Why I Stopped Ignoring My VO2 Max & What Surprised Me Most
I love strength training. It’s grounding, empowering, and I know it’s making me the strongest version of myself both inside and out. Now that it’s so ingrained in my routine, I can’t imagine not lifting weights regularly.
But last year, I found myself wondering if perhaps I’d swung too far in one direction. Was I getting enough cardio in my weekly workouts? Despite my healthy, active lifestyle, would my heart health benefit from more? Afterall, heart disease1 is still the leading cause of death for women (of any age) in the U.S.
That question led me down an unexpected path, one that included signing up for my first HYROX race, running earlier than I necessarily want to, and a 6-point jump in my VO2 max. I didn’t start out trying to change this metric, but along the way, I learned why it matters more than most of us realize—especially for women in midlife.
From casual runs to competitive training
In early 2025, I wasn’t chasing performance metrics. My VO2 max hovered around 37, and I was content doing a short, leisurely run (about 25 minutes) or a HIIT-style workout once a week, complemented by strength training at the gym.
By June, I was pleasantly surprised to see my VO2 max was up to 41.
Around that same time, I found myself intrigued by the growing buzz around HYROX, a fitness competition that blends cardio challenges like running and ski ergs with functional strength exercises like sled pushes, rowing, farmer’s carries, and wall balls.
I signed up for an April race with my trainer and friend, Ashley Damaj. Suddenly, I had a new purpose behind my runs. Within two weeks of upping my training, my VO2 max ticked up to 42. Then, just two weeks later, it hit 43.
The biggest change? Intensity. Training with Ashley forced me to push harder, especially during our early morning runs. On our first run together, I spent nearly 15 minutes in zone 5. Just a few weeks later, I was only in that zone for about 35 seconds.
My body had clearly adapted to the cardio load. Intensity seems to be a much greater driver for me than frequency, as even when I’ve experimented with running daily for a week, I saw no major changes.
Another shift was my appetite: running more often was leaving me much hungrier so I had to pay greater attention to how I was fueling. I also noticed my heart rate variability (HRV) had declined, which makes sense in response to added strain on the body, but it’s a pattern I’ll be watching over the long-term.
The power of a training partner
Running with Ashley didn’t just motivate me; it changed my pace entirely. Running with a fitter, faster partner challenged me in ways solo runs never did. I had to keep up, and that meant working in zones I rarely touched on my own.
Running outside at 5:30 a.m. with a phone flashlight wasn’t something I would have done alone. But those efforts added up quickly: I got better at “compromise running,” pushing through fatigue after strength intervals, just like I’ll have to do in my HYROX race.
The difference in my cardiovascular conditioning is unmistakable.
Why even prioritize VO2 max?
Cardiovascular health is not just about exercise performance—it’s a critical marker of both lifespan and healthspan.
VO2 max is the maximum amount of oxygen your body can use during intense exercise, reflecting how efficiently your heart, lungs, and muscles work together.
Higher VO2 max is strongly linked to lower risk of mortality and cardiovascular disease. In one study2 of more than 120,000 adults, individuals with the highest aerobic fitness had the lowest risk of death, and another study found VO2 max was a more efficient lever for reducing cardiovascular disease risk and blood pressure3 than general physical activity.
Yet another large meta-analysis4 reported that higher cardiorespiratory fitness was consistently associated with lower death rates from all causes, including cardiovascular events, across diverse populations.
Beyond all that, improving VO2 max is also linked to blood sugar regulation5 and better cognitive health and brain structure.
So while I’m all-in on strength training, I’m also keeping the importance of a heart-pumping cardio session in mind with my own weekly routines.
I couldn’t help but wonder…
While I was excited about my results, my experience sparked questions. Why did time in Zones 4 and 5 move the needle so quickly? Is this the best approach for women in midlife?
I asked Kristen Holmes, Ph.D., Global Head of Human Performance at WHOOP, to help me fill in the gaps.
“Zones 4 and 5, roughly 80 to 100% of max heart rate, stimulate the systems that drive VO2 max: cardiac output, capillary density, and mitochondrial function. Structured intervals here, especially when combined with a strong aerobic base, are the most effective lever for increasing VO2 max,” Holmes explained.
She also noted that this type of training develops the body’s ability to tolerate lactate and other anaerobic byproducts, which helps athletes sustain harder efforts for longer periods. One likely reason I was able to adapt quickly to my more challenging runs with Ashley.
Holmes had some other helpful insights for framing how I train at this stage of life. “A woman in her mid-40s doesn’t have some completely different zone 4/5 training requirement versus her mid-30s self, but she may need to pay closer attention to recovery, overall volume, and supporting muscle mass as part of a holistic program. Age doesn’t change the type of stimulus needed to improve VO2 max, but it does change things like recovery pacing and the relative ease with which your body adapts."
That explains my dip in HRV and encourages me to lean into rest days.
I was also extra curious why I fell into the top 1% VO2 max ranking on WHOOP for my age group, but other tables showed different results. Holmes explained it this way, “WHOOP percentiles are based on data from WHOOP members around the world. By contrast, external charts like those from ACSM, the FRIEND registry, or other VO2 max databases are built from research or lab-tested samples.” I do like knowing that, compared to real people (not athletes in a lab), I’m at the top of my game.
My takeaways
I’m not training for a PR, and I plan for HYROX to be a one-and-done goal. I’m doing this because I want a baseline level of cardio health that sustains me through life’s demands as a busy mom and CEO. I really do enjoy strength work, but cardio has reentered my life as a joyful, energizing force. I love running outside, enjoying nature, and feeling centered in my body.
Here’s what helped me the most:
- Train with intensity. Zone 4 and 5 work, when done safely and strategically, can accelerate fitness gains. After reaching a higher VO2 max level, I’ve been able to keep it stable while staying in lower zones more often.
- Get a partner. Running with someone faster made a measurable difference in how hard I pushed.
- Track and listen. Wearables aren’t perfect, but they offer useful benchmarks. I saw trends that allowed me to understand the inner results of my outer work.
- Creatine support. Even with less strength work, my muscle mass held steady, possibly thanks to my daily 12 to 15 grams of creatine.
I’ll never be the person sprinting on a treadmill for fun, but I do plan to keep running toward a fitter future while checking a HYROX competition off this year’s goals.
