“How much time do I need to spend exercising?” It’s a question I hear often, and it is the subject of countless research studies and popular press articles. And yet, this question misses the point.

When it comes to exercise, we should only concern ourselves with duration insofar as it influences what we really care about: results. Exercise is not a goal in itself – rather, it is a means of achieving good cardiorespiratory fitness, strength, and metabolic health, and the ultimate indicators of sufficient exercise are therefore a good VO2 max and adequate muscle mass.

Why do we care about VO2 max and muscle mass?

The rationale for emphasizing VO2 max and muscle mass is simple: these are the metrics with the greatest implications for healthspan and lifespan.

VO2 max, a measure of the body’s maximal ability to utilize oxygen during intense exercise, is indicative of overall cardiorespiratory fitness and, as discussed in detail in a recent premium newsletter, has been shown in multiple large-scale studies to be strongly and inversely associated with all-cause mortality risk across all adult age groups. Indeed, a low VO2 max is reported to be a far better predictor of mortality than diabetes, cancer, cardiovascular disease, smoking, or even age¹. The strength of this association can in large part be attributed to the fact that, in contrast to many other performance metrics, a high VO2 max requires consistency in training over relatively long spans of time and reflects not only aerobic fitness but body composition as well, underscoring the importance of maintaining this metric at a high level throughout life.

In addition to VO2 max, muscle mass – and to a greater extent, muscle strength – is also inversely correlated with mortality. As explained in AMA #27, low muscle mass (meeting clinical definitions of sarcopenia) has been reported to be associated with a 60% increase in risk of mortality relative to the absence of sarcopenia². Inadequate muscle leads to metabolic dysfunction and frailty, both of which can limit both quality and duration of life, but unfortunately, gradual losses of muscle mass and muscle strength are features of the aging process that cannot fully be avoided. Therefore, the most effective strategy for preventing sarcopenia in our latter decades of life is to build and maintain as much muscle as possible leading up to (and including) those decades – in other words, to ensure that we have enough muscle to buffer against the inevitable losses over time.

Focus on outputs over inputs

Many research studies claim to identify an “optimal” amount of time to devote to exercise each day or week in order to maximize health and lifespan benefits, but in the short video below, I explain why these results can be deceiving – and why focusing on outcomes of exercise, i.e., VO2 max and muscle mass, is a better strategy for setting goals around exercise and determining what is or isn’t “enough.”

If the goal for exercise is to improve health and extend lifespan, then the metrics that matter are those most closely related to health and lifespan – i.e., VO2 max and muscle strength. Exercise duration is another step removed from that aim and is only one of the various “inputs” – along with exercise intensity and consistency over time, for instance – that impact the more relevant “outputs” of cardiorespiratory fitness and muscle mass. While setting goals for exercise duration may be valuable for some as a means of keeping oneself accountable on a day-to-day level, it’s critical to keep in mind that such short-term “goals” are merely stepping stones in a longer path; they are not ends in themselves. And to keep our eyes on that ultimate end of a longer, healthier life, we must focus instead on metrics that are indicative of how exercise is affecting our overall fitness and strength.

For a list of all previous weekly emails, click here. 

podcast | website | ama

References

1. Kokkinos P, Faselis C, Samuel IBH, et al. Cardiorespiratory Fitness and Mortality Risk Across the Spectra of Age, Race, and Sex. J Am Coll Cardiol. 2022;80(6):598-609.
2. Liu P, Hao Q, Hai S, Wang H, Cao L, Dong B. Sarcopenia as a predictor of all-cause mortality among community-dwelling older people: A systematic review and meta-analysis. Maturitas. 2017;103:16-22.