by Jean-Jacques Grimm
The importance of changing the injection site when doing sports or being physically active continues to be actively debated.
Various factors speed the rate of insulin absorption, including increased blood flow to the injection site due to exercise, increased ambient temperature21-22 or local massage.23 There is considerable intra-individual variation in insulin absorption rate, up to 15 per cent difference for the same site from day to day24, and it has been shown that insulin (NPH, soluble) absorption from sites in the abdomen is significantly more rapid than that from sites in the thigh. This difference is much smaller with the short-acting insulin analogues and does not have clinical relevance. 24 In the 1970s, experimental data25 showed that muscular activity speeds insulin absorption from an exercising limb. This was considered at least part of the explanation for the increased insulin action during exercise.
Many considered that injecting the insulin in a non-exercising area would help to prevent hypoglycemic attacks during and after exercise, but Kemmer et al 26 showed that this strategy did not prevent effort-related hypoglycemia. Because of the difference between various injection sites, using a different site on an on-off basis specifically for athletic activity is not recommended — this would simply add another variable. Because absorption rates vary from site to site, it is sensible to restrict short-acting insulin injections to one site. If the abdomen is used routinely, this obviates worries about varying insulin absorption rates from an exercising limb. If the basal insulin (slow acting) is injected into the thigh, we suggest not changing the injection site, but eventually decreasing the dosage, as described later in this chapter.
Intramuscular injection of insulin is a cause of hypoglycemia27 independent of exercise. It is clear that this risk is increased if the injection is followed by exercise. The physically active diabetic person must be informed of the need to avoid intramuscular injections and to take particular care with the injection technique.
Short needles (8.0 mm) have been marketed with the claim that they avoid the risk of intramuscular injection and obviate the need to pinch the skin. Unfortunately, it was proposed at the same time to inject without folding the skin. However, it seems that even with 8.0 mm needles some insulin injections can be intramuscular when injected without a skin-fold in lean persons. Furthermore, short needles expose the patient to the risk of intradermal injections or insulin leaks when the technique is not perfect. Consequently, we suggest routinely using a skin-fold when injecting insulin, whatever the length of the needle used (5.0,8.0, 10.0 or 12.7 mm).
Recommendations for exercise and insulin injections
- Inject the insulin into the usual location.
- Take special care with the injection to make sure it is not intramuscular.
- Learn to adapt (decrease) the insulin dose, depending on the type, duration and timing of exercise.
- Use frequent blood glucose measurements, especially during unfamiliar activities
The risk of hypoglycemia during exercise in the insulin-dependent diabetic person was expertly described, a few years after the discovery of insulin, by the British physician R.D. Lawrence28. In contrast to the non-diabetic subject, where the insulin level falls shortly after exercise commences, the insulin level in the person with diabetes is governed mainly by the amount and timing of the last injection. It follows that he or she must anticipate strenuous activities and make appropriate reductions in the insulin dose. If this is not done, the only option is to take extra carbohydrate to try to compensate for excess circulating insulin.
The fear of hypoglycemic comas has often been the cause of discrimination against children with diabetes, leading to their exclusion from gymnastics or summer camps. Some children with diabetes decide spontaneously not to participate in group or team activities, for fear of upsetting their team-mates because of the need for regular blood glucose checks and the necessity to eat snacks at precise times, or because a hypoglycemic episode might upset the team performance.
Hypoglycemia may happen during exercise, but also or up to 12-14 h or even longer after the end of the effort.29-30 Late-onset hypoglycemia is explained both by the body’s need to replenish glycogen stores and by a sustained increase of the tissue sensitivity to insulin. When the exercise sessions continue for several days, insulin needs usually decrease progressively from day to day.
Repeated episodes of hypoglycemia lead to an unfortunate vicious circle whereby there is decreased hypoglycemic awareness, leading to the risk of more hypoglycemia.29 Furthermore, physical activity makes the recognition of hypoglycemia difficult because sweating and tachycardia due to physical effort can mask similar signs warning of impending hypoglycemia.
When hypoglycemia happens during exercise despite all efforts to avoid it, it is often extremely difficult to treat. Very often the activity has to be temporarily suspended, and the amount of carbohydrate required to correct the blood glucose may be unusually high, often 30-40 g or more. Exercise-onset hypoglycemia tends to be recurrent and more carbohydrate may be needed within half an hour (preferably after a repeat blood glucose test).
21. Vora JP. Relationship between absorption of radiolabeled soluble insulin, subcutaneous blood flow and anthropometry. Diabet. Care 1992: 9: 236-239.
22. Sindelka G, Heinemann L, Berger M. Frenck W, Chantelau E. Effect of insulin concentration, subcutaneous fat thickness and skin temperature on subcutaneous insulin absorption on healthy subjects. Diabeto!ogia 1994: 37: 377-380.
23. Kohlendorf K Bojsen J, Deckert T. Absorption and miscibility of regular porcine insulin after subcutaneous injection of insulin-treated diabetic patients. Diabet. Care 1983; 6: 6-9.
24. Braak EW. Woodworth JR, Bianchi R et al. Injection site effects on the pharmacokinetic and glucodynamics of insulin lispro and regular insulin. Diabet Care 1996; 19(12): 1437- 1440.
25. Koivisto VA, Felig P. Effects of leg exercise on insulin absorption in diabetic patients. New Engl. 1. Med. 1978; 298: 77-83.
26. Kemmer FW, Berchtold P. Berger M et al. Exercise-induced fall of blood glucose in insulin-treated diabetics unrelated to alteration of insulin mobilization. Diabetes 1979; 28: 1131-1137.
27. Frid A, Ostman J, Linde B. Hypoglycaemia risk during exercise after intramuscular injection of insulin in the thigh in IDDM. Diabet. Care 1990: 13: 473-477.
28. Lawrence RD. The effect of exercise on insulin action in diabetes. BI: Med. 1. 1926; 1: 648-650.
29. McDonald MJ. Post-exercise late-onset hypoglycaemia in insulin-dependent diabetic patients. Diabet. Care 1987; 10: 584–588.
30. Sonnenberg GE. Kemmer F\V, Berger M. Exercise in type 1 (insulin-dependent) diabetic patients treated with continuous subcutaneous insulin infusion: prevention of exercise-induced hypoglycemia. Diabetologia 1990; 33: 696-703.
The new edition of this acclaimed title provides a practical guide to the risks and benefits of undertaking sport and general exercise for patients with diabetes.
Fully updated to reflect the progress and understanding in the field, the book features new chapters and material on insulin pump therapy and exercise, physical activity and prevention of type 2 diabetes, dietary advice for exercise and sport in type 1 diabetes, and fluid and electrolyte replacement.
Next week: New Joslin Diabetes Deskbook excerpt
For more information on this book and how to get a copy, just follow this link to Amazon.com, Exercise and Sport in Diabetes (Practical Diabetes), Dinesh Nagi 2nd Edition.
Copyright © 2010 by Blackwell Publishing Ltd, UK