Your watch says 175 bpm. You feel like you're jogging. What's going on?

Heart rate data issues are common. Here's how to troubleshoot.

Sensor Issues

Optical Sensor Problems

Common causes of bad readings:

Poor fit:

• Watch too loose
• Watch positioned wrong on wrist
• Movement during running

Environmental:

• Cold weather (poor blood flow to wrist)
• Very sweaty conditions
• Direct sunlight on sensor

Physical:

• Tattoos under sensor
• Very dark or very hairy skin (some sensors)
• Certain skin conditions

Fix attempts:

1. Tighten watch band (snug, not cutting off circulation)
2. Position watch higher on wrist
3. Clean sensor and skin
4. Wait a few minutes for readings to stabilize

Chest Strap Problems

Common issues:

Dry electrodes:

• Strap needs moisture to conduct
• Wet the electrodes before starting
• Use electrode gel for reliability

Battery dying:

• Intermittent readings
• Spikes or dropouts
• Check/replace battery

Interference:

• Other electronic devices
• Certain fabrics
• Power lines (rare)

Worn out strap:

• Elastic stretched
• Electrodes degraded
• Replace every 2-3 years with heavy use

Signs of Sensor Problems (Not Real HR)

• Sudden spikes to 200+ that don't match effort
• HR exactly matching cadence (common optical error)
• Instant drops from high to low
• Readings that don't respond to effort changes
• Data flat-lines at specific numbers

Real Physiological Causes

High HR That's Actually Real

Heat and humidity:

• HR rises 10-20 bpm in hot conditions
• Heart works harder to cool body
• Normal response, not sensor error

Dehydration:

• Less blood volume
• Heart beats faster to compensate
• Can add 10+ bpm to HR

Caffeine:

• Stimulant effect on heart
• Can elevate HR 5-15 bpm
• Effect varies by individual

Poor sleep:

• Recovery compromised
• Elevated baseline HR
• May see 5-10 bpm increase

Stress:

• Cortisol affects heart rate
• Life stress shows up in HR data
• Both baseline and exercise HR affected

Illness (even mild):

• Body fighting infection
• Elevated HR is protective response
• Take extra easy days

Overtraining:

• Elevated resting HR
• Higher HR at same pace
• Sign to back off

Cardiac Drift

What it is: HR gradually rises during long runs despite constant pace

Why it happens:

• Dehydration reduces blood volume
• Body temperature rises
• Normal physiological response

Normal range: 5-15 bpm increase over a long run

Concerning range: 20+ bpm increase suggests significant dehydration or overheating

Low HR That's Actually Real

Improved fitness:

• Stronger heart pumps more per beat
• Same pace, lower HR over time
• Good sign!

Cool conditions:

• Less cardiac demand for cooling
• Normal and expected

Downhill or tailwind:

• Less effort for same pace
• HR appropriately lower

When to Worry

See a Doctor If:

During exercise:

• Chest pain or pressure
• Extreme shortness of breath
• Dizziness or lightheadedness
• Palpitations (feeling heart skip/flutter)
• HR won't come down despite stopping

Resting HR changes:

• Sudden, sustained increase (10+ bpm above normal)
• Very irregular heart rhythm
• Concerning symptoms accompanying changes

Probably Not Concerning:

• Occasional single spike in data
• HR variations day to day
• Higher HR in heat or when tired
• Lower HR as fitness improves

Fixing Bad Data

Improve Data Quality

Hardware solutions:

• Switch to chest strap for accuracy
• Try different optical sensor positions
• Use electrode gel on chest strap
• Replace worn equipment

Practice solutions:

• Let sensor stabilize before starting
• Tighten watch band appropriately
• Run a few minutes, then check readings

Clean Up Recorded Data

In most platforms:

• Manually edit obvious errors
• Note conditions that affected readings
• Exclude bad data from analysis

For analysis:

• Focus on clearly good data
• Compare similar conditions
• Use trends, not single points

When Data Conflicts with Feel

Trust Your Body If:

• You feel good but HR says "too high"
• Sensor has been unreliable
• Conditions explain the discrepancy

Investigate If:

• You feel bad but HR looks normal
• Pattern persists across multiple runs
• Other symptoms present

The Middle Ground:

Use HR as information, not instruction.

• Elevated HR is a data point
• Combine with RPE and performance
• Adjust if pattern is consistent

Heart rate data is a tool, not a truth detector. Use our Heart Rate Zone Calculator to set accurate zones, and track your HR trends on your dashboard.