![Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 1347)](/media/articles/images/article-10945-1347.png)

[Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 1347)

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

In the research field of the swimming section, the latest biomechanical analyses and physiological studies have revealed more subtle performance codes. This research report is translated from cutting-edge 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 evidence-based training plan guidelines.

Underwater Signal Interference Mechanisms of Optical Heart Rate Sensors

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 caused by stroke movements, along with strap displacement, can severely interfere with the stability of the green light signal. This study compared acceleration data and heart rate errors during freestyle strokes and found that the higher the stroke rate, the more significantly the error rate of optical heart rate monitoring increased. Especially when the stroke rate exceeds 60 strokes per minute, the signal noise is sufficient to cause the algorithm to misjudge heart rate peaks.

Physiological Signal 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 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 quality of contact 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, reducing conductivity, brief signal loss may still occur.

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

The following is a comparison of the experimental control group and multi-dimensional data compiled for you:

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: For 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 built-in optical sensor of a watch.
• 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 analyzing swimmers’ training data, coaches should apply smoothing to outliers (spikes) in optical heart rate data to avoid misjudging fatigue status.
• Cross-Model Validation: Algorithm differences among optical sensors from different brands are substantial. It is recommended to check the official error statements for swimming scenarios of the specific watch model before purchase.

Common Research Q&A (FAQ)

Q: Why is the optical heart rate on a watch 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 can severely interfere 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 fit. Before wearing, wet the electrode pads with water to improve conductivity, and ensure the chest strap is positioned at the lower edge of 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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