Training Zones From a Real Test: Why Percentage Formulas Get Yours Wrong
Most people train in zones that were never theirs to begin with.
If you have ever been told to keep your heart rate under 180 minus your age, or to sit at 70% of your maximum for your easy runs, you have been given a population average and asked to treat it as a personal prescription. The formula does not know your physiology. It knows your birthday.
There is now controlled trial evidence that this matters, and that the size of the difference is not trivial.
The problem with percentage based zones
Percentage formulas work backwards from an estimated maximum. Usually that estimate is 220 minus your age, or a variant of it, and then zones are carved out as fixed slices of that number or of your heart rate reserve.
Two errors stack up.
The first is the estimate of maximum heart rate itself. Age based formulas describe a population average, and individual maximums scatter widely around that average. Plenty of people sit well above or well below what the formula predicts for their age. If the anchor point is wrong, every zone built on top of it is wrong by the same margin.
The second error is the assumption that everyone's physiological thresholds sit at the same percentage of maximum. They do not. Your first lactate threshold, the point where blood lactate starts to rise above baseline, and your second threshold, where it rises steeply and you can no longer hold steady state, sit at genuinely different percentages of maximum from one person to the next.
A 2025 study of 50 experienced cyclists put numbers on how bad this gets. The researchers compared seven different commonly used definitions of "Zone 2" in the same riders, including 72 to 82% of maximum heart rate, 1.5 to 2.5 mmol/L blood lactate, 65% of VO2 peak, and the first ventilatory threshold. Coefficients of variation across the group ranged from 6 - 29% depending on which boundary was used (Meixner et al., Translational Sports Medicine).
Read that again. Seven definitions of the same zone, applied to the same 50 riders, and they do not land in the same place. Some of those definitions disagree with each other by a wider margin than the zone itself is wide.
What a threshold based zone actually is
A real test does not estimate your thresholds. It finds them.
During a graded exercise test with gas analysis, your expired air is measured breath by breath while the workload climbs. Two inflection points show up in the data.
The first ventilatory threshold, where ventilation starts to rise faster than oxygen uptake. This is the ceiling of genuinely easy aerobic work.
The second ventilatory threshold, where ventilation rises faster than carbon dioxide production and the effort stops being sustainable. This is your functional limit for hard steady work.
Your zones are then drawn around those two measured points rather than around an assumed percentage. The boundaries are yours. They also move as you train, which is exactly why they are worth retesting.
The controlled trial
This is the part that turns an argument into evidence.
Weatherwax and colleagues randomised 39 previously inactive adults aged 30 to 75 into two groups for 12 weeks of training, three sessions per week (Weatherwax et al., Sports Medicine International Open).
The standardised group trained by percentage of heart rate reserve, starting at 40 to 45% and progressing to 60 to 65%.
The individualised group trained to zones anchored on their measured ventilatory thresholds.
Both groups did the same number of sessions. Adherence was almost identical at 82.9% and 86.1%. VO2 max was confirmed with a verification protocol rather than assumed from a single test.
Group | Baseline VO2 max | Week 12 | Change over 12 weeks |
Percentage of heart rate reserve | 24.3 mL/kg/min | 26.0 | +1.7 |
Measured ventilatory thresholds | 29.5 mL/kg/min | 32.8 | +3.4 |
The threshold based group gained twice as much aerobic capacity from the same training frequency over the same 12 weeks. Both groups improved significantly by week 8, but only the individualised group kept improving significantly between week 8 and week 12.
Two honest caveats. The sample is modest at 39 completers, and the groups started at different baseline fitness levels, which complicates a direct head to head reading. But the direction is consistent with the mechanism, and the mechanism is simple: if your prescribed intensity happens to land in the right place, percentage zones work fine. If it lands too low you undertrain, and if it lands too high your easy sessions are not easy and your recovery suffers.
Who this actually matters for
It does not matter much if you are a beginner doing almost anything for the first time. Untrained physiology responds to most stimuli.
It matters when:
You are already training consistently and your progress has flattened.
You are doing polarised or zone based training and need your easy sessions to genuinely be easy.
Your watch has told you a zone and your perceived effort strongly disagrees with it.
You are training for an endurance event and pacing decisions carry a real cost.
You have a heart rate that runs unusually high or low for your age, which makes every age based formula worse for you specifically.
What you get from a test at Precision Body Lab
A VO2 max test takes 60 minutes. You ride or run on a graded protocol to volitional exhaustion while expired gas is measured continuously. The output is not just a single number.
Your measured VO2 max, in mL/kg/min, with percentile context by age and sex.
Both ventilatory thresholds, expressed as heart rate and power or pace ranges.
Training zones built from your own thresholds, ready to load into your watch.
Peak heart rate measured rather than estimated.
Retest every four to six months if you are training seriously. Your thresholds shift with fitness, and stale zones become wrong zones.
The short version
Percentage based zones are a reasonable default when you have no data. They are a poor substitute for data once you are training seriously. The evidence suggests the cost of guessing is roughly half your potential aerobic gain over a 12 week block.
If you want the number behind the zones first, start with what a VO2 max result actually means.
VO2 Max testing is $349 as a single test, or $449 bundled with a DEXA scan. Book online or call 1300 910 163.
Related reading
Sources
Meixner B, Filipas L, Holmberg HC, Sperlich B. Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries. Translational Sports Medicine, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC11986187/
Weatherwax R, Harris N, Kilding AE, Dalleck L. Time Course Changes in Confirmed 'True' VO2 max After Individualized and Standardized Training. Sports Medicine International Open, 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6559817/
Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Medicine, 2015. https://pubmed.ncbi.nlm.nih.gov/26243014/
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