CGM Accuracy During Exercise: Which Sensor Wins?

What Was Studied — and Why It Matters

Continuous glucose monitors (CGMs) are life-changing tools for people with type 1 diabetes, but there's a known weak spot: physical activity can cause blood sugar to shift quickly, and some sensors struggle to keep up. Researchers wanted to know which of three popular CGM systems — the Dexcom G7, FreeStyle Libre 3, and Medtronic Simplera — stays most accurate when you're actually moving and exercising.

Twenty adults with well-managed type 1 diabetes took part in the study. They wore all three CGM sensors at the same time over a seven-day period that included three supervised 90-minute group exercise sessions, followed by four days of normal home activity. Every two hours, participants also took a traditional fingerstick blood sugar reading to use as the gold-standard comparison.

What the Researchers Found

Accuracy was measured using something called the Median Absolute Relative Difference (MedARD) — essentially, how far off the sensor reading was from the real fingerstick result, on average. Lower numbers mean better accuracy.

• FreeStyle Libre 3: Most accurate overall, with a MedARD of 7.5%
• Dexcom G7: Close behind at 8.4% — statistically no different from the Libre 3
• Medtronic Simplera: Noticeably less accurate at 13.8%, a statistically significant gap from both other sensors

In plain terms, the Libre 3 and G7 were essentially tied for accuracy during and around exercise. The Simplera, by contrast, showed nearly double the error rate — meaning it could display a reading that was off by a more meaningful margin when blood sugar was shifting during activity.

What This Means for Real Patients

If you're an active person with type 1 diabetes — whether you enjoy weekend hikes, gym sessions, or sports — sensor accuracy during movement isn't just a technical detail. It directly affects decisions you make about insulin dosing, eating, and safety.

A sensor that reads too high during exercise might lead you to take insulin you don't need. One that reads too low could cause unnecessary panic. Choosing a sensor that performs well during activity is a practical, important consideration.

Both the Dexcom G7 and FreeStyle Libre 3 performed strongly in this real-world, active setting. If you currently use either of these sensors, MDS Diabetes carries the supplies you need — including replacement sensors and compatible readers — so you can stay stocked and confident heading into any workout.

A Few Things to Keep in Mind

This study involved only 20 participants, all of whom had well-controlled diabetes (average HbA1c of 6.6%). Results may differ for people with higher HbA1c levels or different exercise routines. Always talk to your diabetes care team before making changes to your monitoring approach.

Bottom Line

When blood sugar is moving fast during exercise, sensor accuracy matters most. This study confirms that the Dexcom G7 and FreeStyle Libre 3 are both highly accurate during physical activity, while the Medtronic Simplera showed significantly more error. For active adults with type 1 diabetes, these findings support choosing either of the top two sensors — and keeping your supplies reliably stocked through a trusted source like MDS Diabetes.