Most people train at one intensity and wonder why fitness stalls. A GP's guide to heart rate zones, and how I'm using them to train for Hyrox at almost 50.
In December I'm racing Hyrox. Eight one kilometre runs, each followed by a workout station: SkiErg, sled push, sled pull, burpee broad jumps, rowing, farmer's carry, sandbag lunges and wall balls.
I'm almost 50. I run a clinic and I'm a single dad. Training time is limited, so every session has to earn its place.
I'm treating the lead up as an experiment. What changes when you train with precision instead of guesswork? I'm tracking bloods, VO2max and body composition from start to finish. The first number I set was simpler than any of those. Heart rate.
Here is how heart rate zones work, how I set mine, and where the numbers stop being useful.
The problem with training by feel
Most people train at one intensity. Moderate. Too hard to recover from properly, and too easy to force real change.
Easy days drift faster. Hard days never get properly hard. The week feels busy and fitness stalls.
Heart rate fixes this by giving every session a target. An easy run gets a ceiling. A hard session gets a floor. Stay inside the lines and each session does its job.
Start with your maximum
Zones are usually set as a percentage of maximum heart rate (HRmax). This is the highest rate your heart reaches in an all out effort.
Genetics sets most of it. It falls slowly with age, by about a beat a year. Getting fitter does not raise it. What fitness changes is how fast you can go at any given heart rate.
Most people start with a formula. I'm 48. The old Fox formula (220 minus age) gives me 172. Tanaka (208 minus 0.7 × age) gives me 174. Tanaka holds up better in adults, so that is my starting point. For women, the Gulati formula (206 minus 0.88 × age) was developed from data in women and is worth using instead.
Every formula describes a population average. Any one person can sit 10 to 15 beats either side, sometimes more. Be 10 beats out and every zone moves with it. Your easy runs stop being easy, and your hard sessions stop being hard enough.
Testing it, and who should check first
A test beats a formula. The gold standard is a graded exercise test with an exercise physiologist or sports physician. Speed and incline rise in stages until you cannot continue. The same test can measure VO2max, which I'll come back to.
A hard field session gets you close. Warm up properly, then do a couple of short, hard uphill efforts and note the highest reading.
Either way, you are pushing to your limit. Talk to your GP first if you:
have known heart, lung or metabolic disease, including diabetes
have had chest pain, fainting, palpitations or unusual breathlessness with exercise
have been inactive for a long time and are starting vigorous training
In Australia, gyms and exercise physiologists use a short questionnaire called the Adult Pre-exercise Screening System. It is a sensible place to start.
My zones
Using an estimated maximum of 174, here is where my zones fall. To work out yours, multiply your own maximum by each percentage.
Zone | % of maximum | My range (bpm) | Its job |
|---|---|---|---|
1 | 50 to 60 | 87 to 104 | Recovery, warm up and cool down |
2 | 60 to 70 | 104 to 122 | Aerobic base. Most of my running |
3 | 70 to 80 | 122 to 139 | Race pace practice, used sparingly |
4 | 80 to 90 | 139 to 157 | Threshold work |
5 | 90 to 100 | 157 to 174 | Short intervals and top end speed |
Many watches use a different method based on heart rate reserve, the gap between resting and maximum heart rate. It usually produces higher numbers. Neither method is wrong. Pick one and stay with it.
What each zone builds
Zones 1 and 2: the engine room. Zone 1 is recovery. It moves blood through tired muscles without adding fatigue. Zone 2 is where most of the change happens. Long, easy effort builds more mitochondria, grows the small blood vessels that feed muscle, and increases how much blood the heart pumps with each beat. You should be able to talk in full sentences. Most people find it frustratingly slow at first.
Zone 3: the middle ground. Useful for practising race pace. Costly as a default, because it adds fatigue without delivering the specific benefit of easy or hard work.
Zone 4: threshold. Your lactate threshold is the point where lactate builds faster than your body can clear it. Below it, you can hold an effort for a long time. Above it, you have minutes. Unlike maximum heart rate, threshold responds well to training. One session a week is enough for most people.
Zone 5: the ceiling. This is where VO2max improves, the upper limit of how much oxygen your body can use. You can only hold it for a few minutes, so it comes in short, controlled doses once your base is built.
VO2max matters well beyond racing. In large studies, cardiorespiratory fitness is one of the strongest predictors of long term survival. That is the real reason I care about these numbers.
How I'm applying it to Hyrox
Roughly 80 percent of my running sits in zones 1 and 2. It is slow and humbling, and it is the part most people skip.
One session a week goes into zone 4. Hyrox adds a twist here. Every run starts straight after a station, with heart rate already high and legs already tired. So some of my threshold work is running on tired legs, learning to bring heart rate down while still moving.
Zone 5 appears in small doses. Short intervals, not every week.
Race day is where the watch earns its keep. Adrenaline makes the first runs feel easy, and going out too hard is the classic mistake. The number keeps me honest early. Late in the race, heart rate climbs even at a steady pace as body temperature rises and fluid is lost. That is cardiac drift, and it is normal. By then I race on effort, not the number.
I'll share what the data shows as December gets closer.
When the number misleads
Heart rate responds to more than pace. Heat and humidity push it up, which matters in a Sydney summer. So do dehydration, poor sleep, alcohol, caffeine, stress and a brewing illness.
Some heart and blood pressure medicines lower heart rate and cap how high it can go. If you take one, formula based zones will not apply to you. Ask your doctor how to set your training intensity instead.
The device matters too. A chest strap reads the heart's electrical signal and tracks fast changes well. A wrist sensor reads blood flow through the skin. It is fine for steady running but can lag during intervals. With an irregular rhythm such as atrial fibrillation, wrist readings can be unreliable.
Resting heart rate is worth watching as well. A morning reading several beats above your usual often means poor recovery or an illness on the way.
When heart rate and effort disagree, trust the effort, back off, and look for the reason afterwards.
When to see a doctor
A naturally high exercise heart rate is common and usually harmless. Get it checked if heart rate is persistently higher than expected on easy runs, or if exercise brings on any of these:
chest pain, pressure or tightness
palpitations or a racing, irregular heartbeat
dizziness or fainting
breathlessness out of proportion to the effort
unusual fatigue that does not settle with rest
Chest pain, or fainting during exercise, needs urgent attention. Call 000.
Beyond race day
Hyrox gives me a deadline. The real goal is bigger. Cardiorespiratory fitness is one of the few health markers you can measure, train and watch improve at any age. Heart rate zones make that work deliberate.
You do not need a race to benefit. You need a sensible maximum, a few clear targets, and the discipline to keep easy days easy.
If you want to understand your own numbers in context, including resting heart rate, VO2max and how recovery fits in, that is a conversation worth having in consultation.
General information only, not individual medical advice. Speak to your own doctor before starting a new training program.
