Physiologically Speaking

This interview was originally published on September 24, 2024.

David Roche is a decorated trail runner, coach, and co-founder of SWAP Running. He's a two-time national champion and a three-time Team USA member, and he recently set the course record at the Leadville 100 trail run with a time of 15 hours, 26 minutes, 34 seconds.

David and his wife, Megan Roche, M.D., offer coaching that blends science, training theory, and a philosophy of joy and long-term growth for all athletes. Megan just launched a website—Huzzah—“to empower female endurance athletes by providing accessible sports science knowledge and fostering a love for sport through content, insights, and scholarships, with a focus on supporting overall health, education, and competitive edge.”

I’ve become a bit obsessed with how David thinks about running and how invested he and Megan are in reading and implementing the science of training and racing. So I needed to nerd out with him on some topics.

In this interview, I picked David’s mind about his scientific approach to training, and we detail several of the training practices he used in his buildup to the race, including:

Sodium bicarbonate

Downhill running

High-carb fueling

Super shoes

Post-exercise exogenous ketones

Heat training/hot water immersion

Caffeine

Heart rate zones

And more!

Relevant links

For more details about David and SWAP Running, visit their About Us page

Follow David on X @MountainRoche

Watch the documentary about David’s record: Leadville 100 Ultramarathon & David Roche's Run for The Impossible Record and the other kick-ass videos he posts about training on his YouTube channel.

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Welcome to the recap of my first live subscriber Q&A! It was a lot of fun connecting with you all and answering your thoughtful questions. In this post, I’ll walk through the key topics we discussed, including my marathon training approach, supplement routine, fueling strategies, and more.

Thank you Zach Bitter, Esther VanderMark, dr_cois, Barbell Mentality, and many others for tuning into my live video! Join me for my next live video in the app.

Table of contents

* My Training Philosophy: Running Less, Biking More

* My Supplement Routine (and Philosophy)

* Fueling for Long Runs and Marathons: How I Changed My Approach

* Live Q&A Questions

* Have you experienced low blood sugar or bonking during runs?

* What’s your advice for returning to running after an injury?

* Does cycling help build your aerobic base for running?

* What are your thoughts on nitrate supplements like beetroot juice?

* What’s your approach to warming up before races and workouts?

* Do you lift after long runs or interval workouts?

* What do you think about concerns over eating high amounts of carbs during marathons?

* How does race-day nutrition affect your recovery afterward?

* If I’m a slower marathoner, should I train differently than you?

* What’s your approach to returning to training after illness?

* Is cycling useful even if your running mileage isn’t maxed out yet?

* How does L-glutamine help with gut health?

My Training Philosophy: Running Less, Biking More

One of the most common questions I get is about how I structure my training week, particularly how I balance running and cycling. For my Boston Marathon build, I chose to run five days per week and ride the bike two days per week. This approach stems from years of battling injuries, particularly bone stress injuries. Every time I tried running six or seven days per week—even at moderate mileage—I seemed to get hurt.

To avoid that, I started squeezing more mileage into fewer running days, reaching 75 to 85 miles per week while running just five days. On the two non-running days, I cycled for 90 minutes to two and a half hours using Zwift. Cycling allowed me to maintain a high aerobic load without the musculoskeletal strain of running. Having two full days without running each week seemed to give my body the time it needed to recover and regenerate. I felt fresher on all my runs and stayed injury-free throughout the training block, which hadn't been the case in past training cycles.

My Supplement Routine (and Philosophy)

Supplements are something I get asked about all the time, and during the Q&A, I walked through my current supplement stack. I take a fairly extensive range of supplements, but my general philosophy is simple: if you have the discretionary income and a curiosity to experiment, supplements can be worth exploring.

Each morning, I start with a whey protein shake, usually mixing 20 to 30 grams of whey protein with almond milk. I add a greens and probiotic powder, and I take L-glutamine daily, mostly for gut health and immune support. Creatine monohydrate is also a daily staple, as is an omega-3 supplement, iron (to correct low ferritin), and vitamin D3. I also occasionally use ashwagandha to support stress adaptation. Supplements aren’t magic, but they can help support an already solid foundation of training, nutrition, and sleep.

Fueling for Long Runs and Marathons: How I Changed My Approach

Fueling during training runs and races has been one of the biggest shifts in my approach over the past year. Previously, I barely fueled during runs, often going fasted. Now, for most morning runs, I eat a small snack about 30 to 45 minutes beforehand. During long runs or runs over 90 minutes, I take energy gels every 30 to 40 minutes. Science in Sport Beta Fuel gels have been my favorite because of their high carbohydrate content and easy consistency.

Proper fueling has made a noticeable difference not just in performance but also in recovery. By ending long workouts with a smaller energy deficit, my next-day performance has been consistently better.

Live Q&A Questions

Have you experienced low blood sugar or bonking during runs?

Yes, especially after I started eating before runs. I experienced mild reactive hypoglycemia about three miles into runs, which I confirmed using a continuous glucose monitor. It turned out the timing of my pre-run snack was causing a dip in blood sugar. Adjusting the timing—either eating earlier (45–60 minutes before) or just minutes before starting—helped eliminate the issue.

What’s your advice for returning to running after an injury?

I recommend the walk-run method, regardless of experience level. Coming back slowly with a run-walk protocol reduces injury risk and helps you rebuild fitness without overwhelming your musculoskeletal system. Even elite runners use this strategy when returning from time off.

Does cycling help build your aerobic base for running?

Absolutely. Cycling has been a key part of maintaining and building my aerobic fitness while sparing my body from the pounding of running. Two days of cycling per week allowed me to maintain a high training load without increasing injury risk during my Boston build.

What are your thoughts on nitrate supplements like beetroot juice?

Nitrate supplements have strong evidence for enhancing performance, especially in clinical or less-trained populations. For highly trained athletes, the benefits are likely smaller but still potentially meaningful. They are safe and can also support cardiovascular health, so if you're curious, they are worth trying.

What’s your approach to warming up before races and workouts?

I’m a big believer in long, extensive warmups—typically 4–6 miles of easy running with some race-pace surges. You want to feel warm and ready when the race starts, not spend the first few miles getting into rhythm. A proper warmup can make a big difference in early race pacing and overall performance.

Do you lift after long runs or interval workouts?

Yes, but strategically. I usually lift after my Sunday long runs because it’s easier to stack hard efforts on the same day and allow easier recovery days afterward. I do my best to get into the gym immediately after the run while I’m still warm, even though it's not always easy.

What do you think about concerns over eating high amounts of carbs during marathons?

I think it's mostly fear-mongering. Race-day fueling is not the same as everyday eating. Consuming 80 grams of carbohydrates per hour during a marathon is performance-enhancing and supports recovery. There’s no strong evidence that race-day carb intake leads to metabolic disease when your daily nutrition is solid.

How does race-day nutrition affect your recovery afterward?

Proper fueling during the race has a huge impact on how you feel in the days afterward. After Boston, although I still had muscle soreness, my recovery was far smoother compared to previous marathons. I believe fueling adequately during the race played a major role in that.

If I’m a slower marathoner (around four hours), should I train differently than you?

Not drastically. You don’t need to run more hours per week, but your long runs should probably be longer in duration compared to mine. I would recommend aiming for three to three and a half hour long runs, even if your weekly mileage stays relatively modest.

What’s your approach to returning to training after illness?

Slow and steady. I focus first on building back volume at low intensity and delay introducing intensity until I feel fully recovered. Low-intensity walking, biking, or easy running can be good first steps before resuming hard efforts.

Is cycling useful even if your running mileage isn’t maxed out yet?

Definitely. Cycling can be a supplement to running even if you’re not at your maximum running volume. It’s an excellent tool to add more aerobic training stress without the same injury risks as running.

How does L-glutamine help with gut health?

L-glutamine may help support the gut lining and reduce gastrointestinal permeability, especially important during periods of heavy training or exercising in the heat. I’ve added it recently to help support digestion during intense marathon training blocks.

Final Thoughts

This Q&A was a blast. I’m so grateful for everyone who tuned in, asked thoughtful questions, and stayed engaged throughout the session. Going forward, I’m considering doing more Q&A sessions, maybe focused more narrowly on specific topics like fueling strategies, supplements, or injury prevention.

If you have any feedback or ideas for future Q&As, I’d love to hear them. Thanks again for being part of this awesome community. I'll see you next time—whether it’s here, on X, or maybe even in real life!

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

This talk dives into the science of cardiovascular fitness, its profound impact on longevity, and how to train smarter without overcomplicating it. I delivered it at the Golden Age Health Summit on March 15, 2025, in Austin, TX.

Key Takeaways:

Why VO2 max is your longevity superpower

How aerobic fitness declines with age—and what to do about it

A simplified 3-zone training model: Easy (50-70% HR max), Moderate (70-85% HR max), and Hard (85-100% HR max)

Practical tips to train effectively without overcomplicating it

Part I explores why VO2 max—your body’s maximal oxygen consumption—is a critical marker of health and performance. Learn how VO2 max integrates multiple physiological systems (lungs, heart, blood vessels, mitochondria, and more) and why it’s a stronger predictor of longevity than traditional risk factors like cholesterol or BMI. With compelling data, he reveals how boosting your VO2 max by just 3.5 ml/kg/min can slash all-cause mortality risk by 11%, and how top-tier aerobic fitness cuts that risk by 45%. But fitness fades with age—this talk breaks down why VO2 max declines (thanks to the Fick equation!) and how building a "fitness investment account" now can keep you above the frailty threshold later in life.

Part 2 demystifies heart rate percentages, lactate thresholds, and complex zone models with a practical 3-zone approach—Easy, Moderate, and Hard—showing you how to improve your VO2 max and cardiovascular health without obsessing over metrics. From the foundational benefits of the Easy Zone (think base endurance and mitochondrial efficiency) to the ceiling-raising power of the Hard Zone (hello, VO2 max gains!), this section offers actionable insights for everyone, whether you’re a beginner or a seasoned athlete. Plus, discover why wearables aren’t perfect, how individual differences matter, and why effort—not exact percentages—drives adaptation.

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

In this episode, I sit down with Brian Heiderscheit , a professor in the Department of Orthopedics and Rehabilitation at the University of Wisconsin-Madison and director of the Badger Athletic Performance program. Brian also collaborates with Springbok Analytics, a company specializing in advanced full-body MRI scans. Together, we discuss my recent experience with a Springbok scan, how MRI data is revolutionizing athlete performance analysis, and actionable insights for reducing injury risks and improving training outcomes.

Key Topics Covered:

* Introduction to Springbok Analytics: Overview of their advanced MRI technology and its application in research and athletic training.

* Brian’s Background: Insights into his role at UW-Madison and collaborations with Springbok Analytics on research initiatives, including a grant with the NFL.

* My MRI Experience:

* The scanning process, which takes 10-15 minutes.

* Analysis of over 74 muscles rendered in 3D.

* Comparison to population norms and evaluation of muscle size, asymmetry, and fat infiltration.

* Key Findings from My Scan:

* Notable asymmetry in muscle size between the left and right legs.

* Larger left-side muscles, likely due to targeted rehabilitation post-injury. My left semitendinosus and other hamstrings were larger, while the right biceps femoris was bigger by about 10%.

* Smaller right-side plantar flexors (e.g., soleus, gastroc) compared to the left, with a 7% size difference in the soleus. These findings align with subjective feelings of less power on the right side during runs.

* My quadriceps showed strong development, particularly on the left, with right-side muscles slightly smaller.

* Fat infiltration analysis, showing low levels typical of an active individual, with slight increases in the quadratus lumborum.

* Actionable Insights for Athletes:

* Targeted strength training to address imbalances, particularly focusing on the right-side soleus and quadriceps.

* The potential value of pairing MRI data with gait analysis for a comprehensive view of biomechanics.

* Using follow-up scans to evaluate the effectiveness of training programs.

* The Role of MRI in Longitudinal Tracking:

* Establishing a baseline for future comparison.

* Monitoring recovery from injury or changes in training plans.

* Brian’s Recommendations:

* Adjust training to improve right-side strength, especially in the soleus and hamstrings.

* Consider integrating gait analysis to identify asymmetries during running.

Resources Mentioned:

* Springbok Analytics: springbokanalytics.com

* Badger Athletic Performance Program: BAP at UW-Madison

* Brian Hederscheidt’s Google Scholar Profile for published research

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings!

For today’s post, I’m sharing (with permission) my appearance on the Life in Stride podcast, hosted by a few good friends and outstanding runners.

Here’s the episode description and links to their content. Please give them a follow/subscribe!

On this episode, the boys had on special guest Brady Holmer! The best way to describe Brady would be an expert in the science of running and human performance. We covered several interesting tops as they relate to runners such as creatine use, VO2 max, proper race weight, and more!

Brady also just ran a 2:26 marathon at Indianapolis, and he told he just ran 4 days a week training for it! We get into his training block some and learned how he dropped a 10 minute PR in just his second marathon.

Enjoy!

FOLLOW BRADY

X: https://x.com/B_Holmer

Strava: https://strava.app.link/a1EYBlCC6Ob

FOLLOW US ON STRAVA

Chris: https://www.strava.com/athletes/29985667

Scotty: https://www.strava.com/athletes/98633526

Danny: https://www.strava.com/athletes/23504210

CHECK OUT OUR INSTAGRAM: https://www.instagram.com/lifeinstridepodcast/

CHECK OUT OUR YOUTUBE CHANNEL: https://youtube.com/@LifeInStridePodcast?si=icd7XfQ4HMmuBRyX

EPISODE RECOMMENDATIONS

Floberg Runs Interview

Sobriety and Running 2:42 in the Marathon

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings!

Happy Black Friday to those who celebrate.

Are you looking for a new health, fitness, or nutrition product for yourself or to give as a gift to family and friends? Here are a few Black Friday/Cyber Monday deals from brands I’m affiliated with and use myself.

Save up to 60% on an Examine.com membership

Get 30% off of your Ketone-IQ purchase

30% off of FSTFUEL electrolytes with the code BRADY30 at checkout

30% off of Presleep sleep supplement with the code BRADY30 at checkout

10% off of a Pedal Industries Race Day bag with the code INF-BRADY at checkout

Get Decaf Drip coffee

Additionally, for a limited time, you can snag a yearly subscription to Physiologically Speaking for $39.99 (originally $50) or purchase a subscription for a friend or family member as a gift.

Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.

Today, instead of a new study, I’m sharing the video of a podcast appearance I made on The Mind Muscle Connection with Jeff Hoehn.

We talk about:

* Research

* Endurance exercise performance

* Sleep

* Training & nutrition

* Supplements

* Cardio

* Recovery

* Calorie intake

* Metabolism

* Aerobic exercise training

* Exercise volume and intensity

* How to measure improvements in cardiovascular fitness

* My 7 rules for health

* And more!

*

Be sure to check out Jeff’s podcast, subscribe, and give him a follow on Instagram and X.

Thanks so much for subscribing. I’m grateful to every one of my audience members!

~Brady~

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings!

David Roche is a decorated trail runner, coach, and co-founder of SWAP Running. He's a two-time national champion and a three-time Team USA member, and he recently set the course record at the Leadville 100 trail run with a time of 15 hours, 26 minutes, 34 seconds.

David and his wife, Megan Roche, M.D., offer coaching that blends science, training theory, and a philosophy of joy and long-term growth for all athletes. Megan just launched a website—Huzzah—“to empower female endurance athletes by providing accessible sports science knowledge and fostering a love for sport through content, insights, and scholarships, with a focus on supporting overall health, education, and competitive edge.”

I’ve become a bit obsessed with how David thinks about running and how invested he and Megan are in reading and implementing the science of training and racing. So I needed to nerd out with him on some topics.

In this interview, I picked David’s mind about his scientific approach to training, and we detail several of the training practices he used in his buildup to the race, including:

Sodium bicarbonate

Downhill running

High-carb fueling

Super shoes

Post-exercise exogenous ketones

Heat training/hot water immersion

Caffeine

Heart rate zones

And more!

Relevant links

For more details about David and SWAP Running, visit their About Us page

Follow David on X @MountainRoche

Watch the documentary about David’s record: Leadville 100 Ultramarathon & David Roche's Run for The Impossible Record

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings friends!

In this interview, I sit down with Christina Smith, the Associate Director of Athlete Relations for the Enhanced Games.

Per the Enhanced Games website:

“The Enhanced Games are a celebration of the union of athletic excellence and scientific achievement.The Enhanced Movement believes in the medical and scientific process of elevating humanity to its full potential, through a community of committed athletes.”

Some are calling the Enhanced Games the “Enhanced Olympics” — but I think that this movement is more than just that. After attending numerous press conferences and doing this interview with Christina, I think that the Enhanced Games has the chance — if executed correctly — to change the way that we watch sports (and the way that athletes compete in them).

Due to a few issues with recording, the first 10 minutes of this interview are audio only. But the rest of the interview is video.

Enjoy!

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings!

Today’s interview is with Andrew Koutnik, Ph.D.

Andrew is a research scientist at Sansum Diabetes Research Institute, where he’s investigating metabolic therapies for health and disease. His mission is to optimize metabolic health and patient outcomes for people living with type 1 diabetes.

Andrew is unique because he himself has type 1 diabetes. This allows him to add a bit of personal touch and a lot of passion into the work he’s doing.

Andrew joins me to talk about a case study (two papers) that he and colleagues just published on the long-term safety and efficacy of the ketogenic diet for an individual with type 1 diabetes who had been using the ketogenic diet for more than 10 years (spoiler alert: it’s Andrew).

We talk about why the ketogenic diet is helpful for people with diabetes and then dive into the details of each study to explore how 10 years on the diet affected cardiovascular health risk factors and clinical biomarkers.

Andrew posted two great threads about the papers on X. You can check those out below. Make sure to give Andrew a follow as well while you’re there.

Part I: 10-Years longitudinal data on KETOGENIC DIET and Safety, Efficacy & Advanced Cardiovascular Physiology in a patient with HIGH RISK cardiovascular disease (Type 1 Diabetes)?

Part II: 10-Year Longitudinal Data On Ketogenic Diet Adverse Events, Bone Mineral Density, Thyroid Function, and Kidney Function

Here are the links to each paper:

Advanced Cardiovascular Physiology in an Individual with Type 1 Diabetes After 10-Year Ketogenic Diet

Efficacy and Safety of Long-term Ketogenic Diet Therapy in a Patient With Type 1 Diabetes

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe

Greetings!

Welcome to the Physiology Friday newsletter.

ICYMI

Check out my guest appearance on The Neuro Experience podcast with Louisa Nicola, where we talk about the science of V̇O2 max.

On Wednesday, I published a post about some of the most common myths about coffee and caffeine.

Details about the sponsors of this newsletter including Examine.com and my book “VO2 Max Essentials” can be found at the end of the post!

Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.

If you can fill the unforgiving minute

With sixty seconds’ worth of distance run,

Yours is the Earth and everything that’s in it,

And—which is more—you’ll be a Man, my son!

— Rudyard Kipling, If—

In my book “VO2 Max Essentials”, I make the case for why cardiorespiratory fitness should be considered the most important vital sign. Among all risk factors, V̇O2 max is the only one that’s a composite of multiple physiological systems, rather than a snapshot of health at one point in time or a single biomarker measured via a blood test.

Your maximal oxygen utilization capacity (V̇O2 max) represents the maximum integrated capacity of the pulmonary, cardiovascular, and muscular systems to uptake, transport, and utilize oxygen during whole-body, dynamic exercise. The function of your autonomic nervous system, your heart and blood vessels, your lungs, your muscles, and your mitochondria all influence your maximal aerobic capacity. It’s not just a strong heart that gives someone a high V̇O2 max. A strong body is a prerequisite.

This is, in my opinion, why a high V̇O2 max is so often associated with beneficial health outcomes. You won’t find someone with a high V̇O2 max who is in poor health, and often people with an extremely low V̇O2 max are in poor health.

Though it’s not routinely measured in clinical practice (yet), V̇O2 max has recently appeared on the radar of many healthcare professionals. People are becoming aware of the predictive power of cardiorespiratory fitness and are increasingly interested in how (and why) to improve it.

Over the last 20 years, evidence has emerged linking higher cardiorespiratory fitness to lower risks of all-cause mortality and other diseases. Thus, it’s about time we had a scoping review of the evidence, which brings us to today’s study.

The study, published in the British Journal of Sports Medicine was an overview of all previously published systematic reviews and meta-analyses on the relationship between V̇O2 max and an array of health outcomes.

The studies were eligible if they included adults with or without health conditions and measured cardiorespiratory fitness using a maximal graded exercise test, a maximal or submaximal exercise test with a prediction equation (i.e., without direct measures of gas exchange), or a non-exercise prediction equation. When pooling the data and examining the outcomes, the authors compared the groups with the highest cardiorespiratory fitness to those with the lowest cardiorespiratory fitness.

Overall, a total of 26 studies with over 20.9 million participants from 199 different cohorts were included in the review. 

Eight of the included studies examined the association between V̇O2 max and death (mortality) from all causes, cardiovascular disease, sudden cardiac events, all cancers, and lung cancer. 

Compared to low cardiorespiratory fitness, having high cardiorespiratory fitness was associated with a 41% to 53% lower risk for premature mortality. Furthermore, each 1 metabolic equivalent (MET) increase in cardiorespiratory fitness (1 MET is equal to an increase in V̇O2 max of 3.5 mL/kg/min) reduced the risk of premature mortality by 7% (all cancers) to 51% (sudden cardiac mortality).

A notable limitation for mortality outcomes was the large disparity in male vs. female participants — more than 1.8 million male participants were included in the studies while only 180,000 females were included.

Having a higher cardiorespiratory fitness was also associated with a lower risk of developing hypertension, heart failure, stroke, atrial fibrillation dementia, kidney disease, depression, and type 2 diabetes. Specifically, the risk of a new onset condition was 37% (hypertension) to 69% (heart failure) lower when comparing high vs. low cardiorespiratory fitness.

For every 1 MET increase in fitness, the risk of developing a new chronic health condition was reduced by 3% (stroke) to 18% (heart failure).

Similar to mortality outcomes, a majority of the evidence was from male populations, although two studies investigated the effects in female-only cohorts. In these groups, high cardiorespiratory fitness was found to be more protective against stroke and type 2 diabetes among females compared to males. Among men, a higher cardiorespiratory fitness was not associated with prostate cancer risk.

What about individuals who already have a chronic health condition? Does having a high cardiorespiratory fitness protect them from early death or adverse events?

This seems to be the case. A lower risk of premature death or adverse events was observed for people with a higher vs. a lower cardiorespiratory fitness and ranged from 19% (for an adverse event among adults with pulmonary hypertension) to 73% (for cardiovascular mortality among people living with cardiovascular disease).

Based on this comprehensive review, not only does having a higher cardiorespiratory fitness reduce the risk of premature death from all causes, but it also reduces the risk of developing a new condition or dying from a condition you already have. 

Put another way, low fitness is a consistent and important risk factor for early death and chronic disease.

If this isn’t enough evidence that cardiorespiratory fitness should be considered a vital sign, I don’t know what is. The authors even suggest that a minimum clinically important difference or MCID for V̇O2 max be established as 1 MET (3.5 mL/kg/min). Exercise trials and other interventions can be deemed “effective” if the participants achieve this degree of fitness improvement. It’s a goal you should strive for in your own exercise regimen.

Because this was merely an overview of published literature, we unfortunately don’t have specific numbers for the “high” and “low” V̇O2 max groups. But I did a quick scan of the included studies on mortality risk to find a quick estimate.

Low cardiorespiratory fitness is somewhere in the range of less than 8—9.5 METs or a V̇O2 max of less than 28—33 mL/kg/min. High cardiorespiratory fitness is about 11—13.7 METs or more, or a V̇O2 max of 38.5—48. If you’re below or near one of these categories, act accordingly.

The certainty (quality) of the evidence was also downgraded mostly due to a large variation in how the studies measured V̇O2 max and the large proportion of male participants. And, of course, the main limitation is that these associations (correlations) may not imply causation. 

One of the main criticisms of this literature is that, because nearly 50% of one’s V̇O2 max can be explained by genetics and is therefore unmodifiable, the association between cardiorespiratory fitness and healthspan/longevity may not represent an effect of a high fitness level per se, but rather, an underlying predisposition to health. Healthy people have a higher V̇O2 max, but they’re not healthy because of it.

I don’t buy this. To explain why, I’ll use the Bradford Hill criteria. 

The Bradford Hill criteria, also known as Hill’s criteria for causation, are a set of nine principles used to establish epidemiologic evidence of a causal relationship between a presumed cause and an observed effect. These criteria have been widely used in public health research and were proposed by the English epidemiologist Sir Austin Bradford Hill in 1965.

The nine criteria are:

* Strength (Effect Size)

A small association does not rule out causality, but a stronger association increases the likelihood of a causal effect.

* Consistency (Reproducibility)

Consistent findings across different studies, populations, and settings strengthen the evidence for causality.

* Specificity

A specific association between a factor and an effect suggests a higher probability of a causal relationship.

* Temporality

The cause must precede the effect in time

* Biological Gradient (Dose-Response Relationship)

Generally, greater exposure leads to a higher incidence of the effect.

* Plausibility

A plausible mechanism linking cause and effect enhances the evidence.

* Coherence

Consistency between epidemiological findings and laboratory evidence strengthens the likelihood of causality.

* Experiment

Experimental evidence can support causality.

* Analogy

Similarities between the observed association and other known causal relationships can provide additional support.

Now, let’s apply the Bradford Hill criteria to V̇O2 max.

* Strength of Association

Numerous studies consistently demonstrate a strong inverse relationship between cardiorespiratory fitness and mortality risk. Case in point: this review.

* Consistency of Effect

Research findings consistently support the link between fitness and health outcomes. Multiple studies across diverse populations consistently show that better fitness is associated with improved health and longevity. Again: see this review.

* Specificity

While cardiorespiratory fitness impacts overall health, it specifically reduces the risk of cardiovascular diseases, diabetes, and certain cancers.

* Temporality

The temporal relationship is well-established: higher fitness precedes better health outcomes. Individuals who maintain or improve their fitness levels over time experience reduced mortality risk.

* Dose-Response Relationship

A dose-response pattern exists: as cardiorespiratory fitness increases, mortality risk decreases.

* Plausibility

Mechanisms underlying this association include improved cardiovascular function, enhanced metabolic health, and reduced inflammation. We know that regular exercise improves heart health, insulin sensitivity, lipid profiles, and overall physiological function.

* Coherence

The association aligns with existing knowledge about exercise physiology and health.

* Experiment

Although we cannot perform a randomized controlled trial where we randomly assign people to have higher VO2 max, observational studies provide strong evidence.

* Analogy

Analogously, we can draw from other well-established causal relationships. For example, the association between smoking and lung cancer was initially based on observational studies, and later experimental evidence confirmed the causal link.

The evidence (and my personal biases) would indicate that improving fitness is a cause of better health. I explain why this may be the case in my book.

If you don’t know your V̇O2 max, I provide several methods to estimate V̇O2 max in my book, and for a limited time, I made this chapter open to everyone on my Substack. Feel free to look at some of the protocols and do some testing!

Regardless of your current fitness level, take comfort in knowing that improving your V̇O2 max by 1–3 METs (and reducing your risk of death and disease substantially) is very attainable with some dedicated aerobic exercise training.

Out of all of the risk factors, V̇O2 max is the one that’s most fun to improve. It might also be the most important.

Thanks for reading. I’ll see you next Friday.

~Brady~

The VO2 Max Essentials eBook is your comprehensive guide to aerobic fitness, how to improve it, and its importance for health, performance, and longevity. Get your copy today and use code SUBSTACK20 at checkout for a 20% discount. You can also grab the Kindle eBook, paperback, or hardcover version on Amazon.

Examine.com: Examine is the largest database of nutrition and supplement information on the internet.

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe