Big Fitness Equals Big Survival Benefit, New Study Shows

The fitter you are, the longer you’ll live.

Those are the main findings from a large analysis of adults who underwent exercise treadmill testing, with investigators reporting that cardiorespiratory fitness was inversely associated with all-cause mortality and that there appeared to be no upper limit to the fitness gains. For example, even individuals with “high” levels of cardiorespiratory fitness had a higher risk of dying in long-term follow-up when compared with adults considered to have “elite” fitness.

“We found that there was no ceiling for benefit,” senior investigator Wael Jaber, MD (Cleveland Clinic, OH), told TCTMD. “It’s almost a dose effect, with no toxicity at the higher end.”

The new findings, which were published October 19, 2018, in JAMA Network Open, are based on an analysis of more than 122,000 adults referred for exercise treadmill testing between 1991 and 2014 at the Cleveland Clinic. Cardiorespiratory fitness was classified as low (< 25th percentile), below average (25th to 49th percentile), above average (50th to 74th percentile), high (75th to 97.6th percentile), and elite (≥ 97.7th percentile). During the study period—the median follow-up was 8.4 years—there were 13,637 deaths over 1.1 million person-years of observation.

It’s almost a dose effect, with no toxicity at the higher end. Wael Jaber

Individuals with a low degree of fitness had a fivefold higher risk of death when compared with adults with elite-level fitness (HR 5.04; 95% CI 4.10-6.30). Similarly, those with low fitness levels had nearly a fourfold and threefold increased risk of death versus adults with high and above-average fitness levels, respectively. Even when compared with individuals with below-average fitness, those with the lowest levels of fitness had a near twofold increased risk of death in follow-up (HR 1.95; 95% CI 1.86-2.04).

On the higher end of the fitness scale, those with above-average fitness had an 84% increased risk of dying in follow-up compared with adults with elite-level fitness and a 42% increased risk of dying compared with adults with high cardiorespiratory fitness. For those with high levels of fitness, still there was a higher risk of death compared with individuals with elite-level fitness (HR 1.29; 95% CI 1.05-1.60).

When comparing the adjusted risk of death among elite versus high performers, the lower risk of death among the elite-level adults was not observed if these individuals had coronary artery disease, diabetes, or hyperlipidemia. The lower risk of mortality among elite-level adults compared with those with high levels of fitness did hold, however, if these individuals had hypertension. There was also a lower risk of death among adults 70 years and older with elite cardiorespiratory fitness compared with similarly aged adults with high levels of fitness.  

Jaber said they were taken aback by the magnitude of benefit, particularly in the elderly patients, and that these results suggest very high levels of fitness might be particularly important as patients age. High fitness level in older adults is likely a reflection long-term activity and/or exercise habits, “and the cumulative benefits of high aerobic fitness may contribute to a more significant effect on long-term survival,” according to the investigators.  

Fitness Is Partly Genetic, Though

Carl “Chip” Lavie (John Ochsner Heart and Vascular Institute, New Orleans, LA), who has been involved in numerous exercise studies, even some that suggested a loss of clinical benefit or possibly even harm at high or extreme levels of physical activity, stressed the present study is an evaluation of cardiorespiratory fitness levels, not physical activity or exercise intensity. “No one has suggested harm of having a higher cardiorespiratory fitness,” he told TCTMD in an email.  

He also noted that while physical activity and/or exercise training are the main way to improve cardiorespiratory fitness, and that most people who have high- or elite-level fitness also likely exercise a great deal, as much as 15% to 30% of cardiorespiratory fitness may be inherited.

Lavie said that while there was a significantly lower risk of all-cause mortality as fitness levels increased, the reduction in risk was modest as one moves from below to above average, above average to high, or high to elite fitness. “The biggest bang for the buck is just getting out of the lowest level into the next level [below average], and this can typically be accomplished by just following the international physical activity guidelines,” said Lavie. That would require more than 150 minutes per week of moderate physical activity or more than 75 min per week of more vigorous, moderate/high-intensity physical activity.

To TCTMD, Jaber pointed out that past studies linking physical activity levels with clinical outcomes have largely relied on self-reported data and/or questionnaires, which limits their interpretation because of recollection bias.

“The data about exercise and cardiovascular mortality is predominantly based on reporting how much you exercise,” said Jaber. “Basically, it’s self-recollection. ‘I exercise twice or three times per week,’ and it’s collected over a long period of time. It’s very subjective. Some people tend to inflate how much they exercise, some people underestimate how much they do. We wanted to look at an objective measure of aerobic fitness, [functional capacity], to see if we could link it with mortality.”

In general, Jaber said they encourage all their patients to exercise and if they are currently physically active, they will aim to push them a little harder. For patients who have never exercised, they are first sent for an evaluation that leads to a personalized exercise prescription plan that matches current fitness and needs. “From this study, I think we can push patients harder than we currently push them,” said Jaber. “The recommendations for 10,000 steps per day is probably adequate to get you off the couch, but it’s not adequate to get you the most benefit you can get. It’s almost like giving some antihypertensive medication but not using the maximum dose.”