📘 Physical activity in T1DM

Absolutely yes. Many Olympic and professional athletes have type 1 diabetes, demonstrating that the disease doesn't limit athletic potential when well managed [1]. Examples of sports with top-level performances include Olympic swimmers, Tour de France cyclists, tennis players, professional footballers and elite marathon runners. The key to success is meticulous planning, intensive monitoring (CGM during training), precise adjustment of insulin and carbohydrate doses for the specific type of effort and collaboration with a medical team specialized in diabetes and sport [2]. Modern technology (pumps with exercise mode, CGM with predictive alarms) has eliminated most technical barriers.

Specific challenges include different management for aerobic sports (lower glucose) versus anaerobic (temporarily raise it) [3]. Other issues to solve include travel for competitions with time zone changes, competitive stress (raises glucose) and sports regulations about using medical devices in competition. The adaptation period lasts one year, until you learn your individual response to different types and intensities of effort. Performance can even be improved through nutritional discipline and superior metabolic monitoring that diabetes imposes [1].

Preparation starts 2-3 hours before. Target a starting glucose of 180 mg/dl (10 mmol/L) for aerobic exercise and 120 mg/dl (6.7 mmol/L) for strength training [3]. Don't forget to check the trend on CGM (stable or slightly rising arrow) [4]. Reduce the previous meal bolus by 50% and/or basal rate by 50% starting 90 minutes before effort. For unplanned exercise, consume 15g carbohydrates without insulin if glucose is below 150 mg/dl (8.3 mmol/L) [3].

Check ketones if glucose is above 300 mg/dl (16.7 mmol/L) [3]. Their presence temporarily contraindicates exercise until correction. The sports kit includes glucometer/CGM, fast carbohydrates (gels, glucose tablets), complex carbohydrates (cereal bar), nasal glucagon for emergencies and visible medical identification bracelet. Preventive hydration and electrolytes help achieve optimal performance in safe conditions.

Aerobic exercise increases insulin sensitivity [5]. Muscular glucose consumption increases up to 50 times compared to rest, through insulin-independent mechanisms [5]. Muscle contraction activates glucose transporters without needing insulin. Simultaneously, circulating insulin from previous injections continues to act [6]. The effect amplifies during efforts over 30 minutes, when muscle glycogen stores are depleted and muscles take up even more glucose from blood.

Glucose drop is accelerated by increased temperature (vasodilation and rapid absorption), time of day (higher sensitivity in the afternoon), physical effort on an empty stomach and alcohol consumed in the last day [3]. Paradoxically, very intense or competitive exercise can initially raise glucose through release of stress hormones (adrenaline, cortisol), followed by significant delayed drop [7]. The hypoglycemic effect persists 24 hours after exercise [5]. During this period muscle glycogen stores are restored, generally requiring reduction of overnight basal insulin.

Paradoxical rise occurs after intense anaerobic exercises (sprint, weight lifting), stressful competitions or HIIT training, when counter-regulatory hormones (adrenaline, cortisol, growth hormone) exceed the hypoglycemic effect of effort [7]. Glucose can rise temporarily by 100 mg/dl (5.6 mmol/L) in the first 60 minutes, but don't rush with correction [3]. In 2-3 hours there usually follows a significant drop, when hormones normalize and insulin sensitivity increases. If needed, correct conservatively with half the calculated dose and monitor carefully.

For prevention, you can give a small bolus (one unit) 15 minutes before intense exercise known to raise your glucose [1]. Alternatively, you can combine anaerobic exercises with 15 minutes of light aerobic effort for balance [3]. Don't confuse temporary physiological glucose rise with significant insulin deficiency. Closed-loop systems automatically manage these fluctuations.

If planned exercise follows, you can reduce basal rate by 50% starting 90 minutes before [3]. The bolus for the meal before exercise is also reduced by 50% [3]. You can reduce more for longer aerobic exercise or less for shorter training, especially if it involves strength exercises. For team sports with variable intensity, consider temporarily suspending the pump during effort and reconnecting during breaks with micro-boluses as needed [1].

Post-exercise, reduce the next meal bolus by 20% and overnight basal rate by 20% for preventing delayed hypoglycemia [8]. If you start unplanned exercise, consume 15g carbohydrates without compensatory bolus, repeating every hour or more frequently depending on glucose evolution [3]. Keep a detailed journal (type of exercise, duration, intensity, adjustments made, results) to identify personal patterns. Response varies enormously between individuals and requires continuous adjustments for one month for each new type of activity [1].

For exercise under 45 minutes moderate use glucose tablets (3-4 tablets = 15g, absorption in 10 minutes) or sports gels (20-25g per packet, action in 15 minutes), which are sufficient for rapid glucose corrections [9]. For prolonged effort over one hour combine fast carbohydrates with complex ones, such as banana (25g, bonus minerals), cereal bars (20-30g, easy to carry), dried fruits with nuts (30g, have fats for sustained effect) or a jam sandwich (40g, balanced). Isotonic sports drinks (8% carbohydrates) offer hydration and carbohydrates simultaneously.

As a general estimate you need 30-60g carbohydrates per hour for moderate exercise and 75-90g for very high intensity [9]. Consume these carbohydrates in small doses every 15 minutes [3]. Avoid foods rich in fiber, fats or proteins before and during short duration effort. They slow absorption when you need quick energy. Test all products in training before competitions to avoid gastrointestinal surprises.

The presence of blood ketones above 1.5 mmol/L or in urine (++ or more) contraindicates physical exercise [3]. Values between 0.6-1.5 mmol/L require caution. In these conditions it's better to postpone physical effort because effort in the absence of sufficient insulin level accelerates ketone production and can precipitate diabetic ketoacidosis in just a few hours [10]. If you have low ketone level (urine + or blood 0.6-1.5 mmol/L) correct with insulin and rehydrate. Check after two hours to see if it's resolved and if yes you can do light physical effort. You need to differentiate between "starvation" ketones, which appear in the context of normal or low glucose after prolonged fasting and truly pathological ones, associated with severe insulin deficiency with high glucose [3].

If glucose is above 300 mg/dl (16.7 mmol/L), always check ketones before sports [3]. If present, correct with 150% of normal correction dose, hydrate intensely and postpone exercise until ketones completely disappear and glucose reaches 180 mg/dl (10 mmol/L). In case of insulin pump, presence of ketones with high glucose suggests an insulin delivery problem. Change the complete set in this case and make a correction with a pen or after you've mounted the new set.

Post-exercise nocturnal hypoglycemia occurs in up to 25% of nights after intense sports due to increased insulin sensitivity and restoration of muscle glycogen stores [11]. Preventive strategies include reducing overnight basal rate by 20% and glucose target for bedtime at 180 mg/dl (10 mmol/L) [8]. For intense afternoon or evening exercise, consider reducing basal by 20% [3].

Monitoring with a glucose sensor is essential [4]. Set the alarm threshold higher on nights following more intense physical effort than usual, especially performed toward evening. Alcohol after exercise amplifies hypoglycemia risk [3]. Individual pattern varies, with maximum risk usually in the first 6 hours, but some may have it at 12 hours [11]. Keep fast carbohydrates and glucagon by the bed and instruct partner about symptoms and treatment of nocturnal hypoglycemia.

All sports are possible, but some offer extra advantages for glycemic management [4]. Moderate aerobic exercises (brisk walking, low intensity swimming, long distance cycling) have predictable hypoglycemic effect and easy to manage. Resistance training with moderate weights maintains muscle mass (major reservoir for glucose) and improves insulin sensitivity long term [5]. Yoga, Pilates and Tai Chi combine metabolic benefits with stress reduction and balance improvement.

Team sports (basketball, football, tennis) offer social motivation but require complex strategies for adapting to variable effort intensity [1]. Extreme sports (mountaineering, diving, skydiving) require special safety protocols and extensive experience in diabetes management [3]. Swimming presents unique challenges because glucose sensor doesn't transmit information underwater, access to carbohydrates is limited and hypoglycemia symptoms can be masked [2]. Choose sports you enjoy and will practice consistently. Regularity is important because gradually you learn how you respond to various situations.

Most glucose sensors are resistant to sweat and moderate impact, but require additional protection for contact or aquatic sports [2]. For swimming, most sensor models temporarily lose bluetooth transmission underwater but continue to record data, which syncs upon exit. Check the trend before starting physical effort and check the sensor every 20 minutes during effort, especially for endurance sports [4].

Calibration on the day you've already done intense exercise can be affected by dehydration or tissue perfusion variations [12]. Compression of the sensor area (from equipment or specific positions) can sometimes give falsely low values [13]. Carefully remove pressure from sensor in this case and check glucose with glucometer. Set alarms somewhat higher to have time to react during effort [4]. After sports, the sensor may have greater delay until peripheral circulation completely normalizes [12].