【Research Review】Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Study on Elite Athletes’ Physiological Characteristics (No. 300)

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

In the swimming section of sports science, the latest biomechanical analyses and physiological studies have revealed more subtle performance indicators. This research report is compiled from cutting-edge literature in the European Journal of Sport Science, providing a detailed analysis of the performance of subjects in both experimental and control groups. This study explores athletes’ physiological adaptations, mechanical benefits, and their practical applications in training 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 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 arm strokes with heart rate errors and found that the higher the stroke rate, the more significantly the error rate of optical heart rate monitoring 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 patches. 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-skin contact—if a tight swimsuit causes the chest strap to slide, or if the skin is not sufficiently wetted to reduce conductivity, temporary signal loss may still occur.

Comparative Experimental Data on Optical vs. Chest Strap Heart Rate Measurement Errors

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

Core Scientific 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 that requires precise heart rate zone control, prioritize a chest strap heart rate monitor over the wrist-worn optical sensor.
• Equipment Wearing Details: The chest strap should fit snugly against the lower edge of the ribs, and the electrode patches 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 monitoring 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-Model Verification: Algorithm differences among optical sensors from different brands are substantial; it is recommended to review the manufacturer’s official error statements for swimming scenarios before purchasing.

Common Scientific FAQs

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 chest strap specifically designed for swimming with good electrode adhesion. Wet the electrode patches with water before wearing to improve conductivity, and ensure the 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”

Related Reading

• 【Research Review】Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Sports Performance (No. 1347)
• 【Research Review】Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Advances in Frontier Exercise Physiology Research (No. 471)
• 【Research Review】Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming: Quantitative Biomechanics Experimental Report (No. 177)
• 【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)