One of the most common questions I get from athletes is: “Should I trust my HbA1c test from the doctor, or the data I’m getting from my CGM?” The answer depends on what you want to know. Both tools are useful, but they tell very different stories.
What HbA1c Tells You
HbA1c is a blood test that reflects your average glucose levels over the past 2–3 months. It’s widely used in healthcare to assess long-term glucose control and diabetes risk. For athletes, it can be a general indicator of metabolic health.
But here’s the catch: it doesn’t tell you anything about daily fluctuations, meal responses, or in-ride glucose dips. A “normal” HbA1c doesn’t guarantee you’re fueling optimally for endurance performance.
As athletes, our daily average glucose will be higher because we need it higher to workout and compete optimally. This alone will skew your HbA1c high.
Many athletes also have longer living red blood cells, and this will also skew the HbA1c high.
For a in depth read into this issue, I encourage you to check out this excellent article.
https://www.gethealthspan.com/research/article/a1c-levels-of-endurance-athletes
What CGM Tells You
Continuous Glucose Monitoring, on the other hand, gives real-time data. It tells you:
- How your glucose responds to meals.
- How stable your energy is during rides.
- Whether your recovery fueling is effective.
For athletes, this context is gold. It helps prevent bonking, guides fueling, and fine-tunes recovery.
Why Cyclists Benefit More From CGM
Think of HbA1c as the “big picture” and CGM as the “daily detail.” If your goal is general health, HbA1c matters. If your goal is performance, CGM matters more.
Coaching Story
A rider I worked with had a perfectly normal HbA1c. But his CGM showed rollercoaster spikes and crashes during long rides. Once he stabilized his fueling, smaller, more frequent carbs, his endurance improved dramatically. His doctor said he was “healthy,” but his CGM revealed the performance issue. When we analyzed his nightly average glucose levels, they were very stable and low, which was more important than looking at his HbA1c for overall health. As endurance athletes, we are going to have more fluctuations than non-exercising people, and it is important to keep things more stable, but also understand that your CGM can give you insights that a HbA1c blood test can’t.
The Balanced View
For most cyclists, using both perspectives is ideal. HbA1c assures you of overall health, while CGM guides daily training. Together, they paint the full picture.
Conclusion
HbA1c and CGM aren’t competitors, they’re complementary. But if performance is your priority, CGM gives you the actionable insights you need.
Want to explore how CGM can change your fueling? Visit www.trainingandcompetingwithacgm.com for resources and strategies.