Safe and effective exercise with diabetes

Metabolic Control Before Exercise
• Start exercise blood glucose levels should be between 7-12mM (120-210mg/dl).
• Consider ingesting extra carbohydrate at the start if levels are <7.
• For levels >12mM without ketosis delay glucose replacement during exercise until glucose has fallen.
• Avoid exercise if ketosis is present.
Blood Glucose Monitoring Before, During and After Exercise
• Measure blood glucose before, every 30minutes during and at the end of exercise.
• Identify when changes in insulin or food intake are necessary, where possible sudden unaccustomed changes should be avoided e.g. if a reduction in insulin is thought to be required trial a 20% reduction insulin first don’t jump straight to a 75% reduction.
• Learn the glycaemic response to different exercise conditions
Food Intake
• Consume additional carbohydrate as needed to avoid hypoglycaemia. As a general guide for moderate intensity endurance activities high glycaemic index carbohydrate should be consumed after 20minutes of exercise at a rate of up to approximately 1g/kg/hr. Lower intensity activities or intermittent high intensity activities are likely to require smaller rates of carbohydrate supplementation.
• Carbohydrate-based foods with a high glycaemic index should be readily available during and after exercise.
• Adequate hydration is essential.
General Safety
• Where possible avoid exercising alone and alert others to potential signs of hypoglycaemia.
• Extra care should be taken when exercising after a recent hypoglycaemic episode as risk of hypoglycaemia during exercise is increased.
Strategies to Prevent Hypoglycaemia in Moderate Intensity Activities
Although hyperglycaemia can lead to withdrawal from an activity, hypoglycaemia is most likely to prevent an individual from completing an activity. Furthermore, as described in section 1 hypoglycaemia is a common complication of moderate intensity endurance activities that typify many sports e.g. running/cycling, it may also complicate common team sports e.g. football where periods of moderate intensity activity are interspersed by high intensity bursts. Although an element of trial and error is unavoidable effective strategies to prevent hypoglycaemia are critical to keep errors to a minimum without compromise to glycaemic control:
1. Insulin Dose Adjustment
For moderate intensity endurance exercise involving continuous or prolonged effort exercising 90 minutes post pre-meal lispro bolus studies have been able to quantify the reductions in bolus insulin required to produce euglycaemia in relation to exercise duration and intensity. Furthermore, reductions of morning insulin dose of 50-90% prior to moderate intensity endurance activities have been successful in both basal bolus regimes and twice daily insulin regimen (30% regular/70% NPH insulin), without worsening metabolic control.
However, although these results have been reproducible within controlled study environments the adjustments can only be used as a template and consideration must be given for other key variables affecting glucose homeostasis when planning for exercise.
2. Ambient Insulin Level
Importantly insulin activity and time since last pre-meal bolus insulin dose must also be considered7, the reductions are for exercise 90 minutes post pre-meal lispro dose. If exercising 30minutes after a meal insulin activity would be higher and even greater pre-meal insulin reduction may be required. Similarly, if using an older pre-meal insulin analogue rather than lispro the activity will last longer and greater reductions may be required even if exercising at 90 minutes post pre-meal dose.
Basal insulin levels may also need to be adjusted especially if exercise is not performed on a daily basis. The degree of change required is again going to vary depending on the intensity and duration of activity. As a general guide reductions of 20% on the night following exercise and 10% on the night after that may be required to cover the period of increased residual insulin sensitivity following an episode of unaccustomed exercise that would otherwise lead to an inappropriately high insulin level. Generally if exercise frequency is greater than once every 2 days no adjustment in basal insulin is required on a day to day basis although overall basal insulin requirements are likely to change over time with training and fitness.
3. Carbohydrate Supplementation and Diet
a. General Principles
Insulin adjustment cannot be considered in isolation. Studies similar to those above but with smaller insulin reductions and greater carbohydrate intake have been equally effective in preserving euglycaemia during exercise. It is not always possible to plan for exercise and carbohydrate intake gives individuals with diabetes greater flexibility to manage exercise. Rigid carbohydrate supplementation without regard for pre-exercise blood glucose, previous metabolic response to exercise and individual insulin therapy is no longer appropriate. Indeed such an approach may neutralize the beneficial glycaemic lowering effects of exercise in diabetes and may be one explanation for why studies have failed to show an improvement in HBA1C with exercise training in type 1 diabetes.
b. General Dietary Requirements
The overall dietary requirements of athletes with or without diabetes are essentially similar, ideally with 60-70% of energy taken as carbohydrate 5-10% protein and less than 30% as fat. Consideration must be given to whether exercise is part of a weight control plan as carbohydrate supplementation may hinder weight loss and goals are different to nutrition for athletic performance. In both circumstances involvement of a specialist dietician is often helpful if available.
c. Calculating Carbohydrate Requirements for Exercise
Pre-exercise there is evidence that a low glycaemic index meal may improve performance in individuals with diabetes. After exercise typically 60-120g of carbohydrate is needed depending on level of depletion to replenish muscle and liver glycogen stores and a further bolus of insulin may be required to cover this. As a general guide in total endurance athletes are likely to require between 8 and 10g/kilogram of carbohydrate of body weight per day, recreational athletes and endurance athletes training at lower intensities are likely to require considerably less than this.
Extra carbohydrate during exercise both prevents hypoglycaemia and improves exercise capacity, as a rough guide up to 1g/kg/hr may be required but once more this will need to be tailored to the individual. Although no exact formulae is available recent studies suggest that heart rate at aerobic thresholds (up to approximately 75% maximum HR) follows a linear relationship with the amount of glucose oxidised. Therefore, the higher the heart rate whilst working aerobically the more carbohydrate is likely to be required to maintain euglycaemia. Furthermore, just as with insulin dose adjustments ambient insulin level is critical, carbohydrate requirement to prevent hypoglycaemia decreases as time elapses from the period of maximum action of the last insulin injection if other key physiological factors are controlled for.
d. Methods for Carbohydrate Supplementation
Sports drinks containing 6-10g of carbohydrate per 100ml can be used to provide carbohydrate and replace fluids and electrolytes when glucose is stable (commercially available sports drinks typically contain 6-8g carbohydrate/100ml). In the absence of reductions in insulin dose, concentrations closer to 10g/100ml have been shown to be most affective in preventing hypoglycaemia individuals with type 1 diabetes without gastro-intestinal side effects. However, higher concentrations for example 15g/100ml may be needed to correct falling blood sugars, unfortunately gastric discomfort is more likely at these levels. The need to maintain adequate hydration must not be overlooked and many individuals supplement sports drinks with water or squash to achieve this particularly in warm conditions. Over reliance on sports drinks with no regard for blood glucose in an individual with type 1 diabetes could lead to hyperglycaemia.
Some individuals prefer to follow strict carbohydrate regimes however all need an understanding of general principles of carbohydrate replacement. In general low glycaemic index foods (e.g.pasta, rice, noodles or porridge) are recommended 3-4 hours prior to exercise to boost carbohydrate stores whereas high glycaemic index foods which give more immediate carbohydrate (e.g. ripe banana, jelly sweets, energy bars) can be used in addition to or instead of sports drinks pre, during and immediately following exercise.
4. Integration of a 10 second Maximal Sprint
There is increasing evidence that a 10 second maximal sprint either immediately before or after exercise is an effective, well tolerated, novel strategy to prevent hypoglycaemia following moderate intensity exercise. The exact identity of the counter-regulatory hormones responsible for this remain to be established and at present evidence is limited to efficacy for short duration (20minutes), moderate intensity (40% VO2 Max) exercise only. However, until further evidence is available this provides another option for athletes following unplanned short duration moderate intensity exercise that is effective without the need to adjust insulin or carbohydrate intake.
Summary of Strategies to Prevent Hypoglycaemia in Moderate Intensity Activities
There is currently no one best strategy to prevent hypoglycaemia for individuals with type 1 diabetes participating in moderate intensity endurance activities. Table below summarizes the strategies discussed and the relative advantages and disadvantages currently recognised. For each strategy there is no exact formula for adjustments. Figures included in this section are intended to act as a guide. These can then be adjusted using knowledge of variables known to impact on glucose homeostasis (see part 1) and individuals own measurements and awareness of their usual responses to a particular type of exercise. For example, an athlete with type 1 diabetes running 10 kilometers in training may expect to require larger reductions in insulin than during an intense competition race where increased levels of counter-regulatory hormones are likely to enhance glucose production and reduce the risk of overall risk of hypoglycaemia.
If we apply these strategies to different types of sport an individual competing in an intermittent high intensity activity such as a football consisting of periods of moderate intensity activity may require smaller reductions (or no reduction at all) in insulin due to increased levels of counter-regulatory hormones following high intensity bursts.
Planning for Safe Participation in Sport and Exercise
It is important to recognise that hypoglycaemia is one of the commonest and potentially most serious complications during participation in sport and exercise, particularly as it may occur in remote or dangerous environments. Its detection however, can prove difficult as symptoms may be similar to those of exercise itself. In this respect the importance of closely monitoring blood glucose pre, during and post-exercise cannot be overemphasised. These measurements can then help individuals form a template for different activities so that they can recognise patterns to predict their own glycaemic response, learn to manipulate their insulin dose and carbohydrate intake and reduce their need for quite so frequent monitoring.
General guidelines to help individuals with type 1 diabetes participate in sport and exercise safely are detailed in table 4 below:

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