![Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Biomechanical Quantification Experiment Report (No. 177)](/media/articles/images/article-9775-177.png)

[Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Biomechanical Quantification Experiment Report (No. 177)

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 science journal European Journal of Sport Science. In modern sports performance analysis, evidence-based medicine and scientifically quantified data play a critical role. This study explores athletes’ physiological adaptations, mechanical benefits, and their practical applications in training under long-term training or extreme race conditions, aiming to provide endurance sports enthusiasts with evidence-based training plan guidelines.

Mechanisms of Optical Heart Rate Sensor Signal Interference 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 underwater environments, water pressure compresses the gap between the wrist skin and the sensor, and the repetitive contraction of wrist muscles during arm strokes, along with strap displacement, can severely disrupt the stability of the green light signal. This study compared acceleration data from freestyle strokes with heart rate errors and found that the higher the stroke rate, the more significantly the optical heart rate misjudgment rate increased. Particularly when stroke rate exceeded 60 strokes per minute, signal noise was 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 (electrocardiogram) principle to directly measure cardiac 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 to reduce 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 conclusions of this paper, the following arrangements are recommended for actual training or equipment selection:

• Training Intensity Assessment: When performing swimming interval training, if precise heart rate zone control is required, prioritize a chest strap heart rate monitor over the built-in optical sensor on a watch.
• Equipment Wearing Details: The chest strap should fit snugly 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 optical heart rate outliers (spikes) to avoid misjudging fatigue status.
• Cross-Device Validation: Algorithm differences among optical sensors from different brands are substantial; it is recommended to review 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 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 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 swimming-specific heart rate strap 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 slipping during arm 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”

Further Reading

• [Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: International Research Literature Compilation and Review Report (No. 1119)](/articles/10717)
• [Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Latest Academic Literature Review and Training Practice (No. 1242)](/articles/10840)
• [Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Latest Academic Literature Review and Training Practice (No. 1416)](/articles/11014)
• [Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Frontiers in Exercise Physiology Research Progress (No. 471)](/articles/10069)