How Your Hormones Impact Physical Activity

Insulin injection

The human body only has insulin to lower blood glucose but has five hormones that raise it (with some overlap). This hormone redundancy tells you is that, at least from a survival standpoint, your body is desperate to make sure you do not run out of blood glucose; it is not as concerned about you having too much. Insulin is an important hormone for regulating your body’s storage of fuels (carbohydrate, fat, and protein) after you eat. It tells your insulin-sensitive cells (mainly your muscle and fat cells but also your liver) to take up glucose and fat to store them for later as muscle and liver glycogen (the storage form of glucose) as well as stored fat. During exercise, any insulin in your bloodstream can make your muscles take up extra blood glucose. In people who have a pancreas that functions normally, insulin levels typically decrease during exercise, and levels of a hormone called glucagon (released from the alpha cells of the pancreas) rise to stimulate glucose release (1).

Your blood glucose levels are managed by your liver, which would normally respond to the relative amounts of insulin and glucagon (see table that follows). Insulin and glucagon released from the pancreas go directly to the liver via the portal circulation: after a meal, high insulin and glucose levels tell the liver to store glucose for later use; fasting overnight or doing extended exercise leads to glucagon signaling the liver to release glucose. How people with type 1 diabetes respond hormonally to exercise is a major issue: the insulin and glucagon at the level of the liver are seldom perfectly normal because their insulin is injected or pumped under the skin rather than released directly from the pancreas. People with type 1 diabetes have an altered hormonal response to exercise when their peripheral insulin is relatively high; lowering the circulating level of insulin helps normalize their hormone response.

All exercise causes the release of hormones that increase the production of glucose by your liver and lower your muscular use, based on how long and hard you exercise. Easy and moderate activities only release a small amount of glucose-raising hormones (unless you do them for a very long duration), but intense exercise such as heavy resistance training, sprinting, or high-intensity intervals causes an immediate rise in your blood glucose and leads to an exaggerated release of hormones. These hormones include adrenaline (formally known as epinephrine) and norepinephrine, which are released by the sympathetic nervous system (allowing your body to respond to physical or mental stressors with an increased heart rate), as well as glucagon, growth hormone, and cortisol (also shown in table). The effects of these glucose-raising hormones can easily exceed your body’s immediate need for glucose, especially because high-intensity exercise may not last long. As a result, your blood glucose often rises during and after short bouts of intense activity. In fact, you should expect intense exercise potentially to cause a large increase in blood glucose because of your body’s exaggerated release of glucose-raising hormones such as adrenaline and glucagon. 

Hormones That Affect Blood Glucose During Exercise
Hormone Source Main Actions
Insulin Pancreas (beta cells) Promotes blood glucose uptake into muscle cells and adipose (fat) cells (the latter mainly during rest); stimulates liver uptake and storage of glucose; inhibits fat release from adipose
Amylin Pancreas (beta cells) Supplements action of insulin by slowing digestion and absorption of glucose from food; blocks glucagon release; promotes early satiety (fullness after eating); cosecreted with insulin from functional beta cells but absent in type 1 diabetes and in individuals with type 2 who produce a little of their own insulin
Glucagon Pancreas (alpha cells) Stimulates liver glycogen breakdown and new glucose production from precursors to increase blood glucose; is affected by changes in the insulin-to-glucagon ratio at the liver
Epinephrine (Adrenaline) Adrenal medulla Stimulates muscle and, to a lesser extent, liver, glycogen breakdown, and mobilizes free fatty acids from adipose cells
Norepinephrine Adrenal medulla, sympathetic nerve endings Stimulates liver to produce new glucose from available precursors; acts as “feed-forward” control of glucose during intense exercise along with epinephrine
Growth hormone Anterior pituitary Directly stimulates fat metabolism (release of free fatty acids from adipose) and indirectly suppresses glucose use; stimulates amino acid storage
Cortisol Adrenal cortex Mobilizes amino acids and glycerol as precursors for glucose production by the liver and releases free fatty acids for muscle use in the place of glucose (during fasting, starvation, and long-duration exercise)

You may be more insulin resistant immediately after intense exercise and for a few hours due to these hormones. In one study, after near-maximal cycling to exhaustion, one group of people with type 1 diabetes on insulin pumps experienced elevated blood glucose levels for nearly 2 hours. Similarly, in exercisers with type 2 diabetes, blood glucose also rose for 1 hour in response to maximal cycling, as did their insulin levels (because their bodies still produced their own insulin). You may need some supplemental insulin to bring your blood glucose back to normal (albeit less than normal), or it may drop slowly over time on its own. After these hormones wane, your blood glucose may easily drop later when your body is working hard to restore the muscle glycogen you used during the activity. Be on the lookout for later-onset lows in these cases.

Reference:

  1. Excerpted from Colberg, SR, Chapter 2, “Balancing Exercise Blood Glucose” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.
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Debunking Some Physical Activity and Training Myths

woman doing exercise inside gym

Photo by The Lazy Artist Gallery on Pexels.com

By Sheri Colberg, PhD

How often have you heard that things about physical activity and exercise training that you thought sounded correct, but found out later they were totally wrong? If you hang out at a gym or even talk with training coaches, you’ll hear about everything, including contradictory statements about how to be active the right way.

Should you work out in a “fat burning” range? Is weight training going to make you bulk up? Will your muscles turn to fat if you stop working out? Do you need to eat a lot more protein to get bigger muscles? Confused? Here is the truth about some of the more common myths you’ll hear about being active.

Myth: Exercising regularly makes you more tired.

Although you may feel somewhat tired during a workout, when you’re done you usually feel more invigorated after you recover, not less. Doing any regular physical activity is guaranteed to raise your overall energy levels and may you better able to handle everything you have to undertake. If you’re having trouble concentrating at work or getting too stressed, it helps to take a short walk or do any type of physical activity to clear your mind, bump up your energy levels, and decrease your mental stress. Doing regular physical activity also helps you sleep better at night, leaving you more refreshed and energetic during the day.

Myth: If you want to lose fat, you have to work out at a “fat burning” range.

Exactly what is “fat-burning” range you see on a lot of aerobic exercise machines? You have to understand what fuels your body uses during rest and exercise. Typically, during rest 60% of your energy needs are supplied by fat (stored or eaten), with the other 40% coming from carbohydrates. As soon as you start to do any type of physical activity, though, carbs go up to a much higher percentage of your total energy supply. In fact, when you’re doing just moderate aerobic exercise like brisk walking, you’ll use very little fat, so you’re burning mostly carbs even when you’re in a so-called “fat-burning” range. During more vigorous exercise, your body can’t use fat effectively, so almost all energy is supplied by carbs when you’re working out hard. You do use slightly more fat at a lower intensity, but most of its use is during your recovery from exercise, so just try to expend as many calories during exercise as possible without worrying about what types of fuels are supplying them.

Myth: When you don’t use your muscles, they turn into fat.

Have you ever found yourself looking at someone who used to be more fit and thinking that his or her muscles had really turned into flab? While there is no discounting how it looks, it is physically impossible for inactive muscles to turn into fat. What is really happening is this: when you work your muscles out regularly, they can increase in size or simply look more toned; if you stop using them, the muscle fibers will atrophy and disappear—similar to what happens with aging if you don’t fight against it. Then, as your muscle mass becomes less, your caloric needs decrease, and if you don’t start eating less, you’ll gain weight—as fat that then can be stored under your skin (among other places). The reverse is true as well. If you drop body fat, your muscles will look more defined simply because there is less fat in your skin covering them. The bottom line is that it is never good to lose muscle mass, but if you don’t gain fat weight at the same time you lose some muscle, you’ll look thinner, but not like fat replaced your muscles.

Myth: Weight training will bulk you up.

This myth probably arose because you can look bigger as your muscles are stimulated to expand out with heavy weight training. Women are especially worried about bulking up and getting bigger arms or legs. Remember how losing muscle can make you look thinner if you’re not gaining fat at the same time? Well, the same applies here, only in reverse. If you’re losing fat all over (including from under your skin) while you’re gaining muscle mass, you’ll stay about the same size. If you gain muscle without losing fat, you may look slightly bigger, or simply more toned. Either way, most people don’t gain enough muscle from weight training to ever look bulked up. More likely, you’ll just look more toned. When you first start exercising, your weight may go up slightly or just not come down as much as you think it should, simply because as you gain muscle while losing fat, the heavier of the two (muscle) will keep your scale weight higher. Focus less on your scale weight and more on your measurements and how well your clothes fit.

Myth: No pain, no gain.

If you’ve ever hung around a gym, you’re sure to have come across this myth. The “pain” part of exercise results from the build-up of acids in active muscles (like lactic acid), and acids drop the pH of your muscles and sensitize pain receptors. Usually, it’s just a sign that you’re working hard or that your muscle is fatiguing. However, you can certainly have gains in your strength and endurance without pushing yourself to the point of having a lot of pain in the process. The more fit you become, the more easily your body can clear out those excess acids produced by physical activity. Too much pain can also signal that you’re likely to get injured.

Myth: Lifting weights slowly builds larger muscles.

Remember how we just debunked the “no pain, no gain” myth? If you try lifting weights more slowly, you’ll certainly feel the pain, but it absolutely doesn’t mean that your muscle or strength gains will be more. On the contrary, lifting weights slowly when you could lift them faster will build more muscular endurance, while lifting the heaviest weight as quickly as possible will recruit extra muscle fibers and cause you to build bigger muscles. So, the rule of thumb should be that if you are lifting a weight slowly, but could lift it faster, you either need to move it faster or try a heavier weight for optimal results.

Myth: Working on your abdominal muscles will give you a flat belly.

You’ve probably always heard that if you want to get rid of that stomach flab that you have to do a lot of abdominal work, but don’t be fooled into believing that. As much as we’d all like to pick and choose where we lose our fat, it is not possible to spot reduce, and doing hundreds of crunches will not make you lose stomach fat any faster than you lose it from the rest of your body. If you want a flat belly, you can certainly work on toning up your abdominal region, but focus more on simply burning off excess calories. Doing harder workouts will also build more muscle, and having more muscle increases your daily caloric needs. One side benefit of including abdominal exercises, though, is that having toned abs makes it easier for you to pull in your stomach in case anyone is looking at it, even if you can’t spot reduce there.

Myth: The more exercise you do, the better off you’ll be.

There is a limited benefit to anything and that includes exercise that is excessive. When you do more than 60 to 90 minutes of aerobic exercise daily, you’re much more likely to develop overuse injuries—such as stress fractures, tendinitis, bursitis, and other joint issues. You don’t want to get injured because then you’ll have trouble working out. You are better off doing slightly more intense exercise for less long, which you can do with any type of interval training (including some of the latest crazes like HIT and CrossFit). You can push yourself a bit harder from time to time during a workout, or do the whole thing at a higher intensity if you can, while cutting back on the duration—and you will gain the same benefits, or even more, from your workout. Most of us don’t have time to work out all day anyway, so it’s good to know that we really don’t need to.

Myth: If you want to gain muscle mass, eat more protein.

Ah, yes, the protein myth. It is true that you have to eat some protein to gain protein (muscles are made of amino acids, the building blocks of protein). And, yes, physically active people do need more protein than sedentary ones, but not that much more. In fact, no training athlete needs more than 1.6 to 1.7 grams of protein per kilogram of body weight (~0.75 grams per pound), or just twice that of a sedentary person. Does that mean you need to take protein supplements or up the protein in your diet? Not usually. Most Americans already eat well over 15% of their calories as protein: about 75 grams of daily protein in a 2,000 calorie diet (or 112 grams per 3,000 calories), more than enough to cover protein needs. Taking in some protein (especially whey) with carbs right after hard workouts may be beneficial, but make sure your protein is coming from good sources without a lot of extra saturated or trans fats. Instead of spending money on supplements, try eating more egg whites or drinking chocolate milk post-exercise.

Myth: If you’re not sweating, you’re not working hard enough.

Everyone equates sweating with working hard, but that simply isn’t always the case. People vary in their sweating rates. Being physically trained improves your ability to sweat more and to start sweating sooner, but men always tend to sweat more than women. Sweating is related to not only exercise intensity, but also to the environment. If it’s hot and humid, you’re going to sweat more, even if you’re not working hard. You will also sweat less if you’re dehydrated or lose too much fluid while you’re working out as your body has mechanisms to limit fluid losses to keep enough in your blood. So, sweating is often not reflective of your effort level.

Interpretation and Management of Hyperglycemia and Exercise

In some circumstances, elevated blood glucose levels can be indicative of medical concerns like insulin deficiency. People with type 1 diabetes are more susceptible to insulin deficiency since they have almost no ability to produce any insulin; therefore, they need to receive instruction on why and when to check for ketones (1). This is especially important if the individual is using an insulin pump. If ketones are present, then the higher blood glucose levels are a result of insulin deficiency, and corrective action should be taken immediately.

People with type 2 diabetes can experience hyperglycemia from a combination of insulin resistance and inadequate insulin secretion; in their case, extremely elevated glucose levels in combination with severe dehydration can result in hyperosmolar hyperglycemia, which may be aggravated by other extenuating health variables such as severe illness and infections (2). These individuals typically do not produce ketones; if ketones do exist, they may be due to dietary restriction, as opposed to insulin deficiency.

Most diabetes specialists teach people with type 1 diabetes to check for ketones when their blood glucose levels are consistently above 300 mg/dL (16.7 mmol/L), but they should check whenever they have unexplained hyperglycemia (≥200 mg/dL, or 11.1 mmol/L) that persists more than a couple of hours. Exercise should be postponed or suspended if blood ketone levels are elevated (≥1.5 mmol/L or 8.7 mg/dL), equivalent to moderate to large urine ketones, since blood glucose and ketones may rise further with even mild activity (3).

Insulin regimens paired with frequent blood glucose checks greatly diminish the chance of insulin deficiency developing, and significant levels of ketones are rarely found when performing blood or urine checks. In most circumstances, slightly elevated blood glucose levels should not interfere with exercise performance; however, some people report headaches, blurry vision, or lack of energy with even mild hyperglycemia, which may be reason enough to avoid physical activity until the glucose level improves. The health care facilitator must consider the ability of the individual to perform blood glucose and ketone testing and understand the complexity of the information.

In other situations, physical activity itself can raise normal blood glucose levels when performed at high intensity (4). The catecholamine response to very intense activity results in an exaggerated hepatic production of glucose for fuel, and after the activity is stopped, the insulin need can double during the post-activity period. If not corrected with insulin dosing in insulin users, this hyperglycemia may last for several hours before drifting down, or it may not decrease without additional insulin (5).

Those using insulin pump therapy may bolus with a small amount of insulin to address this physiological need. If the injecting insulin by syringe, an additional dose of short- or rapid-acting insulin can also be administered. The timing and amount of insulin given require careful consideration and monitoring to accomplish the desired blood glucose result. Individuals must consider any insulin remaining from their last injection or bolus in making subsequent adjustments to doses, as well as factor in the residual effects of the last bout of activity on blood glucose use (ie, postexercise enhanced insulin action). Regardless of the delivery method, this additional insulin dose can result in hypoglycemia and may not be advisable in all cases.

                                                                                                                                                                           

References:

  1. Kamata Y, Takano K, Kishihara E, Watanabe M, Ichikawa R, Shichiri M. Distinct clinical characteristics and therapeutic modalities for diabetic ketoacidosis in type 1 and type 2 diabetes mellitus. J Diabetes Complications 2017;31:468-72. doi: 10.1016/j.jdiacomp.2016.06.023.
  2. Umpierrez G, Korytkowski M. Diabetic emergencies – ketoacidosis, hyperglycaemic hyperosmolar state and hypoglycaemia. Nat Rev Endocrinol 2016;12:222-32. doi: 10.1038/nrendo.2016.15.
  3. Riddell MC, Gallen IW, Smart CE, et al. Exercise management in type 1 diabetes: a consensus statement. Lancet Diabetes Endocrinol 2017;5:377-90. doi: 10.1016/S2213-8587(17)30014-1.
  4. Fahey AJ, Paramalingam N, Davey RJ, Davis EA, Jones TW, Fournier PA. The effect of a short sprint on postexercise whole-body glucose production and utilization rates in individuals with type 1 diabetes mellitus. J Clin Endocrinol Metab 2012;97:4193-200.
  5. Aronson R, Brown RE, Li A, Riddell MC. Optimal Insulin Correction Factor in Post-High-Intensity Exercise Hyperglycemia in Adults With Type 1 Diabetes: The FIT Study. Diabetes Care 2019;10-16. doi: 10.2337/dc18-1475.

Can You Benefit from Using Exercise Technologies and Wearable Devices?

wearable tech

What do you do when someone asks you to participate in physical activity on the spur of the moment, but you just took some insulin? You may be stuck trying to compensate for this activity entirely with food, but you may have some newer options that come from technology. For starters, if you wear a pump you can choose to lower your basal insulin delivery, and you can use its insulin-on-board calculator to see how much insulin you need to offset with either insulin reductions or food intake. However, just using your blood glucose meter can help you stay on top of your glucose levels, so check often during the activity. If you use a CGM (continuous glucose monitor), you can continue to monitor throughout to detect downward trends and treat yourself early enough to prevent lows (but just remember that there is a lag time). If you use the other wearable devices we will be discussing next, feedback on your heart rate, steps, or other variables can help you figure out how many extra calories you may need to take in to match your activity and prevent a drop in your blood glucose. With these newer technologies, at least you have options that you may not have had otherwise (1).

Exercise Technologies and Wearable Devices

You may benefit from exercise-related technologies that allow you to monitor your heart rate, blood pressure, steps, sedentary time, exercise intensity, calorie use, and other variables in real time. For instance, heart rate monitors are good for achieving and maintaining appropriate exercise intensity, particularly if you are a data-driven person and are motivated by such feedback. However, keep in mind that you need to use individualized target heart rates based on your health status. Any medications that you are taking that may limit your heart rate also need to be considered. Many apps can track your heart rate in real time and allow you to train more effectively.

Tracking steps and other physical activity can also be useful. Step counters can motivate you to be more active throughout the day, not just during your planned workout times. Keeping a daily log of step counts can allow you to determine correlations between your activity and blood glucose responses. Apps for tracking workout progress and analyzing glucose patterns related to different forms of exercise can supply the feedback, allowing you to make regimen adjustments

in real time to avoid glucose lows and highs. Many smartphones now also have integrated accelerometers that can give you data on all daily movement including your steps, along with your sleep patterns and other useful information. It is likely in the future that some of the issues surrounding exercise with fully closed-loop systems may be addressed with wearable devices that provide input about changes in activity and heart rate that can impact your blood glucose.

Whether you choose to partake of the latest technologies or not, it helps to keep some general principles in mind whether you are already regularly active or getting ready to be. These vary somewhat by your diabetes type, but are largely based on whether you have to manage your insulin levels during exercise because you use insulin. Read through these general recommendations as well as the precautions for any complicating health issues and keep these points in mind to get the most out of your workouts.

Reference:

1. Excerpted from Colberg, SR, Chapter 5, “Using Technology and Monitoring to Enhance Performance” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019

Are Other (Nondiabetes) Medications Affecting Your Physical Activity?

Daily pillsIf you take any other medications to help lower your blood cholesterol, manage your blood pressure, or control other health problems, be aware that some of them can potentially impact your ability to be physically active. Although most drugs do not affect exercise, several common nondiabetes medications with such potential effects are statins, beta-blockers, diuretics, vasodilators, and blood thinners.

Statins

Statins are a class of medications prescribed to lower cholesterol levels or abnormal levels of blood fats to reduce your risk of having a heart attack or stroke. Brand names include Altoprev, Crestor, Lescol, Lipitor, Livalo, Mevacor, Pravachol, and Zocor. If you are someone who is unwilling or unable to change your diet and lifestyle sufficiently to lower your cholesterol enough or you have genetically high levels of cholesterol or triglycerides (another blood fat), then the benefit of statins on lowering your cardiovascular risk may exceed its risks. Given that cardiovascular disease (leading to heart attack and stroke) is the leading cause of death in adults with diabetes of any type, doctors often prescribe statins to people with perfectly normal cholesterol levels.

Although undesirable muscular effects are not that common, statins potentially can cause unexplained muscle pain and weakness with exercise, likely related to these medications compromising the ability of the muscles to generate energy. Other muscular conditions like myalgia, mild or severe myositis, and rhabdomyolysis, although relatively rare, are doubled in people with diabetes, along with an increased susceptibility to exercise-induced muscle injury. Other symptoms, such as muscle cramps during or after exercise, nocturnal cramping, and general fatigue, generally resolve when you stop taking statins. If you experience any of these symptoms, talk with your doctor about potentially switching to another statin or a different cholesterol-lowering medication.

About one-third of the athletes surveyed (of all ages) reported taking or having taken a statin. Many take the lowest possible dose of a statin as a heart disease preventative. Some reported getting side effects such as more frequent and severe leg cramps, muscle pain, and weakness, and others have complained of dizziness and foggy memories. Although people in the survey did not report any negative side effects, a few had to either stop taking statins or switch to another drug. (Examples of athletes’ use of statins and issues encountered are included in Chapter 3 in The Athlete’s Guide to Diabetes).

Beta-Blockers

Another class of medications called beta-blockers (e.g., Corgard, Inderal, Levatol, Lopressor, Tenormin, and Zebeta) are used to treat heart disease and hypertension (high blood pressure). They lower both your resting and your exercise heart rate. If you are taking one, your heart rate will not reach an age-expected value at any intensity of exercise, and you may not be able to work out as hard as you would like to. Be aware that your exercise responses may differ from normal when taking one of these drugs, that they can blunt your hormone response to hypoglycemia, and that they can increase your risk of more severe lows during activities.

Diuretics

Diuretics—or “water pills”—such as Lasix, Microzide, Enduron, and Lozol reduce the amount of water in your body and thereby lower your blood pressure. They can also lead to dehydration if you lose too much fluid. They are unlikely to affect your blood glucose, but using diuretics can cause dehydration with associated low blood pressure and dizziness during exercise.

Vasodilators

Taking a vasodilator like nitroglycerin allows more blood to flow to your heart during exercise, which can keep you from having to treat chest pain (angina) both at rest and during exercise. Be forewarned that vasodilators can also induce a drop in your blood pressure (hypotension), which can cause you to faint or feel light-headed during or after an activity.

Blood Thinners

If you have a high stroke risk, your doctor may put you on a blood thinner to keep clots from forming. However, aspirin and other blood thinners like Coumadin have the potential to make you bruise more easily or extensively in response to athletic injuries or to bleed longer before clotting if you get a cut or scrape while working out. If you take aspirin chronically to reduce your risk of stroke, you may only need a dose equivalent to a baby aspirin a day to limit these possible side effects. Luckily, none of these blood thinners usually have any direct impact on your ability to exercise.

Medications Without Exercise Effects

You may be prescribed a number of medications to treat a variety of health conditions. Luckily, many of these have no impact on your ability to exercise. For example, if you take an angiotensin-converting enzyme (ACE) inhibitor (e.g., Capoten, Accupril, Vasotec, Lotensin, or Zestril) or angiotensin II–receptor blocker (such as Cozaar, Benicar, or Avapro) to reduce your blood pressure or protect your kidneys from possible damage, you should not expect it to have any impact on your being physically active. In fact, certain ACE inhibitors may lower your risk of a heart attack during exercise if you have heart disease. Other medications that treat heart disease and high blood pressure (calcium-channel blockers like Procardia, Sular, Cardene, Cardizem, and Norvasc), depression (such as Wellbutrin and Prozac), or chronic pain (Celebrex) also have no known effect on exercise.

Aiming for an Ideal Exercise Blood Glucose

BG meterThere is no official ideal blood glucose range to start with and maintain during physical activity, but we do know that being too low negatively impacts performance, as does being too high. As for what blood glucose target or range most athletes aim for, it depends on a number of factors, including the type, intensity, and duration of their activity. A consensus statement about exercise and type 1 diabetes published in The Lancet in 2017 suggested that a reasonable target for most people doing aerobic exercise lasting up to an hour is 126 to 180 mg/dL (7.0 to 10.0 mmol/L), only aiming higher for added protection against lows in some situations (1).

For anaerobic (power) exercise or high-intensity interval training session, you may want to start with your glucose lower—around 90 to 126 mg/dL (5.0 to 7.0 mmol/L) simply because the intensity of the activity may cause your blood glucose to stay more stable, fall less than during aerobic workouts, or possibly even rise slightly (1).

An ideal or optimal blood glucose target during most physical activities may be in the range of 108 to 144 mg/dL (6.0 to 8.0 mmol/L).

Most of the athletes surveyed for The Athlete’s Guide to Diabetes (2019) said the range of 80 to 180 mg/dL (4.5 to 10.0 mmol/L) was their stated target during exercise. Only a few of them aim for lower or higher than that range, although most admittedly have a narrower target.

Canadian Scott L. from British Columbia agrees with recommended ranges for performance reasons, saying, “My aim is to be 6.0 to 8.0 mmol/L [108 to 144 mg/dL]. I feel the strongest at 6.0 mmol/L [108 mg/dL], but it gives me less opportunity to catch lows. Above 10.0 mmol/L [180 mg/dL], I start to feel a little sluggish—and above 15.0 mmol/L [270 mg/dL] very sluggish!”

But the blood glucose target depends on the activity and other factors. Just to give you a few examples, Chris C., a resident of New Jersey, tries to keep her blood glucose as close to 100 mg/dL (5.6 mmol/L) as she can, saying, “With high-intensity interval training my glucose will jump here and there throughout the workout with the intensity of the exercises. As soon as I am done, though, my glucose usually starts to drop.”

New York resident Riva G. uses a similar range of 80 to 150 mg/dL (4.5 to 8.3 mmol/L) for all her activities, but she likes to start on the higher end for walking. Jason O. of Ireland also varies his target based on his activity: 126 to 180 mg/dL (7.0 to 10.0 mmol/L) for cycling, just to make sure he has some leeway if he needs to make a big effort, and a tighter range of 90 to 144 mg/dL (5.0 to 8.0 mmol/L) for walking. For surfing, he aims for 5.5 to 9.0 mmol/L (100 to 162 mg/dL) in the water but uses a different target range of 4.5 to 7.5 mmol/L (80 to 135 mg/dL) for all other sports. Likewise, Ginger V. from Vermont sets the lower end of her range at 80 mg/dL (4.5 mmol/L) for all her activities, but she varies the higher end depending on whether she is doing fasted (120 mg/dL [6.7 mmol/L]) or nonfasted (150 mg/dL [8.3 mmol/L]) exercise.

The key is to find out what works best for you and maintain your blood glucose in that range during activities. Keep in mind that your glucose target may vary with the type of activity you do (mode, intensity, duration, etc.), exercise timing, insulin (or other medication) regimen, recent or concurrent food intake, environmental conditions, and multiple other factors. It’s not usually a one-size-fits-all solution.

References:

  1. Excerpted from Colberg, SR, Chapter 5, “Using Technology and Monitoring to Enhance Performance,” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.

Insulin Pump Use and Exercise Strategies

imd_insulin_pump_en

Whether you have type 1 or type 2 diabetes, if you use insulin, you may choose to use a specialized insulin pump for both your basal and bolus insulin delivery (1). Pumps have a small catheter placed under your skin and are programmed to cover your basal insulin needs by delivering small doses of fast-acting insulin to mimic normal insulin release by the pancreas. Insulin pumps are programmed to deliver small, basal doses of fast-acting insulin to replicate quasi-normal insulin release by the pancreas throughout the day. These pumps are not ideal for everyone, and the choice to use one should be an individual one.

The goal of insulin pump therapy is to provide insulin just like your body would—that is, in small doses all day long, with bigger doses after meals. Although this physiological pattern can be closely mimicked using injection regimens (e.g., Levemir for basal and Apidra boluses), insulin pumps make delivery easier and offer more flexibility by allowing you to have different basal rates of insulin delivery during the day or use temporary basal settings (such as during and after exercise). Pump users have the luxury of suspending the pump or immediately reducing basal delivery of insulin for activities, which you cannot do as easily without planning ahead if you use injections.

Although the number of insulin pump companies has dwindled recently, a number of pumps with various features are still available. Although you still have to be smarter than your pump, these “smart pump” features have helped take a lot of the guesswork out of it. Most pumps have options for small basal increments (0.05 unit per hour or less), temporary basal rates, insulin-on-board calculators, menu-driven programming, and various bolus patterns. Normal boluses, for instance, give the insulin dose all at once, but extended ones allow a dose to be given over a longer period to avoid peaks and valleys in coverage for foods that are more slowly absorbed; combination boluses combine these two strategies for optimal coverage of foods like pizza. Some are waterproof at shallow depths. The race is on to create the best combination of insulin pump therapy and continuous glucose monitoring (CGM) with algorithm-driven control systems. These “closed-loop” systems integrate features and make decisions for you, although exercise remains a sizeable management hurdle to overcome.

Insulin Pump Exercise Strategies

Insulin pumps give users the opportunity to reduce basal insulin levels and/or bolus doses in desired amounts and for different durations. As a result, pump use may reduce your exercise-induced hypoglycemia risk compared to multiple daily injections. Some strategies using pump features may be helpful, based on the purpose and timing of insulin dosing (1).

Altered Bolus Doses Before Exercise: You can adjust your meal and correction doses of insulin with a high degree of accuracy to accommodate for exercise. Calculate boluses as usual (entering the actual carbohydrates and blood glucose) and then adjust them using a percentage. For postmeal activity (i.e., when bolus insulin is still peaking, such as within 2 hours after eating), reduce your meal bolus by 25, 33, or 50 percent, depending on your upcoming activity.

Lower Basal Rates During Exercise: Reducing your pump’s basal rate before, during, or after exercise by programming a temporary basal rate can allow you to eat less to compensate and prevent lows, particularly when exercising for 2 hours or more. If you can plan ahead, try reducing your basal rate somewhat starting 1 to 2 hours before exercise to make sure your insulin levels are lower when you begin. Try reducing it by 50 percent, although you may need to lower it by 80 percent for prolonged exercise.

Lower Basal Rates After Exercise: Lowering your basal insulin for a time after exercise can also keep you from getting low later when your muscle glycogen is being restored. How much you will need to reduce it will vary by person and by situation. A common starting point is to reduce your basal rate by 25 percent for 6 to 8 hours afterward if you anticipate possibly getting low later.

Alternate Basal Insulin Profiles: You can use altered delivery patterns if you are going to be doing a full-day activity, such as during summer camp, or while engaging in intense sports conditioning, or when completing major projects around your home. Pumps allow you to switch to a basal pattern that is entirely different from your usual one, allowing for significant delivery rates during peak activity and more modest reductions when you are resting afterward. If you have a pump that allows you to alter bolus calculation formulas along with basal settings (insulin delivery profiles), such as the Tandem pump, you can also use a lesser hyperglycemia correction factor, decrease your insulin-to-carbohydrate ratios, and raise your target glucose during times when you will be more insulin sensitive.

Challenges to and Solutions for Pump Use During Exercise

Insulin pump use does present its own set of challenges related to physical activity and sports. For instance, some athletes have issues with getting infusion sets to stay in place during certain activities or with excessive sweating. Others have complained that the pump or tubing simply gets in the way during exercise, and they may prefer to remove the pump entirely while active. Given that pumps deliver rapid-acting insulins only, removal of the pump for an excessive length of time (longer than 1 hour) can result in severe hyperglycemia and ketone formation, potentially leading to diabetic ketoacidosis (DKA). Exposing your pump to water and extreme weather conditions can also threaten its integrity and the insulin in it.

Reference:

  1. Excerpted from Colberg, SR, Chapter 3, “Ups and Downs of Insulin and Other Medications,” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.