Together With NOBULL
Why Many of the Fittest People You Know Are Missing Half the Picture
Danielle has done this long enough that she's stopped second-guessing herself.
She wakes at 5:30 (not because she has to: she runs her own architecture firm, sets her own hours) but because that's when the streets are empty, and the air is still cold, and she can get whatever mileage she has scheduled before the city remembers itself. She's been running for eleven years. Three marathons. A half-ironman at 44. Her resting heart rate hovers around 47 beats per minute. At her last checkup, her cardiologist looked at her chart with the expression of someone about to compliment their own work.
"Whatever you're doing," he said, "keep doing it."
Danielle has no intention of changing a thing. And she has no reason to think she should.
That's the part worth paying attention to.
On the other side of the country, Marcus has a different relationship with exercise and an identical relationship with certainty.
He's been lifting weights since his sophomore year of college, going on nineteen years, long enough that the habit stopped feeling like discipline and started feeling like architecture: just the shape of his days. He is 182 pounds. Lean, strong, the kind of physique that makes other people at the gym ask what program he follows. His doctor, at his last physical, examined his muscle mass, his lipid panel, and his blood pressure, and said something Marcus has heard more than once: "Your body is doing a lot of the work for you."
Marcus doesn't do cardio. Nothing structured, nothing intentional. He's never felt like he needed to, and his doctor has never pushed him toward it.
He leaves every appointment feeling like he's figured something out.
He has. Just not everything.
Two Kinds of Fit. One Healthy Heart.
I've spent years talking to cardiologists, exercise physiologists, and coaches about what it actually takes to protect the heart: not the fitness-industry version of that question, but the clinical one. What happens inside the cardiovascular system when you train, and what doesn't happen, and why.
The answer you get, consistently, is not the one most people who exercise regularly are operating on.
Think about the debate that surrounds protein and fiber. For years, people treated them as competing priorities. High-protein advocates dismissed fiber as secondary. Plant-focused eaters sometimes undersold the protein question. The reality, which any dietitian will tell you, is that the argument itself is the mistake. You need both. They serve different systems. Optimizing one does not substitute for the other.
The same logic applies to your heart and the training you're asking it to do. More specifically, it applies to what raises your heart rate, and why that distinction matters far more than most people who exercise have ever been told.
A lot of lifters carry a quiet assumption: that if the heart rate is climbing, the cardiovascular system is getting the same work it would from a run. It's a reasonable intuition. It's also incomplete.
And that gap between what feels true and what's actually happening inside the cardiovascular system turns out to be one of the more consequential misunderstandings in fitness.
All Cardio Isn’t Equal
There's a version of this conversation that starts with heart rate. When you’re lifting heavy, your heart rate spikes. Some people might call this their cardio. And it is, but it’s a different type of cardio than what you get from walking or running.
Different types of activities have different needs and different reactions. It doesn’t matter if it’s having the right footwear or adjusting your nutrition.
Heart rate is a measurement. It tells you how hard your heart is working in the moment.
What the science of cardiac adaptation is really about is not just how hard the heart works; it's what kind of work it's being asked to do, and what the heart builds in response over months and years of that demand.
Start with what happens when Marcus lifts.
The moment he takes a big breath and braces before a heavy squat, he's doing something his body figured out long before he did. That breath-hold (the same thing that happens when you're straining to open a stuck jar lid) is called the Valsalva maneuver, and it's not a quirk. It's a feature. Holding your breath and bracing your core creates a pressurized column inside your torso, like inflating a balloon in your midsection. That internal pressure becomes a rigid support system for your spine, making it far harder to collapse under a heavy load.
The trade-off is cardiovascular. All that internal pressure temporarily squeezes the large veins that carry blood back toward the heart, so less blood arrives with each beat. The heart responds the way any pump would when its supply line gets restricted: it speeds up to compensate. This is why heart rate spikes during a heavy set, even though the actual movement might last only a few seconds.
The heart isn't building aerobic endurance. It's managing a pressure crisis, trying to keep blood flowing despite the squeeze.
Do that repeatedly over the years, and the heart adapts. Think of it like a water balloon with muscular walls.
Resistance training keeps putting the heart in that high-pressure, restricted-supply situation, so the walls respond the same way your bicep responds to curling weight: they get denser and stronger. But the balloon itself doesn't get much bigger. The rubber just gets thicker. This is concentric hypertrophy, and it makes the heart exceptionally capable of generating force in short, intense bursts.
And that’s a genuinely beneficial adaptation, not a consolation prize. But it’s different from your traditional aerobic exercise.
When Danielle runs for an hour, her heart faces a completely different problem. Her working muscles need a continuous, high-volume supply of oxygenated blood. There's no pressure crisis. There's a volume demand.
The heart responds by learning to fill more completely and eject more blood with each beat. And over time, the chamber itself expands to hold that larger volume. The balloon gets bigger. This is eccentric hypertrophy, and it's why Danielle's resting heart rate sits at 47. Each beat now moves so much more blood that her heart doesn't need to beat as often to do the same work.
Two different problems. Two different solutions.
A weightlifter's heart is like a compact, powerful engine, built for short, explosive bursts of force. An endurance athlete's heart is like a high-displacement engine with a bigger fuel tank, optimized for sustained, efficient output over long distances.
Neither is better. They're solving different problems.
And the research suggests the healthiest cardiovascular profile comes from training both. The thick, strong walls from lifting and the expanded, efficient chambers from aerobic work don't cancel each other out. They compound.
It’s a bit of a buzzword, but there’s real value to becoming a hybrid trainer. Creating a plan that includes cardio and weights. For Arnold, that means riding his bike to and back from the gym (the cardio) and then hitting the weights (resistance training).
If You Do Aerobic Exercise, Here’s What You’re Missing
Danielle's heart is a volume machine. It's excellent at sustained, efficient output. Her stroke volume (the blood pumped per beat) is almost certainly higher than average. Her cardiac chambers have adapted to endurance. Her resting heart rate of 47 is a genuine marker of real fitness.
But there's another part of the cardiovascular equation that running, on its own, does not fully address: the health of the blood vessels themselves.
The inside of every artery is lined with a thin layer of cells called the endothelium. Think of it as the interior surface of a pipe, except unlike a pipe, it's alive, it produces compounds, and its health or dysfunction has downstream consequences for almost everything we care about when we talk about heart disease.
When the endothelium is functioning well, it produces nitric oxide, which keeps vessels flexible, helps regulate blood pressure, and makes the environment inside your arteries hostile to the plaques that cause heart attacks. When the endothelium is damaged or dysfunctional, you are accumulating cardiovascular risk that no fitness test at your gym will detect.
Here is the part that should interest Danielle: sustained aerobic exercise is one of the most reliable stimuli we know of for maintaining and improving endothelial function. The rhythmic shear stress of blood moving continuously through vessels during sustained cardio — not intervals, not HIIT, but sustained, moderate, continuous effort — is precisely the stimulus the endothelium needs.
A 2023 meta-analysis of randomized controlled trials found that continuous aerobic exercise significantly improved vascular endothelial function across diverse adult populations, reducing inflammatory markers and increasing antioxidant capacity, which helps keep vessel walls healthy.
Danielle gets this. Danielle gets this better than almost anyone.
The same meta-analysis found that vascular benefits begin to diminish when training stops, and endothelial health is not a one-time achievement. It's an ongoing practice. Which is fine if you're Danielle. But it also means the adaptation is specific. The cardiovascular system is not a single dial you turn up with enough mileage. It has multiple systems. Aerobic training, however excellent, primarily speaks to one of them.
If You Resistance Train, Here’s What You’re Missing
Marcus's heart is a different kind of machine. The wall of his left ventricle is, by training, thicker and more powerful than average. His heart handles pressure well. The data on what resistance training does for the cardiovascular system has gotten substantially clearer in the last five years, and the picture is encouraging in ways the fitness conversation has been slow to absorb.
A meta-analysis found that any amount of resistance training was associated with a 15% lower risk of cardiovascular disease mortality compared to no resistance training.
A separate systematic review and meta-analysis published in the European Journal of Preventive Cardiology, drawing on over 370,000 participants with an average of nearly 9 years of follow-up, found that resistance training alone was associated with a 21% lower risk of all-cause mortality.
These are not small numbers. And they should, to anyone who has absorbed the fitness industry's long-running narrative that cardiovascular health means aerobic exercise, come as something of a recalibration.
But here is what the same data shows about Marcus's situation: resistance training alone does not appear to produce the vascular adaptations that aerobic exercise does.
The heart muscle benefits. The pressure-handling capacity benefits. But endothelial health — nitric oxide production, vessel wall flexibility, and anti-inflammatory effects in the arterial interior — are not the primary targets of resistance training, and the research suggests they don't reliably improve with lifting alone.
So Marcus has a powerful heart muscle and a cardiovascular mortality risk meaningfully lower than someone who does nothing. And Marcus may have blood vessels that are not getting the sustained, rhythmic stimulus that keeps them elastic and healthy. His doctor's comment was true: "Your body is doing a lot of the work for you." It was also incomplete.
The lifter who avoids cardio is not making the same mistake as someone who never exercises. But they are leaving something on the table. Something the heart wants. Something the arteries need. Something that doesn't get built in the weight room, regardless of how high the heart rate climbs during a hard set.
The Science is Clear: It’s Not Cardio Vs. Weights
The European Journal of Preventive Cardiology meta-analysis mentioned above did something that most studies don't do cleanly: it compared mortality outcomes across training modalities, including what happens when you combine them.
Resistance training alone: 21% lower all-cause mortality.
Resistance training combined with aerobic exercise: 40% lower all-cause mortality.
Not 21% plus some marginal gain from adding cardio. Not resistance training doing the heavy lifting with aerobic as an afterthought. Forty percent — nearly double the benefit of resistance training in isolation — was the signal that emerged when both modalities were present.
The researchers were appropriately cautious about the mechanism. These are observational data, meaning they tell us what people who do both tend to experience, not what's happening causally inside each body. But the consistency of the signal matters. And the physiological explanation is coherent: resistance training and aerobic exercise produce distinct, non-overlapping cardiac adaptations, so combining them stacks benefits that otherwise remain separate.
Your heart does not want to choose. It wants both challenges.
It has the architecture for both responses: the pressure-driven adaptation that builds a stronger muscle, the volume-driven adaptation that builds a more efficient pump, and the vascular adaptation that keeps the pipes clean.
These are not competing programs. They are complementary ones.
We want to be careful here, because the fitness internet has a tendency to take a finding like this and turn it into a threat that feels like a “you've been doing it wrong” argument. Or into another reason to feel like your current routine is insufficient.
That's not what the data is doing.
Danielle is genuinely fit. Her heart has made real adaptations that protect her. Her resting heart rate and her endothelial health are genuine assets, not performances. What the research suggests is not that she's been wrong but that there's more available to her: a different kind of cardiac protection that her miles don't automatically produce.
Marcus is genuinely strong and genuinely protected. The mortality data on resistance training are not weak. His heart muscle is stronger for what he's done. The gap is not a failure. It's an opportunity.
The American Heart Association's Scientific Statement on resistance exercise training, which examined both healthy populations and those with existing cardiovascular disease, concluded that approximately 30 to 60 minutes per week of resistance training is associated with a meaningful reduction in all-cause mortality and cardiovascular disease risk. And it explicitly supports resistance training alongside aerobic training for cardiovascular health, not instead of it.
Both tools. Not either/or.
The conversation we keep having in fitness (lifters versus runners, strength versus endurance, barbells versus miles) is more about identity than about physiology. The body doesn't care about the team. It adapts to what you give it. And what the evidence consistently suggests is that giving it both creates something neither training style can build on its own.
Make It Work For You
We’re aware that "do more things" is the kind of advice that sounds obvious until you try to actually structure your week around it.
The research doesn't require you to become a triathlete. The mortality benefits from aerobic exercise appear at moderate doses: 30 to 45 minutes of continuous, sustained effort at a conversational pace, two to three times per week. It doesn’t have to be intervals or sprints (it can be, if you want). Just enough sustained effort to produce the shear stress on your vessel walls that triggers the endothelial response.
If you're Danielle, the lift doesn't have to be heavy. But it has to be intense and push the boundaries of failure. Two or three sessions per week of any resistance training appear to be where much of the cardiovascular mortality benefit is concentrated. Bodyweight exercises count, too. Moderate loads count. You don't need to become Marcus to get Marcus's cardiac adaptations.
If you're Marcus, the cardio doesn't have to be miserable. A 35-minute walk at a pace where you could hold a conversation but wouldn't want to is enough to trigger the vascular adaptations that lifting alone doesn't produce. The sustained, rhythmic, moderate-intensity work is what the endothelium responds to. You can listen to a podcast. You can go with your dog. The stimulus doesn't require suffering.
This is not a burden. This is information. And information, when it doesn't come loaded with urgency, is just permission: permission to add something that costs less than you think and pays more than you'd expect.
Danielle doesn't have to stop running. She just has to pick up something heavy twice a week.
Marcus doesn't have to become a runner. He just has to sustain something moderate for 35 minutes, a few times a week, until his arteries remember what they were built to do.
The heart you're building right now is real. There's just more opportunity available.
Get Your Mind Right, And Your Feet
The hard part is being consistent with exercise and putting in the work. But don't overlook the details.
Committing to hybrid training — actually showing up for both the weights and the cardio — is the decision most people never make. You're making it. That matters.
But here's something worth considering: the shoes you train in weren't designed for both.
A flat lifting shoe keeps you stable under a barbell. A cushioned running shoe absorbs impact on the treadmill. Neither was built for the full range of what your week actually looks like. Most people pick one and quietly accept the tradeoff. Or they swap mid-session and don't think much about it.
Here's why that matters more than most people realize: running shoes are engineered for forward motion and shock absorption. That’s a single, predictable movement pattern. The gym is the opposite. You're moving laterally, explosively, and under load. Research suggests that training in the wrong footwear compromises stability, reduces force transfer, and increases injury risk. It's one of the most overlooked variables in performance. Subtle enough that most people never connect the shoe to the limitation.
A shoe built for the full training week needs to do five things well simultaneously.
It needs enough stability to keep you balanced under a loaded barbell without feeling rigid. Enough cushioning to absorb impact during cardio without going soft underfoot when it counts. Traction that works across surfaces and directions. Breathability that holds up through high-intensity sessions without sacrificing structure. And materials durable enough to survive the actual grind — not just a few months of it.
Most shoes optimize for one or two of those. The rest is compromise.
NOBULL built the Drive 2 for people who train the way the research says to train.
It's a hybrid shoe engineered around the reality of a complete training week: strength work, cardio, circuits, and everything in between. The 4mm heel-to-toe drop gives you the flat, stable platform your lifts need. The compression-molded EVA (CMEVA) foam midsole makes it responsive, light, and comfortable. The re-engineered mesh upper stays breathable when the effort is sustained.
One shoe. Every move. No compromises. The work you're building is real. The details that support it should be too.
As an APC reader, you get the Drive 2 for just $99. Use code ARNOLD99 at checkout. But this special offer will only last for 48 hours.
Show up, put in the reps, and you’ll find yourself better than you were yesterday.
—
Publisher: Arnold Schwarzenegger
Editors-in-chief: Adam Bornstein and Daniel Ketchell
