Resting Heart Rate

Definition

Resting heart rate (RHR) is the number of times your heart beats per minute when you are completely at rest - ideally measured first thing in the morning while still lying down. A lower RHR generally indicates a stronger, more efficient heart that pumps more blood per beat. For HYROX^® athletes, RHR is a simple daily metric that tracks long-term cardiovascular adaptation and provides early warning signs of overtraining or illness.

The Science

RHR reflects cardiac efficiency. With aerobic training, the heart's left ventricle enlarges and stroke volume increases - meaning more blood is ejected per beat. Because the body's resting oxygen demands remain constant, the heart needs fewer beats per minute to meet them.

Factors influencing RHR:

• Fitness level - endurance training lowers RHR by 10-20 bpm over months of consistent training.^[1]
• Age - RHR remains relatively stable throughout adulthood but may rise slightly in later decades.
• Genetics - baseline RHR has a hereditary component.
• Autonomic tone - higher parasympathetic (vagal) activity lowers RHR.
• Acute factors - caffeine, alcohol, stress, illness, and dehydration temporarily elevate RHR.

Why It Matters for HYROX^®

• Fitness tracker - a declining RHR over weeks confirms that your aerobic base is developing.
• Overtraining alarm - a sustained elevation of 5-7+ bpm above your baseline for 3+ days signals accumulated fatigue, poor recovery, or early illness. This is a cue to reduce training load.
• Race readiness - athletes in peak condition often reach their lowest RHR during a taper, confirming supercompensation before race day.
• Complements HRV - while HRV captures daily readiness, RHR trends over weeks provide a longer-term fitness trajectory.

How to Measure It

Best practice: measure at the same time each morning, before getting out of bed and before caffeine. Use a 7-day rolling average.

How to Improve It

• Consistent aerobic training - Zone 2 running 3-5x per week is the primary driver.^[2]
• Adequate sleep - 7-9 hours per night allows full parasympathetic recovery.
• Hydration - dehydration raises RHR by reducing blood volume and stroke volume.
• Stress management - chronic stress elevates sympathetic tone and RHR.
• Avoid alcohol before bed - even moderate consumption can raise overnight RHR by 5-10 bpm.

HYROX^® Benchmarks

Note: individual variation is significant. A healthy, fit athlete may have a RHR of 55 bpm due to genetics, while another equally fit athlete sits at 45.

FAQ

What is a dangerously low resting heart rate? For trained athletes, RHR in the low 40s or even high 30s is normal and healthy. Below 35 bpm with symptoms like dizziness, fainting, or extreme fatigue warrants medical evaluation.

How quickly does RHR drop with training? Most new athletes see a 3-5 bpm drop within 4-8 weeks of consistent aerobic training. Further reductions occur gradually over months.

Is morning RHR or overnight average more reliable? Both are useful. Overnight averages from wearables reduce single-reading variability. Morning spot-checks are simpler and still highly informative.

Track your resting heart rate alongside every training metric with ROXBASE.