Managing exercise on multiple daily injections (MDI)

This information leaflet is for patients who are using MDI. Its aim is to help explain why various sports have different effects on blood glucose levels and offer some tips that you may find useful.

Can I exercise?

Yes, absolutely. Being on insulin should not stop you exercising and achieving your goals providing there are no medical reasons why you have been advised not to. Hopefully, this leaflet will help you be more creative and flexible with your diabetes management; but try not to give up if your blood glucose levels are unpredictable.

This is frustrating but entirely normal. There is no such thing as a perfect strategy that will work for you every time so try not to feel that you have failed when your glucose levels don’t do what you expected them to do.

Effects of exercise on blood glucose levels

Most people find that different exercises will affect glucose levels in different ways. Low to moderate intensity exercise tends to lower the glucose levels. This can be referred to as aerobic activity. This happens because your muscles are using up the glucose in your body for energy. Your body stores glucose in the muscles and liver. The longer the exercise, the more likely it is that your glucose levels will drop because you are using up your stores of glucose. Exercising muscles take up glucose at a higher rate which also contributes to this lowering effect.

High intensity exercise tends to increase the glucose levels. This can be referred to as anaerobic activity. During anaerobic activity your body tends to produce a surge of hormones, such as adrenaline, causing the glucose levels to rise. You may also notice your glucose levels rising if you are in a competitive environment, such as during a race, match, or at an event. Lactic acid, which is often produced during high intensity exercise, can also increase glucose production.

Whether your body is working aerobically or anaerobically will depend on the exercise you are doing and how fit you are. The effect on glucose levels will differ from person to person. For one person, going for a 30-minute brisk walk may be aerobic. For somebody less conditioned to walking this may push them into the anaerobic system.

1. The first step in developing a strategy to help you manage exercise is to try to optimise your diabetes management on non-exercise days so you can get your basal (long-acting) insulin and bolus (mealtime) insulin suited to your general requirements. Your diabetes educator will be able to help you with this.
2. The second step is testing and monitoring your levels before, during and after exercise to work out what happens to your levels during different exercises. You may find that going to the gym to weight train on one day will have a completely different effect on your glucose levels than running on the treadmill. You may need a different strategy to manage your exercise for different sessions.

Where to start

A sensible target range for blood glucose level at the start of exercise is seven to 10mmol/L. Different people feel comfortable exercising at different levels, they may prefer to start a little higher if they are new to the exercise and are not sure which way their glucose levels will go. The table below offers a guide of how to aim for a safe level of glucose before starting your exercise session.

Exercising after a hypo: knowing the risk

We are all reluctant to delay or reschedule exercise when it has been planned into the day. For many it’s an important part of their relaxation, training regime or even part of their job. However, the advice is to avoid exercising altogether if you have had a severe hypo in the last 24 hours.

A ‘severe hypo’ is one that requires third-party assistance (someone else treating the hypo for you). Research has found that your body is at far greater risk of another hypo if you have already had one in the last 24 hours. One study found that people exercising after a hypo needed three times more glucose infused into their body than somebody who had not had a hypo. Your body is less able to produce the hormone response needed to keep your glucose levels topped up during exercise following a hypo.

Consider whether you have noticed a pattern of evening exercise followed by a pattern of hypoglycaemia the following day. There is some evidence to suggest that if you are an afternoon or evening exerciser, you might be at higher risk of hypoglycaemia the following day compared to if you were to do the same exercise in the morning, probably due to the hormonal shifts in your body during the day.

Guidance for low blood glucose (less than 3.5mmol/L)

• Severe hypoglycaemia (needed help): Do not exercise for 24 hours.
• Self-treated hypoglycaemia: Be careful for 24 hours.
  • If it occurs before exercise, treat and have stable glucose for 60 minutes before starting.
  • If it occurs during exercise, stop, treat and recommence after stable for 45 minutes.

Tips for managing your insulin

Those keen to exercise, or to start exercising, often ask for tips on managing insulin. Frustratingly, there is not one strategy that will work every time. It takes a lot of experimentation and practice to understand what insulin adjustments and/or carbohydrate consumption that will work for you. Monitoring before, during (every 30 minutes) and after the exercise and recording/uploading your data will help you track your progress and decide what strategies are working. Never forget your diabetes team is on hand to offer a fresh perspective and work with you on this. The most valuable thing we can learn from is you and your experiences.

Step 1: Try to find a pattern of glucose trends (if there is one) with different workouts and note it down. Remember, if it doesn’t work well, it’s not a failure. Whatever glucose data you get can be banked as useful experience in helping you find a better strategy for next time.

Step 2: Try using insulin, carbohydrates and/or exercise (ICE). ICE looks at the three ways of managing your glucose during exercise.

Insulin

Bolus (mealtime) insulin

It is best to avoid exercising when there is active insulin working in your body from a previous dose. This helps to avoid hypos from exercising when your bolus insulin is at its peak action which is usually one to two hours after taking it. Insulin can also reduce your liver’s ability to release glucose into the bloodstream during exercise, so the further away from a bolus of insulin the better the liver will be able to top up the glucose if necessary.

Exercising in a fasted state has been shown to improve predictability of glucose levels during exercise compared to exercising after a meal. This may not always be practical or possible so you may need to look at reducing the insulin you take with a meal prior to exercise.

Basal (long acting) insulin

Some people find that they need to reduce their long acting as well as their quick acting insulin. This tends to be for longer duration events (eg long walks/hikes, long bike rides, day long events etc) where reducing the quick acting insulin alone is not enough to stop low glucose levels.

Some long-acting insulins are more responsive to dose changes than others. For example, if you reduced your levemir on the morning of a six-hour long hike then that dose would become active straight away.

However, if you were to adjust your lantus on the day of an event or even the night before, it would take around two to three days, sometimes longer, for that reduced dose to be established.

Long-acting insulins:

• that are flexible around exercise are Levemir/Detemir, Insulatard and Humulin I
• that are not flexible around exercise are Lantus/Glargine, Tresiba/Degludec and Toujeo

You may find that swapping to a more flexible long-acting insulin would suit your routine better. This is best discussed with your doctor or educator.

Deciding on how much to reduce your long-acting insulin by will take practice. You may like to start by reducing it by 10% to 20% on the morning of the exercise and go from there. Many people find they go low during the night after exercise. The duration, intensity and the timing of the exercise you have done that day will all affect whether or not your long-acting insulin at bedtime will need reducing.

Refer to ‘Glycogen replenishment’ below. A starting place might be to reduce your night-time long-acting insulin by 10% to 20% and set an alarm at 03:00 (3am) to check that your glucose levels are not dropping.

Carbohydrate

You may find that you need extra carbohydrate to support your exercise if the insulin alterations are not enough, or you prefer to use this strategy on its own to stop your glucose levels dropping. Usually, exercise under 30 to 45 minutes would not require top-up carbohydrate. However, if you find that you need extra carbohydrate then a good starting point would be to aim for 30g carbohydrate per hour, ‘drip fed’ in over the hour (eg 10g every 20 minutes rather than in one go at the start). Another way of estimating the amount of extra carbohydrate you might need is worked out using your body weight:

• For moderate activity: 0.5g/kg body weight/hour of activity.
• For intense activity: 1g/kg body weight/hour of activity.

For example, Sally weighs 60Kg and is going for a light jog for 60 minutes (she would consider this moderate intensity – for others it may be more intense). Sally might need 30g carbohydrate over the hour (best taken as three smaller 10g snacks over the hour).

You may find ExCarbs (opens in a new tab) useful in helping you to calculate the insulin and carbs needed for the exercise you are doing.

It is worth noting that your body is not able to digest more than ~60g glucose per hour. However, your body can take on extra energy from fructose so you may want to try 2:1 glucose:fructose gels/supplements etc if you find you need more than ~60g glucose per hour to fuel the exercise. This may be the case for more extreme endurance type events (lasting several hours).

Personal preferences for food and/or drinks while exercising varies. The amount you might need and whether it is fast release carbs (eg for sessions lasting 45 to 90 minutes) or slower release carbs (for longer sessions/day events). You may need a combination of both depending on what you are doing. Try experimenting; see what works best for you. The table below offers suggestions.

Always check the nutritional label for exact carbohydrate amounts.

Exercise

Recent evidence suggests that it can be possible to stabilise your glucose levels by altering the order in which you do your exercises rather than altering your insulin and/or carbohydrate intake. For example, if you find that your levels drop quickly after starting aerobic activity (running, walking, cycling etc) then you might choose to do some anaerobic exercise first which will raise your levels to allow a buffer before lowering them with the aerobic exercise.

In practice, this could be doing your weights/press-ups etc first before going on the treadmill, bike (aerobic workout). You may still need extra carbohydrate to prevent low blood glucose levels, but you could try this strategy and monitor closely to see the effect first.

Similarly, if you have trouble with your levels going high, due for example to interval or weight training, then you might start with a longer warm-up or factor in some gentle running halfway through your session to try to bring the levels down.

High levels after exercise

High levels after exercise is a problem people often encounter. It can be due to several factors such as over treatment of carbohydrate, the body’s response to the exercise (hormones, lactate) or too much of an insulin reduction. You could try one of the following to manage this situation:

• Additional stretches and warm down period.
• Wait 30 minutes after the above before giving a corrective bolus. In this time drink plenty of sugar-free fluids which will rehydrate you and help to reduce glucose levels.
• Take 50% of the correction you would normally give to reduce glucose levels.

Ten-second sprints

This is another tip for trying to prevent hypos from happening during an aerobic activity. It can be applied to most sports in a situation where you want to get a boost of counter regulatory hormones (eg adrenaline) to raise your levels. People have tried this successfully during a long run where they sprint for 10 seconds. Other people have tried this by going up a few gears on their bike and sprinting during a long cycle ride or sprinting in the pool for a length when they are swimming. Some people have even done press-ups during a long hike when they were running low on carbohydrates to try to prevent hypos.

Remember that even if you manage to protect your levels during the exercise you will need to ‘pay back’ the glucose later or you are more likely to hypo due to the additional energy you have expended.

If you find that your glucose levels are above target following a bout of anaerobic exercise or a build up of lactic acid, one solution to this would be to factor in a longer cool-down period after your main workout. For example, some gentle lengths of the pool after an intensive swim, a gentle jog/walk after a fast run or a low intensity warm down after rugby training.

Refuelling after exercise

Low glucose levels after exercise can happen quite soon after exercise, or several hours later. Your body will seek to replenish all the glucose it has used up during the exercise. It is important to support this process so that your body stays fuelled up and ready for the next session. Failing to adequately refuel after exercise can increase the risk of further hypos either before or during your next exercise session.

You have probably heard the term glycogen replenishment used when talking about low glucose levels after exercise. Your body has a constant store of glucose (glycogen) in the liver and muscles which are used during exercise. On recovery, your body will seek to replenish these stores of glucose which can lead to low levels either during, shortly after or several hours after exercise.

Some people they find that their glucose levels are stable for several hours after exercise but then suddenly drop. This delay in glycogen replenishment can be addressed if there is a pattern detected of when your levels start to reduce.

It is recommended that you have a small carbohydrate and protein snack directly after exercise in a 3:1 ratio (30g carbs to 10g protein). Whether or not to correct this with some insulin is an individual decision.

It might be best to monitor first and see what happens to your glucose levels. A starting point might be 0.5 units insulin and go up from there if necessary. People often say that they stay high directly after exercise due to the hormones lingering around once they have finished so covering the refuelling snack with a small amount of insulin might be sensible.

Here are some refuelling snack ideas:

• chocolate milkshake (low fat)
• low-fat yoghurt smoothie
• banana and low-fat yoghurt
• peanut butter/cream cheese on rice cakes/crumpets
• hummus on toast

It is also important to make sure that you are meeting your overall carbohydrate requirements at your other meals and snacks. Evidence supports basing your larger carbohydrate portion on slow-release carbohydrate.

As mentioned earlier, delayed glycogen replenishment can happen several hours after exercise has finished which can cause problems of hypos. Exercising in the afternoon or evening can lead to a higher risk of hypos overnight. It may be safer to reduce your long-acting insulin before bed by 10 to 20% if you have started a new exercise that day.

The degree of glycogen replenishment will be proportional to the duration and intensity of the exercise. Endurance events (marathons, hikes, long bike rides) may cause lower glucose levels a day or so afterwards until the body’s stores of glycogen are replenished. You may find that you need a lower dose of long-acting insulin the day after a long event while your body recovers.

Sports nutrition

This is a huge topic and a very active area of research. However, we do know that keeping your body well-nourished is essential for any training plan for you to get the training gains you want. There are several schools of thought when it comes to high vs low carbohydrate diets, ketogenic diets and high protein diets.

Carbohydrate intake

We often get asked in clinic about following a ‘low carbohydrate’ or a ‘ketogenic’ diet. It can be very confusing when there is so much information available online these days to know what information to trust. Firstly, it’s helpful to know what the definition of a ‘low carbohydrate diet’ is.

Definitions of low carbohydrate diets

• Very low carbohydrate diet (ketogenic): 20 to 50g per day or <10% of total energy.
• Low carbohydrate diet: >50g but <130g per day or 10 to 26% of total energy.
• Moderate carbohydrate diet: 130 to 230g per day or 27 to 45% of total energy.
• High carbohydrate diet: >230g per day or >45% of total energy.

Why do people follow low carbohydrate diets?

Some people try to restrict the carbohydrate in their diet for several reasons. These reasons might be to control their weight, enable them to use less insulin, fewer hypos related to mealtime bolus insulin, less variability of post meal blood glucose levels.

To date, there is no robust evidence to support these reasons for a low carbohydrate diet apart from requiring less insulin.

As a clinic, we strive to support people in making their own decisions and do not like to dictate to people what they should and should not do. We prefer to take the available evidence at the time and help people understand the pros and cons so that they can make an informed decision. To date, there are several reasons why we do not currently endorse a low carbohydrate diet. These reasons include:

• Little evidence of efficacy.
• No evidence for long-term cardiovascular system safety. Remember, a ‘low carb’ diet can also be referred to as a ‘high fat/protein’ diet due to the nature of the foods substituting the carbohydrate. It is of paramount importance that your cholesterol levels are closely monitored if you are following a low carbohydrate diet.
• Impairs performance in both endurance and high intensity sports (Arciero PJ J Nutr Metab 2015).
• Risk of diabetic ketoacidosis (DKA) due to mild ketotic state. This has been seen in clinical practice due to the lower circulating levels of insulin putting the person at risk of tipping into DKA. This can put you at risk of developing ketones if your carbohydrate intake should suddenly increase (such as because of a holiday).

How much carbohydrate should I be consuming?

The advice on how much carbohydrate to consume is calculated on your level of training and your body weight. Remember, not giving your liver and muscles enough glucose through your daily diet can lead to fatigue, lack of training gains and increased hypoglycaemia both during and after training.

Protein intake

Protein is needed in the body for growth and repair. Protein also helps the body refuel with glucose after a workout, which is why the advice is to have a small amount of protein with any post-exercise refuelling snack (see examples above). Many people ask how much protein they can or should consume because they want to increase their muscle mass. Below are some guides to help you decide a safe limit of protein to consume to support your training.

Your kidneys are responsible for processing and excreting protein in the diet, so consuming too much may put additional pressure on them. You may wish to speak to your doctor if you are unsure if you have any kidney impairment which would affect your safe limit of protein.

Before buying expensive supplements, it might be worth keeping a food diary to assess how much protein you are getting in your normal diet and whether you can optimise this first. To do this you could keep a diary on a simple food diary app on your phone or use the basic list below to calculate your protein intake. Food labels will also be a useful guide.

If it becomes obvious to you that you are not consuming enough protein to meet your daily requirements, you may decide to look at a supplement to meet (but not to exceed) them.

Further reading

Hopefully this has provided you with some ideas, information and advice around managing exercise with your insulin pump. For more general reading around diabetes and managing exercise you may find the following useful:

• 'Type 1 Diabetes – Clinical Management of the Athlete' by Ian Gallen
• Runsweet website (opens in a new tab)
• Team Novo Nordisk website (opens in a new tab)
• Diabetes Education Online (University of California, San Francisco) (opens in a new tab)