the start of a game3. However, it must be stressed that people respond very differently to any strategy and there is no one-size fits all approach.
What should I do if struggle to avoid hyperglycaemia during a game?
High blood glucose levels can raise ketone levels, increases the perception of effort, and reduces performance. As discussed elsewhere, carbohydrate intake before a game is important for both performance and managing the risk of hypoglycaemia. If hyperglycaemia is an issue prior to a match, try eating earlier in the day and maintaining a normal mealtime insulin dose; most mealtime insulins peak in strength by 2-3 hours meaning that a normal insulin dose can be administered with an earlier meal and taking a small snack before exercise omitting insulin – this may reduce the risk of starting exercise with high glucose levels whilst ensuring adequate carbohydrate availability and lowered insulin levels for the game. If hyperglycaemia is a continual issue, starting glucose management preparations earlier in the day gives a longer window to achieve glucose targets. Unless glucose levels are above 10 mmol/L it is not recommended to take a correction dose of insulin because of the increased risk in developing hypoglycaemia.
If you are interested in learning how to tailor strategies like the ones presented to your own individual requirements, contact Matthew at: firstname.lastname@example.org
- Bally L, Laimer M, Stettler C. Exercise-associated glucose metabolism in individuals with type 1 diabetes mellitus. Current opinion in clinical nutrition & metabolic care. 2015;18(4):428-433.
- McAuley SA, Horsburgh JC, Ward GM, et al. Insulin pump basal adjustment for exercise in type 1 diabetes: a randomised crossover study. Diabetologia. 2016;59(8):1636-1644.
- West DJ, Morton RD, Bain SC, Stephens JW, Bracken RM. Blood glucose responses to reductions in pre-exercise rapid-acting insulin for 24 h after running in individuals with type 1 diabetes. Journal of sports sciences. 2010;28(7):781-788.
- Campbell MD, Walker M, Trenell MI, et al. Large pre-and postexercise rapid-acting insulin reductions preserve glycemia and prevent early-but not late-onset hypoglycemia in patients with type 1 diabetes. 2013;36(8):2217-2224.
- Berger M, Berchtold P, Cüppers H, et al. Metabolic and hormonal effects of muscular exercise in juvenile type diabetics. Diabetologia. 1977;13(4):355-365.