I Have a Limited Amount of Time to Exercise. Should I Do Cardio or Lift Weights?

Back in 2016, I wrote a column with the rather glib headline: “Yes, Professional Runners Are Weak.” In my defense, I was merely paraphrasing the recently retired marathoner Ryan Hall. After hanging up his running shoes, the American record holder in the half marathon had hit the weight room hard and transformed himself from a scrawny endurance athlete into a muscle-bound beefcake. “I’ve been small and weak all my life,” Hall said in an interview with Runner’s World. “I’ve always wondered what it would feel like to be big and strong.”

For Hall, getting jacked was also a boon for his overall vitality. As he told CNN in 2021, his energy levels are “ten times better” now that he spends “60 to 90 minutes a day” lifting weights, as opposed to when he was grinding out 130-mile weeks. Who can’t relate?

Ryan Hall may be a physical outlier, but his example speaks to one of the more enduring debates in popular fitness culture: Is one better off prioritizing cardio or strength training? (With apologies to gym bro taxonomists, in this article “strength training” will be used interchangeably with “resistance training.” While strength training is usually more specifically about gaining muscle mass, both forms of exercise involve working the muscles with some kind of counterforce, e.g. dumbbells or one’s own bodyweight.)

Although the pendulum is always swinging back and forth, the resistance-training over cardio movement seems to be gaining momentum, at least among certain fitness influencers. The popular “She’s a Beast” newsletter, from the runner-turned-weightlifting-evangelist Casey Johnston describes itself as “counter-programming for the alleged ‘thin is in’ era.”

Meanwhile, even accounts that explicitly promote weight loss and body fat reduction are pushing back against a perceived overemphasis on aerobic exercise. “What if I told you that by doing less cardio, you could actually lose more fat?” asks the online fitness coach and trainer Katie Neeson, who runs the TikTok account @thefitmamalife. “The number one reason that doing less cardio is going to be great is because you can spend more time getting your ass in the weight section.”

A common refrain among those advocating for more of us to get our collective asses into the weight section is that resistance training will “improve body composition,” a euphemism for “make you look hotter.” It’s a reminder that often the cardio vs. weights debate is as much about aesthetics as anything else. Indeed, if you have specific fitness goals, whether it’s to acquire a certain physique or run your fastest marathon, it should be pretty clear which form of exercise you need to prioritize.

But what about when we consider the question from a general health standpoint?

Which Is Healthier: Cardio or Strength Training?

Professor Duck-Chul Lee is the director of the Physical Activity and Weight Management Research Center at the University of Pittsburgh, and the author of many papers on exercise and long-term health. Earlier this year, he co-authored a study comparing how different kinds of exercise help mitigate risk factors for cardiovascular disease (CVD). The study, published in the European Heart Journal, looked at 406 adults (53 percent women) between the ages of 35 and 70, all of whom were either overweight or had high blood pressure. Participants were divided into groups doing one of the following three times a week over the course of one year: one hour of resistance training; one hour of aerobic training; 30 minutes of resistance training and 30 minutes of aerobic training; or no training at all. After one year, only the groups who had done aerobic-only or aerobic and resistance training showed an improvement in their composite CVD risk-profile, compared to the no-exercise group.

However, while the CVD-related benefits for those who focused exclusively on aerobic exercise and those who couple it with strength training were almost identical, the latter group also showed additional improvement in metrics like lean body mass. “The message that I wanted to deliver from that study was that if people switch half of their cardio with resistance training, they get the same magnitude of benefits to reduce CVD risk factors, but they get extra benefits like increased strength and muscle mass,” Lee says.

This isn’t the first time that Lee has published a study implying that many of the benefits of running can be gleaned from relatively small doses. A 2014 study in the Journal of the American College of Cardiology (JACC) that looked at the relationship between running and all-cause and cardiovascular mortality in over 55,000 adults found that running as little as five to ten minutes a day at slow speeds showed similar benefits to running over three hours per week.

“Runners were not happy about those findings,” Lee told me, noting that he received a fair amount of hate mail from hardcore endurance athletes who felt that their fanaticism was being put on trial. But according to Lee, the contentious question of whether it’s possible to do too much cardio is still undecided.

What about overzealous weightlifters? A widely-cited 2022 study from the Japanese sports science professor Haruki Momma found that resistance training did, in fact, reduce one’s risk of all-cause mortality, but that the maximum benefits appeared to top out at 30 to 60 minutes per week. The study cautioned that more research is needed to determine the potential benefits (or downsides) of high volume muscle-strengthening exercise. To that end, Lee told me that he had just received a grant to conduct a year-long study to compare the effects of a weekly weightlifting regimen of varying degrees of intensity–from zero to 120 minutes per week.

The Difference in Benefits for Men vs. Women

Unsurprisingly, more research is also needed when it comes to assessing the relative benefits of exercise for men and women. That was the upshot of another JACC paper published this year, titled “Sex Differences in Association of Physical Activity With All-Cause and Cardiovascular Mortality.” The authors of the study examined the relationship between the exercise habits of 412,413 Americans (55 percent women) and all-cause and cardiovascular mortality from 1997 through 2019. Looking at the data for nearly 40,000 deaths in this time period, the authors of the study found that men got the greatest mortality benefit (18 percent risk reduction in all-cause mortality) from 300 minutes per week of moderate-to-vigorous physical activity (MVPA). Notably, women got a similar benefit from only 140 minutes per week of MVPA.

Sex difference was significant when it came to the specific benefits of muscle-strengthening exercises, too. Among those who regularly engaged in muscle-strengthening activities, men showed a cardiovascular risk reduction of 11 percent, while among women, the risk reduction was a whopping 30 percent.

There are certainly caveats with this study (as with most large-scale fitness studies, all exercise behaviors were self-reported), but the central point that sex differences should probably be given more consideration when making general exercise recommendations seems hard to argue with. As Susan Cheng, a professor of cardiology at Cedars-Sinai Medical Center and one of the lead authors of the study, told me, “A certain person, with a certain physique, might get a lot more out of 75 minutes of exercise, than somebody with a completely different physique and body stature, who might need 350 minutes to get the same benefits.”

Another co-author of the study, Professor Martha Gulati, who among other things is the president of the American Society for Preventive Cardiology, told me that “anytime I see identical recommendations for men and women, my usual question is: ‘Where did that come from?’ Because chances are the data is not strong.”

The Bottom Line: How Much Cardio and Strength Training You Need

Nonetheless, while more studies need to be conducted to fine-tune sex-specific recommendations, the current evidence suggests that most people, regardless of gender, would still be well-served to target the American Heart Association’s recommendation of 150 minutes per week of moderate intensity aerobic activity, combined with at least two days a week of moderate-to-high intensity muscle-strengthening activity.

If that sounds a little ambitious, everyone I spoke to was adamant that the difference between doing a small amount of exercise–as little as five to ten minutes a day–and doing nothing was far more significant than discrepancies in health gains between those on the other end of the spectrum.