Sports and Type 1 Diabetes

Aerobic Exercise and Type 1 Diabetes Control:

Every sport is different; within those differences come various affects on blood sugar levels, before, during and after exercise. 


Aerobic exercise counts for physical exercise which largely uses your main muscle groups, making the heart beat faster and working the cardiovascular system to manage oxygen more effectively throughout the body. The forms of exercise usually relate to more continuous activity, such as running, walking, cycling and swimming. 

In living with type 1 diabetes, when you burn energy at a continuous rate such as in many forms of aerobic exercise, the likely outcome is that your blood sugar levels will gradually decrease DURING activity. For example in going for a causal walk for 2 miles, this still very much counts for exercise and your movements may be slow and calm, yet they are still very much movements! As you walk along if you test blood sugar levels at the start of the walk and again at the end, or walk with a Continuous Glucose Monitor (CGM), you will probably find the blood sugar level to be lower at the end of the walk than what it was at the start (assuming you haven’t just eaten an absolute feast or not taken insulin…). 

If you was to go for a jog, keeping the same level of pace going as you run, that is an increased level of movement and burning of energy. Whilst the effect is the same, blood sugar levels lowering, the increased rate of energy means that your blood sugar levels are likely to decrease at a more rapid speed DURING exercise, than when you were casually walking along. 

The movements of the arms and power from the legs when running, the full endurance of the body too, show that the body is being worked harder and burns more energy. If the pace is continued at a consistent level than blood sugars decrease faster.

Cycling again works the legs continuously on the pedals and energy is burned up at a more rapid pace than when walking, therefore decreasing – in general – in blood sugar levels during exercise. 

Of all aerobic activities, Swimming is the most rapid of burning up energy. Not only are you working the whole body, particularly the arms and legs, but you are doing so under water. Swimming in the sea furthermore so, where the body is working against the current. This means that blood sugar levels will decrease more rapidly than any other aerobic exercise during activity, when swimming.

Methods of control can vary to counteract the risk of hypoglycemia. Accumulating the levels of carbohydrates to consume before and during exercise to balance your body being one area. The mathematical equation to figure out is: what the rate of exercise is X by the gs of carbohydrates your body requires to stop the fall, per hour. For example, when running a marathon you know that for the next few hours every part of your body is going to be worked and blood sugar levels will decrease as your pace remains a similar rate throughout. You are going to be burning over 2,500 calories at least during a marathon – the body requires fuel for this in general and with type 1 diabetes, it needs fuel plus further glucose supplies to keep a balance. 

So lets work out that someone is running a marathon burning approx 2,500 calories in 4 hours, that equals 625 calories burned per hour. What is needed in the burning of this energy is carbohydrates, as the body will start burning into stored fat once out of glycogen reserves. The more weight the runner carries the more glucose is needed to fuel muscles (and vise versa) and that is without diabetes. In addition, we need the glucose to keep levels afloat!  Calculations of body weight can help your maths in working this out, if you weighed 10.5 stone / 66 kgs, in general when running a marathon your body would ideally require 46gs of carbs per hour (body-weight in kilograms x 0.7 grams of carbs per hour) – so that would be your minimum intake. With diabetes the best advice is to add an additional 10gs per hour in order to prevent any risk of hypoglycemia. These can be consumed by energy drinks, gels, tablets, small sweets such as fruit pastels…


If you see all those numbers and workings out and think ‘that’s not my language!’ I get that. The best advice is to test blood sugars as regularly as possible especially when training, learn your body for yourself, and take with you carbohydrates such as the gels or drinks, and keep a note of it. How much carbohydrates did I consume per hour on that run? In doing so, you can keep an idea of what goes on in your own body. 

The other key area to consider is less of the carbohydrate pondering and more on the side of INSULIN MANAGEMENT. If in an aerobic activity you know that the levels of exercise is going to be consistent and will lower blood sugars during activity. In light of this your body will require much less Basal Insulin (your background insulin). There are many forms of basal insulin: Levemir, Lantus, Humalog, Humalin, Apidra and Novolog. For those on an insulin pump, effectively the form of insulin that those on injections know  as their quick acting bolus, usually Novorapid, is used as your basal insulin per hour. Planning ahead for the exercise and rate it will decrease blood sugar levels is the key to getting the adjustment of Basal insulin correct. Swimming for example will burn at a much quicker rate than walking, as we know. Therefore you will need less Basal insulin in the system during activity when swimming then you would for walking. The more background insulin present during aerobic exercise means the higher risk of hypoglycemia.

The option on injections to go on ‘split’ insulin can lead to a more flexible and effective method of control during activity. Being able to lower the rate of insulin in your system in the morning to suit the activity ahead, working with the energy burned during exercise, can help to keep control during exercise – and to prevent a possible hyperglycemia later, when the background insulin runs short, you can then inject your second dosage of basal to the normal amount (or slightly reduced amount depending on the exercise earlier in the day) to keep strong control.

Consider your insulin and seek advice from a healthcare professional to find further details on your insulin type – such as Levemir basal not being quite as strong as Lantus, meaning you might need less Lantus in the system on a split dosage. And again, the best way to know your body is to test, test, test your blood sugars to see what is going on – and then you can make a more accurate decision to suit your body from there.


Blood Sugar Spikes:     

Blood sugar level spikes can come into play during activity, even in some of these aerobic exercises such as running and cycling. There are different forms of these sports which can lead to sudden bursts of energy – losing that consistent rate of energy being burned and causing an adrenaline effect, key organs such as liver releasing naturally stored glucose into the bloodstream. The effect can mean that DURING activity blood sugar levels actually RISE high. However, in sports such as running and cycling, you have still burned a high amount of energy and the likely effect is that hours later your blood sugar levels will come falling downwards. 

For an example of the different kinds of exercises, within a similar form of activity, running! You can run a 5k race and run the distance of 5km to simply keep fit, and find two very different effects. When racing there is adrenaline, you are competing. The pace is likely to change as you challenge to do your best, you might start slower and save energy and then increase your pace, then finish with a sprint. The outcome is likely to cause that ‘adrenaline effect’ and release the naturally stored glucose from the liver into the bloodstream during the activity. So you could find you finish the run at a higher blood glucose level than what you started it at. 

Whereas, in a causal 3.1 mile jog to keep fit, you are not competing. You are simply running at that consistent level again and therefore, although it might be the same distance as a 5km race, you are running in a different style. Blood sugars will therefore gradually decrease during activity. 

And a completely different circumstance, yet, still running, is a 100m sprint. Usain Bolt, for example, if he had type 1 diabetes he’s blood sugars are likely to increase without crashing lower too much afterwards. 100m is anaerobic exercise…


Anaerobic Exercise and Type 1 Diabetes:

Anaerobic exercise counts for high intensity exercises, which are shorter-lasting activities.  The exercise isn’t depending on the oxygen supplies, like in aerobic excise, but from the power within the muscles. 

This usually entails sudden bursts of energy, as mentioned above with Usain Bolt in the 100m races. This sudden impact triggers the ‘adrenaline effect’ and the body reacts by releasing naturally stored glucose from the liver into the bloodstream. Where we have type 1 diabetes and have to inject our insulin ourselves, this means we cannot counteract the release naturally during activity with insulin and therefore our blood sugar levels increase. 

Depending on the level of energy burned up during the activity, the levels can crash lower later on after the exercise. In Bolt’s case, running 100m is a quick burst. He is able to pose like an arrow after catching his breathe. This means it is unlikely the post exercise hypo crash will happen. However, on other sports, it very much can happen and even hours later during the night time, there is a risk of a hypo. 

Test the sugars!

A Bit of Both Exercises…

A lot of competitive sports account for aerobic exercises in terms of being ongoing endurance for a long time, yet, also include aspects of anaerobic activity. Many of the most popular sports around contain this: football, tennis, rugby, cricket…

It is very common for someone with type 1 playing a team sport, such as football, to have dashed around the pitch burning plenty of energy for 90 minutes continuously and to then test blood sugars and find blood sugars up in the hyper levels of the teens (or even above). 

Whilst the exercise is ongoing for 90 minutes, what that 90 minutes entails is a consistent changing of pace – quick bursts to get the ball, jogging to get into position, sprint, jog, walk (if lazy), sprint… and these movements again trigger the adrenaline effect. So during the game the blood sugar levels increase. 

In this case, oranges or energy drinks at half time aren’t best advised – being too hyper means it becomes harder to concentrate on the game. Water is the best answer, and once again, a check on blood sugar levels before, during and after! 

It may even be more advisable to get the carbohydrate energy supplies the evening beforehand, with a good pasta dish, and for the morning have a low / no carb  breakfast before the sport. 

Whilst coming off of the pitch higher in blood glucose levels, there is a far higher risk of blood sugar levels crashes after burning up plenty of energy. Getting a strong, substantial meal on board, afterwards, is very important – perhaps even with a unit less than required of bolus insulin for the meal. 

To perform to the best of ability and to help prevent a hyper in a competitive sports game, a trick is to take on a unit more basal insulin than normal. This can help maintain levels from dramatically increasing during activity. However, if you do this, be aware that the decrease post exercise, the crash, is more imminent and is likely to also happen sooner. Get a good meal in soon after the game! (and check blood sugars!!!) 


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