Fixed percentages of maximum heart rate misplace the top of easy training for many athletes; measured thresholds or the talk test locate it more reliably
Interpretation
In 100 adults (46 F, 54 M) the lactate threshold ranged from 60% to 90% of maximum heart rate (Iannetta 2020), and a review judged maximal-anchor percentages of little merit for domain-specific prescription (Jamnick 2020). Lactate thresholds agreed with VT1 and were reproducible in 14 trained male cyclists (Pallarés 2016); the talk test matched VT1 within about 2 bpm on average in 18 highly trained cyclists (Rodríguez-Marroyo 2013); an HRV method (DFA alpha1) matched VT1 on average but with individual error of roughly -12 to +8 bpm in 15 men (Rogers 2021). Gaps: small, mostly male validation samples, short incremental tests, no swimming, no trial of whether precise zones improve training outcomes. A 2025 review (Storoschuk) also found no evidence that Zone 2 is an optimal intensity in itself.
Practical implication
Set the ceiling for easy sessions from a lab lactate or ventilatory test if available, otherwise from a talk test, cross-check with perceived effort, set zones separately for bike and run, and treat the ceiling as a limit for easy days rather than a precise target. Validation is mostly in men and from short tests.
Sources
6 sources, independently verified.
Ramp test plus constant-load trials for maximal lactate steady state. Lactate threshold fell between 60% and 90% of maximum heart rate, 45-74% of VO2max and 23-57% of peak work rate; maximal lactate steady state between 75% and 97% of maximum heart rate. Women's threshold occurred at a higher %HRmax and %VO2max than men's. Fixed-percentage methods conformed poorly to intensity domains. Training status not stated in the abstract.
Judged intensity-prescription methods by how well they produce domain-specific responses. Percentages of VO2max, maximum heart rate and maximum work rate have little merit; LT1, gas-exchange threshold and VT1 have some support for the moderate-heavy boundary; critical power/speed best supported for heavy-severe. Calls for training studies.
Two graded tests with lactate and gas exchange. Most lactate threshold methods had test-retest CV 3.4-3.7% (DMAX 10.3%); ventilatory thresholds 1.6-3.5%. The lactate threshold agreed with VT1 (no significant difference, r = 0.72). Lactate tests judged a valid, reliable alternative to ventilatory thresholds. Small, all-male.
Incremental test with gas exchange vs the same protocol while reading aloud. First uncomfortable-talking stage: 3.6 W/kg, 148 bpm vs VT1 3.7 W/kg, 150 bpm; first stage where talking was impossible: 5.3 W/kg, 176 bpm vs second threshold 5.3 W/kg, 177 bpm; no significant differences; workload correlation 0.86 at VT1. Short incremental tests only.
Incremental treadmill test. Heart rate at DFA alpha1 = 0.75 was 154 bpm vs 152 bpm at VT1 (r = 0.97); Bland-Altman limits of agreement for heart rate about +8 to -12 bpm. Authors call for research in women, steady exercise and other devices. Small, all-male, running only.
Zone 2 (low-intensity exercise below the lactate threshold) recommendations rest largely on observational data from elite athletes training at high volume; current evidence does not support Zone 2 as the optimal intensity for improving mitochondrial capacity or cardiorespiratory fitness in the general public, and higher intensities matter, especially when volume is lower. Narrative, general-population focus.