Diabetes and exercise is a topic of its own, and sometimes managing blood sugars around exercise and activity turns out to be more challenging than the workout itself.
On the one hand, it’s hard because your body reacts completely different depending on the time of day and how fit you are. And on the other side, it’s hard because your blood sugar behavior varies depending on what kind of exercise or activity you’re doing. Yikes! Talk about introducing a ton of variables into the mix! But exercise is so good for you that it’s worth the trouble. It’s a surprisingly powerful tool in your diabetes toolbox. When you spend a bunch of time before, during, and even after your exercise worrying about how to stay in range and avoid nasty lows. Then, in the end, your blood sugar does whatever it wants. That can be so frustrating. Sometimes situations sneak up on you, too! It’s so easy to forget that everyday activities like gardening, pushing a baby stroller or shopping cart, or even doing your shopping also count as activity. It’s not only physical activity that burns a lot of sugar. Your brain also needs a lot of energy, so deep thinking can also lower your blood sugar levels.
What exactly does exercise do to your body?
Power sports (anaerobic) In anaerobic sports (for example, lifting weights, climbing, volleyball, tennis, sprinting (i.e., mostly stop-and-go sports)), blood sugars may stay stable or even go up, and then fall again afterward while you’re recovering. Anaerobic exercises are usually brief, intense bursts of physical activity where the oxygen demand surpasses the oxygen supply. The cells can’t go through their usual ways of getting the energy to perform whatever the action is (lifting weights, sprinting, etc.). In situations like these, adrenaline rushes in to help which causes sugar stores in the muscles to dump their load. You can already guess what happens next – your blood sugar rises quickly. This is especially common in competitive situations. Some athletes with diabetes take a little bit of fast-acting insulin to stay on track here.
Endurance sports (aerobic) In aerobic exercise (for example, jogging, walking, swimming, cycling), blood sugar usually drops, both during and for a long time after. You can often do aerobic exercises for more extended periods of time (10-minutes or more). They are usually rhythmic and repetitive and will increase your heart rate and breathing. Here, your body is burning oxygen along with glucose stores or fat to supply the energy you need. For exercise newbies and those getting back in shape, low-intensity steady workouts are ideal, since your body will use fats as the primary energy source, and burn sugar reserves at a slower pace. This lets you last longer and also reduces the hypo risk. With increased intensity and duration, more glucose is used, and your risk for low blood sugars also increases. The more often you exercise, the more efficient your muscles will get at using energy, and the better it will get at using fats for energy. Additionally, the glycogen store in your muscles (200-300 g) gets bigger the more you use it. So you can expect that at the beginning of a new activity, you’ll have to be more aggressive with planning and precautions than you will once your body gets used to it.
And while you relax ...
After exercising, while you’re recovering and basking in the glow of doing something great for yourself, the work for your body is just getting started. Especially after any endurance exercise, your glucose stores will be empty and hungrily snatch up any sugar floating through your bloodstream for the next 7-11 hours. It might feel like your insulin is supercharged, and you need to stay mindful of lows. For extreme events, like a marathon or a weekend sports tournament, it may take several days until things are back to normal. This is partly due to small insulin-independent transporters that help shovel sugar into the cells to replenish the sugar stores in your muscles and liver. Did you catch that? Those special transporters work even without insulin! That’s part of what makes exercise so cool!
Diabetes and exercise tips and tricks
- It can be hard to feel lows during exercise because the symptoms are hard to feel when you're exercising. Check your blood sugar often and stay mindful about it until you get the routine figured out – especially if it’s a new exercise for you.
- 120-180 mg/dL (6.6-10 mmol/L) is a great blood sugar target to start your exercise session.
- Keep fast-acting glucose nearby and readily available to treat low blood sugars. For more extended duration activities, you may need to consume carbohydrates during your exercise to prevent lows.
- If you use an insulin pump, consider reducing your basal rate or even disconnecting your pump for a while. Generally, you can program basal rate reductions for 4-5 hours or longer. Start your basal rate reductions on a pump 60-90 minutes ahead of time. You need at least that long before you’ll see any change in your blood sugar.
- Rapid drops in blood sugar during exercise often come from too much active insulin on board. Be extra careful of this if you’re starting a workout with lots of insulin on board, and plan if you know you’ll be working out soon after taking any insulin. For pre-breakfast exercise, average basal rate reductions are 20-50%, depending on insulin type, exercise intensity, and current fitness level.
- For endurance sports lasting more than 1-2 hours, you may only need 20-75% of the usual amount of insulin for the meal before exercise.
- Full-time (all day) activities often require lowering meal and basal insulin for the next 24 hours after the exercise. For medium intensity activities, the basal requirement is reduced by 30-50% and for very high and long intensity activities by 50-75%.
- For type 1 diabetes, eating at least 90 minutes after your workout may reduce the risk of overnight lows. Especially in the afternoons or evenings, you can reduce your insulin intake by up to 50% or eat small extra fat and protein snacks before you go to sleep without insulin. Everyone, however, is unique and you’ll need to experiment a little bit to find the right balance for you.
- After the strength training, which can initially lead to higher blood sugars, insulin requirements may fall over the following 6 hours as the liver replenishes its reserves. You can compensate for this with less insulin at the next meal or additional snacks. For pump users, a basal rate reduction of about 30% might also be an excellent place to start.
- Take special care with alcohol after exercise – this will prevent your liver from releasing sugar. In this case, increased insulin sensitivity and reduced sugar release overlap! Watch out for low blood sugars! Keep your wits about you and your glucose tabs ready!
What else is there to consider?
If you have type 1 diabetes and start your exercise with high blood sugars (above 250 mg/dL (14 mmol/L)), be sure to check for ketones. If you have ketones, it’s best to sit this one out. Exercising may accelerate/encourage more ketones, and that’s something you want to avoid for sure.