Aerobic Fitness and Longevity

Research perspective: evidence, tools, and the question "do we all respond to exercise the same way?".

Key takeaways: 

• Aerobic fitness is a powerful predictor of longevity (perhaps one of the best).

  
  

• Non-response to exercise doesn’t mean you're not improving — it may just depend on what variable you’re measuring.

  
  

• If you're not seeing results, try changing the style of training, adjusting the intensity, or increasing volume.

How long do we want to live - and more importantly, how well do we want to live… and what to do about it?

Many people know that avoiding smoking, managing blood pressure, or eating well are critical ways to increase lifespan - and they are incredibly important. But there is evidence that one thing may be even more important: 

Exercise.

Particularly aerobic fitness is the single most powerful predictor of longevity. 

A large study followed 122,227 people for approximately 8.5 years [1]. When you add it all up, this is equivalent to around 1.1 million “life years”. The researchers recorded every participant’s fitness at baseline, and then monitored their health during follow up. This study was enormous and presented some of the most clear findings to date on the question, what matters for longevity? This study considered many noteworthy variables, but If you read nothing else, the key findings are here: 

• Smoking = 40% increased risk of early death

• Diabetes or hypertension = 20-40% increased risk 

• Low aerobic fitness = 504% increased risk, compared to elite (yes, 5x higher risk for being of low fitness!) 

This clearly shows that being fit, appreciably outweighs other risk factors. More interestingly, this effect also appears to be almost linear:

Figure 1: Adjusted hazard ratios (HR) for all cause-mortality comparing each classification of fitness to "low fitness". Figure from Montsager et al., (2018). The article is open access and can be found here: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2707428

This has some good news, and some even better news. The good news is, there seems to be no change in trajectory for this relationship. The fitter you are, the more the odds are in your favour. 

The better news is we don’t have to be elite athletes - any improvement in our fitness is meaningful. Simply moving from low fitness to below average halves the risks. In fact, for those less than 70 years old, there is no significant difference between “high” fitness and “elite” fitness, so being in the top 25% for your age is a really great goal [1]. 

But then you may ask, what about fitness as we age? Well, something that is more profound, is that the protective effect of fitness is especially powerful in older age. For those 70 and older, being of high fitness reduces risk of all-cause mortality by a further 30% (so, around a 534% reduction for elite level fitness) [1]. 

So, no matter someone’s age, having higher fitness is critical. Even more so, making changes sooner likely leads to 1) better outcomes, but 2) likely makes it easier to be of high fitness later in life. The compounding effect of exercise on health cannot be understated. 

A collection of such studies supports this perspective, and shows that for every improvement in fitness of 3.5ml/kg/min of maximum oxygen uptake (VO2max), there is a 10-25% reduction in all-cause mortality [2, 3]. So we define this improvement as a “meaningful change”. If we consider the “average healthy adult” (mean VO2max = about 35 to 45 ml/kg/min; it’s typically higher in males, and for younger people) [4], this equates to a 7-10% improvement in fitness. Which leads us to the next question:

VO2Master: Used to measure VO2max outside of a lab environment

What is VO2max? 

Simply, it is the maximum amount of oxygen your body can take in and use to produce energy during its maximal demand (high intensity exercise) [5-7]. It involves and is influenced by numerous systems, which can be grouped into two fields: Central, and peripheral factors. Central includes cardiac output, which is a product of the amount of blood our heart can pump out (called “stroke volume”), and our heart rate per minute. The oxygen carrying capacity of the blood is also considered to be a central factor impacting VO2max. Peripheral factors include things like the size and amount of capillaries that bring blood to the exercising muscle (more is better), as well as how effectively oxygen crosses over into the muscle cells (among other variables). These give us some key target adaptations: central and peripheral. Exercises that target these will have the best crossover for cardiorespiratory fitness associated longevity.

What is the best type of exercise for longevity?

To do this justice, let’s first define what we’re really after. Longevity isn’t just about living longer, it’s about living better. So, the best exercise would be the one that improves both lifespan (years lived) and healthspan (quality of life). In general, both aerobic and resistance exercise play key roles here. With most evidence suggesting that aerobic exercise leans more to the lifespan angle, while resistance training helps with healthspan. But, both resistance and aerobic training make meaningful impacts on both aspects of longevity [8, 9]. In the context of the research we present here [1], the evidence points to any style of exercise that improves your aerobic fitness as the best type of exercise for longevity. 

But not all types of aerobic exercise are equal so we’ll break it down here:

We think of aerobic exercise as four main variables: duration of the exercise session, type of exercise, frequency of exercise per week, and intensity of the exercise. Using these as our points of difference between training styles, there are three different strategies that reliably change VO2max: Low intensity exercise (zone 2), moderate intensity continuous exercise (MICT), and high-intensity interval training (HIIT). Below, we’ll briefly break these down from least impact on VO2max, to most impact (though each carries their own benefit that may be worth considering): 

Low intensity, or zone 2 training:

• Slow jog, cycle, or row at a “conversational pace”

• 45-90 minutes 

• Effect on aerobic fitness: Zone 2 training likely has the smallest “magnitude of change” on VO2max, however it improves many systems that are required to achieve a high VO2max. For example, zone 2 has been shown to improve both cardiovascular and metabolic factors that contribute to fitness. However, the intensity isn’t high enough to really push the “top-end” of our fitness (our VO2max). 

• Best used for: 

• Building a strong aerobic foundation without fatigue 

• Long-term metabolic and cardiovascular benefits 

• Because it generates such low fatigue, it pairs very well with occasional high intensity exercise, or a great fit for people who do high-load resistance training 

Moderate intensity continuous training (MICT), also sometimes called moderate intensity steady state (MISS)

• Examples may be: Jogging, cycling, swimming, or brisk walking (especially up hill). Difficulty should be about 60-75% of your estimated HRmax (or actual HRmax if you know it). Otherwise about a 10-13 on the Borg Scale (“somewhat hard”)

• Duration: 30-60 minutes 

• Effect on aerobic fitness: Improves VO2max by about 2.4 ml/kg/min (or about 7% based on an “average” VO2max of 35ml/kg/min) [10]. MICT has also independently been shown to reduce all-cause mortality when people do 150-300 minutes per week (that’s where a lot of the exercise guidelines come from: e.g. 30 mins, 5 times per week)

• Best used for:

• Long term cardiovascular and metabolic health. Generates more fatigue than Zone 2, but less than HIIT. Likely pairs well with a variety of other training styles

• MICT seems to be more effective in “young and healthy” individuals, where the average increase in VO2max are reported to be around 4.0 ml/kg/min (11% improvement) after 4 to 8 weeks of doing MICT 3x per week. 

• Can be a great sustainable approach 

High intensity interval training (HIIT)

• Most effective strategies are “high volume HIIT” e.g. 4x4 method or 8-12 x 2 mins (more details here), though low-volume approaches (e.g. 10 x 1 min) also have support, but likely produce slightly less change in VO2max than what we’ll outline below [11].

• Intensity should be 85-95% of HRmax, or a 15-17 or higher on the Borg scale “hard” to “very hard”

• Duration: 15-38 minutes 

• Effect on aerobic fitness: Improves VO2max by 3.3 ml/kg/min (9%) [10] and up to 5.5ml/kg/min [12]. But is even more effective in middle-aged or older individuals, with an average improvement of 4.5 ml/kg/min. The key difference here is that the time needed is much lower: 75 minutes of HIIT is equivalent to 150 minutes of MICT

• Best used for: 

• Short, time effective training strategies 

• As few as four-weeks of HIIT, 3 x per week produces rapid adaptation

• Big improvements in other health outcomes (insulin sensitivity, as well as a variety of muscle based markers)

A bonus note on sprint interval training (SIT), also sometimes thought of as very low-volume HIIT

• These are exercises performed ABOVE the maximal oxygen uptake intensity. Meaning, you could not possibly sustain this intensity for long enough to measure a VO2max. 

• This is an all out effort, as few as 6 seconds to about one minute. Repeated multiple times with an active rest in between (think repeated, very short hill sprints where you walk back down)

• Sprints: running, cycling, rowing, swimming etc. 

• Effect on aerobic fitness: improves VO2max by around 2.5ml/kg/min, but depending on the study, this change may or may not be statistically significant [10]. It seems to be more impactful in younger, more active individuals (and some clinical populations). While it likely doesn’t have an enormous impact on VO2max, it does contribute to muscular changes, intensity tolerance, and potentially capillary density around working muscles, all of which may contribute to your VO2max [13], but certainly contributes to performance in sports that require short sprints.

• SIT shares some adaptations that crossover with types of resistance training, and SIT doesn’t have a huge net energy demand. Therefore they could be done in conjunction with a resistance training program, and likely have little to no impact on muscle mass (that is, if you already carry a very high amount of muscle mass with you - and if losing some is something you’re concerned about). Otherwise, exercise like HIIT and SIT have been shown to INCREASE muscle mass in more “regularly” muscled individuals (a very neat payoff of these styles of training). 

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Does everyone respond the same way?

This is a big question, and the simple answer is no, we don’t respond the same way. The slightly longer answer is we respond in different ways, and this gives us some options for what we can do that will be best for us. 

It has been shown that of the exercise types listed above, the highest rate of response was in HIIT, with 31% of people labelled as responders, and a further 33% were determined to be likely responders [10]. So together, it is suggested that around 64% of people who participated in high volume HIIT likely experienced a clinically meaningful change*. This is compared to 55% in MICT, though only 21% of those were labelled definite responders, and 48% in SIT (16% responders). So it appears that HIIT is more likely to result in a meaningful change in VO2max than either MICT or SIT [10]. But, as we mentioned previously, there may be some groups that respond slightly better to different exercise intensities.

The researchers found that HIIT was more effective in people older than 50-70+, as well as people with coronary artery disease and metabolic disease [10, 14]. While MICT appears to result in larger VO2max changes in younger and mostly healthy individuals. 

These findings are important, and give us a great insight into exercise and how to approach this pragmatically:

One thing it shows us is that not only is high intensity - highly challenging - exercise safe for older individuals (who may or may not have significant clinical considerations), it is uniquely super effective in this stage. When comparing this to the limited impact that MICT had in these groups, it further highlights that considering a perspective of “adaptation guided exercise” is critical. 

Remember, a high VO2max in this group is an enormous reduction in risk. It is important to encourage people in these categories to do any form of exercise. If the only thing they’re willing to do is walk, then great, definitely do that. But, if there is any willingness to push further, using HIIT is second to none in this group (using a stationary bike, or using inclines on a treadmill or walk offer higher safety and accessibility). There are many good reasons for this, but one critical thing to recognise is that this style of training likely works most effectively in this age group and conditions because HIGH Intensity exercise targets the exact systems that deteriorate with aging (see central and peripheral factors above - these all reduce with aging!). Meaning, low intensity exercise, even lots of it, may fundamentally miss the mark. If you are in this age group, and are cognisant of some of these considerations (or know someone who is), perhaps consider (or reconsider) introducing some high intensity exercise into your life.

For younger individuals this introduces a degree of nuance. It’s not that HIIT is completely ineffective, rather that it seems the adaptations derived from HIIT push on systems that are likely not the “bottleneck” for aerobic fitness in this age-and-stage. So, getting a few sessions of longer, moderate intensity exercise may be the way to go if your main goal is to improve your VO2max. But, again, it’s not that HIIT is completely ineffective. HIIT is still a great tool for improving exercise “performance”. Meaning, it may not push up one’s VO2max as much, but it may still increase your tolerance of intensity throughout your VO2 range. In other words, HIIT may allow you to handle a higher pace, or power output for longer at a given intensity of exercise. So, if you’re planning to use your fitness for some form of event or specific sport, or if you simply want to train in a shorter amount of time, HIIT could be a great tool. 

There are plenty of options, but there is one big thing to pay attention to: we are all different!

So, while this research is a good guide to suggest which way you may be predisposed to respond, there is still a chance you lean one way more than the other. Some people are seemingly “primed” to respond, and if this is you, you may experience a rapid, dramatic change with a certain style of exercise. So, there is good logic in at least trying a style of training consistently for about four-weeks and just pay attention to how your body feels, and how you seem to adjust. 

Perhaps counter intuitively, this may also be a good idea if you feel you may be somewhat “resistant” to responding. Being resistant to adaptation with exercise is likely dose/exercise selection dependent. For example, the individuals who were found to so dramatically respond to HIIT in this study, would have been more likely to be non-responders to MICT, and vice versa. So, if you’re not responding to one style of training, try switching it up and sticking to a different style for four- to eight-weeks. This should be enough time to really tell if you are feeling any changes. The other angle with exercise non-response is dose. There is evidence that increasing the amount of exercise (total minutes per week) is a way to bring about a response. However, it is very understandable that adding many minutes or even hours of exercise into your week is not everyone’s cup of tea, and there may not even be enough spare time. So, if this sounds like you, increasing the intensity may be a more practical way to increase this dose without increasing the time spent exercising. 

The final key consideration for context around “non-response”: non-response is decided using a single variable. In this case; aerobic capacity. But we know that exercise impacts many systems in such powerful and positive ways, that being too regressive in what we measure often misses the point. In fact, it should be made clear again, simply doing exercise results in enormous benefits to health. Research that we have been involved in, as well as work of others has also shown that those who are “non-responders” when measuring VO2max have significant responses in many other important ways including systemic inflammation improvements, muscle composition and functional improvements, metabolic and body composition improvements, and improvements in depression, anxiety and stress [15-17]. So, in research, and day-to-day life, we can often miss the point when we focus too much on one variable. 

So if you are someone who feels you don’t respond “well” to exercise, consider instead that there are many things that are not so easily measured that are changing significantly with every bout of exercise that you do. 

Our recommendation is that you consider this “adaptation targeted” approach to exercise. By aiming to do exercise that improves aerobic capacity you give yourself the best chance of making this change, but also, you’ll have the opportunity to view exercise as a few variables that you know how to use. 

You’ll know how to increase intensity in your training, and continue to make great adaptations. You’ll know that it maybe isn’t the distance that you ran today, it’s actually the 40 minute dose of exercise that it took to do it that is the important part. It might be that you know that putting these ingredients together can be just as effective in a variety of different modes of exercise: cycling, walking, running, swimming. They all work for you. 

For now, be kind. Stay curious. Happy exercising. 

If you’re interested in getting personalised plans based on the latest research, or further information about your exercise, send us a message or an email! If you want us to take care of all the exercise planning for your goals, experience, and response characteristics, check out our Tmrw Premium programming to get a program that works and adapts to you. 

References:

1.             Mandsager, K., et al., Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open, 2018. 1(6): p. e183605.

2.             Gulati, M., et al., Exercise capacity and the risk of death in women: The St. James Women Take Heart Project. Circulation (New York, N.Y.), 2003. 108(13): p. 1554-1559.

3.             Han, M., et al., Cardiorespiratory fitness and mortality from all causes, cardiovascular disease and cancer: dose-response meta-analysis of cohort studies. Br J Sports Med, 2022. 56(13): p. 733-739.

4.             Loe, H., et al., Aerobic Capacity Reference Data in 3816 Healthy Men and Women 20-90 Years. PloS one, 2013. 8(5): p. e64319-e64319.

5.             Rosenblat, M.A., C. Granata, and S.G. Thomas, Effect of Interval Training on the Factors Influencing Maximal Oxygen Consumption: A Systematic Review and Meta-Analysis. Sports medicine (Auckland), 2022. 52(6): p. 1329-1352.

6.             Bassett, D.R., Jr. and E.T. Howley, Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc, 2000. 32(1): p. 70-84.

7.             Poole, D.C. and R.S. Richardson, Determinants of oxygen uptake. Implications for exercise testing. Sports Med, 1997. 24(5): p. 308-20.

8.             Westcott, W.L., Resistance training is medicine: effects of strength training on health. Curr Sports Med Rep, 2012. 11(4): p. 209-16.

9.             D'Onofrio, G., et al., Musculoskeletal exercise: Its role in promoting health and longevity. Progress in Cardiovascular Diseases, 2023. 77: p. 25-36.

10.          Williams, C.J., et al., A Multi-Center Comparison of O2peak Trainability Between Interval Training and Moderate Intensity Continuous Training. Frontiers in Physiology, 2019. 10.

11.          Wen, D., et al., Effects of different protocols of high intensity interval training for VO(2)max improvements in adults: A meta-analysis of randomised controlled trials. J Sci Med Sport, 2019. 22(8): p. 941-947.

12.          Milanović, Z., G. Sporiš, and M. Weston, Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med, 2015. 45(10): p. 1469-81.

13.          Mølmen, K.S., N.W. Almquist, and Ø. Skattebo, Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports Med, 2025. 55(1): p. 115-144.

14.          Weston, K.S., U. Wisløff, and J.S. Coombes, High-intensity interval training in patients with lifestyle-induced cardiometabolic disease: a systematic review and meta-analysis. Br J Sports Med, 2014. 48(16): p. 1227-34.

15.          Khalafi, M. and M.E. Symonds, The impact of high-intensity interval training on inflammatory markers in metabolic disorders: A meta-analysis. Scand J Med Sci Sports, 2020. 30(11): p. 2020-2036.

16.          Martland, R., et al., Can high-intensity interval training improve physical and mental health outcomes? A meta-review of 33 systematic reviews across the lifespan. J Sports Sci, 2020. 38(4): p. 430-469.

17.          Poon, E.T., et al., High-intensity interval training for cardiometabolic health in adults with metabolic syndrome: a systematic review and meta-analysis of randomised controlled trials. Br J Sports Med, 2024. 58(21): p. 1267-1284.