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Continuous Glucose Monitors in Sport - What are they for?

Continuous glucose monitors (CGMs) are a helpful adjunct for athletes without diabetes, providing clarity, and removing some of the guesswork, around how the body utilises different energy sources during athletic performance. 

Before Exercise
Glucose is a fuel used by our bodies. Immediately before a workout or competition, our bodies need high levels of glucose so they are ready to be burnt the moment we start exercising. Not having enough fuel on board prior to a work-out potentially leads to fatigue, early cessation of exercise and poor performance. 

Experts recommend blood glucose levels of 90-140 mg/dl (5.0-7.8 mmol/l) immediately prior to exercise. Conversely, rapid spikes in glucose such as those seen following a sugary snack are often followed by sudden drops in blood glucose, again leading to poor performance and fatigue. So CGM helps athletes make correct food choices, helping them eat the right food at the right time.

Each athlete’s metabolism is different and each sporting discipline has different glucose requirements, so using CGM helps each individual identify how soon before exercise they should eat and which foods give them sufficient and sustained glucose in preparation for exercise while avoiding rapid spikes.

During Exercise
When exercising, particularly for an extended period, our muscles quickly consume the glucose in our bloodstream. However, this does not lead to a sudden drop in blood glucose levels as adrenaline produced by our bodies (in response to exercise) causes more glucose to be released from the body’s glycogen stores, causing the blood glucose level to rise.

Studies in marathon runners have shown these glycogen stores are slowly depleted over time, eventually leading to glucose levels to fall. CGM allows the athlete to understand their real-time glucose levels, even during a workout, helping them know which foods/sports gels to consume and when to maximise athletic performance.
 
Following exercise
Replenishing the body’s glycogen stores is a crucial part of recovery. CGM helps athletes monitor their blood glucose levels to ensure they are taking enough energy onboard after a workout. 

In times when athletes are not working out or competing, high blood glucose should be avoided, as this can lead to long-term damage to small blood vessels around the body, resulting in chronic health problems. It is recommended that when not exercising, blood glucose should be between 65-90 mg/dl (3.5-5.0 mmol/l) .


Conclusion
CGM is an important tool for determining an athlete’s fuelling strategy. The advantage using CGM gives is unlikely to turn the reluctant athlete into a world-beater, but a sportsperson who understands the impact of what they eat and drink has on their bodies will have a much better chance of improving their performance. 

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Outside Magazine, Jan 2022 (Amended)