Decide When to Trust Heart-Rate Data
Heart rate is useful only after you know when the sensor is measuring you and when it is measuring noise.
Recognize believable readings before using them to guide a run.
Know what the sensor measures
A chest strap detects the heart's electrical signal. A wrist watch estimates pulse from changing blood flow, so fit, skin contact, cold weather, arm movement, and sweat can affect the trace.
Spot an implausible trace
A sudden jump, a flat line that matches cadence, or a reading that disagrees sharply with breathing and effort deserves investigation before interpretation.
Match the sensor to the session
A smooth wrist trace is often adequate for steady easy running. Rapid intervals, threshold work, and maximum-heart-rate observations benefit more from a well-fitted chest strap.
Put it into practice
- Tighten the watch or wet and position the chest strap correctly.
- Compare the trace with breathing, effort, and cadence.
- Repeat the same easy section before deciding a sensor is unreliable.
You can explain why a trace is believable and know when a chest strap would materially improve the session.
Stop exercise and seek appropriate medical advice for unexplained chest pain, fainting, severe breathlessness, or an irregular rhythm. Do not dismiss symptoms as sensor error.