【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. 1416)

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 scientific quantitative data play a critical 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 academically supported training plan guidelines.

Underwater Signal Interference Mechanisms of 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 from stroking movements, along with strap displacement, can severely interfere with the stability of the green light signal. This study compared acceleration data during freestyle stroking with heart rate errors and found that the higher the stroke rate, the more significantly the misjudgment rate of optical heart rate increased. Especially 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 controlled within ±2 bpm. However, in practice, attention must still be paid to the quality of electrode-to-skin contact—if the swimsuit is too tight causing the chest strap to slip, 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

The following 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 Interpretation: When performing swimming interval training, if precise heart rate zone control is required, it is recommended to prioritize a chest strap heart rate monitor over the wrist-worn optical sensor built into the 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 coaches analyze swimmers’ training data, they should apply smoothing to outlier 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 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 stroking 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 at the lower edge of the sternum to prevent slipping during stroking.

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”

Related Topic Reading

• 【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)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: International Research Literature Compilation and Review Report (No. 1119)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Frontiers in Exercise Physiology Research Progress (No. 471)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Biomechanical Quantitative Experiment Report (No. 177)