CGM Accuracy During Exercise: Which Sensor Wins?

What This Study Found

A 2026 study tested three popular continuous glucose monitors (CGMs) in 20 adults with type 1 diabetes during a physically active camp. Researchers found that the Dexcom G7 and FreeStyle Libre 3 were highly accurate, performing similarly to each other. The Medtronic Simplera was significantly less accurate, especially during and after exercise sessions.

Why Does CGM Accuracy During Exercise Matter?

Exercise causes blood sugar to rise and fall quickly. During these rapid changes, CGM sensors can struggle to keep up with your actual glucose levels. If your sensor gives you an inaccurate reading during a workout, you might treat a low that isn't really there — or miss a real one. For people with type 1 diabetes, that gap between what the sensor says and what your blood sugar actually is can lead to serious decisions about insulin or food intake.

That's why researchers wanted to know: which sensors hold up best when the going gets active?

How the Study Was Done

Twenty adults with type 1 diabetes wore all three CGM systems at the same time for seven days. The first three days included a lab phase with three 90-minute group exercise sessions. The final four days were spent at home going about normal life.

Every two hours from 8 AM to 10 PM, participants took fingerstick blood glucose readings using the Contour Next One glucometer. Those readings were used as the gold standard to score how accurate each CGM was. Researchers used a measure called Median Absolute Relative Difference (MedARD) — basically, how far off the sensor reading was from the true blood glucose, on average.

What the Numbers Showed

• FreeStyle Libre 3: MedARD of 7.5% — most accurate overall
• Dexcom G7: MedARD of 8.4% — nearly as accurate, no statistically significant difference from Libre 3
• Medtronic Simplera: MedARD of 13.8% — significantly less accurate than both other sensors

To put that in plain terms: during exercise, the Simplera's readings were off by nearly double the margin of the other two sensors. That's a meaningful gap when you're trying to make real-time decisions about your diabetes management.

What This Means for You

If you're physically active — whether that means gym sessions, hiking, team sports, or even a busy weekend — CGM accuracy matters more than ever. This study suggests that not all sensors are created equal when your glucose is moving fast. The Dexcom G7 and FreeStyle Libre 3 both performed well in real-world active conditions, while the Simplera showed wider errors that could affect safety and dosing decisions.

It's also worth noting that the study group had excellent average blood sugar control (HbA1c of 6.6%), so these findings apply to well-managed type 1 diabetes in active adults.

If you use a CGM and are active, talk to your diabetes care team about which sensor may be the best fit for your lifestyle. At mdsdiabetes.com, MDS Diabetes carries a range of CGM supplies and accessories to help you get the most out of your sensor — including adhesive patches, sensor covers, and overtape designed to keep your device secure during physical activity.