Exercise
Zone 2 Training for Longevity
Zone 2 is steady cardio just below the first lactate threshold. Moderate activity is linked to lower death rates; no trial shows Zone 2 beats other intensities.
Plenty of fitness trends sell suffering. Zone 2 sells the opposite: long, steady sessions at a pace where you can still hold a conversation, pitched as the key to healthier mitochondria—the structures in cells that help release energy—and a longer life. That sounds almost too reasonable, so Humanic Blue checks the four claims that usually come bundled with Zone 2 training for longevity.
A 2025 sport-science panel proposed placing Zone 2 just below the first lactate or ventilatory threshold: the point where blood lactate or breathing first begins to rise more noticeably as exercise gets harder. Other training systems use the label differently. Regular moderate activity is linked to lower death rates: in a Harvard study that followed about 116,000 US adults for 30 years, people who met the moderate-activity guideline were 19% to 25% less likely to die during the study. But no trial shows that Zone 2 specifically helps people live longer, and a 2025 review concluded the evidence doesn’t support it as the optimal intensity for mitochondria.
In This Article
- Zone 2 lands in different places on different charts
- The mitochondria pitch comes from elite athletes
- Moderate and vigorous activity are both linked to lower death rates
- A five-year trial in older adults found no edge for moderate training
- Where easy exercise fits, and where harder efforts add something
- The studies and numbers behind all of this
Key Takeaways
- Moderate and vigorous activity at guideline levels are both linked to lower death rates in large, long-running studies. The studies show an association, not proof of cause and effect.
- “Zone 2” has no single agreed definition; a 2025 expert panel placed it just below the first lactate or ventilatory threshold. Definitions differ across training systems.
- A 2025 review found the evidence doesn’t support Zone 2 as the optimal intensity for mitochondria in the general public, and argued for harder efforts. That is the review authors’ interpretation, not a settled prescription.
- A five-year trial in about 1,600 older Norwegians, with death as its main outcome, did not detect lower death rates with moderate continuous training than with guideline advice. That finding comes from one trial with important limitations.
- No study cited here has shown that Zone 2 training specifically extends lifespan.
Claim 1: Is “Zone 2” one specific intensity?
It depends on whose zones you use. Training systems split effort into as few as three zones or as many as seven, marked out by heart rate, power, blood lactate or how hard the effort feels. “Zone 2” lands in a slightly different place in each.
A panel of 14 sport scientists and coaches, with Sebastian Sitko of the University of Zaragoza as first author and Stephen Seiler of the University of Agder among the members, tried to settle it in a 2025 commentary. Their focus was cycling. They noted that “there is no clear consensus among coaches, athletes, and scientists regarding the definition of zone 2 training.” Their proposal: it “should preferably be performed at intensities located immediately below the first lactate or ventilatory threshold.”
That’s expert opinion rather than a trial, and the panel flagged a limit itself. The adaptations they expected “might not be unique to zone 2 and could also be induced with sessions performed at slightly higher and lower intensities.” How to find that threshold without a lab is its own question. How the panel defined it
What needs to match before two programs labeled Zone 2 can be compared?
Claim 2: Is it the ideal way to build mitochondria?
That claim remains unestablished. A 2025 review challenged it most directly.
Kinesiology researchers at Queen’s University in Canada, led by Kristi Storoschuk with senior author Brendon Gurd, reviewed the training evidence with Martin Gibala of McMaster University in Sports Medicine. They traced Zone 2 recommendations to “observational data of elite endurance athletes who engage in large volumes of Zone 2 training.”
One example of that athlete data: in a 2018 study, Iñigo San-Millán of the University of Colorado School of Medicine and George Brooks of UC Berkeley compared professional endurance athletes, moderately active people and people with metabolic syndrome. In the same exercise tests, the athletes burned more fat and had lower blood lactate. That was a one-time comparison of different groups, not a training trial. It shows how the groups differ, not what caused the difference.
When Storoschuk’s team weighed the training studies, they concluded that “current evidence does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity.” They added that evidence suggests prioritizing higher intensities is “critical to maximize cardiometabolic health benefits, particularly in the context of lower training volumes.” It’s a narrative review, so the authors chose and weighed the studies rather than pooling them statistically. Gibala advises and holds equity in Longevity League, a US company whose services partly involve exercise. The review and the athlete study in detail
Claim 3: Is it the intensity that adds years?
The death-rate data don’t single out Zone 2. They show that moderate and vigorous activity both count.
Harvard researchers Dong Hoon Lee and senior author Edward Giovannucci followed about 116,000 US adults from two long-running studies of nurses and other health professionals for 30 years, asking about their exercise up to 15 times. People who met the moderate-activity guideline, 150 to 299 minutes a week, had a 19% to 25% lower risk of dying from any cause, from heart disease or from other causes. Meeting the vigorous guideline, 75 to 149 minutes a week, was linked to similar drops.
The association with lower death rates looked “nearly maximum” at about 300 to 600 minutes a week of moderate activity, or 150 to 300 of vigorous. Beyond that, the researchers saw no clear extra benefit, and no clear harm.
This is an association. Activity was self-reported, and people who exercise a lot may differ in other ways. The study also measured “moderate” activity broadly, not Zone 2 as a lab would define it. The cohort numbers
What a five-year trial found
Norway’s Generation 100 study, run by Dorthe Stensvold, Ulrik Wisløff and colleagues at the Norwegian University of Science and Technology, tested exercise directly. It randomly assigned about 1,600 adults in their 70s to five years of twice-weekly moderate continuous training at about 70% of peak heart rate, high-intensity intervals at about 90%, or Norway’s national activity guidelines. Death from any cause was the main outcome.
Deaths didn’t differ between the two training groups combined and the guideline group. Looked at separately, the interval group had 1.7 percentage points fewer deaths than the guideline group and the moderate group 1.2 points more, but neither difference was statistically significant. The authors reported a “lower all cause mortality trend after HIIT compared with controls and MICT,” meaning a tilt, short of statistical significance, toward intervals over both the guideline group and moderate training.
The authors also explained why differences were hard to detect. Most volunteers were already healthy and active, many in the guideline group did high-intensity exercise on their own, and only half of the interval group met the strict interval criteria. The trial in detail
What would establish a lifespan effect specific to Zone 2 rather than activity more broadly?
Claim 4: Is easy exercise enough?
The 2018 US Physical Activity Guidelines call for 150 to 300 minutes a week of moderate activity for adults, or an equivalent amount of vigorous activity. A session labeled Zone 2 contributes to the moderate total when its actual effort is moderate; the zone label alone does not establish that. The guidelines say most people “are not likely to be injured” doing moderate activity in those amounts.
The same guidelines describe swapping some moderate activity for vigorous as “one time-efficient way to achieve greater fitness and health goals.” The Harvard data match that: for people doing less than 300 minutes of moderate activity a week, “additional leisure-time VPA was associated with lower mortality.” VPA is the researchers’ shorthand for vigorous physical activity.
Harder training also moves fitness a little further. A pooled analysis of 28 controlled trials in healthy adults aged 18 to 45, led by Zoran Milanović of the University of Niš in Serbia, found that steady endurance training and intervals both raised VO2 max—the maximum rate at which the body uses oxygen during hard exercise—substantially, with slightly bigger gains from intervals. A separate University of Tsukuba analysis linked higher measured fitness with lower death rates. It used METs, units of oxygen use during activity; each one-MET higher fitness level was associated with about 13% lower relative risk of death. That comparison between people does not show that the extra fitness gained from intervals causes a survival benefit. More on both in Improve VO2 Max After 40 and VO2 Max and Longevity. The fitness studies
What’s Interesting
Zone 2 is a training idea borrowed from elite endurance sport. According to the expert panel, world-class endurance athletes log large volumes at low intensity, and the panel’s favorite Zone 2 session was a ride of more than two hours.
That’s exactly where the 2025 critique aims, favoring higher intensities “particularly in the context of lower training volumes.” A method shaped around a professional cyclist’s week may land differently for someone with 40 minutes before work. Sessions at moderate intensity still count toward the guidelines. It’s the bigger claims about them that researchers are arguing over.
What This Means in Practice
For readers hoping to live longer and in better health, note what the death-rate research above actually measured: total weekly activity, not precise zones.
- Adult guideline amounts: the US guidelines recommend 150 to 300 minutes a week of moderate activity, or 75 to 150 minutes of vigorous activity, or an equivalent mix.
- Actual intensity matters: a Zone 2 session contributes to the moderate total when the effort is moderate. Different zone definitions prevent a blanket equivalence.
- Time and progression: the guidelines describe vigorous activity as a way to meet equivalent activity amounts in less time, and advise increasing activity gradually.
- Precise zone targets are optional for this evidence. The Harvard death-rate data measured broad moderate and vigorous activity, not lactate thresholds.
- Strength activity: the guidelines also recommend muscle-strengthening activity on 2 or more days a week for adults.
- If you have a chronic condition or symptoms, the guidelines advise being under the care of a health care provider.
These findings are averages across large groups. The Generation 100 volunteers, for example, were mostly healthy, active Norwegians in their 70s, and results can differ for someone younger, less active or managing a diagnosis.
A primary care clinician can advise on safe intensity. A cardiologist or exercise physiologist can use a supervised exercise test to set individual training zones if you want precise targets.
For the practical boundary check, How To Know If You’re in Zone 2 compares the talk test, heart-rate bands and measured thresholds.
Bottom Line
Under the 2025 panel’s definition, Zone 2 is steady effort just below the first lactate or breathing threshold. When the effort is moderate, it contributes to the moderate activity linked with lower death rates in large studies. Researchers have pushed back on the bigger claims: experts still disagree on the definition, a 2025 review found no support for Zone 2 as the optimal intensity for mitochondria, and a five-year trial found no survival edge for moderate continuous training. No study has shown that Zone 2 specifically helps people live longer. The US adult guidelines allow moderate activity, vigorous activity or an equivalent mix, alongside strength activity; they do not require Zone 2 targets. They advise people with chronic conditions or symptoms to be under a health care provider’s care.
A NOTE FROM LONGEVITY365
We read research, consult expert perspectives and work to make complicated health information easier to understand. What you’re reading here reflects how we’ve interpreted and organized that information. It is educational content—not personal medical advice, diagnosis or treatment guidance.
We’re not perfect, and neither is the available research. Evidence changes, new studies emerge and what’s appropriate for one person may not be appropriate for another.
Use this article as a starting point for your own research and conversations with qualified professionals. Always talk with your doctor or another trusted healthcare professional before making decisions that could affect your health, particularly if you take medications, are receiving treatment, have existing health conditions, are pregnant or have other circumstances that could affect what’s appropriate for you.
Reader Questions
A few questions to carry into the comments or your next conversation. Please leave out identifying or personal medical details.
- 01Which measurement or milestone would feel useful to track without letting it take over the whole point of moving?
- 02Which real-world barrier did the article address most usefully: time, confidence, access, recovery, or knowing where to start?
- 03What question would you bring to a clinician, physical therapist, trainer, or exercise professional after reading about Zone 2 Training for Longevity?
Extra Insights & Sources
For readers who want the details behind each claim above.
What We Know
- Regular moderate or vigorous activity at guideline levels is associated with substantially lower mortality. Supported (cohort).
- Zone 2 lacks a universal definition; the 2025 expert proposal places it just below the first threshold. Established.
- Elite endurance athletes have high fat oxidation and mitochondrial capacity. Established (cross-sectional), but that doesn’t show Zone 2 caused it.
- In a five-year trial in older adults, the comparison did not establish lower mortality with moderate continuous training than with guideline advice. Supported (single RCT).
- In young and middle-aged adults, intervals raise VO2 max slightly more than continuous endurance training. Supported (meta-analysis).
What We Don’t Know
- Whether Zone 2 training extends human lifespan. Unknown. We found no trial testing Zone 2, as the expert panel defines it, against other intensities for survival; Generation 100’s moderate arm is the closest match.
- Whether Zone 2 improves mitochondrial function more than other intensities in non-athletes. Contested, with the 2025 review arguing against it.
- Which mix of easy and hard training does most for longevity. Unknown.
Reading the technical details
In the sections below, oxygen-use measurements describe aerobic fitness, not years of life. A hazard ratio (HR) compares event rates over follow-up: 1 means no difference, and a value below 1 means a lower rate in the group being compared. A 95% confidence interval (CI) shows the estimate’s uncertainty; when it includes 1, the comparison does not clearly establish a difference. RCT means randomized controlled trial.
How the expert panel defined Zone 2
Sitko et al., International Journal of Sports Physiology and Performance, 2025. The commentary pooled the views of 14 male applied sport scientists and professional cycling coaches from 8 countries, gathered over three rounds of review, “with a particular focus on the cycling field.” The authors noted that some schemes use as few as 3 intensity zones, “others propose 5, and some as many as 7 zones.” Twelve of the experts used a 5-zone model for training prescription and located Zone 2 just below LT1 or VT1 (the first lactate and ventilatory thresholds).
Lactate is a substance produced and used during energy metabolism. The first lactate threshold (LT1) and first ventilatory threshold (VT1) mark an initial sustained rise in blood lactate or breathing as effort increases. Critical power is an exercise-testing estimate used to separate efforts that can remain relatively stable from harder efforts that lead toward exhaustion. These measures describe different aspects of effort; they are not interchangeable personal targets.
At that intensity, the panel expected blood lactate of about 1 to 2 mmol/L (millimoles per liter, a measure of lactate concentration in blood), heart rate of about 70% to 80% of maximum, a rating of perceived exertion of about 10 on the 6-to-20 Borg scale, and power of about 75% to 80% of critical power. A Borg rating describes how hard an effort feels: 10 lies between the scale’s very light (9) and light (11) descriptions, as illustrated by University Hospitals Sussex. These numbers describe the panel’s proposal, not personal targets. Their preferred session was a continuous ride of, ideally, more than 2 hours. Expected adaptations included more tiny blood vessels supplying muscle (capillaries), more energy-processing proteins inside mitochondria (enzymes) in the slow, fatigue-resistant muscle fibers called type I, and modest gains in critical power and VO2 max, “although research is warranted in this regard.” In their words: “Although scientific evidence is still lacking, this consensus statement suggests that continuous sessions performed immediately below the LT1/VT1, and for durations exceeding 2 hours might be the preferred method for inducing a wide range of central and peripheral adaptations associated with zone 2 training.” (Note 4)
The mitochondria evidence in detail
Storoschuk et al., Sports Medicine, 2025. “Much Ado About Zone 2” is a narrative review by Kristi L. Storoschuk, Andres Moran-MacDonald and Brendon J. Gurd (Queen’s University) and Martin J. Gibala (McMaster University). It opens by noting that popular media has positioned Zone 2 training “as the optimal intensity for improving mitochondrial and fatty acid oxidative capacity.” Its full conclusion: “We conclude that current evidence does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity. Further, evidence suggests prioritizing higher exercise intensities (> Zone 2) is critical to maximize cardiometabolic health benefits, particularly in the context of lower training volumes.” Disclosure, per the paper: “Martin J. Gibala is an advisor to and holds equity in Longevity League, Ltd., a US-based company whose services in part relate to exercise.” The other three authors reported no directly relevant conflicts. (Note 2)
San-Millán and Brooks, Sports Medicine, 2018. Using indirect calorimetry (estimating energy use from breathing gases) and blood lactate measurements during exercise, the study compared professional endurance athletes, moderately active people and people with metabolic syndrome. Fat oxidation—using fat as fuel—was significantly higher in the athletes (p < 0.01) and lactate significantly lower. Fat oxidation and lactate were inversely correlated within each group (r = −0.97, −0.98 and −0.92) and across everyone studied (r = −0.76). Here, r describes the strength and direction of a relationship: negative values mean one measure tended to fall as the other rose. The p value describes statistical evidence against no difference; it does not show that Zone 2 caused the findings. The authors proposed lactate and fat-oxidation measurements as an indirect way “to assess metabolic flexibility and oxidative capacity.” (Note 5)
The Harvard cohort in detail
Lee et al., Circulation, 2022. The analysis combined the Nurses’ Health Study and the Health Professionals Follow-up Study (1988 to 2018): 116,221 adults, self-reported leisure-time activity repeated up to 15 times, and 47,596 deaths over 30 years.
| Activity level (long-term, per week) | Association with mortality |
|---|---|
| Vigorous, 75–149 min vs none | All-cause HR 0.81 (95% CI 0.76–0.87); cardiovascular HR 0.69 (0.60–0.78); non-cardiovascular HR 0.85 (0.79–0.92) |
| Moderate, 150–299 min | 19% to 25% lower all-cause, cardiovascular and non-cardiovascular mortality |
| Vigorous 150–299 min, or moderate 300–599 min | A further 2% to 4% (vigorous) and 3% to 13% (moderate) lower mortality than meeting the guideline |
| Vigorous ≥300 min, or moderate ≥600 min | No clear further reduction, and no clear harm |
In joint analyses, extra vigorous activity was associated with lower mortality among people doing less than 300 minutes a week of moderate activity, but not among those already doing 300 minutes or more. The authors concluded: “The nearly maximum association with lower mortality was achieved by performing ≈150 to 300 min/wk of long-term leisure-time VPA, 300 to 600 min/wk of long-term leisure-time MPA, or an equivalent combination of both.” Here, MPA means moderate physical activity; VPA means vigorous physical activity. The authors declared no conflicts of interest. (Note 1)
The Generation 100 trial in detail
Stensvold et al., BMJ, 2020. From 6,966 people in Trondheim born between 1936 and 1942, 1,567 (790 women) aged 70 to 77 were randomly assigned to high-intensity intervals (400 people), moderate continuous training (387) or national guideline advice (780). At baseline, 87.5% reported good overall health and 80% reported medium or high activity levels.
| Comparison | Deaths | Absolute difference | Hazard ratio (95% CI) |
|---|---|---|---|
| Guideline group (reference) | 37 of 780 (4.7%) | — | 1.00 |
| Both training groups combined | 35 of 787 | Did not differ | 0.92 (0.58–1.47) |
| Intervals vs guideline group | 12 of 400 | 1.7 points lower | 0.63 (0.33–1.20) |
| Moderate vs guideline group | 23 of 387 | 1.2 points higher | 1.24 (0.73–2.10) |
| Intervals vs moderate | — | 2.9 points lower | 0.51 (0.25–1.02) |
MICT means moderate-intensity continuous training; HIIT means high-intensity interval training.
The authors concluded: “This study suggests that combined MICT and HIIT has no effect on all cause mortality compared with recommended physical activity levels. However, we observed a lower all cause mortality trend after HIIT compared with controls and MICT.” Among their stated limitations: “participants in the control group had a high level of activity throughout the study, and many exercised using HIIT”; “only 50% of participants in the HIIT group were able to follow the strict criteria for fulfilling the HIIT protocol”; and participants “were more active and had better overall health than non-included participants.” They also wrote that the null results “do not refute a causal association between physical activity and longevity.” Their summary adds that future guidelines, “at least for older adults, should be more specific in requiring that at least part of the physical activity should be performed at high intensity.” The moderate arm’s target, about 70% of peak heart rate, sits at the low end of the roughly 70% to 80% of maximum heart rate the Zone 2 panel associates with Zone 2. The authors declared no financial relationships with any organizations that might have an interest in the work. (Note 3)
Fitness, intervals and survival
VO2 max is the maximum oxygen used during hard exercise, expressed here in milliliters per kilogram of body weight per minute (mL/kg/min). One metabolic equivalent (MET) equals 3.5 mL/kg/min. A risk ratio compares risk between groups; 0.87 means 13% lower relative risk, not 13 percentage points lower absolute risk. HIT in the quoted paper means high-intensity training.
Milanović et al., Sports Medicine, 2015. A meta-analysis of 28 controlled trials (723 healthy participants aged 18 to 45; mean age 25.1; average starting VO2 max 40.8 mL/kg/min). Compared with no-exercise controls, endurance training raised VO2 max by 4.9 mL/kg/min and interval training by 5.5 mL/kg/min. Head to head, intervals had a “possibly small” extra benefit of 1.2 mL/kg/min. The authors concluded that “Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.” (Note 6)
Kodama et al., JAMA, 2009. A meta-analysis of 33 cohort studies (102,980 participants and 6,910 deaths for all-cause mortality). Each 1-MET higher level of maximal aerobic capacity, which the authors equate to a 1 km/h higher running or jogging speed, was associated with a risk ratio of 0.87 for all-cause mortality (95% CI 0.84–0.90) and 0.85 for heart disease and cardiovascular events. People with low fitness (under 7.9 METs) had a risk ratio of 1.70 for all-cause mortality compared with people with high fitness. These are observational associations. (Note 6)
Sources
- University Hospitals Sussex NHS Foundation Trust: Cardiac rehabilitation: exercise for heart health and wellbeing — Borg effort-scale descriptions; checked October 15, 2026.
- Sitko S, et al. What Is “Zone 2 Training”?, International Journal of Sports Physiology and Performance, 2025: PubMed 40010355
- Storoschuk KL, et al. Much Ado About Zone 2, Sports Medicine, 2025: PubMed 40560504
- San-Millán I, Brooks GA. Assessment of metabolic flexibility, Sports Medicine, 2018: PubMed 28623613
- Lee DH, et al. Long-term leisure-time physical activity intensity and mortality, Circulation, 2022: PubMed 35876019
- Stensvold D, et al. Generation 100, BMJ, 2020: PubMed 33028588
- Milanović Z, et al. HIT and continuous endurance training for VO2max, Sports Medicine, 2015: PubMed 26243014
- Kodama S, et al. Cardiorespiratory fitness and mortality, JAMA, 2009: PubMed 19454641
- US Department of Health and Human Services: Physical Activity Guidelines for Americans, 2nd edition (2018)
Notes
Note 1: Funded by grants from the US National Cancer Institute (National Institutes of Health), according to the PubMed record.
Note 2: No specific funding was used to prepare the review; Kristi Storoschuk is supported by a doctoral scholarship from the Natural Sciences and Engineering Research Council of Canada.
Note 3: Funded by the Research Council of Norway, the K.G. Jebsen Foundation for Medical Research, the Norwegian University of Science and Technology, the Central Norway Regional Health Authority, St Olavs hospital and the National Association for Public Health, Norway.
Note 4: The published commentary does not list funding or competing interests.
Note 5: The authors state that no financial support was received for the study, and that they have no directly relevant conflicts of interest.
Note 6: Funding for the Milanović and Kodama meta-analyses isn’t listed in their PubMed records.
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