Cardio Fitness, Longevity, and What a Treadmill Test Can Tell Us About Life Expectancy

It’s a cold Chicago morning, around minus 12 degrees. I’m looking out the window with a cup of coffee, thinking less about the cold itself and more about what comes after it. Spring. Clear sidewalks. Getting back into a steady running rhythm. This moment reminded me of an interesting and foundational study about how much cardio fitness really matters for long-term health. It’s easy to think of aerobic work as optional, something you do when time and motivation align. Strength training gets priority. Steps get tracked. Cardio often gets treated as flexible. But when you look closely at the research on longevity, that framing doesn’t really hold up.

One of the clearest examples comes from a large study published in JAMA Network Open, titled Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. The researchers did not rely on trends or speculation. They looked directly at measured fitness and long-term outcomes, and the message is hard to ignore.

Before getting into the data, one important note. As always, anyone starting or significantly increasing a cardio program, especially if they have medical conditions or have been sedentary, should do so with their physician's guidance.

What the researchers studied

This study followed more than 122,000 adults who underwent exercise treadmill testing in a clinical setting. These weren’t elite athletes or fitness enthusiasts recruited for a trial. They were everyday patients referred for testing, tracked over a median follow-up of about eight years. Instead of asking people how much they exercised, the researchers measured cardiorespiratory fitness directly during treadmill tests, expressed in metabolic equivalents (METs). That’s important. Self-reported activity is unreliable. Fitness reflects what your cardiovascular system can actually do. Participants were grouped by fitness level relative to others of the same age and sex, ranging from the lowest performers to the highest. The outcome they tracked was simple and meaningful: all-cause mortality.

The core finding, in plain terms

The results were straightforward and consistent. Higher cardiorespiratory fitness was associated with lower risk of death from any cause (see figure below). Each increase in fitness level corresponded to a meaningful reduction in mortality risk. What stood out was that there was no point where this benefit stopped. The most fit individuals, those well above average for their age and sex, had the lowest risk of death. There was no plateau and no signal of harm at higher fitness levels. From a longevity perspective, this matters because it challenges the idea that “moderate” fitness is enough and anything beyond that is unnecessary. At least in this data, more aerobic capacity continued to pay dividends.

Fitness compared to traditional risk factors

One of the most striking aspects of the study was how fitness compared to well-known health risks. Low cardiorespiratory fitness carried a mortality risk comparable to, and in some cases greater than, smoking, diabetes, or coronary artery disease. This reframes how we should think about cardio. Being unfit isn’t a small issue or a background variable. It’s a major risk factor in its own right. If longevity is the goal, aerobic fitness belongs in the same category as blood pressure, metabolic health, and smoking status.

What “elite” fitness means in this context

The authors labeled the highest fitness group as “elite,” which sparked some debate. These participants weren’t professional endurance athletes. Their treadmill performance would be achievable for many recreational runners or cyclists with consistent training. That’s actually encouraging. The largest longevity benefits weren’t limited to genetic outliers or extreme training volumes. They showed up in people who maintained a high level of aerobic fitness relative to their age. Longevity rewards sustained capacity.

Why the findings matter more with age

Another important detail is that the survival advantage of high fitness was especially pronounced in adults over 70 and in people with hypertension. In these groups, higher fitness levels were associated with significantly lower mortality risk. This runs counter to the idea that aerobic training is mainly for younger people. Maintaining cardiorespiratory fitness as we age may be one of the most protective things we can do, not just for lifespan but for independence and resilience. From a healthspan perspective, this aligns with what we see outside the lab. Older adults with good aerobic capacity tend to move better, recover faster, and tolerate stress more effectively.

What the study doesn’t claim

This was an observational study, not a randomized trial. It can’t prove that increasing fitness directly causes longer life. People who are fitter may differ in other ways that matter.  That said, the strength of the association, the size of the sample, the objective measurement of fitness, and the consistency with decades of prior research all point in the same direction. Cardiorespiratory fitness is one of the strongest markers we have for long-term survival, and it’s modifiable.

Bringing it back to everyday training

Looking out at a frozen sidewalk and thinking about spring running might seem trivial, but studies like this give those instincts real weight. Cardio is about preserving the systems that deliver oxygen, manage stress, and support movement over decades. Spring will come. Training cycles will restart. The question is whether cardio stays something we fit in when convenient, or whether we treat it as a core investment in long-term health. If the goal is not just to live longer, but to stay capable and independent as the years add up, cardiorespiratory fitness deserves a permanent place in the plan.

Finally, age is not a reason to pull back. If anything, it’s a reason to be more intentional. The study showed that higher fitness levels were especially protective in older adults and people with hypertension. Maintaining aerobic capacity as you age may be one of the most powerful ways to preserve independence, resilience, and quality of life. In practical terms, longevity training requires showing up, challenging your cardiovascular system often enough to maintain capacity, and doing it in a way you can repeat for decades. This study makes a strong case that the effort is worth it. More to come on cardio training in the coming weeks….

Citation: Mandsager K, Harb S, Cremer P, Phelan D, Nissen SE, Jaber W. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open. 2018;1(6):e183605. doi:10.1001/jamanetworkopen.2018.3605