Type 1 Diabetes and Sports Participation
Strategies for Training and Competing Safely
Martin B. Draznin, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 12 - DECEMBER 2000
In Brief: Athletes with diabetes require intensive diabetes management to balance insulin, carbohydrate intake, and the effects of exercise. Effective care of active patients who have diabetes starts with a targeted preparticipation exam. Decreasing the insulin dosage may be necessary for heavier exercise programs if carbohydrate supplementation alone is insufficient. The documented risk for either hypoglycemia or ketoacidosis requires careful planning for training or competition. Analysis of 'high-risk' activities is essential to determine which may need to be modified, diminished, or restricted.
Approximately 16 million people with diabetes mellitus live in the United States. Of the 10% who have type 1 diabetes (also known as insulin-dependent or juvenile-onset diabetes), about half are under 20 years old, with the prevalence in this age-group estimated at 260 per 100,000 (1). The other 90% have type 2 diabetes, also called non-insulin-dependent or adult-onset diabetes. Wider recognition of the benefits of intensive diabetes management is a recent phenomenon (2,3), but there has long been a philosophy among diabetes specialists to advise patients to become more physically active in hopes of improving their diabetes control and enhancing their quality of life. The development of type 2 diabetes can be significantly delayed by exercise and by maintaining an active lifestyle. We should anticipate increasing numbers of athletes with diabetes to be involved at all levels of participation and competition because the incidence of both types of diabetes is increasing (4,5). This review, however, focuses on active people who have type 1 diabetes.
The Effects of Physical Activity on Metabolism
During physical activity, exercising muscles significantly increase their use of oxygen and of substrates such as muscle and liver glycogen, muscle triglycerides, and free fatty acids (6). These substrates are mobilized by the action of epinephrine, glucagon, cortisol, and growth hormone. In a healthy person, blood glucose concentration continues to be regulated by these hormones and by insulin so that it remains within an appropriate range (7).
The brain requires a minimum concentration of plasma glucose for maintaining normal functions, including surveillance of the space surrounding the athlete, judgment, and consciousness. Because of this requirement, hypoglycemia is severely maladaptive during exercise. At the other extreme, the kidneys may not be able to maintain adequate circulating plasma volume if hyperglycemia and glycosuria diminish the ability to deliver oxygen to exercising muscles. Additionally, the metabolism of fatty acids for energy results in the generation of ketones that, in excessive concentrations, depress plasma pH and interfere with the normal function of nerves and muscles, including the heart. In short, in the healthy person, the concerted action of several hormones allows for as much as a 20-fold increase in oxygen consumption without departure of several key substances from a narrow range of plasma concentrations needed for normal function.
Type 1 diabetes may involve normal hormonal responses mediating the release of fuels or degrees of deficiency of glucagon and/or epinephrine response (8). The availability of insulin to counter excess elevation of plasma glucose is not under the exquisite control seen in a healthy individual. To increase glucose absorption and insulin levels in a diabetic person, capillary blood flow increases in exercising muscle to enhance the accessibility of insulin receptors to the insulin in circulation. Also, blood flow to the insulin injection sites increases. With the loss of the tight normal control of circulating insulin and glucose, dangerously disabling hypoglycemia may occur during exercise. Another risk is delayed hypoglycemia occurring several hours after exercise, possibly during sleep.
Conversely, if preexisting mild ketosis or significant hyperglycemia is present at the start of vigorous physical activity, ketoacidosis may be precipitated. This occurs when the so-called counter-insulin hormones raise the level of glucose and free fatty acids more rapidly than the enhanced insulin uptake by muscle receptors and the exercise-induced increase of insulin concentration can act to suppress lipolysis and ketogenesis. By careful assessment of metabolic control, athletes with type 1 diabetes must learn to regulate the injection of correctly adjusted doses of insulin and ingest appropriate nutrients to duplicate the system that runs automatically and without conscious effort in healthy athletes.
Exercise Benefits in Diabetes
There are obvious social benefits to exercise and sports participation: peer relationships developed and enhanced by shared experiences, enhanced self-esteem and confidence from mastery of a skill, learning about teamwork, character, and courage, etc (7). In addition, some studies (9-12) suggest health benefits for athletes with type 1 diabetes. Mosher et al (9) found that aerobic circuit training helped adolescents improve cardiorespiratory endurance, muscle strength, lipid profiles, and glucose regulation. Research by Lehmann et al (10) showed that adults with type 1 diabetes safely reduced cardiovascular risk factors such as abdominal fat content, blood pressure, and adverse lipid levels by exercising 135 min/wk. Soukup and colleagues (11,12) were enthusiastic about the benefits of resistance training for individuals with diabetes but cautioned that when there is microvascular disease, such as retinopathy, athletes should avoid lifting excessively heavy weights, which could increase intravascular pressure. Maintaining good metabolic control is also important. Other studies (13,14), however, suggest that the changes in type 1 diabetes are not that substantial or lasting.
Finally, several athletes have told their stories of self-improvement, advocacy, how they learned to deal with insulin balances, and a bit of the frustration felt as they discovered how to manage their diabetes and their sports participation by trial and error (15-18). Because each patient's body chemistry and circumstances are unique, it is difficult to make generalizations about what kind of insulin regimen is needed for a particular sport. Most of the day-to-day care and assessment of diabetes is done by the athletes and their families; therefore, their physicians provide more counseling and education than direct care.
The basics of preparticipation assessment of the athlete with diabetes are identical to those of any other athlete. All aspects of general health and fitness (cardiovascular health, flexibility, freedom from injury, neurologic integrity, absence of any critical paired organ, etc) should be assessed for suitability for that particular sport for that participant (table 1) (7).
Complications of diabetes that would preclude certain sports activities should then be determined. Retinopathy would make it risky to engage in activities that rapidly or explosively elevate intraocular pressure that may cause hemorrhage into the vitreous humor. Bleeding from damaged retinal capillaries during Valsalva's maneuver while lifting heavy weights or from collisions with other athletes also poses a risk. An examination for early signs of retinopathy should be done by an expert at least once a year (7).
Peripheral neuropathy increases the risk of injuries because of lack of sensation or abnormalities of gait. Autonomic neuropathy heightens the risk for lack of cardiac responsiveness to rapidly changing needs for increased cardiac output and may interfere with the absorption of nutrients. Gastroparesis could also make absorption of carbohydrates unpredictable. The presence of nephropathy and hypertension could also be risky. It is not known how many individuals with diabetic neuropathy or nephropathy are currently attempting to pursue sports; thus, the nature and magnitude of the risks to those individuals is unclear.
Next, a careful history should be taken of how the athlete manages diabetes so that adjustments can be made to match the changes caused by training and participation in the sport in question. It is also important to learn whether previous sports-related difficulties (injury, poor performance, etc) were due to problems with managing diabetes and whether the athlete understands the mechanism of the problem. Important characteristics of the athlete such as emotional stability, maturity, dedication to training, and acceptance of the need to master care of diabetes should also be evaluated. It is vital as well to ensure the adequacy of support systems such as family, coaches, and athletic trainers, all of whom may need to be involved in any problems that need resolution to allow the athlete to participate at an optimal level and with reasonable safety.
Any sport involves a risk of injury. This risk is likely to be magnified by inattention or loss of coordination, such as during an episode of hypoglycemia. In extremely risky sports and activities, the risks are much higher. For example, rock and mountain climbing may expose participants to a lethal danger of falling if their concentration lapses, so a climber with diabetes would have to ensure that hypoglycemia was not going to happen. Skydiving requires continuous focus of attention as well.
Scuba diving is another potentially high-risk activity; thus, its suitability for individuals with diabetes has been studied. For example, military diving is not allowed in Great Britain for people with type 1 diabetes (19), and in the United States they cannot join the military at all. Sport scuba diving may be safe with adequate preparation and a skilled partner who can handle trouble with diabetes during the dive. A carefully designed plan to prevent and remedy any hypoglycemia without undue risk to the diving partner should be in effect before diving is attempted (20,21). Any sport that tends to expose the athlete to significant periods of isolation from outside sources of assistance—for example, a long-range dogsled race—would have to be similarly assessed.
Sports in which the danger of inattention or loss of motor control would endanger others, in addition to endangering the athlete with diabetes, should not be entered into casually; in fact, many would oppose any participation in such activities by athletes with diabetes. Proper sports etiquette suggests soliciting in advance of participation the assent and support of anyone who may be affected by an adverse event.
Preparation for Sports
A thorough understanding of the nature of the training, practices, and competition, and in the potential effects on metabolic control in diabetes, is necessary to craft a plan for safe and productive training and optimal performance. Some factors to consider are:
Given a thorough preparticipation evaluation, it is possible to tailor diabetes care to allow for very active sports participation, including extremely difficult participation, such as an ironman triathlon. Intensive diabetes management with multiple daily injections of insulin, or an insulin pump, and numerous checks of blood glucose throughout the day will give a clearer picture of the effects of exercise (table 2).
A standard strategy for moderate training schedules is to offset the increased efficiency of insulin use by ingesting 15 g of carbohydrate for every half hour of moderate aerobic exercise. Monitoring of blood glucose during practices of several hours duration is advised. Adjusting insulin downward may be necessary for heavier exercise programs if carbohydrate supplementation alone is insufficient, or if the extra food intake is too uncomfortable and limiting to the athlete. It may be necessary, in some cases, to decrease the total insulin dosage by a third or more during sports seasons, unless the athlete is active at the same level all year. In that case, the dosage may not need to be modified. Blood glucose should be checked more often early in the training season to assess how to balance insulin, carbohydrate intake, and exercise. (See, "Success Stories of Insulin Adjustments," page 55.)
It is critical to counsel the athlete to check for and prevent delayed hypoglycemia that often occurs after muscle and liver glycogen has been depleted and not replenished during exercise. Another way to lessen the risk of this problem is to avoid the use of intermediate-acting insulin during the afternoon or early-evening hours by shifting its injection to bedtime, or by replacing intermediate-acting insulin with a long-acting insulin option that does not "peak."
Newer insulins include a synthetic aspart that, like lispro, is very rapidly utilized and gone from the circulation and glargine, an extended insulin zinc suspension that is advertised to be administered once daily. Ultralente works more safely if given twice a day. Glargine has not had the exposure yet to determine whether it truly is a once-a-day basal insulin (table 3).
Testing is done before meals and at bedtime regardless of the type of insulin used. To establish the dose (given by injection or by pump) for long-acting insulin plus lispro for meals, the patient also tests blood glucose 2 hours after each meal for 3 to 4 weeks. Careful record keeping will determine if assumptions are correct and which doses work best.
Proper use of an insulin pump, with its adjustable "basal" rates for differing sensitivities to insulin, should offer even more protection against nocturnal hypoglycemia. Pumps are about the size of pagers and are worn on the belt of regular clothing or in a sports pack. In the past, pump use in sports was very complicated, but some current models can be worn even while swimming if placed in a waterproof pack. The infusion set is a soft plastic catheter that remains in the skin for up to 2 days, attached to the pump by a flexible plastic tube.
For collision sports and those in which the athlete experiences extreme degrees of flexing, twisting, and contact near the area of skin where the infusion set is attached, it may be necessary to inject subcutaneous insulin and detach the pump during the activity. The infusion set remains in place. The amount of insulin injected should initially be the same number of units the pump would have delivered over the time it is to be replaced. Adjustments to the dosage are then made until the blood glucose level remains in a suitable range.
In addition to preventing hypoglycemia during and after exercise, it is also necessary for the athlete with diabetes to monitor blood glucose prior to exercising to avoid precipitating hyperglycemia and ketoacidosis. These may occur if exercise is done in the absence of adequate insulin.
Signs of hypoglycemia include apparent loss of concentration and focus, shaking or shivering, and loss of consciousness. A designated person must be available at all practices and competitions to look for signs of hypoglycemia, check athletes for hypoglycemia in case there is any question of it, and help manage hypoglycemia when athletes are unable to treat themselves. This person should know how to administer rapidly absorbed forms of glucose to conscious athletes and glucagon when athletes are unable to safely swallow glucose. In cases of hypoglycemia with carbohydrate depletion, glucagon is less effective. Plans for intravenous fluids containing glucose may be needed as well. Many hospitals have diabetes educators who provide training classes, and family members involved in day-to-day care are also knowledgeable.
Some manufacturers claim that glucose gels can be absorbed in adequate quantity by just rubbing them on the gums, but in my experience, the volume needed to provide adequate glucose is on the order of several milliliters, so swallowing is required. Thus, to protect the airway from aspiration of the gels, the athlete who is being treated with gels should be responsive and cooperative.
The Physician as Educator
Participation in sports often enhances the health and quality of life for those with diabetes. Knowledge of the specific metabolic changes that exercise induces, and how to adjust the management of insulin and nutrition, will allow these benefits to be safely enjoyed by diabetic athletes. The goals of the physician caring for an individual with diabetes should include allowing participation in as wide a range of life-enhancing activities as can be safely done. Because the care of diabetes is done mostly by the patient and family, the physician's key role in facilitating sports activities is as an educator.
Success Stories of Insulin Adjustments
I had the pleasure of watching televised portions of the Hawaii Ironman Triathlon in 1984 during which Brad Carlson, an athlete who has type 1 diabetes, participated with the support of his physicians. He removed his insulin pump and took subcutaneous insulin before the swimming portion of the race, then put the pump back into service for the bicycle ride and the run. He was required to make numerous stops to check his blood glucose level and to discuss with his physicians what to do next. His comment on finishing the race was that he would log a better time if he didn't have to check in as much. He subsequently did exactly what he predicted—the next time he competed, he did his own adjustments and improved his performance.
A 14-year-old skater in my clinic switched her insulin from her usual mixture (intermediate- and short-acting insulin at breakfast, short-acting at the evening meal, and intermediate-acting at bedtime) to a twice-a-day extended insulin zinc suspension for basal insulin and lispro, a very short-acting insulin, for meal coverage. She needed to awaken and eat at 4 am to get on the ice to practice before school. Additionally, the high school had a 10:30 am lunchtime that gave other students with diabetes some difficulty. My patient found it fit her schedule perfectly.
A 16-year-old swimmer in my clinic had numerous instances of hypoglycemia. He is a very hard-working athlete and would push himself beyond the safe limits of his insulin shots. He often needed to stop in the middle of practice to eat, and felt very weak and panicky when hypoglycemia occurred in the middle of the pool. Fortunately, the patient never lost consciousness. He switched to using an insulin pump that he could detach from the infusion set during practice and competition. He has not had trouble with hypoglycemia caused by over-rapid absorption of insulin since he switched to the pump method and is now much safer in the water.
An elite high school tennis player was happy with an extended insulin zinc suspension injection twice a day and regular insulin for meal coverage but switched his short insulin to lispro. This suited him even better since the wait between injection and eating is only 10 minutes with lispro rather than the 40 minutes for the regular insulin. He then noticed that he had more bedtime hyperglycemia when using lispro for dinner coverage. He independently adjusted his regimen to include half lispro and half regular insulin with dinner, and his hyperglycemia resolved without hypoglycemia (18).
Dr Draznin is the director of Pediatric Endocrine Specialty Clinics at Michigan State University Kalamazoo Center for Medical Studies in Kalamazoo, Michigan. Address correspondence to Martin B. Draznin, MD, Pediatric Endocrine Specialty Clinics, Michigan State University College of Human Medicine, 1000 Oakland Dr, Kalamazoo, MI 49008; e-mail to [email protected].