Why Improving VO₂ Max Increases Confidence Outside of Workouts

Something shifted about three months into training seriously. Not during a run—during a meeting.

I was presenting to a room of people I'd normally feel nervous around. My heart rate climbed, the way it always does before a big moment. But instead of the usual spiral—shallow breathing, racing thoughts, the quiet dread of being exposed as unprepared—I just... handled it. I noticed the discomfort and moved through it.

It took me a while to connect this to what was happening with my VO₂ max. I'd been following a polarized training approach for several months, watching my cardiovascular fitness climb from average to above average for a 35-year-old. But I hadn't expected the changes to show up in a conference room.

The more I dug into the research, the more I realized this wasn't a coincidence. Cardiovascular fitness doesn't just change your body. It changes your brain, your stress response, and your relationship with discomfort itself.

Your body learns to handle stress differently

Here's something I didn't appreciate until recently: your body uses the same stress machinery whether you're sprinting up a hill or walking into a difficult conversation.

The hypothalamic-pituitary-adrenal (HPA) axis—the system that releases cortisol when you're under pressure—doesn't distinguish between physical and psychological threats. It just responds to stress. And how efficiently it responds turns out to be strongly influenced by your cardiovascular fitness.

A study published in PLOS ONE measured cortisol patterns in healthy older men grouped by fitness level. The high-fit group (determined by VO₂ max) had significantly lower daily cortisol output than the low-fit group. Their stress hormone levels were lower across the entire day—not just during exercise, but at rest, in the evening, even at midnight.

The researchers suggested that regular aerobic exercise helps buffer the gradual dysregulation of the HPA axis that normally occurs with aging. In plain terms: fitter people have a calmer baseline stress response.

This maps onto what I experience day to day. I'm not less stressed—the stressors haven't changed. But my body recovers from stress faster. The spike comes, and then it passes. That shift alone changes how I approach difficult situations.

The cross-stressor adaptation effect

There's a concept in exercise science called the cross-stressor adaptation hypothesis. The idea is straightforward: when your body learns to handle one type of stress efficiently, that adaptation carries over to other types of stress.

A 2014 study from the University of Chicago tested this directly. Researchers put 111 healthy adults through the Trier Social Stress Test—a standardized lab protocol designed to induce psychological stress through public speaking and mental arithmetic. They compared responses between regular exercisers and sedentary individuals.

The exercisers showed greater emotional resilience. Not because the stressor was less stressful—their bodies still reacted. But they recovered faster, and their mood bounced back more quickly.

This makes intuitive sense once you think about it. Every time you push into Zone 4 during an interval session—heart pounding at 90% of max, lungs burning, everything in your body screaming to stop—you're practicing something. You're practicing the experience of being under severe physiological stress and continuing to function. You're proving to yourself, at the cellular level, that discomfort is temporary and survivable.

That practice translates.

What happens inside your brain

The confidence piece isn't just psychological. Cardiovascular fitness physically changes your brain.

Research published in Scientific Reports found that higher VO₂ max in older adults was associated with thicker cortex in the superior temporal gyrus—a brain region involved in processing complex information. The researchers also found that fitter individuals had lower grey matter blood flow in the hippocampus, suggesting their brains were more efficient at meeting metabolic demands.

The mechanism behind this likely involves brain-derived neurotrophic factor (BDNF), a protein that supports the growth and maintenance of neurons. A meta-analysis of 29 studies found that a single session of exercise produces a moderate increase in BDNF levels, and that regular exercise programs raise baseline BDNF over time.

BDNF matters because it's heavily concentrated in the hippocampus and prefrontal cortex—the areas responsible for memory, learning, and executive function. These are the same areas you rely on when you need to think clearly under pressure, hold a complex argument in your head, or make a decision when the stakes feel high.

When I look back at that meeting where something felt different, I think what changed wasn't my preparation or my material. It was my capacity to think clearly while my heart rate was elevated. That's a skill my cardiovascular system had been training for months without my knowing it.

The mastery experience loop

Psychologist Albert Bandura identified four sources of self-efficacy—the belief in your ability to succeed at specific tasks. The most powerful source, according to decades of research, is what he called "mastery experiences." These are moments where you set a goal, push through difficulty, and succeed.

Training for cardiovascular fitness is essentially a mastery experience machine.

Every interval session that felt impossible but you completed anyway. Every month where your VO₂ max inched up even though progress felt painfully slow. Every morning you chose to show up when you'd rather stay in bed. These are small proofs of competence that accumulate over time.

What's interesting about Bandura's framework is that mastery experiences in one domain don't stay contained. They inform a more general sense of capability. A study on college students found that physical fitness predicted general self-efficacy, with exercise behavior mediating the relationship. Students with better fitness didn't just feel more confident about exercise—they felt more confident about life.

I notice this in small ways. I'm more willing to start things I'm not sure I can finish. I trust the process more because I've watched it work with something as concrete and measurable as VO₂ max. When my Apple Watch records a new reading that's slightly higher than last month, it's not just a fitness data point. It's evidence that sustained effort produces results—evidence my brain generalizes to other challenges.

Anxiety, depression, and the fitness connection

The mental health research is harder to ignore than I expected.

A meta-meta-analysis aggregating data from 92 studies found that physical activity reduced depression by a medium effect size (SMD = -0.50) and anxiety by a small effect size in non-clinical populations. These aren't people with diagnosed conditions—they're regular people who feel a bit less anxious and a bit more emotionally stable when they're physically fit.

A 2025 dose-response analysis published in eClinicalMedicine found that physical activity levels equivalent to about 150 minutes per week of moderate exercise were associated with a 42% reduction in the risk of developing anxiety. The maximum benefit appeared around 12.5 MET-hours per week—roughly the volume you'd accumulate following an 80/20 polarized training plan.

None of this means exercise is a cure for clinical anxiety or depression. But it does suggest that the cardiovascular system and the emotional regulation system are more deeply connected than most people realize. Improving one seems to meaningfully support the other.

The quiet confidence of a strong engine

There's a particular kind of confidence that comes from knowing your body works well. Not confidence in how you look—that's a different thing. Confidence in what you can do.

When you know your cardiovascular age is younger than your biological age, something subtle shifts. You stand differently in the world. Not because you're thinking about it, but because the physical substrate of your confidence—your nervous system, your stress response, your brain chemistry—has actually changed.

I think about the mortality research sometimes when people ask why I care about this number. The Cleveland Clinic study showing that low fitness carries greater mortality risk than smoking or diabetes is compelling on its own. But what keeps me training isn't the fear of dying. It's how much better I feel while living.

The paces that used to leave me gasping feel manageable now. The presentations that used to keep me up the night before feel approachable. The stressful conversations that used to linger for hours dissolve faster. These aren't unrelated observations. They're all reflections of the same underlying adaptation—a cardiovascular system that handles stress more efficiently and a brain that functions better because of it.

What this means practically

If you're training primarily for the longevity benefits or the race times, that's great. But pay attention to what's happening outside the workouts too. The psychological returns might be the most valuable part.

A few things I've noticed that track with the research:

The benefits seem to follow consistency more than intensity. Two or three sessions per week over months matters more than occasional heroic efforts. The timeline for cardiovascular improvement is measured in months, and the psychological shifts seem to follow a similar arc.

High-intensity work seems to matter for the confidence piece specifically. There's something about regularly choosing to be uncomfortable at 85-95% of max heart rate that rewires your relationship with discomfort everywhere else.

And tracking progress helps. When you can look at a number that objectively shows you're fitter than you were three months ago, it provides the kind of concrete evidence your brain needs to update its beliefs about what you're capable of. That's the mastery experience at work.

The deeper insight

What surprised me most isn't that exercise improves mood—everyone knows that. It's that cardiovascular fitness, specifically, seems to change the machinery of how you respond to challenge. Not through willpower or positive thinking, but through measurable biological adaptation: lower baseline cortisol, more efficient brain blood flow, higher BDNF, a stress response system that recovers faster.

Your VO₂ max isn't just a fitness metric. It's a rough proxy for how well your body handles being alive—the daily push and pull of stress, recovery, and adaptation. When that system works better, everything downstream works better too.

Including the version of yourself that shows up in rooms where the stakes are high.

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Track your VO₂ max trend over time with VO2 Max Pro. See your biological age, get notified when your Apple Watch records new data, and understand how your cardiovascular fitness is improving.