People with type 1 diabetes tend to have three main problems when exercising. These are; 1) problems controlling blood glucose during and immediately following exercise, 2) unexplained severe hypoglycaemia, particularly at night following exercise, 3) reduced performance due to excessive fatigue and reduced muscle strength. These problems arise because the usual physiological changes in insulin and counter-regulatory hormones do not occur. These deficiencies can be overcome when changes to insulin dose and nutritional intake are made in line with the normal expected physiological responses to the exercise being performed. Where this is achieved, people with type 1 diabetes can undertake exercise safely and effectively. Here we describe a simple management plan for helping people with type 1 diabetes to exercise safely. We have divided this into 1) assessment of the patient, 2) initial advice, 3) further advice
Assessment of the patient
Injection techniques and sites: Checks should be make of injection sites for lipohypertropy, and injection techniques to ensure that “air shots” of at least 2 units are being performed to clear any bubbles out of the needle before injections and that insulin vial re-suspension is being carried out if the patient is on NPH insulin. Needle sizes should ideally be 4 or 5mm, and injection into areas that will be used in the forthcoming exercise are to be avoided (eg. thighs before cycling) because the increased blood flow will increase insulin absorption.
A detailed history of the exercise program: The type, duration and intensity of exercise will determine blood glucose fluxes both during and after exercise. Endurance events will tend to lower glucose. Anaerobic or intense exercise will tend to increase glucose during and sometimes after exercise.
A detailed history of hypoglycaemic symptoms: A detailed history of hypoglycaemia should be obtained at each visit. Many of this will occur at night, therefore information from partners should be requested, and scheduled 2 am and 4 am blood glucose checks performed.
When patients first start increasing their exercise levels, our practice is to advise maintaining the same insulin doses, and to manage blood glucose with increased CHO intake. The three areas that we address initially are 1) when and when not to exercise, 2) insulin regime, 3) simple carbohydrate replacement.
- When and when not to exercise:
Clear advice can be given in the form of a flow diagram (figure 1). In particular, hypoglycaemia within the previous 24 hours significantly increases the risk of exercise-induced hypoglycaemia. Therefore patients should be advised not to exercise within 24 hours of severe hypoglycaemia (low blood glucose requiring third party assistance). They should also not exercise within an hour of self-treated hypoglycaemia. Take extra precautions when there has been an episode of self-treated hypoglycaemia within the previous 24 hours. This would include more frequent glucose testing, exercising with an informed partner, and if possible including an anaerobic component to their training because this will tend to raise their blood glucose.
Figure 1: (Click to enlarge) initial algorithm for insulin and carbohydrate management for blood glucose management before, during and after exercise in people with T1D. Carbohydrate and insulin dosages are reviewed at each appointment.If there is hypoglycaemia during exercise, exercise should be discontinued and the hypoglycaemia treated. The individual should wait at least 45 mins before recommencing activity (or until blood sugars are stable). If an episode of severe hypoglycaemia occurs during exercise, then the activity should be stopped altogether due to the high risk of further hypoglycaemia.
When the blood glucose level is greater than 14 mmol/l before exercise, a check should be made for the presence of ketones (capillary or urine). If ketones are present, exercise is contraindicated and supplemental insulin should be considered (1 unit for 2-3mmol glucose reduction). Exercise may be commenced only when ketone free and blood glucose below 14 mmol/l. Where the blood glucose level is greater than 14 mmol/l and ketones are not present, advice depends on timing of the last meal (and, therefore, last quick acting insulin dose).
- If a meal has been eaten in the last 1 – 2 hours, commence exercise but monitor blood glucose closely.
- If the last meal was eaten more than 2 hours ago, then 30% of their usual correction dose should be given.
2. Insulin regimes
Generally, premixed twice-daily insulin regimes incur an increased risk of exercise-induced hypoglycaemia than basal (long-acting background insulin) - bolus (fasting-acting insulin taken when eating) regime. We use fast-acting insulin analogues as part of this regime because their window of action is shorter, and they are therefore associated with a lower risk of late postprandial exercise induced hypoglycaemia. The longer duration of action of the long-acting basal analogues, whilst helpful in routine clinical care, can result in higher insulin concentrations during exercise and an increased risk for hypoglycaemia during endurance exercise. For this reason we consider using twice daily NPH insulin (insulatard (Novo Nordisk), Humulin I (Eli Lilly)) as our first-line basal insulin. On the basis of our experience and one clinical trial , the risk of hypoglycaemia is lower with insulin levemir (Determir) compared to Lantus (Glargine) and therefore this is our next basal insulin of choice.
3. Simple carbohydrate (CHO) replacement regime
Adequate fuel and fluid replacement is one of the most important components in ensuring safe and effective training in people with type 1 diabetes. A common cause of hypoglycaemia and of fatigue during and following exercise is simply insufficient calorie intake. Therefore, all patients should see a dietician for regular review.
Table 1 provides a summary of daily carbohydrate (CHO) recommendations for athletes based on the intensity and duration of training. Athletes with type 1 diabetes have similar nutritional requirements, so this chart can be used for them. This CHO should be spread across the day and if possible be low GI carbohydrate.
|Training Load||CHO Recommendations|
|Very light training (low intensity exercise or skill-based exercise)||3-5 g/kg/day|
|Moderate intensity exercise for 1 hour per day||5-7 g/kg/day|
|Moderate to high intensity exercise for 1-3 hours per day||6-10 g/kg/day|
|Moderate to high intensity exercise for 4-5 hours per day||8-12 g/kg/day|
Table 1: Carbohydrate requirements relating to body mass, exercise intensity & duration.
An initial strategy for managing blood glucose during exercise is to replace the CHO orally that will be used during exercise. In its simplest form, this is a fixed CHO replacement regime. In adults, we initially recommend 15g of CHO for every 30 min of exercise . Although activities vary widely in terms of fuel requirements, this range represents a safe starting point for most patients beginning moderate-intensity exercise. However, it is important for the patient to limit the intensity to mild- or moderate, and to monitor blood glucose at least every 30 min. This regime does not require any adjustment of the insulin dosage for meals or food or correction boluses. If 15g is not enough then this is doubled to 30 g. Further adjustment can be made using equation that take into account body weight or tables that have calculated carbohydrate needs for each sport (see www.excarbs.com).
At the next appointment we propose an assessment of how the basic algorithm has worked for the individual. If this has worked well, simple minor adjustments to the algorithm could be considered depending on how their blood glucose has behaved during exercise. Further education is provided on post exercise management to aid the replenishment of stores, prevention of late hypoglycaemia, and management of post exercise hyperglycaemia.
Whilst our initial approach is to advise maintaining the same insulin doses, and to manage blood glucose with increased CHO intake, changes to fast-acting insulin doses can be undertaken when the exercise is being undertaken within 2 hours of a meal (3 hours if on Human Actrapid). A number of studies have examined insulin dose reductions for exercises of different intensity. This has enabled dose reduction tables to be developed (Table 2).
|% Dose reduction|
|Exercise intensity||30 min of exercise||60 min of exercise|
|Low (<50% MHR or RPE <10)||25||50|
|Medium (51-74 MHR or RPE 10-15)||50||75|
|Moderate (>75 MHR or RPE >15)||75||-|
Table 2: Quick acting insulin dose reduction for exercise for low, medium or moderate intense activity [adapted from reference ]. Intensity of activity is calculated by percentage of maximum heart rate (MHR) or rating of perceived exertion (RPE) on Borg scale.
Reduction in background insulin can however be helpful if patients are undertaking prolonged exercise in the morning, or in afternoon two hours after their meal.
Additional advice for patients on continuous subcutaneous insulin infusion (CSII, insulin pumps)
Administration of insulin via insulin pump should be considered if glycaemic variability around exercise remains a problem with insulin pens. The advantage is that simply disconnecting the pump can significantly reduce circulating insulin, and thus the risk of post exercise hyperglycaemia. We recommend that T1D athletes participating in contact sport (rugby, combat sports) disconnect the pump during the event, and reconnect during the rest interval or at the end of the event. A patient can remain off the pump for an hour without increasing the risk of hyperglycaemia and ketonaemia.
Figure 2: (Click to enlarge) initial algorithm for insulin and carbohydrate management for blood glucose management before, during and after exercise in people with T1D on insulin pump. Carbohydrate and insulin dosages are reviewed at each appointment.Where exercise is planned, our initial advice is to reduce the basal insulin infusion rate by 80% for 60mins before, until end of exercise. If the exercise is planned to be within 1-2hrs of a meal (and hence bolus insulin), the bolus can also be reduced by 50%. During exercise patients should take 0.3 grams /kg /hr of carbohydrate, with this being adapted at a later date dependent on blood sugars.
Post exercise we suggest a 10% decrease in basal rate for the first 4 hours of the night, with this extended to the whole night if high intensity aerobic activity has been done. When exercise is going to be purely anaerobic, we consider an increase in the basal insulin infusion rate by 10% starting 30mins before exercise starts, to 60mins after the training. No changes to night-time rate are made (figure 2).
On-line supplementary websites
^ Arutchelvam V et al. Plasma glucose and hypoglycaemia following exercise in people with Type 1 diabetes: a comparison of three basal insulins. Diabet Med. 2009;26(10):1027-32.
^ Burke LM et al. Carbohydrates for training and competition. J Sports Sci. 2011;29:S17-27.
^ Dube MC et al. Exercise and newer insulins: how much glucose to avoid hypoglycemia. Med Sci Sports Exerc. 2005;37:1276-82
^ Rabasa-Lhoret R et al. Guidelines for premeal insulin dose reduction for postpradial exercise of different intensities and durations in type 1 diabetic subjects treated intensively with a basal-bolus insulin regimen (ultralente-lispro). Diabetes Care. 2001;24:625