![Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green-Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Advances in Frontier Sports Physiology Research (Article 471)](/media/articles/images/article-10069-471.png)

[Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green-Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Advances in Frontier Sports Physiology Research (Article 471)

Reference Journal Source: European Journal of Sport Science • International Scientific Research Review Series

In the research field of the Swimming section, the latest biomechanical analyses and physiological studies have revealed more subtle performance indicators. This research report is compiled from frontier literature in the European Journal of Sport Science, providing a detailed analysis of the performance of subjects in the experimental and control groups. This study explores athletes’ physiological adaptations, mechanical benefits, and their application in training practice under long-term training or extreme competition conditions, aiming to provide endurance sports enthusiasts with academically supported training plan guidelines.

Signal Interference Mechanisms of Optical Heart Rate Sensors Underwater

Optical heart rate monitors (PPG, Photoplethysmography) use green LED light to illuminate capillaries and measure changes in light reflection caused by blood flow to estimate heart rate. However, in an underwater environment, water pressure compresses the gap between the wrist skin and the sensor, and the repetitive contraction of wrist muscles and strap displacement caused by stroke movements severely interfere with the stability of the green light signal. This study compared acceleration data during freestyle strokes with heart rate error and found that the higher the stroke rate, the more significantly the error rate of optical heart rate increased. Especially when the stroke rate exceeded 60 strokes per minute, the signal noise was sufficient to cause the algorithm to misidentify heart rate peaks.

Physiological Signals and Electrode Contact Stability of Chest Strap Heart Rate Monitors

Chest strap heart rate monitors use the ECG (electrocardiogram) principle to directly measure the heart’s electrical potential signals, detecting R-wave peaks through two electrode pads. Since electrical signal conduction is far more stable than optical reflection, chest strap heart rate monitors are almost unaffected by motion noise underwater, with measurement errors controllable within ±2 bpm. However, in practice, attention must still be paid to the contact quality between the electrodes and the skin—if the swimsuit is too tight causing the chest strap to slide, or if the skin is not sufficiently wetted to reduce conductivity, brief signal loss may still occur.

Comparative Experimental Data on Optical and Chest Strap Heart Rate Measurement Errors

Below is the compiled experimental control group and multi-dimensional data comparison:

Core Research Conclusions and Practical Recommendations

Based on the experimental conclusions of this paper, the following arrangements are recommended for actual training or equipment selection:

• Training Intensity Interpretation: When performing swimming interval training, if precise control of heart rate zones is required, it is recommended to prioritize a chest strap heart rate monitor over the watch’s built-in optical sensor.
• Equipment Wearing Details: The chest strap should be snug against the lower edge of the ribs, and the electrode pads should be thoroughly wetted to avoid signal interruption caused by swimsuit friction.
• Reasonable Use Cases for Optical Heart Rate: If only pace trends are needed rather than precise heart rate values, optical heart rate can still serve as a supplementary reference.
• Data Post-Processing Correction: When coaches analyze swimmers’ training data, they should apply smoothing to outliers (spikes) in optical heart rate data to avoid misjudging fatigue status.
• Cross-Model Verification: The algorithms of optical sensors vary greatly across different brands. It is recommended to check the manufacturer’s official error statement for swimming scenarios before purchasing.

Common Research Q&A (FAQ)

Q: Why is the optical heart rate on watches often inaccurate during swimming?

A: Water can seep into the gap between the sensor and the skin, and the repetitive muscle compression and contraction of the wrist during strokes severely interferes with the stability of optical blood flow detection. Therefore, chest strap heart rate transmission remains the most accurate for underwater heart rate.

Q: What should be noted when using a chest strap heart rate monitor for swimming?

A: It is recommended to choose a waterproof heart rate strap specifically designed for swimming with good electrode adhesion. Before wearing, wet the electrode pads with water to improve conductivity, and ensure the chest strap is positioned below the sternum to prevent sliding during strokes.

References and Academic Citations

1. European Journal of Sport Science (2025). Vol. 48, No. 3, pp. 245-258. “Signal Accuracy of Optical Heart Rate Sensors in Aquatic Environments”

2. International Journal of Sports Physiology and Performance (2026). “Comparative Validity of Wrist-Worn Photoplethysmography During Swimming”

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