Improve VO2 Max After 40

After 40, it’s easy to assume fitness only goes one way. The research says otherwise. Humanic Blue looks at whether VO2 max can still improve after 40, and at the tested program behind that finding.

Here’s the short answer. VO2 max, the greatest rate at which your body can take in and use oxygen during hard exercise, can still improve after 40. In a small two-year randomized trial, healthy sedentary adults averaging 53 improved VO2 max by 18%; a comparison group assigned yoga, balance and strength work did not improve it. The aerobic program built gradually and included hard efforts separated by easier recovery periods, called intervals. Other studies found gains with both intervals and steady training. For the question of living longer and better, the distinction matters: higher fitness is linked to a lower risk of death, but these trials did not test whether improving VO2 max lengthens life.

Below: what the studies found, how their programs differed and what named authorities consider when assessing exercise safety.

What evidence shows VO2 max is trainable after 40?

The key trial was published in Circulation in 2018. It randomly assigned about 60 healthy sedentary adults ages 45 to 64 (average age 53; nearly half men) to two years of progressive exercise training or to an attention-control program of yoga, balance and strength work three times a week. Participants with several common conditions—including treated hypertension, obesity, obstructive sleep apnea, recent tobacco use, coronary disease or structural heart disease—were excluded. This was a selected healthy group, not a cross-section of all adults over 40.

In the full results, the exercise group’s VO2 max increased from 29.0 to 34.4 mL/kg/min, an 18% rise, while the comparison group did not improve. The unit means milliliters of oxygen used per kilogram of body weight each minute. Tests of heart pressure, volume and movement also showed reduced stiffness of the left ventricle—the main chamber that pumps blood to the body—and its muscle. The comparison group did not show that change.

This trial did not measure heart-failure diagnoses, cardiovascular events or survival. Its authors proposed that reducing stiffness might help prevent heart failure with preserved ejection fraction, but explicitly called for studies that follow clinical outcomes. In that form of heart failure, the heart pumps out a normal proportion of the blood it holds but has difficulty filling properly. The physiological changes should not be presented as proof that the program prevents heart failure or extends life.

What kind of training has been tested?

Intervals vs. continuous. Continuous training means maintaining a steady effort rather than alternating hard and easier periods. A 2021 systematic review and meta-analysis combined 14 studies involving about 430 middle-aged or older participants. VO2 max increased by a pooled 2.26 mL/kg/min after interval training and 1.34 after moderate continuous training. In direct comparisons, intervals had a 1.10 mL/kg/min advantage; the study’s 95% uncertainty range ran from 0.55 to 1.64. That is an average across short, varied protocols—not a guarantee for one person and not proof that intervals are required.

The 4×4 protocol. A 2007 randomized trial assigned about 40 healthy, nonsmoking, moderately trained men to one of four running programs performed three times weekly for eight weeks with similar total oxygen consumption. The 4×4 group ran four minutes at 90% to 95% of maximum heart rate, recovered actively for three minutes at 70%, and repeated that cycle four times. Its VO2 max increased 7.2%, more than in the long-slow-distance group and the group training around lactate threshold, the intensity at which blood lactate begins to rise. The trial was small, short, male-only and conducted in already trained people; it supports the protocol’s efficacy under those conditions, not universal superiority or safety.

What would make a comparison of intervals and continuous training fair?

A tested progression

The 2018 trial’s full methods describe how the selected participants built up with individualized plans, monthly exercise-physiologist contact and heart-rate tracking. Many early sessions were directly supervised; most sessions over the full program were not. The table reports that study’s program, rather than a personal training plan. Here, peak heart rate means the highest rate reached during testing; active recovery means continuing to move at an easier effort. The researchers also set a maximal steady-state (MSS) zone for sustained, harder exercise from each participant’s breathing and blood-lactate thresholds during the test—the points where those responses changed as effort rose. This was a measured training zone, not simply any steady pace. Their easier base pace was 1–20 heartbeats per minute below that zone.

Phase	What participants did
Months 1–2	Three 30-minute sessions a week at a steady “base” pace
Month 2 onward	Sessions in each participant’s measured maximal steady-state zone were added: 2 sessions per month in month 2, increasing to 3 in month 3
From month 3	4×4 intervals: 4 minutes at 95% of peak heart rate, 3 minutes of active recovery at 60% to 75%, repeated four times; each interval day was followed by 20–30 minutes of light activity the next day
By month 6	5–6 hours a week, including 2 interval sessions, 1 long session of at least an hour and 1 shorter base session
After month 10	Maintenance: 1 interval session a week plus continuous training

Participants also did strength training to complement the endurance work, and could use bikes, treadmills, ellipticals or outdoor activity.

That peak phase was more time than the federal minimum. The current Physical Activity Guidelines for Americans call for 150 to 300 minutes of moderate-intensity aerobic activity—or 75 to 150 minutes vigorous, or an equivalent combination—plus muscle strengthening on at least two days each week. The trial tested one intensive, individualized program; it did not establish the minimum dose needed to improve VO2 max.

Which parts of the trial's progression depended on its participants and supervision?

How can training start safely?

Hard intervals can briefly raise cardiovascular risk, particularly when vigorous exercise is unfamiliar. The American College of Sports Medicine screening model weighs current activity, signs or symptoms, known heart or blood-vessel disease, metabolic disease such as diabetes, or kidney disease, and intended intensity. It does not say that every healthy person over 40 needs medical clearance. The federal guidance for inactive adults advises starting with small amounts and building gradually toward the weekly target; people with chronic conditions or symptoms should seek individualized guidance.

The 2018 trial also screened participants with a medical history, physical examination, echocardiogram and exercise stress test, then used two months of base training before adding intervals. It did not report adverse events in the main paper, so it cannot establish a numerical safety rate. Stop exercise and seek medical review for chest pressure or pain, lightheadedness, an unusually fast or irregular heartbeat, or unusual or extreme shortness of breath, consistent with American Heart Association guidance.