VO₂ Max versus HRV
VO₂ Max, Heart Rate Zones, and HRV: What These Fitness Metrics Really Mean
When it comes to improving fitness, longevity, and recovery, data only helps if you understand what it’s telling you. Three key metrics — VO₂ Max, Heart Rate Zones (HRZs), and Heart Rate Variability (HRV) — offer powerful insight into how your body performs, adapts, and recovers.
This article breaks down what each of these terms actually means, how they’re measured, and what you can do to improve them.
VO₂ Max: How Fit Are You, Really?
VO₂ Max is the maximum amount of oxygen your body can use during intense physical activity. It reflects how efficiently your heart, lungs, and muscles can deliver and use oxygen — making it a strong indicator of cardiorespiratory fitness.
A higher VO₂ Max means better endurance, greater aerobic efficiency, and, in many studies, a reduced risk of chronic disease and all-cause mortality.
VO₂ Max can be measured directly in a lab using a treadmill or stationary bike with a face mask to analyse your breath. More commonly, wearables like Garmin, Apple Watch, and others provide estimates based on heart rate and workout data.
To improve VO₂ Max: Focus on structured aerobic training, especially tempo runs, zone 2 endurance sessions, and interval workouts in the 70–90% max heart rate range.
Gradual progression and consistency over time are key to raising your aerobic ceiling.
Heart Rate Zones: Training with Intention
Heart Rate Zones divide your heart rate into intensity bands based on your estimated maximum heart rate (typically 220 minus your age). Each zone corresponds to a different energy system and training effect:
Zone 1: Very light effort — good for active recovery and warm-ups
Zone 2: Easy but sustained — ideal for building aerobic endurance and fat metabolism
Zone 3: Moderate effort — improves general cardiovascular fitness
Zone 4: High intensity — pushes your lactate threshold and increases speed
Zone 5: Maximum effort — used for short, powerful bursts and sprint conditioning
Using a heart rate monitor or smartwatch helps you stay in the right zone to match your training goal — whether that’s burning fat, increasing endurance, or improving top-end performance.
To improve zone performance: Spend time training in the specific zones aligned with your goals. For example, Zone 2 for endurance and metabolic efficiency; Zone 4 for speed and power.
Improving your ability to stay in a zone longer — or transition smoothly between them — builds both aerobic capacity and metabolic flexibility.
HRV: How Well Are You Recovering?
Heart Rate Variability (HRV) measures the variation in time between heartbeats. A common misconception is that a steady rhythm is always good — but in fact, more variability usually reflects a well-recovered, adaptable nervous system.
HRV is largely regulated by your autonomic nervous system — specifically the balance between the sympathetic (“fight or flight”) and parasympathetic (“rest and digest”) branches. A higher HRV generally indicates good recovery, resilience, and stress tolerance. A lower HRV may suggest overtraining, illness, poor sleep, or elevated stress levels.
Wearables like Oura, Whoop, and Apple Watch can track HRV over time, ideally measured first thing in the morning for consistency.
To improve HRV: Prioritise sleep quality, manage stress, stay hydrated, and avoid overtraining.
Regular light aerobic exercise, meditation or breathwork, and minimising alcohol intake can also improve HRV over time.
HRV is one of the best non-invasive markers of your body’s recovery status and training readiness.
Putting It All Together
VO₂ Max tells you how fit you are
Heart Rate Zones tell you how hard you’re working
HRV tells you how well you’re recovering