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Top things to consider when training for a marathon and your diabetes

The Boston Marathon will occur on April 15th, 2024. People with Type 1 Diabetes (T1D) dealing with extra challenge to maintain their glucose in a safe range and reduce the risk for low blood glucose (hypoglycemia). In preparation for completing the Marathon successfully, you should consider the following:

  1. Monitor your glucose: during marathon training you could experience extreme blood glucose fluctuations. You need to check your glucose with a glucometer or use a Continuous Glucose Monitoring (CGM) to learn the trend of your glucose with short or long run, and easy or intense run. When running at a steady pace, you could experience a decrease in your glucose and will be at risk to a have a low blood glucose. When doing hill and speed training, you could experience high blood glucose (Hyperglycemia) as a result of a significant counter regulatory hormones release. Maintaining your blood glucose in a safe range between approximately 120 to 160mg/dl is recommended, If your glucose fluctuates a lot, it will affect your pace and muscle performance. There is a lot of trial and error with figuring out the best range of glucose for you while training. adjusting your insulin dose and fueling your muscles are additional steps to take to achieve your target.

  2. Adjust insulin: As you increase your running distance and pace, you will become more insulin sensitive. This means that your need for insulin will decrease since your muscles will take up significant amount of glucose to replenish. Without reducing the insulin dose in preparation for a run or after a run, you will more likely experience lows. You could experience a decrease in glucose towards the end of the run, right afterwards, and 7-11 hours after running, although the process could last 24-48 hours. Plan to reduce your rapid acting insulin by approximately 25-50% close to training time. In addition, you will need to reduce your basal (long acting) insulin by approximately 10-20% before a long run and possibly after a long run, as you progress with training over months. If you use an insulin pump, you will need to reduce basal rate few hours before your training start by setting a Temp Basal or turning on Activity Mode. You could keep the reduced basal for the duration of the run, plus another 30-60min after running is complete. The key is to fine tune your insulin dose according to your glucose response. Keeping notes of your glucose trends will help you make some important decisions.

  3. Fuel your muscles: aerobic energy production using dietary fat and carbohydrates as a fuel will help your muscles meet the energy needs to prepare for training and complete a marathon. Your muscles and liver have the ability to store significant amount of glycogen particles, which come from dietary carbohydrates that you eat. Glycogen particle comprised of individual glucose molecules and it is the fuel source to meet the demand of muscle contraction. Your muscles contract forcefully with exercise training, which lead to decrease in the storage of glycogen. The greater the intensity you run, the greater the rate at which your muscle glycogen can get depleted. Intensity, speed and duration of running, timing of your meals and snacks, amount of carbohydrates content, duration of recent training, recovery periods, all can impact the glycogen stores in your body and level of muscle fatigue. These factors will translated to running performance. Physical exercise training and nutrition can help manage the muscle fatigue and maintain the energy your muscles need. The food you will consume prior to morning or after noon training run, or the few days before the actual race will impact the results. You need to eat a well-balanced meal plan that includes adequate amounts of whole grains, legumes, fruits, vegetables, lean protein and healthy fats. Low glycemic carbs are recommended to help maintain your glucose Time in Range while fueling few hours before a run. During your long runs and at recovery you should fuel your muscles with fast absorbing (high glycemic) carbs in a form of energy gel, chewables or sports drinks. Having access to a CGM during a run will make it easier for you to decide when and how much to fuel your muscles. By strategically eating low glycemic and high glycemic carbs, you will fuel your muscles to get through the marathon.

  4. Follow periodized training: training for a marathon usually can take 6 months as your body is going through physiological adaptations. Periodized training include: a. Base phase (8-12 weeks) - you will focus on aerobic conditioning and work to improve your cardiovascular and muscular endurance. b. Build phase (4-8 weeks) - you will focus on improving your running efficiency and pace. c. Peak phase (1-2 weeks) - you will focus on running at your race pace, therefore your long runs will be a little shorter. You will add hills and tempo runs to improve your anaerobic threshold. d. Tapering phase (1-2 weeks) - you will focus on reducing your training load in the last few weeks before the race to prevent over training. This is also the phase that you will review the logistics of the race and packing list of your back up insulin, fueling, emergency diabetes supply and anything else you might need to help maintain good pace with a safe glucose control.

  5. Get matched with supportive running shoes: getting the right shoes will make running easier and make your muscles and joints work more efficiently. This is a key to avoid running injuries. In many running shoe stores you can get advise on how to choose the best shoes for your feet and running gait. Contact me at to guide you in achieving your personal goals!


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