C.     Carbohydrate Loading for Athletes with T1D

Storage of Carbohydrates in the Human Body: Glycogen

Carbohydrates can be stored as glycogen in the liver (between 70-100 grams) and in the muscles (a major site for glucose disposal after a meal; between ~400-600 grams, depending on age, sex, and especially the amount of muscle mass). Over the past six decades, skeletal muscle glycogen metabolism has been extensively studied, largely thanks to the development of the muscle biopsy technique [23, 51]. In contrast, the role of liver glycogen during exercise has received less attention, primarily because obtaining tissue samples from the liver is more challenging and dangerous than muscle biopsies. However, advances in non-invasive techniques like 13C-magnetic resonance spectroscopy (13C-MRS) have enabled more detailed investigations. As this method is non-invasive, it allows for repeated measurements of liver glycogen content without triggering the adrenaline response that can sometimes occur with liver biopsy procedures [52].

 

Carbohydrate Loading in People Without Diabetes

Carbohydrate loading is a well-known strategy used by athletes without T1D in the days leading up to a prolonged endurance event. It is generally accepted to increase exercise performance and capacity in events lasting longer than 90 minutes [53]. Typically, carbohydrate-loading involves consuming 8 to 12 grams per kilogram per day of carbohydrates for three days, with carbohydrates making up 70 to 85% of total energy intake [11].  

And what about glycogen storage and carb-loading in athletes with T1D?

Until fairly recently, it was unclear whether people with T1D have impaired glycogen storage, which would make carbohydrate-loading more challenging. One study that used 13C-MRS to measure liver glycogen found that individuals with T1D classified as having poor glucose control exhibited a defect in net liver glycogen synthesis, which appeared to be most pronounced after the evening meal [54, 55]. In this study, the authors also observed a higher contribution of gluconeogenesis to glycogen synthesis in T1D compared to subjects without T1D. Intensification of insulin treatment normalised glycogen storage but not the contribution of gluconeogenesis to glycogen synthesis [54]. The latter finding supports the idea that even advanced insulin replacement regimens do not mimic the physiologic insulin secretion pattern, as the peripheral administration of insulin [56] alters the portal-to-peripheral insulin gradient, thereby affecting hepatic glycogen turnover [57]. Individuals with well-managed T1D showed liver glycogen levels similar to those of their counterparts without diabetes under resting conditions [58]. Another research group compared muscle and liver glycogen content in well-controlled individuals with T1D and matched controls without T1D using 13C-MRS and found no significant between-group differences [58].

While individuals without T1D can automatically regulate insulin secretion to maintain glucose balance, those with T1D must carefully adapt their insulin doses (i.e., increase) to accommodate the greater carbohydrate intake. This can be challenging [9, 59], and there are no specific guidelines for carbohydrate-loading for athletes with T1D.

Only a few studies have examined carbohydrate loading in individuals with T1D. McKewen and colleagues [59] found that a high-carbohydrate diet resulted in poorer glucose levels and exercise performance during a 15-minute time trial in trained men with T1D. However, a more recent study by Mattsson et al. [9] in ten individuals with T1D, reported good glycaemic levels during two days of carbohydrate loading (consisting of the usual diet extended by 2 grams of carbohydrate per kg per day for 2 days in the form of a sports drink mixed in 1 litre of water, 400 ml per hour every half hour, intermittently for 12 hours) followed by a prolonged 90 km cross-country ski race. The authors of this study attributed their success to the gradual increase in basal insulin doses (and additionally 20-30% extra at bedtime) during nights one and two of the carbohydrate loading and because they were careful to achieve stable pre-exercise glucose values [9]. They were likely also aided by modern insulin preparations and CGM technology, which were unavailable during the study by McKewen and colleagues [59]. Nevertheless, participants in the study by Mattsson et al. [9] still spent approximately 10% of their time in hypoglycaemia, suggesting that adaptation of insulin was still challenging.

We conclude that, under adequate conditions (i.e., well-controlled diabetes with sufficient insulin administration), carbohydrate-loading is possible and may benefit exercise performance and/or capacity in people with T1D. Still, athletes with T1D who want to try carbohydrate-loading before an event should be prepared for more intensive blood glucose monitoring to avoid deteriorating glycaemic control. Close consultation with a healthcare professional is essential to developing a safe and effective strategy tailored to the individual's needs.

D.     Principles of Glycogen Resynthesis and Replenishment After Exercise

For athletes with T1D, prioritising blood glucose management 24/7 is crucial. This not only ensures overall health but also optimises various aspects of recovery. Managing blood glucose levels after exercise and achieving adequate physiological recovery are closely linked and should be equally important goals. Ideally, one aspect should not be sacrificed for another; however, this can be challenging. The unique ability of individuals living with T1D to influence their insulin concentration through exogenous administration necessitates greater planning and attention to optimise nutrition and insulin strategies for glycogen resynthesis. Understanding the physiology of glycogen resynthesis can help athletes with T1D manage the risk of hypoglycaemia and hyperglycaemia during recovery.  

The Physiology of Muscle Glycogen Resynthesis and Potential Implications for Athletes with T1D

Muscle glycogen resynthesis begins immediately after exercise and is most rapid during the first 4 to 6 hours [60]. This process occurs in two phases – insulin-independent and insulin-dependent – and each of them presents unique challenges:  

Initial Rapid Phase (Insulin-Independent): This phase occurs immediately after exercise and lasts minutes to hours (typically 30–60 minutes as observed in studies conducted on individuals without diabetes [61-63]), facilitating rapid glycogen resynthesis without insulin. During this time, the muscles quickly take up glucose to replenish glycogen stores. The quantity (and intrinsic activity) of GLUT-4 transporters in the muscle membrane is still increased during this time, even though muscle contractions are not actively occurring anymore! While specific research on T1D athletes is limited 64, [65], it is reasonable to assume that, with adequate carbohydrate intake, this phase should proceed normally. Importantly, for athletes with T1D, insulin requirements may be lower in the first phase. This phase seems like a crucial window of opportunity for rapidly restoring glycogen stores for the athlete with T1D as no or less insulin is needed. Hence, a lower risk for hypoglycaemia could be assumed (if insulin administration is managed properly, of course).

Notably, in endurance athletes with T1D, there might be a considerable overlap of the two phases regarding the need for insulin. Therefore, it might be reasonable to start more quickly with insulin during replenishment since it usually takes 15-30 minutes until insulin action starts. Hence, insulin boluses would need to be administered in the second half of the first rapid phase to allow optimal glycogen resynthesis in athletes with T1D. Still, athletes with T1D should be cautious not to overdose on insulin in this phase to avoid hypoglycaemia. Lastly, the resynthesis rate during this initial phase can quickly decline if exogenous carbohydrates are unavailable [63, 64].   

Long-Lasting Phase (Insulin-Dependent): This is a much longer phase, lasting up to 48-72 hours post-exercise, and mainly relies on insulin for glycogen storage [64]. Insulin helps the muscles absorb glucose more effectively, supporting glycogen restoration. Without carbohydrate intake, this second phase occurs 7 to 10 times slower than the initial rapid phase [66], highlighting the importance of an adequate carbohydrate-fuelling regimen. During this fuelling period, athletes with T1D must carefully manage insulin delivery to support glycogen replenishment while monitoring glucose to avoid hyperglycaemia. On the other hand, increased insulin sensitivity in the post-exercise period (especially the mid- to late post-exercise period i.e., 3–12 hours after exercise) can raise the risk of post-exercise hypoglycaemia in athletes with T1D. Therefore, adjustments (decreases) to bolus and basal insulin doses are required, based on frequent glucose monitoring and individual experience (some trial and error), to help prevent hypoglycaemia [67].

Provided enough carbohydrates are consumed, muscle glycogen is typically restored to pre-exercise levels within 24–36 hours after a workout [68, 69]. This timely replenishment is crucial for optimal performance and recovery, especially if exercise is planned for the next day.

Considerations Regarding Other Nutrients: Protein, Caffeine, Alcohol

Athletes with T1D should consider how different nutrients, besides carbohydrates, interact with and affect blood glucose levels and glycogen resynthesis. While carbohydrates are the primary macronutrient influencing glucose levels, consuming a mixed meal containing varying quantities of fat, protein and fibre can also impact the glycaemic response. This occurs by altering the absorption rate of carbohydrates, the levels of intestinal and pancreatic hormones (e.g., glucagon), and insulin sensitivity [70-74]. Several studies have shown that meals high in protein or fat can increase and/or delay the glycaemic response compared to a carbohydrate-equivalent control meal [71, 72, 75, 76].

Protein

In addition to carbohydrates, certain amino acids can stimulate insulin secretion when consumed orally or intravenously in people without diabetes [77, 78]. Research indicates that combining amino acids or proteins with carbohydrates enhances insulin secretion [78, 79]. This is why athletes without diabetes often consume carbs and protein together after exercise to accelerate muscle glycogen recovery and take advantage of insulin’s effects on muscle repair [11, 80, 81].

Protein consumption combined with carbohydrates elevates post-meal insulin levels, leading to increased glycogen synthase activity, particularly when carbohydrate intake is below the optimal threshold for glycogen storage (i.e., 0.5–0.8 grams of carbohydrates per kilogram per hour) [82-85]. However, when carbohydrate intake is adequate (e.g., more than 1 gram of carbohydrates per kilogram per hour), adding protein does not further enhance glycogen synthesis 86, 87, although protein still aids muscle growth.

For athletes without T1D, the benefits of protein during recovery are well established. Studies have shown improved exercise performance when consuming 0.8 grams of carbohydrates per kilogram per hour combined with 0.4 grams of protein per kilogram per hour, compared with 1.2 grams of carbohydrates per kilogram per hour alone during the first 2 hours of recovery [88, 89]. Although muscle glycogen was not measured in these studies, metabolic data suggested that the glycogen stores did not limit performance after carbohydrate-only intake during the first 2 hours of recovery [88, 89]  Importantly, muscle glycogen synthesis was similar over a 5-hour recovery period with an intake of 0.8 grams of carbohydrates per kilogram per hour in combination with 0.4 grams of protein per kilogram per hour compared with 1.2 grams of carbohydrates per kilogram per hour alone during the first 2 hours after exhaustive exercise 86. However, exercise performance improved when protein was added to the recovery drink.

For athletes with T1D, protein intake will not influence natural insulin production but may increase insulin dose requirements. Consuming protein during exercise may enhance glycaemic stability, and protein after exercise is recommended provided insulin is taken if necessary. During the post-exercise recovery period, protein is likely to assist in glycogen resynthesis and increase net muscle protein balance.

Caffeine and Specific Considerations for Athletes with T1D

There is consistent evidence supporting the beneficial effects of caffeine for endurance-based exercise performance [90-97]. Caffeine affects the body in several ways, including increasing fat breakdown in fat tissue, stimulating glucose production in the liver, and reducing glucose uptake in skeletal muscles [98, 99]. In people without diabetes, consuming caffeine before exercise has been shown to slightly increase blood glucose concentration (~0.5 mmol/L) during moderate-intensity endurance exercise 100. These responses suggest that acute caffeine intake might help reduce exercise-related hypoglycaemia in people with T1D [101].

Consuming modest amounts of caffeine (200–250 milligrams, equivalent to three or four cups of coffee) has been shown to increase hypoglycaemia awareness and hormonal responses (e.g., greater release of catecholamines) in individuals with [102, 103] and without [104] T1D. Regular caffeine intake has also been found to reduce the frequency of moderate overnight hypoglycaemia episodes in individuals with T1D [105].

To date, just two studies have investigated the acute effects of caffeine on exercise-associated hypoglycaemia in individuals with T1D [106, 107],  with both studies suggesting a protective effect, i.e., avoiding or delaying the onset of hypoglycaemia during a bout of moderate-intensity exercise [107].

Currently, there is no data to support using caffeine during the recovery period in athletes with T1D. If caffeine is found to be helpful for post-exercise recovery, future research should aim to define the lowest caffeine intake required to reduce the risk of hypoglycaemia, considering potential disadvantages such as impaired sleep quality if consumed late in the day.

Given the lack of data on caffeine and exercise in individuals with T1D and considering caffeine’s popularity socially and as a sports supplement, this topic deserves further attention. Future studies should explore the optimal dosage and timing of caffeine intake to maximise its benefits while minimising potential drawbacks for athletes with T1D.

Alcohol

Alcohol is an important factor to consider in relation to sports performance and glucose management, as anecdotal evidence suggests that some athletes, particularly those in team sports, may consume large amounts post-exercise after competitions. Alcohol intake has substantial effects on carbohydrate metabolism in the liver and muscle, as well as a negative impact on fluid balance [108], with important implications for post-exercise recovery [109]:

Alcohol and Carbohydrate Metabolism:

• Alcohol inhibits glucose uptake into skeletal muscle [110].

• It reduces the stimulating effect of exercise on muscle glucose uptake [111].

• It impairs glucose utilisation [112] and inhibits glucose production by the liver [113].  

Alcohol and Hypoglycaemia Risk:

• Alcohol increases the risk of hypoglycaemia [14, 115] by inhibiting glucose production by the liver [113], blunting hypoglycaemia symptoms [116], and impairing cognitive function [117].

• For athletes with T1D, the risk of severe hypoglycaemia is potentially additive when consuming alcohol after exercise [118].

 

2.      Fluid Management Considerations for T1D Athletes

To maintain optimal body function and promote overall well-being, athletes with T1D should have comprehensive fluid management strategies before, during, and after exercise to ensure proper hydration. Most athletes end their workouts with a fluid deficit, so replenishing fluids during recovery is crucial [119]. Here are some key factors to consider:

Hydration and Electrolyte Replacement

• Along with water, sweat contains significant yet varying amounts of electrolytes, including sodium, potassium, calcium, and magnesium. Therefore, athletes should not restrict sodium after exercise, especially when considerable sodium losses have occurred [11].

Thermoregulation and Sweat Rates in People with T1D

• There are concerns that people with T1D may experience impaired thermoregulation during exercise, especially in hot and humid conditions [120]. Although the data in this area are limited, studies have shown that young individuals with T1D who do not have diabetes-related complications have similar sweat rates during low- to moderate-intensity exercise compared with individuals without diabetes when matched for age, sex, body surface area, body composition, and physical fitness [121, 122].

• However, Carter and colleagues [121] found that when exercising at higher workloads (≥250 watts per metre squared of body surface area) in hot conditions (35°C at 20% humidity), individuals with T1D had a lower sweating response and a higher core body temperature than participants without T1D. It would be interesting to know whether this relates to the presence of autonomic neuropathy or T1D itself. A reduced sweat rate might reduce the ability to dissipate heat at higher workloads.  

Thirst Perception

• It has not been established whether people with T1D perceive thirst differently than those without diabetes. However, elevated blood glucose concentrations increase blood osmolality, likely signalling an increased thirst sensation [123]. This is supported by Buoite Stella and colleagues [124], who found, through a questionnaire, that self-reported fluid intake during exercise was higher in a group of individuals with T1D compared to age-matched and sport-matched individuals without T1D.

Key Tips for Fluid Management in Athletes with T1D:

Before Exercise:

o    Start Well Hydrated: Ensure you drink sufficient fluids in the hours before the workout.

o    Carbohydrate Content: To effectively manage blood glucose levels, it is important to consider the carbohydrate content of pre-exercise drinks. Sports drinks with a moderate carbohydrate concentration (6-8%) can prove beneficial, depending on individual requirements and the intensity of the forthcoming exercise. Be aware that the type of carbohydrate can differ between drinks as well as the total carbohydrate content.

During Exercise:

o    Fluid Intake: To remain properly hydrated, align your fluid intake with your sweat loss. Bear in mind that sweat rates differ from individual to individual and are influenced by exercise intensity and environmental conditions.

o    Carbohydrate Replenishment: For prolonged or high-intensity exercise, consuming drinks with carbohydrates can help maintain blood glucose levels and provide energy. But keep an eye on blood glucose levels to avoid highs or lows, and always have fluids without carbohydrates available! Having drinks without carbs at your disposal is beneficial because this will avoid restricting fluid intake in case of hyperglycaemia if only carbohydrate-rich fluids are available.

After Exercise:

o    Restoring Hydration: Aim to consume 1.2 to 1.5 times the volume of fluid lost during exercise, accounting for ongoing urine production.

o    Electrolyte Replacement: Incorporating electrolytes, particularly sodium, in post-exercise beverages can improve fluid retention and restore electrolyte balance.

 

3. Considerations Regarding Diabetes Technology for the Endurance Athlete with T1D

Selecting an Insulin Delivery Method

The primary goal of insulin therapy, in general, is to mimic healthy physiological insulin levels and thereby limit dysglycaemia. This is particularly crucial for athletes with T1D during exercise, as they want to avoid hypoglycaemia at all costs while fuelling their workouts with carbohydrates to aim for the highest exercise performance. Completely restoring insulin to physiological levels isn’t possible since insulin is administered under the skin rather than released into the portal circulation. While some athletes with T1D perform well using multiple daily injections (MDI) of insulin [1, 125, 126], others prefer the flexibility insulin pumps provide [127].

The use of insulin pumps provides greater flexibility in insulin administration strategies through:

• Temporary basal rate reductions before and/or after prolonged aerobic exercise.

• Temporary increases in basal rate for intense aerobic or anaerobic exercise.

• Basal rate reductions overnight if nocturnal hypoglycaemia is a concern.

The latest hybrid closed-loop systems may offer improved support for glucose management in athletes compared to traditional pump therapy. These systems adjust insulin delivery based on current glucose levels, predicted glucose levels, previously delivered insulin, and other factors determined by proprietary algorithms to improve overall time in range (TIR) 128. Currently, approved hybrid closed-loop devices perform pretty well during prolonged aerobic exercise [129] if a temporary (higher) glucose target is established well in advance (i.e., 45–90 minutes beforehand). However, as mentioned in Chapter 4, the algorithms of current HCL systems still require improvements in the coming years [130, 131]; for instance, exercise shortly after carbohydrate intake (which results in a blood glucose rise and insulin delivery by the HCL system) poses a significant challenge [130]. Additionally, ultra-endurance exercise can be difficult due to the heightened risk of ketosis resulting from extended periods with very low or no insulin infusion by the pump, particularly when the pump is in “sports mode”, as is often the case for endurance athletes participating in such ultra-events.

Despite their benefits, many people find that insulin pumps can interfere with their sporting activities or that they prefer not to be attached to a medical device [132]. Keeping insulin infusion sets and glucose monitoring devices in place during exercise can be challenging due to increased sweating and the risk of collisions in certain sports. For athletes who prefer to remove their pump during exercise (e.g., rugby players since they are not able to carry a pump during their sports), they can opt for a hybrid approach that combines basal insulin delivery split between a long-acting insulin and 25-75% reduced (or temporarily completely suspended) basal insulin via the pump [133].

 

Recommendations for CGM Use for Athletes with T1D

Adding a CGM is highly beneficial, as athletes (particularly those with hypoglycaemia unawareness [134]) can track glucose data, respond to glucose trend arrows and alerts [135], and strive to further optimise their insulin therapy [136]. Real-time CGM offers the advantage of alerting users when glucose levels drift from the target range. However, athletes must be aware that exercise itself can negatively affect sensor accuracy [136-139].

CGMs have been a game-changer for athletes with T1D [139], offering an ability to better manage glucose levels more effectively during training, competition, and recovery. When used during prolonged exercise, athletes can better plan their carbohydrate feeding based on glucose concentrations, glucose trend arrows [135] and rate of change data [139, 140].

Glucose data may be analysed with a connected smart pen that can automatically log insulin administration [141] or with pump data [142] to better manage complex situations due to exercise. Analysing the ambulatory glucose profile (AGP) for multi-day training can help athletes and clinicians set achievable blood glucose and performance goals [143]. Given the unique challenges of glycaemic management during competition, athletes with T1D might benefit from simulating several training sessions that closely mimic competition-day conditions to practise glucose management strategies.

The glycaemic targets for the health and performance of athletes with T1D should be individualised. However, we support the following ambitious yet achievable goals for training periods identical to the recommendations for the general T1D adult population [144]:

• Time in Range (TIR; 3.9–10.0 mmol/l) >70%

• Time Below Range (TBR; 3.9 mmol/l) <4%

• Time below 3.0 mmol/L <1%

• As hypoglycaemia during exercise can severely impact performance and, potentially, heart rate variability [145], one review paper has suggested that people with T1D should aim for <1% time below target and >75% TIR during competition [146]. Reducing glycaemic variability, measured by a coefficient of variation of ≤36% for CGM values, is also recommended since values above this threshold correlate with increased hypoglycaemia risk [147].

It should be emphasised, however, that these recommendations are challenging to achieve, so it’s important to focus on improvement rather than perfection. To reduce the time below the target range and avoid hypoglycaemia at all costs during competition, it might be more realistic to allow for slightly higher glucose values (i.e., a bit more time in Level 1 hyperglycaemia can be accepted), as long as values above 13.5 mmol/L (250 mg/dL or Level 2 hyperglycaemia) can be avoided. While we acknowledge that these targets are ambitious, they may be attainable with newer technologies and dedication.

 

4.     Other Considerations Related to Recovery and Sports Performance for the Athlete with T1D

While nutritional and insulin adjustment strategies are fundamental considerations for athletes with T1D, several other factors must also be considered. Here, we provide a brief overview of these considerations, evaluating their relevance and potential implications for endurance athletes living with T1D.

Active Cool Down to Mitigate Post-Exercise Hyperglycaemia

Many athletes regularly engage in an active cool-down as part of their recovery routine, typically performing 5 to 15 minutes of low to moderate-intensity exercise after training or competition [148]. While numerous benefits are proposed, such as faster heart rate recovery, reduced muscle soreness, and rapid clearance of metabolic by-products [149, 150], only a few are supported by solid research (reviewed by Van Hooren and Peake [148]).

Interestingly, for athletes with T1D, an active cool-down may serve as more than just a recovery tool. Despite the uncertainty surrounding the cool-down for athletes without diabetes, we feel that athletes with T1D should consider incorporating this practice. The reason is that this short active phase can influence blood glucose concentration and may help manage post-exercise glycaemia. In other words, it may be used as a glucose management strategy in the post-exercise period.

High-intensity or resistance exercise may cause immediate post-exercise hyperglycaemia [151, 152]. Post-exercise hyperglycaemia can also occur after moderate-intensity aerobic exercise [127] due to factors such as: a relative decrease in glucose uptake in the muscle after cessation of exercise, insulin pump suspension or removal [133], pump site failure, (too much) reduced basal insulin delivery pre- or during exercise, or mismatched insulin administration with a high carb intake during exercise (and potentially a lasting carbohydrate effect after ending exercise).

Consider the following scenarios:

• Elevated Blood Glucose: If blood glucose concentration is slightly elevated (around 8–12 mmol/L or 144-216 mg/dL) at the end of an exercise bout, such as after high-intensity exercise or carbohydrate ingestion during exercise, a low-intensity aerobic cool-down may be helpful as it can gradually lower your glucose levels without the need to administer extra insulin, which might otherwise cause hypoglycaemia. However, in case of very pronounced or prolonged rising glucose immediately post-exercise, combining the cool down with small amounts of insulin may help in managing glucose levels and mitigate prolonged hyperglycaemia.

• Low or Trending Down Blood Glucose: If your blood glucose is low or trending down, you may reduce or skip the cool-down (or even do a short all-out sprint) and perhaps have some extra carbs. This may help prevent hypoglycaemia after exercise and support more stable glucose levels.

The active cool-down can be a valuable tool for athletes with T1D to help manage post-exercise glycaemia and increase their chance of achieving stable glucose levels during recovery. By adopting a strategic approach to the active cool down, athletes with T1D can enhance their recovery and optimise their glucose management. The key lies in tailoring the intensity and duration of the cool-down based on real-time blood glucose levels. This exemplifies the power of personalised, data-driven strategies in sports performance and diabetes care.

 

Cold Water Immersion or Ice Baths Dunking your body in cold water (around 10–15°C or 50–59°F) for about 10 to 15 minutes is a widespread recovery practice among athletes in various sports [153]. Ice baths have been proposed to reduce muscle fatigue and accelerate recovery between workouts in the following ways:

• Reduce Muscle Fatigue and Inflammation: Cold water immersion can help decrease post-exercise inflammation, potentially reducing muscle damage and soreness. However, the beneficial effects remain a topic of debate, with some studies even suggesting potentially harmful effects on the rate of recovery [154, 155].

• Glycogen Resynthesis: Some research indicates that cold water immersion might enhance glycogen resynthesis, but more research is needed to understand the potential practical implications for athletes with T1D.

While research has shown that cold water immersion does not impair glycogen resynthesis rates after exercise 156, the potential effects on glucose levels during post-exercise recovery in athletes with T1D have not been studied. Therefore, no solid evidence supports the routine recommendation of ice baths for endurance athletes with T1D.

Given the lack of specific research on the impact of cold-water immersion on glucose levels in individuals with T1D, this recovery method should be approached cautiously. To ensure safety and effectiveness, it is important to consider individual responses and monitor glucose levels closely during and after cold-water immersion.

 

Sports Massage

Massage, ranging from self-myofascial release to professional sports massage, has several potential benefits for recovery:

• Muscle Recovery: Massage can help to relieve muscle tension and soreness, promoting overall recovery.

• Stress Reduction: The relaxing effects of massage can help reduce mental stress, which may positively influence glucose management.

• Blood Flow Enhancement: Massage can stimulate blood flow, potentially aiding nutrient delivery and waste product removal. However, more research is needed to determine whether it has specific benefits or effects for individuals with T1D.

 

Optimising Sleep for Athletes with T1D

People with T1D often experience sleep disturbances at higher rates than those without diabetes [157], which can significantly affect health and performance. Poor sleep is linked to reduced insulin sensitivity [158] and poorer glycaemic management [159, 160]. Additionally, quality sleep is vital for athletic performance and the regenerative processes that occur during training and competition [161].

Strategies for Improving Sleep Quality – General Sleep Hygiene:

Napping, sleep extension, and maintaining good sleep hygiene can be beneficial. A review by Fullagar and colleagues provides comprehensive insights into these strategies 162.

 

The Risk of Eating Disorders and Food-Related Anxiety in T1D

As discussed throughout this book, managing glycaemia is complex, and focusing on hitting targets can unintentionally encourage perfectionism. This can lead to frustration, as it’s unrealistic to expect blood glucose values to be in the target range 100% of the time. Certain aspects of T1D management, like the emphasis on food selection and portion size, can increase the risk of developing eating disorders [163]. Studies have shown that individuals with T1D are at a higher risk of developing eating disorders [163-167] and other psychological disorders such as depression [168, 169] compared to those without T1D.

Weight management is often a motivating factor for exercising 170, but the increased carbohydrate requirements to prevent hypoglycaemia during exercise 171 can be discouraging from a weight management perspective [172]. Worryingly, reports indicate that approximately 28% of female and 7% of male adolescents with T1D skip meals in an attempt to manage their weight [173]. Adolescents engaging in disordered eating behaviours tend to have poorer metabolic control [174]. There is even a name for this behaviour, i.e., “Diabulimia”, referring to patients deliberately giving themselves less insulin than they need in an attempt to control weight. This strategy of insulin restriction to induce a ketotic state and lose weight often comes with the cost of poor diabetes control. Lastly, insulin restriction has been associated with an increased risk of mortality [173].

Given these risks, the American Diabetes Association recommends integrating psychosocial care into patient-centred diabetes care [175]. Future guidelines aimed at improving glucose management in exercise should consider these factors. The goal should be to promote a positive attitude towards exercise in people with T1D while encouraging a balanced approach to nutrition and a healthy body image.

Relative Energy Deficiency in Sport (RED-S) and T1D

A relatively unexplored topic in T1D research is the risk of Relative Energy Deficiency in Sport, or RED-S. This situation occurs when an athlete’s daily energy intake is insufficient to meet the demands of their training load, resulting in adverse health and impaired athletic performance [176, 177]. RED-S can negatively affect various systems, including menstrual function, bone health, endocrine, metabolic, and haematological functions, growth and development, and psychological, cardiovascular, gastrointestinal, and immunological systems.

Certain athletes are particularly at risk of RED-S. These include those involved in sports where a high power-to-weight ratio is beneficial to performance, such as cycling, triathlon, and running; weight-category sports like boxing and lightweight rowing; and aesthetic sports, such as dancing and gymnastics. Athletes with T1D may be at an increased risk of RED-S due to the complexities of managing glucose levels, meeting energy requirements for training, and long-term weight management.

It is important that the athletes, their coaches and their healthcare providers be aware of the potential risks associated with RED-S. Future research should focus on the complex factors relating to RED-S and what it truly encompasses 178, also in athletes with T1D, including:

• Training load and its impact on energy balance.

• Adequate calorie intake to meet the demands of training and recovery.

• Ensuring sufficient recovery time between training sessions

• Effective glycaemic and insulin management and strategies tailored to individual needs.

 

Additional Considerations for Female Athletes with T1D

Female athletes with T1D may experience differing glycaemic responses to training and competition depending on their menstrual cycle phase 179. To optimise performance and maintain stable blood glucose levels, female athletes should be mindful of varying insulin and carbohydrate requirements before and after exercise throughout their menstrual cycle. Here are some points to consider:

• Higher Blood Glucose Levels During the Luteal Phase: In general, blood glucose levels tend to be higher during the luteal phase, which isn’t always fully managed by increasing basal insulin rates 180. The middle of the luteal phase (the phase towards menstruation) is associated with relatively high oestrogen levels combined with rising progesterone levels, which causes hyperglycaemia to be more common in this phase [181].

• Increased Fat Usage: During the luteal phase, the body may rely more on fats as a fuel source during training and recovery [182].

• Less Muscle Glycogen Use: The luteal phase is associated with less muscle glycogen use during endurance exercise, at least in those without diabetes [183], suggesting that less carbohydrate intake may be required for post-exercise glycogen replenishment.

 

Practical Tips for Female Athletes:

• Insulin Adjustments: Female athletes may need to adjust their insulin doses, especially during the luteal phase, to account for the higher blood glucose levels and reduced insulin sensitivity.

• Carbohydrate Intake: Carbohydrate requirements before, during and after exercise may vary throughout the menstrual cycle. Less carbohydrate intake might be needed for glycogen replenishment during the luteal phase.

• Glucose Monitoring: Close monitoring of blood glucose levels is essential to understand the individual responses to exercise during different phases of the menstrual cycle. Working closely with a healthcare professional can help when developing a personalised strategy to manage glucose levels effectively throughout the menstrual cycle.

 

Mastering Travel: Considerations for Athletes with T1D

In today’s globalised world, travel is integral to being a modern-day athlete. For those with T1D, thorough preparation is essential to ensure a safe and manageable journey. Here, we outline key considerations to help you navigate the challenges of travel.

Pre-Travel Preparation:

• Supplies: It’s important to pack enough accessible supplies [184]. If flying, carry-on luggage should include sufficient and accessible supplies, including insulin, glucose meters, sensors, pumps, needles, glucagon, and snacks.

• Travel Insurance: Selecting suitable travel insurance that includes coverage for diabetes-related emergencies and supplies.

• Insulin Storage: Practical decisions about packing insulin and bringing spare diabetes-related supplies may create difficulties. Consider the temperature and storage conditions of insulin. 

• Meal Planning: Arrange appropriate on-board meals and carry extra snacks to manage blood glucose levels during travel.

• Communicate with Airlines and Travel Companions: Ensure that the people you are travelling with are aware of your diabetes management needs and know how to assist in case of an emergency.

• Consult with your Healthcare Provider: Discuss travel plans with your healthcare team to develop a personalised strategy for managing your diabetes during travel. Importantly, in this context, it is also advisable to discuss basal insulin injections with regard to time zone changes.

Navigating Airport Security:

• X-rays, Airport Scanners, and Metal Detectors: Be prepared to navigate airport security procedures and potential delays, keeping essential supplies easily accessible. Manufacturers of insulin pumps and CGMs advise that most technology should not pass through these scanners, either through the whole-body scanners or the carry-on luggage belt. Different devices have varying clearance levels for metal detectors, X-rays, and full-body scanners. For example, the Dexcom G7 and Dexcom ONE+ can safely pass through full-body scanners, but the G6 and Dexcom ONE cannot. Always check the manufacturers’ guidelines or contact them before travelling.  

• Contact the Airport in Advance: Contact the airport before your journey to inquire about its scanners and any alternative security screening methods. Some airlines permit passengers with health conditions to carry extra luggage for medical supplies. Contact your airline to see if they offer this and what documentation they require to verify that you have T1D.  

• Medical Letter: Before travelling, obtain a letter from your GP or diabetes healthcare team proving that you have T1D and providing details about the treatments and technology you are using.

Managing Time Zone Changes and Jet Lag

• Time Zone Adaptation: When flying long distances and crossing multiple time zones, individuals with T1D must develop strategies to adapt to new time zones and limit the effects of jet lag on insulin requirements [185]. If significant time zone changes will occur, those using multiple daily injections may need to alter their basal insulin strategy, such as by splitting the basal dose into two doses spaced ~12 hours apart before departure [186] or using insulin degludec, which has a long half-life (>25 hours) and is more flexible concerning dose timing than insulin glargine (~12 hour half-life) [187].

• Blood Glucose Management: Monitor blood glucose levels closely, especially during long-distance travel and significant time zone changes.

• Be Prepared for the Worst: Athletes should prepare for the possibility of losing diabetes-related supplies, consuming unfamiliar foods, unexpected illness, and managing changes in climate and other environmental conditions.

 

The Final Word

Despite the challenges associated with exercise for people with T1D, many now choose to train and compete in long endurance events. Managing blood glucose levels remains a top priority for anyone living with T1D but fuelling and recovery are also essential elements. With an understanding of sports science principles and their implications for athletes with T1D, and careful preparation, it is possible to start thinking beyond just taking part sports and reaching the podium.