Real-World Test: How ECG and PPG Compare During Workouts

In a previous post, we explored the fundamental differences between ECG (electrocardiography) and PPG (photoplethysmography) in heart rate monitoring. Now it’s time to take the theory into practice.

Our team ran a controlled workout test to see how these two technologies respond to real changes in heart rate. We used two well-known brand devices—one ECG-based, the other PPG-based—worn simultaneously during intervals of physical activity. Below are two examples from the session, illustrating what we observed.

Example 1: Sudden Heart Rate Spike

In this test segment, the athlete executed a short burst of activity. The ECG data immediately reflected the increase in heart rate. However, the PPG data barely registered the change.

PPG (Short Burst)

ECG (Short Burst)

Observation:The PPG sensor did not react fast enough—and in this case, it barely observed the change at all. This highlights a common limitation of PPG technology: its reliance on optical signals makes it prone to delay or signal loss during sudden movements or rapid transitions. This makes PPG less reliable for detecting short bursts of intensity.

Example 2: Sustained Elevated Heart Rate

In this example, the athlete maintained a high heart rate over a longer period. While the PPG reading was still slightly delayed and smoother than the ECG, the general trend remained consistent.

PPG (Sustained Effort)

ECG (Sustained Effort)

Observation:Even during prolonged exertion, the PPG shows a small delay. But in this case, it successfully captured the overall shape and trend of the heart rate data. This confirms that PPG can work well for steady-state monitoring—just not for high-resolution, real-time tracking.

Final Thoughts

From our testing, it’s clear that ECG provides more accurate and immediate heart rate data, especially during rapid changes. PPG is generally sufficient for monitoring heart rate zones and steady efforts, but less reliable when timing and intensity matter most.

We tested devices from reputable and well-known brands, and found that the difference lies more in the technology (ECG vs. PPG) than in the brand or specific device. Whether you use a budget-friendly fitness tracker or a high-end smartwatch, these principles hold true.

If you're a coach, athlete, or serious about performance, especially during intervals or intense training, ECG remains the gold standard.