How to maximize athletic recovery with continuous glucose monitoring (CGM)

Nutrition plays a huge role in athletic recovery. Continuous glucose monitoring (CGM) and Levels software can help personalize nutritional choices to maximize recovery.

Colleen Gulick, Ph.D (ABD), MS, BS (BioE), EIT (ME), CSCS, Podium Sports, LLC, Founder & CEO

Author

Casey Means, MD

Reviewer

Article highlights

  • In order to recover properly from exercise, the body needs to rebuild muscle, clear metabolic waste, and replete energy stores.
  • Approaching athletic recovery with objective biofeedback tools like continuous glucose monitors (CGM) can help develop dynamic plans that maximize effective recovery without generating unnecessary cellular damage.
  • Specifically, CGM provides additional visibility into the impact of recovery variables like glycogen repletion, the effects of carbohydrates and protein on glucose levels, hydration status, and oxidative stress.
  • CGM can also provide objective feedback on the impact of recovery adjuncts and supplements like caffeine and creatine.
  • Having a continuous feedback loop between our choices (recovery nutrition tactics) and reactions (our body’s response) can help us efficiently refine our strategies, build intuition about our bodies, and gain a competitive edge.

Recovery: what is it?

“Recovery” is a term used in sports to indicate the body’s ability to “bounce back” after exertion, and is a vital component of exercise training. The recovery process involves resolving exercise-induced skeletal muscle damage, repleting energy stores, and clearing metabolic waste products generated by the body during exercise. Nutrition is a key component of any recovery strategy, and tools like continuous glucose monitors (CGM)– which can track how carbohydrates are processed by the body in real-time — can help personalize and optimize an individual athlete’s nutritional strategy.

Who needs to think about optimal recovery?

Optimizing recovery from exercise is beneficial for elite athletes and weekend warriors alike. Many athletes participate in sports that have multiple rounds of events in a single day, like tennis and beach volleyball. For these athletes, short term recovery and maintenance of energy stores is critical. The gold medals are decided by the last round, match, or heat, so performing your best for the last event is a requirement to win. There are also the athletes who compete in multiple events within a week, such as soccer and football, and these individuals need to focus on their recovery between days rather than hours.

Recovery from exercise is also important for recreational athletes that want to optimize their body’s adaptations (ie, getting bigger, faster, stronger, etc) in order to look and feel their best, and perhaps not feel so sore the morning after a round of pick-up basketball.

Why do we care?

Effective recovery is important for two main reasons:

  • Restoration of performance
  • Injury prevention

A study on English Premier Soccer athletes found that it can take up to 120 hours to restore the disturbances in metabolic and physical performance induced by a single match of soccer. Athletes rarely have 120 hours to fully recover without any competitions or training. Given that, anything we can do to speed up this process is valuable.

When athletes become fatigued, they are more prone to injury. In fact, soccer players in the English Premier League that play 2 matches per week have a 6.2 fold higher injury rate than players competing in just one match per week. In addition, injury risk increases when less than 96 hours separates soccer games. If we improve the speed and efficacy of our recovery tactics, we can minimize fatigue in back-to-back competitions and reduce injury risk.

For the recreational athletes among us, recovering properly can be beneficial for our overall health, as well. By being smart about how we treat our bodies and fuel after exertion, we can improve overall health. On the flip side, mismanaging post-workout recovery can set us back in terms of health. For instance, while we might think that our post-workout protein recovery shake is doing us good in helping us build muscle, it’s possible that its added sugar is sending our glucose levels through the roof and causing unnecessary inflammation and damaging oxidative stress.

New tools like continuous glucose monitoring can help us dial in our personalized recovery plans, particularly in terms of nutrition. As we try to strike the balance between replenishing our energy stores, minimizing damage to our tissue, and determining the optimal amount of hydration, CGM can give insight into whether we are hitting the “sweet spot.”

Why focus on nutrition?


Athletes use numerous strategies to enhance recovery. Some popular options include: massage, cold water immersion, stretching, compression garments, cardiac biofeedback through wearables like Whoop, and nutritional support.

Nutrition is an especially important component because it is well-studied in the scientific literature, easily accessible, and cost effective.

This article will focus on four areas of nutrition that can be targeted to optimize recovery and have you performing your best over and over (and over!) again. Recovery nutrition is involved in:‍

1. Replenishing glycogen stores. Glycogen is the body’s quick fuel for high intensity or power athletic events, and must be replenished between back-to-back athletic events to ensure optimal performance.

2. Optimizing anabolic adaptations: rebuild and repair. Anabolic processes in the body are those during which we build tissue. If we break down muscle during an athletic event, we must initiate anabolic processes that can rebuild this tissue. Proper nutrition can support this by providing the building blocks for protein synthesis.


3. Replenishing lost sweat: hydration. Fluid and electrolyte loss during exercise is inevitable and, if not addressed, can severely hinder performance and metabolic health.

4. Reducing inflammation and oxidative stress. During recovery, it is important for athletes to be cognizant of excessive oxidative stress in order to prevent as much cellular damage as possible. Reducing oxidative stress is also beneficial for the general population to improve metabolic health.

1. Replenishing Glycogen Stores

Glycogen is a quick fuel source made from stored chains of glucose that is stored in your muscles and liver. It is the primary energy source used for high intensity exercise (greater than 80% VO2 max) and maximal muscle contractions. For athletes performing sprints, explosive efforts, or anaerobic activities, glycogen repletion is important for repeated efforts of maximal performance.

Restoring glycogen levels is particularly important for athletes who have back-to-back workouts within 24 hours of each other and are performing high intensity or power sports. These athletes may deplete their glycogen stores significantly during an event, and are at risk for worsened performance if they do not replenish.

Elite athletes striving for glycogen replenishment will want to consume carbohydrates immediately after exercise in order to take advantage of the increased blood flow and insulin sensitivity that are available for a limited time just after a workout. The benefits of immediate carbohydrate ingestion, as compared to waiting until 2 hours after exercise, was shown in a study that found delayed feeding lowered muscle glycogen concentrations by 45%.

If we choose to refuel immediately after exercise, how much and what types of carbohydrates should we eat?
In research studies, the highest rate of glycogen synthesis was found in individuals consuming 1-1.2 grams carbohydrates/kg body weight per hour after exercise. For a 170-pound (77 kg) individual, this equates to 77-92.4 g of carbohydrates, per hour (e.g. 2 medium baked sweet potatoes and 1 cup of long-grain brown rice, 90.8 g carbohydrates). If you’re thinking this is a large volume of carbohydrates, it is! This amount of carbohydrate consumption has been shown to be an important strategy for athletes involved in competition requiring many events in a single day. It’s important to remember that this large intake of carbohydrates is unique to elite athletes, and far too much for the average individual who is unlikely to be depleting their glycogen stores, and also does not need to replenish them as rapidly.

When seeking to restore glycogen as quickly as possible for a back-to-back athletic event, high glycemic index (GI) foods (such as oatmeal, white rice, baked potatoes, and liquid carbohydrates like sports drinks) are preferred for the first 6 hours after exercise, as compared to slower digesting, low GI foods (such beans, lentils, or leafy greens). If your next workout isn’t for another 24 hours, however, then there is no difference between high or low GI foods, and you can recover properly by consuming low glycemic meals, as there is plenty of time to “fill the tank” of glycogen.


If you’re an athlete who is starting out on a low carbohydrate diet, practicing carbohydrate cycling, or are on a ketogenic diet, there are options that do not require you to eat as many carbohydrates, but still provide adequate recovery and glycogen replacement. If your carbohydrate intake is low for the day (less than 1.2 g/kg/day), then consuming 0.4 grams/kg/hour of protein with 0.8 grams/kg/hour carbohydrate can achieve a glycogen resynthesis rate similar to 1.2 grams/kg/hour of carbohydrates without protein. It is unclear why this is the case, but may be because the combination of glucose and protein generates a higher level of insulin release than glucose or protein alone, which could allow glucose to be taken up more efficiently.

For the average recreational athlete, rapid glycogen repletion is much less critical to think about, as typical glycogen stores will be enough to fuel a short, intense workout, and lower intensity workouts will be supplied primarily by body fat. In fact, excessive carbohydrate consumption could actually be damaging by loading the body with glucose it doesn’t need. See our blog post “Using Continuous Glucose Monitoring to Guide Fueling for Peak Athletic Performance” for more information on this.

 

How can I use my CGM as a guide?

When ingesting carbohydrates for glycogen resynthesis, you will likely see a corresponding rise in glucose levels on CGM, which should return to pre-eating levels within 2 hours. It’s important to keep in mind that repetitive and high blood glucose spikes from carbohydrate ingestion are unhealthy, and you can imagine that it would be easy to overshoot when attempting to quickly replenish carbohydrates and generate a massive glucose elevation. With that, choosing refueling options that do not create excessive glucose spikes is likely a good strategy. While there is not a well defined threshold, aiming to stay below 140 mg/dL blood glucose and ensuring glucose returns back to baseline within 2 hours is likely optimal for the athlete’s body.

 

2. Optimizing Anabolic Adaptations: Rebuild And Repair

Just as carbohydrates are your nutritional tool for glycogen resynthesis, protein is your nutritional weapon of choice to master muscular recovery. Protein is used to stimulate muscular adaptation, repair damaged muscle fibers, and enhance anabolic adaptations. “The golden hour” is a phrase used in athletics to refer to the optimal 1-hour window after exercise in which it is believed that ingesting dietary protein will elicit the greatest increase in muscle protein synthesis.

However, recent unpublished data by Gulick et al. shows promise for the notion of consuming protein during the workout can enhance insulin like growth factor 1 concentrations (IGF-1, a hormone that signals satellite cells to build skeletal muscle). There needs to be more research supporting in-workout protein ingestion is optimal for other hormones as well, but it might be the next big trend in nutrition for muscle protein synthesis.

How much protein should we eat?
Formerly, it was accepted that consuming 20-25 g of protein post exercise was optimal for muscle protein synthesis. However, a recent study showed 40 g of protein after exercise to elicit greater myofibrillar protein synthesis, irrespective of lean body mass.

 

How can I use my CGM as a guide?

Dietary protein has minimal effects on blood glucose levels when eaten alone. When protein is eaten with carbohydrates, however, it can reduce the magnitude of the blood glucose response to the carbohydrates, leading to a lower post-meal spike. As such, when eating carbohydrates as part of a refueling strategy, pairing together with protein can lessen glucose fluctuations, and minimize the amount of carbohydrates that need to be consumed to replenish glycogen.

 

3. Reducing Lost Sweat: Hydration

Exercise leads to an increase in metabolic heat production, raises body temperature, and we sweat to cool down. Everyone’s individual thermoregulating properties are unique, so some people sweat significantly more than others. The goal of rehydrating immediately post-exercise is to replace the volume and structure of fluids lost through sweat. As a general rule, you want to consume 150% of the fluid lost during exercise (the extra 50% comes from urine fluid losses) post-exercise.

For most people, you can monitor whether or not you are well hydrated by the color of your urine. Clear urine indicates you are adequately hydrated (“euhydrated”), while yellow pee is a sign of dehydration. If you want to be more quantitative about your hydration, you weigh yourself before and after exercise and replenish accordingly. If you lost 1 kg during exercise, then you need to drink 1.5 kg of fluid (which is equivalent to about 1.5 L of fluid). Fully rehydrating can be achieved in about 6 hours, which can be minimized by drinking during breaks in competition. Be mindful that temperature and humidity can clearly accelerate the sweat rate, so act accordingly.

 

How can I use my CGM as a guide?


Dehydration causes the release of a hormone called vasopressin. Vasopressin helps to regulate the body’s water retention and signals for the kidneys to store water, and for the liver to breakdown glycogen and release glucose. If you see a rise in your blood glucose levels on your CGM, it could be a sign that you are dehydrated. Monitoring your own blood glucose readings and cross-referencing them with easy-to-measure indicators (like urine color) can help provide insight into how much your individual blood glucose changes with hydration status.


4. Reducing Inflammation And Oxidative Stress‍

Exercising at a high intensity produces free radicals, which are metabolic byproducts that are reactive in the body and can cause damage to surrounding structures and subsequent inflammation. These reactive molecules can be neutralized by antioxidants, but when there is an imbalance and excessive levels of free radicals, this state is called “oxidative stress.”

The harder the workout, the more free radicals are produced, and the greater the potential for oxidative stress. This can be beneficial, to a certain extent. The inflammation and free radicals produced by exercise signal to your body that the exercise was challenging, and in response, your body takes action to adapt. In fact, specific types of free radicals appear to be generated in a controlled manner by skeletal muscle fibers in response to exercise, and seve to optimize contractile performance of muscles, and initiate adaptive changes in gene expression.

This sounds great, right? You may be thinking “bring on the free radicals!” Not so fast. Free radicals are generated from intense exercise, but they can also be produced by biologic stressors like poor diet, elevated post-meal glucose levels, chronic stress, sleep deprivation, cigarette smoke, alcohol, smoked foods, processed vegetable oils, and exposure to pollutants. High levels of free radicals are associated with multiple diseases including cancer, inflammatory joint disease, fibromyalgia, migraines, asthma, and diabetes. Repeatedly increasing free radical production beyond what your body can manage can lead to unhealthy outcomes.

An individual eating a typical American diet, stressed out by work, staying up late to work through their to-do list, and having a few drinks each night will already likely be generating significant amounts of free radicals. For this type of individual, exercise can be a great lifestyle addition, but high intensity exercise could add fuel to the fire of pre-existing excessive oxidative stress. By reducing oxidative stress triggers in our daily lives, we can gain the benefits of exercise while also warding off increases in free radicals.

As previously mentioned, for athletes, controlled free radical generation by muscles can drive adaptations. Similarly, a small amount of free radicals are required by cellular machinery for optimal force production in skeletal muscle, but high levels of free radicals promote contractile dysfunction, resulting in muscle weakness and fatigue.

Antioxidants and polyphenols (antioxidant chemicals that naturally occur in plants) are molecules that counteract free radicals by binding to them and neutralizing them. Some foods that are high in antioxidants or polyphenols are: dark chocolate, green tea, coffee, berries, vegetables, nuts, and spices. There are multiple recovery protocols in the research literature utilizing antioxidants that have been shown to be effective at reducing oxidative stress and/or muscle damage. In one study, drinking 0.682 L tart cherry juice before and after exercise significantly reduced symptoms of muscle damage. In another, theaflavin-enriched black tea extract reduced oxidative stress and muscle soreness after aerobic intervals.

 

How can I use my CGM as a guide?

It’s well established that high blood glucose can lead to oxidative stress, so for athletes trying to reduce fatigue that results from excessive oxidative stress, keeping glucose levels as stable and healthy as possible may be beneficial. Avoiding excessive spikes is a good indication that you are not generating undue oxidative stress from the source. On rest days, aiming to maintain a low and stable glucose line may help the body minimize glucose-associated oxidative stress.

Antioxidant intake as part of a recovery strategy may also feed back into helping improve glycemic control. One study looking at diabetic mice found that a treatment of 10-16 weeks of an antioxidant cocktail (N-acetyl-L-cysteine, vitamin C and vitamin E) reduced blood glucose levels (measured by a glucose tolerance test). The study also found a significantly larger beta-cell mass in the pancreas after antioxidant supplementation, indicating increased capacity to secrete insulin. In humans, a study looking at antioxidant supplementation for 8 weeks showed an improvement in insulin resistance by 15%.

Taken together, these studies indicate that diets high in antioxidants may be protective against fatigue-generating excessive oxidative stress, and that diets which maintain stable and healthy blood glucose levels may reduce the generation of oxidative stress.

 

Supplements, Recovery, And Glucose

There are countless supplements on the market, and it can be difficult to know which will aid in recovery. Creatine and caffeine are two that have been shown to have notable benefits on athletic performance and also impact glucose regulation:

 

Creatine

Creatine is a substance found naturally in muscle cells. Supplementing your natural stores of creatine with a micronized form is traditionally utilized for gains in strength, power, and explosiveness. This supplement has been extensively researched with regard to athletic performance, and there are a few studies emerging that point towards its efficacy for reducing mental fatigue caused by mental activity, sleep deprivation, or traumatic brain injury.

In addition to all of the aforementioned benefits, muscle glycogen resynthesis has been shown to be improved following creatine supplementation. Creatine may also decrease blood sugar by increasing the function of glucose transporter type 4 (GLUT-4). For this reason, it is possible to see a dip in blood glucose levels if you are supplementing with creatine.

Caffeine

Caffeine may improve recovery via enhanced glycogen resynthesis. Research has shown that ingesting 8 mg/kg of caffeine with 4 grams/kg carbohydrates results in 66% greater glycogen accumulation after 4 hour of recovery, as opposed to 4 grams/kg carbohydrates without caffeine.

In addition to improving glycogen resynthesis, caffeine can also be beneficial for metabolic health. A cross sectional study showed that caffeine is associated with lower fasting blood sugar and HbA1c values as well as higher levels of the hormone adiponectin. Adiponectin is an anti-diabetic hormone that modulates metabolic processes including glucose regulation, the body’s response to insulin, and fatty acid oxidation.


Conclusion

Effective recovery is critical for athletes facing back to back events, as well as recreational athletes trying to bounce back from a tough workout and minimize soreness and fatigue. Nutrition is a lynchpin of an effective recovery strategy as it can offer building blocks for tissue repair, replete energy and fluid losses, and serve as signaling molecules for genetic pathways associated with recovery. Carbohydrate-rich recovery nutrition may impact blood glucose levels in its effort to replete glycogen stores, but it is important not to overshoot and generate excessive glucose spikes, as high glucose levels can generate excess oxidative stress which can promote fatigue.

Continuous glucose monitoring can offer an objective peek into how recovery strategies are affecting the body in a number of ways:

  • In the case of refueling energy stores via carbohydrates, CGM can let us know whether we are overshooting our carbohydrate needs and generating an excessive spike that could be detrimental to our recovery goals. For the elite athlete who needs to get carbs in quickly before their next event, they may see a higher than normal glucose elevation, but do not want to see it skyrocket. For the recreational athlete who is at less risk for depleting glycogen and for whom it is less necessary to replete rapidly, CGM can help these individuals stay on track for keeping their glucose line stable and healthy before and after workouts.
  • CGM can tell us how protein intake alone, versus protein intake with carbohydrates, is differentially affecting our glucose levels. We need protein to build and repair muscle tissue, and can simultaneously use protein to buffer excessive glucose spikes from carbohydrate intake, via the impact of protein on secretion of insulin.
  • Given the relationship between dehydration and elevated blood glucose, CGM can offer a window into hydration status and need for more fluids.
  • CGM can give us a long term picture into our free radical and antioxidant balance. We know that high blood sugar spikes generate oxidative stress that can be counterproductive to recovery (and we want to avoid these), and we also know that our body’s antioxidant capacity is associated with better metabolic health. With this, we we can use our CGM data to reinforce the long term need to consume a large quantity of antioxidant rich foods, reduce oxidative stress via antioxidants, and enhance glycogen resynthesis via supplements.

In this way, you can use your CGM to your advantage and make the recovery process as healthy, least damaging, and most productive as possible.