Cardio is important to the health of your mitochondria. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8793839/

> Mitochondrial dynamics, including continuous biogenesis, fusion, fission, and autophagy, are crucial to maintain mitochondrial integrity, distribution, size, and function, and play an important role in cardiovascular homeostasis. Cardiovascular health improves with aerobic exercise, a well-recognized non-pharmaceutical intervention for both healthy and ill individuals that reduces overall cardiovascular disease (CVD) mortality. Increasing evidence shows that aerobic exercise can effectively regulate the coordinated circulation of mitochondrial dynamics, thus inhibiting CVD development. This review aims to illustrate the benefits of aerobic exercise in prevention and treatment of cardiovascular disease by modulating mitochondrial function.

Attia is a fan of "zone 2" training in particular because it trains mitochondria to burn fat, which leads to "metabolic flexibility". https://pubmed.ncbi.nlm.nih.gov/28467922

> Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand. This broad concept has been propagated to explain insulin resistance and mechanisms governing fuel selection between glucose and fatty acids, highlighting the metabolic inflexibility of obesity and type 2 diabetes. In parallel, contemporary exercise physiology research has helped to identify potential mechanisms underlying altered fuel metabolism in obesity and diabetes.

Weightlifting, if anything, depletes muscle glycogen, a sugar, so you aren't really training your fat-burning.

Cardio isn’t super important for what? It certainly has longevity benefits over and above those from resistance training.

Sorry, I meant cardio isn't super important for losing weight if you are already resistance training.

If losing weight is the only goal, then even resistance training isn't important.

You can just reduce portion sizes and caloric intake until you reach your goal weight.

You train strength and endurance for health and body composition, and performance if you care about that.

> Cardio isn't super important if you are already doing Resistance Training.

I'm a bit of a gym rat, mostly lifting though also some bodyweight/calisthenics.

I don't really do cardio.

I was concerned about it, so talked to my doc.

He said "you're lifting for an hour a few times a week. Your heart rate spikes when you're doing heavy lifts, right?"

"Yes".

He replied, "you're fine".

To test the theory, I got into the pool without having done any cardio at all in years. I had no trouble swimming 500 yards straight.

I wouldn't characterize my cardio capability as great, but it's moderate and good enough.

The thing is, you want great cardio capability. https://jamanetwork.com/journals/jamanetworkopen/fullarticle...

> Extreme cardiorespiratory fitness (≥2 SDs above the mean for age and sex) was associated with the lowest risk-adjusted all-cause mortality compared with all other performance groups.

Sure your cardio might be "good" now, but see Table 2 for what happens to you over time (with and without training).

Put more plainly https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6153509/

> Individuals with higher cardiorespiratory fitness (CRF) showed lower risks of all-cause, CVD and cancer mortality; those with higher grip strength (GS) had lower all-cause mortality. All-cause and CVD mortality risk was lowest in adults with both higher CRF and higher. Improving both CRF and muscle strength, as opposed to either of the two alone, may be the most effective behavioral strategy to reduce all-cause and cardiovascular mortality risk.

Your doc, like most docs, is probably woefully undereducated on the subject. Or at the very least he's so used to the average patient that anything above average is just a relief.

But by not doing cardio, you're actually leaving a lot of low-hanging fruit on the table. The second slide in this video might be persuasive: https://youtu.be/ovM3mD5Roow?si=IRSRjsq8MRas9Yq6

Episodes 236-238 of the Barbell Medicine podcast goes more in depth about the health benefits of endurance training and what a good target is for health benefits.

Is your resting heart rate under 70bpm? Can you run 2 miles in 18 minutes? If not, you could use some cardio. If only so you can breathe when you get COVID.

Resting heart rate of 70bpm is the average, so not a good measure.

The average is a huge range of 60-100. 70 is usually on the lower end and implies some cardiovascular fitness. It usually won't be that low from sitting on a couch. Running 2 miles at 9 minutes / mile isn't some accomplishment either, but it does imply some sort of training for an adult. I wanted to list a real standard for health, not athletic performance.

If you want athletic performance, there are the Iron Man / RASP standards and a heart rate between 40-60. Do note that while under 60 is highly trained, 40 is more on the elite athlete side of things.

you seem way more informed than me, but if that's the case, I'm confused by your suggestion: if 70 already implies cardiovascular fitness, why do you recommend cardio, given the person already should have some cardiovascular fitness?

Re-read my post. I am saying cardio is needed if HR isn't below 70bpm. Being concise for clarity, not to be rude.

I don't think I misunderstood you, I was suggesting that if 70bpm is already "cardio fitness", shouldn't that be sufficient for most individuals to prevent the majority of health issues?

Ah, got it. Yes, I agree that it's sufficient to be healthy, that's why it's the only number I initially brought up. I hate when people conflate exceptional fitness with health for people who don't want to specialize on fitness.