Can Runners Trust CGMs During Exercise? What Research Shows

What Was Studied and Why It Matters

Continuous glucose monitors (CGMs) — small wearable sensors that track blood sugar automatically — are no longer just for people with diabetes. Recreational athletes and runners are increasingly strapping them on to understand how their bodies respond to exercise. But here's the problem: nobody had confirmed whether these devices are actually accurate during a run.

A 2024 study published in the International Journal of Sports Physiology and Performance set out to answer exactly that. Researchers tested the popular FreeStyle Libre 2 CGM on 13 well-trained recreational runners — none of whom had diabetes — worn in two spots: the upper arm (the standard location) and the chest.

How the Study Worked

Participants ran on treadmills for up to 90 minutes at three different effort levels — easy, moderate, and somewhat hard. Throughout the runs, researchers compared CGM readings to finger-prick blood glucose tests, which remain the gold standard for accuracy. They also took readings at rest and after meals.

What They Found

The Good News: Trends Are Reliable

• CGMs were accurate at detecting the direction of glucose changes — whether blood sugar was rising or falling during exercise.
• Nearly all readings (99.6–99.8%) fell within clinically acceptable safety zones, meaning the sensor rarely produced dangerously misleading data.
• Arm and chest placements performed similarly, giving runners flexibility in where they wear the device.

The Concern: Exact Numbers May Be Off

• The average error rate was around 12–14%, which is higher than what's considered ideal for precise glucose management.
• Only about half of all individual readings were within 10% of the true blood glucose value.
• Accuracy dropped further at lower glucose levels — which is especially important, since low blood sugar (hypoglycemia) during exercise can be dangerous.

What This Means for Real Patients and Athletes

If you have diabetes and use a CGM during physical activity, this research offers an important reminder: your CGM is a trend-tracking tool, not a perfectly precise meter. Seeing your glucose heading downward during a long run is valuable information — but don't rely on a single CGM number to decide whether you need a snack or an insulin adjustment without a confirmatory finger-prick test.

For people managing diabetes who are active, having reliable supplies on hand matters. MDS Diabetes carries a full range of CGM supplies, finger-prick testing materials, and diabetes management tools so you're never caught unprepared before or after a workout.

The researchers also pointed out that we still don't know whether CGMs reliably catch hypoglycemia during exercise — a critical gap that needs more study before athletes with diabetes rely on them as a safety net.

Bottom Line

CGMs like the FreeStyle Libre 2 are useful for watching glucose trends during steady-state exercise, but they are not accurate enough for precise, point-in-time blood sugar readings during a run. Whether you wear the sensor on your arm or chest, performance is similar. Until more research is done, people with diabetes should continue using finger-prick testing to confirm any CGM readings that will drive treatment decisions — especially during physical activity.