![Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green-Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Latest Academic Literature Review and Training Practice (No. 1242)](/media/articles/images/article-10840-1242.png)

[Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green-Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Latest Academic Literature Review and Training Practice (No. 1242)

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

This article is based on the latest research findings from the internationally renowned sports academic journal European Journal of Sport Science. In modern sports performance analysis, evidence-based medicine and scientific quantitative data play a pivotal role. This study explores athletes’ physiological adaptations, mechanical benefits, and their applications in training practice under long-term training or extreme competition conditions, aiming to provide endurance sports enthusiasts with evidence-based training plan guidelines.

Mechanisms of Underwater Signal Interference in Optical Heart Rate Sensors

Optical heart rate monitors (PPG, Photoplethysmography) use green-light LEDs to illuminate capillaries and measure changes in light reflection caused by blood flow to estimate heart rate. However, in underwater environments, water pressure compresses the gap between the wrist skin and the sensor, and the repetitive contraction of wrist muscles during stroke movements, along with strap displacement, can severely compromise the stability of the green-light signal. This study compared acceleration data during freestyle stroke movements with heart rate errors, finding that the higher the stroke rate, the more significant the increase in optical heart rate misreading. Particularly when stroke rates exceed 60 strokes per minute, signal noise is sufficient to cause the algorithm to misidentify heart rate peaks.

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

Chest strap heart rate monitors use the ECG (electrocardiography) 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 electrode-skin contact—if a tight swimsuit causes 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 vs. Chest Strap Heart Rate Measurement Errors

Below is a compiled comparison of experimental control groups and multi-dimensional data:

Core Research Conclusions and Practical Recommendations

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

• Training intensity assessment: For swim interval training requiring precise heart rate zone control, 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 with the electrode pads thoroughly wetted to avoid signal interruption caused by swimsuit friction.
• Appropriate use of 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.
• Post-data correction: When analyzing swimmers’ training data, coaches should apply smoothing to optical heart rate outliers (spikes) to avoid misjudging fatigue status.
• Cross-device validation: Algorithm differences among optical sensors from different brands are substantial; check the official error statements for swimming scenarios of a specific watch model before purchase.

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 disrupt the stability of optical blood flow detection. Therefore, chest strap heart rate transmission remains the most accurate for underwater heart rate monitoring.

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. Wet the electrode pads with water before wearing to improve conductivity, and ensure the 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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