Quick answer: To raise VO2 max after 40, do one sprint interval session a week: short all-out efforts of 20 to 30 seconds with 90 seconds of very easy recovery, inside a run of under an hour or in the middle of your long run. Beginners start with 2 to 5 sprints, advanced runners do up to 20. Keep sprint sessions at least 3 days apart, and keep every other day truly easy.
VO2 max is the most oxygen your body can take in and use during hard exercise. It is the ceiling of your aerobic engine, and it falls with age faster than most people realize. The good news: it is trainable at any age, and the session that raises it is shorter than you might expect. In the Phaes method, that session is one weekly set of short, all-out sprints, with easy days around it.
Why VO2 max matters after 40
VO2 max matters because it is one of the strongest predictors of how long and how well you live. People with higher cardiorespiratory fitness have lower rates of heart disease and death from any cause, and the link holds after accounting for smoking, blood pressure, and diabetes. For runners, it also sets the ceiling on your pace.
A 2009 meta-analysis in JAMA (Kodama and colleagues) pooled 33 studies of over 100,000 healthy men and women. Each 1-MET increase in fitness (about 1 km/h faster running speed) was linked to a 13 percent lower risk of death from any cause and 15 percent lower risk of heart disease events. A 2018 study of 122,007 patients in JAMA Network Open found mortality fell with every step up in fitness, with no upper limit. The fittest group did best, including people over 70.
These are associations, not proof that raising your VO2 max adds a set number of years. But few health markers are this strongly linked to outcomes and this responsive to training.
How VO2 max changes with age
VO2 max declines in every decade of adult life, and the decline speeds up with age. It drops slowly in your 20s and 30s, then the rate of loss climbs through the 40s, 50s, and beyond. Training cannot stop the decline completely, but it starts you from a much higher point and slows how quickly you lose capacity.
The clearest data comes from the Baltimore Longitudinal Study of Aging, which tracked peak oxygen uptake in 375 women and 435 men over a median of almost 8 years. The loss was about 3 to 6 percent per decade in the 20s and 30s, rising to more than 20 percent per decade in the 70s. From the 40s onward, women declined more slowly than men, but they still declined.
For women, menopause adds another layer. Estrogen supports blood vessel function and muscle, so its decline, alongside muscle loss and less vigorous activity, makes holding on to fitness harder. As hormones change, training has to change too. Our guide to running over 40 covers the other shifts this decade brings.
The Phaes approach: one sprint interval session a week
Phaes raises VO2 max with one sprint interval (SIT) session a week: 20 to 30 second all-out efforts, each followed by 90 seconds of very easy recovery. The number of sprints depends on your level, from 2 for a beginner to 20 for an advanced runner. It replaces long slow miles and repeated threshold intervals as your main quality session.
| Level | Warm-up | Main set | Cool-down |
|---|---|---|---|
| Beginner | 10 min very easy | 2 to 5 x (20 s all-out, 1:30 very easy) | 5 min very easy |
| Intermediate | 10 min very easy | 6 to 10 x (25 s all-out, 1:30 very easy) | 10 min very easy |
| Advanced | 10 min very easy | 11 to 20 x (30 s all-out, 1:30 very easy) | 10 min very easy |
“All-out” means Zone 5: the fastest you can hold for that short effort, with good form. “Very easy” means Zone 1: a walk or the gentlest jog. Judge the sprints by effort, not your watch. Heart rate lags behind a 20 second burst, and if your zones came from 220 minus age they are probably set too high anyway (see heart rate zones in perimenopause).
Where it goes in your week:
- Inside a run of under 60 minutes, after the warm-up, or
- In the middle of your one long run, so the long run does double duty.
- At least 3 days apart from any other sprint session.
Start at the bottom of your range and add a sprint or two over the following weeks. Flat ground or a gentle uphill both work. Uphill sprints are kinder to hamstrings and calves if you have not sprinted in years.
What the research says about sprint intervals
Sprint intervals raise VO2 max about as well as longer, moderate endurance training, in a fraction of the time. Meta-analyses of controlled trials show reliable gains after just a few weeks. Most studies used young adults on bikes, so the evidence in runners over 40 is thinner, but the direction is consistent.
- A 2014 meta-analysis in Sports Medicine (Gist and colleagues) pooled 16 randomized trials of all-out sprint training. VO2 max rose by about 8 percent, no differently from endurance training groups, with much less total exercise.
- A 2013 meta-analysis (Sloth and colleagues) found VO2 max increases of 4.2 to 13.4 percent after programs of just 2 to 8 weeks.
- In a 12-week trial (Gillen and colleagues, 2016), three 20 second sprints per session raised peak oxygen uptake by 19 percent, the same as 45 minutes of steady cycling, with a five-fold smaller time commitment.
- A smaller study that included women (Metcalfe and colleagues, 2012) found that just two 20 second sprints per session raised aerobic capacity by 12 percent in the women.
Phaes also uses SIT for reasons beyond VO2 max: short, very hard efforts recruit the fast-twitch muscle that long easy running barely touches, and they keep you fast. That part is coaching rationale rather than proven in midlife trials, but it is why SIT sits alongside heavy lifting at the heart of the method.
Other formats, and what not to stack
Longer intervals such as the Norwegian 4x4 also raise VO2 max and are a valid alternative if you enjoy them. What does not work well after 40 is stacking them: two or three days a week of Zone 3 and 4 intervals or tempo runs adds fatigue faster than fitness. Pick one quality session, not several.
The 4x4 comes from a 2007 study by Helgerud and colleagues: four 4-minute efforts at 90 to 95 percent of max heart rate, with 3 minutes of easy jogging between. Over 8 weeks it raised VO2 max by 7.2 percent in moderately trained young men, more than easy or threshold running. It is a longer and more draining session than sprints, so if you choose it, it takes the place of that week’s SIT session rather than being added on top.
Keep everything else truly easy
The rest of the week supports the sprint session. Easy days should be genuinely easy: a walk, a very easy run, or yoga. Add heavy strength training by level, one full rest day a week, and a reset week every fourth week with no sprints at all. Less is more: fewer, better sessions beat more mileage.
A sample week for an intermediate runner:
| Day | Session |
|---|---|
| Monday | Strength, then a 20 minute walk |
| Tuesday | Run under 60 min with 6 to 10 sprints |
| Wednesday | Strength |
| Thursday | Very easy run or yoga |
| Friday | Strength |
| Saturday | Long run at an easy effort |
| Sunday | Full rest day |
Easy running still has a place. Our guide to zone 2 training for women over 40 covers how to keep it easy. In this method, though, those runs are active recovery that keeps you moving between the sessions that build fitness, not the engine itself.
Recovery needs in perimenopause
Recovery after all-out efforts often takes longer in perimenopause, which is why sprint sessions sit at least 3 days apart. Poor sleep, night sweats, and heat slow recovery further. When sleep or symptoms are bad, moving the sprint session a day or two, or swapping it for an easy day, is smarter than forcing it.
Some practical guardrails:
- Sleep first. Sprinting after two bad nights adds stress without much benefit. Swap the days.
- Warm up properly. The full 10 minutes, plus a few relaxed strides, before the first all-out effort.
- Fuel and hydrate. Eat something before the run, drink enough, and get protein afterwards. Our guide to recovery between hard sessions covers the rest.
- Watch for warning signs. Chest pain, fainting, unusual breathlessness, or new palpitations during exercise need a doctor, not a training adjustment.
How to tell if it is working
You can tell it is working when your sprints feel stronger, you recover faster between them, and a benchmark effort gets quicker for the same feel. Most women notice a difference within 6 to 8 weeks of consistent weekly sessions. Watch estimates of VO2 max are a rough guide, so track real performance instead.
- Count your sprints. Moving up your level’s range while holding form is progress.
- Time trial. A flat 3 km or 2 mile effort every few months, run on a cool day after a good night’s sleep, is a practical proxy.
- Easy pace. A lower heart rate at your usual easy pace means your aerobic fitness is improving.
If progress stalls, the fix is usually more recovery, more sleep, or more food, not more sessions.
Where Phaes fits
Phaes places one sprint session a week at your level, keeps it at least 3 days from the next, and fills the other days with strength, truly easy movement, and a rest day, with a reset week every fourth week. It reads your daily check-in, so a sprint day can move when you are underslept or flaring. We do not just log your runs. We read how you are recovering and adjust the plan.
The bottom line
VO2 max is one of the strongest predictors of a long, healthy life, and it declines faster with each decade. After 40, one weekly sprint interval session (20 to 30 second all-out efforts with 90 seconds of easy recovery, reps by level) is a time-efficient way to push it up. Keep sprint sessions 3 days apart, keep easy days easy, protect your sleep, and get any chest symptoms checked before you train through them.
Frequently asked questions
Can you improve VO2 max after 40?
Yes. VO2 max responds to training at any age, including in your 50s and beyond. It declines with age even in active people, but training can raise it meaningfully, and a fit 50-year-old can have a higher VO2 max than an untrained 30-year-old. Short, very hard efforts are one of the most time-efficient ways to push it up.
What is sprint interval training?
Sprint interval training (SIT) is a set of short, all-out efforts, usually 20 to 30 seconds, separated by longer, very easy recovery. In the Phaes method each sprint is followed by 90 seconds of walking or very easy jogging. Meta-analyses show SIT raises VO2 max about as much as longer moderate training, with far less total time.
How often should I do sprint intervals?
Once a week is the Phaes default, and sessions should be at least 3 days apart. Sprinting all-out is a big stimulus, and in perimenopause recovery is often slower. One well-recovered session a week, with easy days around it, does more than two tired ones.
Is the Norwegian 4x4 better than sprint intervals?
Both raise VO2 max in studies. The 4x4 (four 4-minute efforts at 90 to 95 percent of max heart rate) is well researched, but it is a longer, harder grind at threshold-plus effort. Phaes uses short sprints as the weekly quality session because they take less time and recovery. If you prefer a 4x4, it should replace the sprint session, not be added to it.
Does zone 2 running raise VO2 max?
In a beginner it can, a little, but easy running is not the main driver. In the Phaes method, easy days are recovery: a walk, a very easy run, or yoga. They keep you moving and help you absorb the hard work. The weekly sprint session and heavy lifting do the main job of building fitness.
Are sprint intervals safe in perimenopause?
For most healthy women who already exercise, yes, if you build up from a few sprints and warm up well. If you are new to hard exercise, have a heart condition, or get chest pain, fainting, or unusual breathlessness during effort, see a doctor first. New palpitations should be checked before you train hard.