Fitness YouTuber Will Tennyson recently embarked on an ambitious 100-day experiment to improve one of the most critical health metrics most people ignore: VO2 max.
His mission? Compete against his brother to see who could make the biggest improvements through targeted training.
The stakes were personal, but the science behind it reveals something far more important for anyone interested in living longer and healthier.
Spoiler: the results were nothing short of remarkable.
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What Exactly Is VO2 Max and Why Should You Care?
VO2 max measures the maximum amount of oxygen your body can utilize during intense exercise. It’s essentially your cardiorespiratory fitness score—and according to longevity experts, it’s the single best predictor of lifespan available.
Testing requires pushing yourself to absolute maximum exertion while monitoring oxygen intake. No shortcuts, no half-efforts.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Having a high VO2 max is going to increase the length of your life and improve the quality of your life. To act in disregard of that is irresponsible.
Tennyson started with an impressive baseline score of 57.5, placing him in the top 2% for his age group. Anything above 44 would be considered “good” for someone his age, while scores above 54 land you in the top 5%.
His brother? An even more impressive 63.4.
The Science-Backed Training Protocol
Rather than guessing, Tennyson turned to Dr. Peter Attia’s book “Outlive” for evidence-based guidance. Attia, a renowned longevity expert, breaks down VO2 max training using a pyramid analogy.
Think about building a pyramid. The VO2 max is the height of the pyramid. If you want to build a really high pyramid, it also has to have a really wide base.
That wide base? Zone 2 training.
Zone 2: The Foundation of Endurance
Tennyson committed 80% of his aerobic training time to zone 2 work. This means exercising at 60-70% of maximum heart rate—an intensity where you can speak but wouldn’t necessarily want to maintain conversation.
Too easy to talk? You’re not pushing hard enough. Can’t speak at all? You’ve gone too hard.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
His preferred zone 2 method: swimming. Low impact, sustainable for extended periods, and something he genuinely enjoyed enough to maintain consistency.
Zone 5: The Brutal Peak Training
Zone 5 training operates at an exertion level so intense you can barely complete four minutes of effort. Think near-maximal intensity with minimal recovery between intervals.
Tennyson’s goal: three zone 2 sessions weekly plus one punishing zone 5 workout.
You have a little bit left in the tank but not much, and then you do that four times.
The Early Struggles: When Technology Lies
Several weeks into training, Tennyson hit a concerning realization. His supposed zone 2 workouts felt conversational, yet his Apple Watch showed heart rates far exceeding zone 2 limits.
Was his training wrong, or was his watch unreliable?
During a zone 5 session, he compared his Apple Watch against a dedicated chest strap heart rate monitor. The results confirmed his worst fear—the devices matched almost perfectly, meaning his zone 2 efforts had been too intense all along.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
The Treadmill Solution
Most people lack sufficient conditioning to run outdoors while staying in zone 2. Tennyson discovered what many trainers already know: controlled environments work better for beginners.
His solution involved setting treadmills to brisk walking paces, then increasing incline until reaching proper zone 2 heart rate (142 beats per minute in his case). Boring? Absolutely. Effective? Undeniably.
Why This Matters Beyond Athletic Performance
Tennyson’s motivation extended far beyond winning sibling bragging rights. Turning 30 triggered serious health concerns—significant weight gain, poor blood work results, and increasing injuries.
He explains the difference between lifespan (total years alive) and healthspan (years spent in good health). Most people’s healthspan declines decades before death, creating extended periods of suboptimal living.
VO2 max training offered a proven method to extend both metrics simultaneously.
Making Zone 5 Bearable
Sprint intervals proved miserable. Tennyson tested multiple approaches to find tolerable zone 5 methods:
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
- Stair running: Brutal on the thighs
- Jump rope: Possibly worse than stairs
- Full-court basketball: The winner
One-on-one basketball provided proper intensity while maintaining engagement. Though the gameplay became “some of the ugliest basketball” he’d ever played, his conditioning improvements were undeniable.
That was by far the most enjoyable zone 5 session I have had this entire challenge. Not only that, but I genuinely feel like my conditioning has improved drastically throughout this process.
The Moment of Truth: Retest Results
After 100 days of disciplined training, both brothers returned for final VO2 max testing.
His brother’s score unexpectedly dropped to 60.8 from the initial 63.4. Tennyson began worrying his own training might have failed to produce results.
Then came his numbers: 62.9.
A four-point jump in just 100 days, catapulting him into the top percentile and—most importantly—two points higher than his brother.
The Bigger Picture on Longevity
Dr. Attia’s principles proved their worth. VO2 max improvements don’t happen by accident—they require consistent, properly structured training over extended periods.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
VO2 max is the single greatest predictor of lifespan of any measurable number we have. The VO2 max measurement is really an integration of work that you have done.
The encouraging news? Anyone can reach the top 25% for their age and sex with proper training. Genetics play a role in absolute ceiling, but dedication determines where you land within your potential range.
Key Takeaways for Your Own Training
- Prioritize zone 2 work: Make up roughly 80% of cardiovascular training
- Don’t skip zone 5: One weekly high-intensity session builds peak capacity
- Verify your heart rate zones: Consumer wearables can be accurate, but validate occasionally
- Use controlled environments initially: Treadmills and bikes help maintain proper intensity
- Find enjoyable zone 5 options: Sustainability beats optimization if you actually stick with it
- Track consistently: Progress happens gradually, requiring weeks or months to manifest
Tennyson’s transformation extended beyond numbers on a test. His conditioning improved dramatically, allowing him to push harder and longer than before. More importantly, he felt his entire health trajectory shift back toward optimal.
Improving VO2 max isn’t about athletic glory—it’s about adding quality years to your life and ensuring those years are spent in vibrant health rather than gradual decline.
