Diabetes Forecast

The Healthy Living Magazine

Endurance Sports and Diabetes Management

By Tracey Neithercott , ,

The phrase "endurance exercise" conjures up images of burning muscles, screaming lungs, sneakers, and sweat. Lots of sweat. Yes, there are indefatigable athletes for whom running, walking, swimming, or otherwise exercising for hours on end gives meaning to the word endurance, but you don't have to race an Ironman to test your stamina. What constitutes endurance for you (a 30-minute 5K? Four hours of cycling?) depends on your fitness level.

Most of the time, doing an endurance sport will lower your blood glucose, so it's important to know how to manage your diabetes before, during, and after a workout—whether you plan to run 3 miles or 30.

Before You Exercise

Take Notes: "People who are really starting this new need to be disciplined," says Nathan LeBrasseur, PhD, an exercise physiologist and endurance athlete with type 1 diabetes, about endurance sports such as triathlons. "Start on a treadmill with your meter nearby so you can see how you're doing." You may want to keep detailed logs of your exercise times, carbohydrate intake, medication doses, and blood glucose levels.

Test Your Blood Glucose: Before you start, test. It's OK if you're running a tad high—say, 160 mg/dl—because exercising will bring your level down. But it's not safe to exercise with type 1 if you have ketones in your urine or blood because that can drive the body toward the dangerous and sometimes life-threatening condition diabetic ketoacidosis (DKA). A blood glucose reading over 250 warrants a ketone check. If you have ketones in your urine, drink water, dose insulin as prescribed, and wait to exercise until your body clears the ketones.

Similarly, beginning exercise with a too-low blood glucose level is dangerous. Exactly how low is too low differs from person to person, though. "For me personally, " says LeBrasseur, who does triathlons and will race in a half Ironman this summer, "I almost want to start out with a blood glucose of 180 or so because I know I'm going to have this drop."

Eat Smart: When you do any form of endurance exercise, your body uses glucose for energy. If you don't have enough glucose stored up, you could become hypoglycemic. Start the day with a meal balanced in carbs, protein, and fat. If you're running low before a workout, try a balanced snack, such as an energy bar or a banana and peanut butter.

Modify Your Meds: Frequent workouts can keep your level lowered for the day, even the week. "It's mind-blowing to me that when I'm fit and exercising, I'm using about 20 percent less of my total insulin," LeBrasseur says. (A person with type 2 diabetes who is on sulfonylurea medications and adds more physical activity may also need to work with a doctor to adjust dosing or switch meds because the drugs put one at a higher risk for lows.)

While You're Exercising

Test and Treat: People with diabetes who do any endurance sport (think triathlons, marathons, and long cycling races) typically test their blood glucose as often as every 15 to 30 minutes.

Keep Eating: Endurance athletes with diabetes work hard to prevent lows before they happen, consuming energy bars or glucose gels or drinks to get about 10 to 20 grams of carbs or more every half hour, depending on the activity.

Adjust Your Pump: Athletes using a pump can lower their basal rate considerably during endurance exercise as their body gobbles up glucose, but disconnecting completely—without injecting via syringe—isn't recommended for exercise lasting more than about one hour. "For people with type 1 diabetes, we always want to make sure there's some insulin going in, even if it's a very little amount," says Karen Kemmis, PT, DPT, MS, CDE, an exercise physiologist and diabetes educator at the Joslin Diabetes Center affiliate at SUNY Upstate Medical University in Syracuse, N.Y. Though most athletes keep their pump attached during events, swimmers may sometimes disconnect for up to an hour if their pump isn't waterproof.

Meet Other Contenders

Learn, train, race, and meet other endurance athletes with diabetes.
InsulINdependence: Recreational activities (such as hiking and surfing trips), Triabetes triathlon club, and youth programs
Riding on Insulin: Ski and snowboarding camps for kids and teens
Team Wild: Training camps and coaching for cycling, running, and triathlons
Teams Type 1 and 2: Professional cycling, triathlon, and running teams
Tour de Cure: Bike ride raising funds for the American Diabetes Association

Manage Your Site: Whether you're on a pump or injections, avoid lows by injecting insulin into an area less affected by the exercise to slow down the absorption. For example, skip the thigh if you're a runner. Also important for pumpers: keeping your infusion set in place, especially during the summer, when sweat can make it unstick. Rob Ragland, 39, a runner with type 1 diabetes, makes sure to change his every three days as directed so his site doesn't begin to peel or fray. If yours peels before that, consider using a stronger adhesive the next time you change your site.

After You've Exercised

Eat Up: Because you've used a lot of your body's stored glucose, you need to replenish it. That means eating enough carbs after a big workout to keep blood glucose from dipping.

Test Often: Even after moderate-intensity activity, it's important to be careful for hours afterward. For people with type 1 diabetes, blood glucose levels can drop even 48 hours post-exercise, says Kemmis. Continue testing your blood glucose regularly to catch any lows.

Stay Hydrated: Dehydration is a real threat to endurance athletes, which is why you'll need to keep drinking plenty of water even after you've finished working out. Not only will dehydration make you sick, but it may also make your blood glucose level spike.

Get Ready for Race Day

If you plan to compete, here are some tips for performing well (and staying safe) during a race.

1. Account for adrenaline.

The start of a race can have your heart pounding and blood glucose soaring. You have adrenaline to thank for both of those. It's normal to run higher at the start of a competition because of the hormone. Just make sure you factor that into your diabetes management plan.   

2. Go ahead, carbo-load.

According to Nathan LeBrasseur, PhD, an exercise physiologist and endurance athlete with type 1 diabetes, it's OK for people using insulin to eat a carb-heavy meal the night before a big event as long as those carbs are covered with insulin. (The insulin won't cancel out the carbs; they'll be stored for use during your race.)

3. Watch what you eat.

What gives one athlete a good supply of glucose may make another's stomach turn. Learn while training—not on the morning of a race—what foods work for you and which don't sit right (usually those with more fiber, such as apples, says Karen Kemmis, PT, DPT, MS, CDE, an exercise physiologist and diabetes educator).   

4. Learn how to eat.

For any long-distance race, you'll need to continually refuel, but eat too much and your performance can suffer. Determine during training just how much food can sit in your stomach. And if you take too much insulin, you might not be able to eat your way out of a low without hurting your ability to perform.

5. Watch the weather.

If your blood glucose acts differently in hot and cold temperatures, take that into account on race day. Type 1 athlete Rob Ragland goes low while competing in hotter temperatures but can more easily keep his blood glucose up when it's cooler.   

6. Do your homework.

Help your race go smoothly by researching the course and contacting the race coordinator about what to expect on race day. Will your food of choice be available? Do the organizers allow you to stash special-needs supplies (such as glucose gel and an extra meter) at various checkpoints? How many stations are there, and where?

Safety Note: Check with your health care provider before making big changes in your exercise plan, which could require adjustments in your meds, foods, or other treatment.


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