“Healthspan” has entered the common vernacular and I think that’s a good thing. The term has been around for a while but Peter Attia has really popularized it. I love the idea of seeing you in your 70s as strong, mobile, durable, and spry um… as heck. Lots goes into this — including genetics and luck — but we’ll, of course, focus on the stuff within your control. Specifically, we’ll look at training your cardiovascular system and decode what zone 2 really means.
When we talk cardio, we are really talking about oxygen and nutrient delivery to everything from your muscles to your brain. We are talking about mitochondrial health (more on that later). We are also talking, more broadly, about building highly adaptive and nuanced responses to physical stress. We do this through regulating blood flow/pressure and by shuttling out waste and metabolites; it’s tough for your muscles to contract when they’re drowning in acidic hydrogen ions.
Let’s count down. 5-4-3-2-1. Zone 5 cardio is all-out. Honestly, I don’t even know why it’s called cardio because it’s considered to be anaerobic (literally, without oxygen). For context, elite 100 metre sprinters often hold their breath for the majority of the race. If you’re asking me, I’d consider an all-out 400 metre race to be a better model for zone 5, since it combines all energy systems — but with aerobic function being completely unsustainable at that pace (those damn hydrogen ions!) I would also argue that most people can’t access zone 5 without extensive training. That’s for the best.
Take a step down from there and zone 4 will still have you moving at an unsustainable pace — BUT where you feel less like your entire body is going to explode. You’re using a combination of oxygen and stored sugar (muscle and liver glycogen) for energy and things will absolutely start to burn. Your heart rate may approach maximum (technically, 77-95% of max). This is where people are mostly likely revving during a hard interval. It’s still pretty gnarly. If you were running for your life, you might be able to maintain this zone for a minute. Two tops.
I think of Zone 3 as a transition zone. Notably, it’s what a lot of cardio equipment refers to as the “fat-burning zone.” This is where you’re shifting into glycogen as a primary energy source — which is required for higher-output cardio. However, you’re still mostly oxidizing fat as an energy source. That’s the theory. The reality is that there is some variance here and many folks are not fully fat-adapted, meaning that they predominantly use sugars (stored and in their bloodstream) for energy. It is weird to imagine doing cardio for fat loss and then barely burning any fat but here we are. Distance runners take note: the more fat-adapted you are, the less you’ll have to rely on gels and other forms of expensive goo for energy. This has the added benefit of taking it easy on the ole tummy. Runner, Ann Trason, once said that “ultra marathons are just an eating and drinking competition with a little bit of running thrown in.”
Finally, we have zone 2. This is around 65-75% of your max heart rate. You should be able to breathe entirely through your nose at this pace. You should be able to chat a bit but not continuously. The benefits of spending a lot of time in zone 2 are myriad. Your heart can fill to its full capacity — and with the greatest elasticity — which leads to lower resting heart rate. Rather than create acute training stress, as you’d see during high-intensity intervals, zone 2 is regenerative. That means you’ll typically feel better afterwards AND enjoy elevated immune function. It is probably also the best place to level-up your ability to oxidize fat as a fuel source — something that goes beyond body composition and into general function and mitochondrial health.
About mitochondria: these little beauties are where ATP, the energy for muscular contraction, gets made. Hence “powerhouse.” Mitochondria are mostly in slow-twitch muscle fibres and keeping them healthy is essential for metabolic health. To wit, mitochondrial dysfunction is considered to be a root cause of insulin resistance, which can cascade into type 2 diabetes. Risk factors for heart attacks, strokes, dementia, and many other legitimately scary things are associated with mitochondrial dysfunction — which may precede these conditions by 5-10 years.
If that all freaked you out, zone 1 cardio, as you’ve probably guessed, is even lighter. Probably more brisk walk than run. Here, you can engage in ongoing conversations. So, if you’re feeling anxious about your metabolic health, call up a friend and have yourselves a walk-and-talk.
I’ll also mention that there are also some powerful strategies For developing mitochondrial health through strength training. The odds are that you’re doing a lot of these things by default, just by training with us. However, If you want to focus on your cardiovascular and cardio-metabolic health, let us know and we will tweak things just so for you.
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