CGM in Cycling – What is It?

By Jiri Kaloc

Continuous glucose monitoring (CGM) has been a term increasing in popularity in cycling and sports in general. It’s time to take a closer look at it to see if it’s something that you should consider trying or if it’s just a fad that will soon go away. Let’s start with a simple question today: what even is it?

What does glucose do in your body?

Most cyclists know that glucose is a simple sugar that fuels muscles during hard rides. Fewer know what happens to glucose at other times of the day. The body constantly keeps a very close eye on glucose levels. It has mechanisms in place to make sure it stays inside a safe range to prevent negative symptoms that could progress to life-threatening situations.

Symptoms of blood glucose being too low – sweating, shakiness, extreme hunger, nausea, dizziness

Symptoms of blood glucose being too high – increased thirst, urination, fatigue, light-headedness

Thankfully, the body is really good at preserving glucose when there’s not enough by switching to fats (ketones) and even breaking down protein to quickly get more glucose. Similarly, it’s quick to send excess glucose to the cells that need it or to the liver for storage.

Eating is the most common way to increase your blood glucose levels just as exercise is a quick way to bring them down. This is common knowledge but it’s not easy to know just how much will certain foods increase your blood sugar and how quickly it will start to fall under what intensity of exercise. This is why glucose monitoring is interesting both to people with diabetes and athletes.

Pasta Bowl
It’s not easy to know just how much will certain foods increase your blood sugar. © Profimedia

How does continuous glucose monitoring work?

Unlike traditional blood glucose meters that require a finger-prick, CGMs measure glucose in the interstitial fluid, which is a thin layer of fluid that surrounds the cells below your skin. A CGM system typically consists of a tiny sensor inserted under the skin, it can stay inserted long-term to monitor your blood glucose continuously. This sensor is connected to a transmitter that sends data to a device, which then displays the glucose levels and trends.

Continuous glucose monitoring is a technology originally developed for people with diabetes who can’t rely on their bodies to automatically maintain stable glucose levels. Seeing how their blood glucose changes after meals, after exercise, and recognising patterns makes it easier to make decisions about medication and lifestyle adjustments. For similar reasons, CGM proved to be useful even for healthy individuals wanting to optimise athletic performance.

What do continuous glucose monitors tell you?

They allow you to see your glucose levels at any moment but that’s not really where the biggest benefit lies. Here is an overview of the main types of data CGMs provide:

  • Current glucose levels – This number alone has limited use. It helps you see whether your glucose levels are in a healthy range while fasting and how much they spike after a given food.
  • Time in range – This tells you how long your body stays in a given range of glucose levels. It’s mainly used for diabetics to see how long their glucose levels remain elevated after meals. However, it can also be used by athletes to find out how well they absorb glucose from different foods.
  • Rate of change of glucose – This tells you how quickly your glucose is rising or falling. This is especially interesting for athletes as the rate of change is much more telling regarding whether you’re about to bonk than the specific glucose level at one moment.
  • Glucose variability – Statistics like glucose variability are also helpful for diabetics because they help them see if their glucose management overall in a given time period has been successful or not. Low variability is a sign of health.

Some companies also developed metrics such as fuelling scores, glucose scores, etc. to target healthy endurance athletes who want to optimise their performance nutrition. The next article will be all about the benefits that CGMs can bring to cyclists and endurance athletes.