Fitness Data: What Really Matters

The bell rings. Your heart jumps. You’ve been waiting for this.

You open the box, peel back the packaging, and finally strap it on. Your brand new fitness tracker. You sync it with the app, ready to track every heartbeat and effort.

Then it happens. The numbers flood in. Heart rate. VO2 max. Recovery time. Training load. So much data, but what actually matters?

Which numbers will make you faster, stronger, better, and which are just noise?

In this edition:

• We explain what VO2 max is and why it matters for all athletes, not just endurance sports.

• We break down why fitness trackers aren’t always accurate and how to test your real training zones.

• We share simple ways to boost your VO2 max so you can perform longer and better.

— Paco Raven, Editor & Founder

How the engine of your body works

You have just completed a great 3-hour session on the bike. Your legs are heavy, but it’s the kind of fatigue that feels like progress.

Today’s training was all about endurance, staying in zone 2, and building that engine. Back home on the couch, you check your fitness tracker. The numbers pop up: heart rate zones, maxHR, VO2 max. You pause.

You know these numbers matter, but which ones tell you if you’re improving? Should you be focusing on raising your VO2 max? Keeping your heart rate lower at the same power output?

Your max heart rate is estimated using a simple formula like 220 minus your age. Only your maximal heart rate is individual. Factors like genetics, fitness level, and fatigue all play a role, meaning the tracker’s estimate isn’t always spot on.

VO2 max, your body’s ability to use oxygen during exercise, is another key number your tracker provides.

While it gives a rough idea, the most accurate way to measure VO2 max is through a lab test, with a mask and gas analysis. Not exactly practical for every athlete.

So, if these numbers aren’t 100% precise, how do you use them to improve your performance?

When it comes to heart rate and VO2 max, these two metrics provide insight into how your body responds to exercise and how efficiently it uses oxygen under stress.

Your max heart rate is the highest number your heart can hit before it’s working at full capacity. This isn’t just a random number. It's a key indicator of how hard your body can work before fatigue sets in. But remember, it is only an estimate.

Now, VO2 max is something more complicated. It's the maximum volume of oxygen your body can use per minute, per kilogram of body weight.

The higher your VO2 max, the better your heart and lungs are at delivering oxygen to your muscles. This translates directly to your endurance. Whether you’re riding your bike for hours or chasing down a breakaway in basketball.

While fitness trackers provide a guess of your VO2 max, there’s a catch: accuracy.

This doesn’t mean the data on your tracker is useless…

It’s about tracking trends. Seeing how your numbers change as you train. If you see improvements over time, you know you’re on the right track.

Here’s the kicker: understanding these numbers isn’t just about cycling, or running, or swimming. It’s universal to all sports, and here’s why. When you have a better understanding of your heart rate and VO2 max, you’re optimizing your body for performance in all sports.

Take a team sport like soccer. A player’s ability to maintain a high-intensity sprint for a few minutes, then recover and repeat that effort multiple times, hinges on aerobic capacity.

If you improve your VO2 max, you’re increasing your ability to perform during those high-speed moments without fatiguing as quickly. It's not just about being fast for one sprint; it’s about sustaining that speed during a game.

In a sport like basketball, heart rate zones come into play. Players who can manage their heart rate during the game can push themselves harder in the fourth quarter when fatigue starts to kick in.

A lower resting heart rate, an indicator of good cardiovascular health, can also be a sign of improved endurance. This allows players to run longer without getting winded.

These numbers matter because performance isn’t just about the high-intensity moments. It’s about how well you can recover, maintain intensity, and perform consistently throughout your game.

From cycling to basketball, every athlete can benefit from understanding and improving their heart rate and VO2 max.

Neglecting heart rate and VO2 max training is like ignoring the foundation of your house. You might get by for a while, but eventually, the cracks will show. In sports, those cracks can be mental and physical burnout, slower recovery times, and fatigue that limits your ability to perform in the moments that matter.

Take football as an example: if your heart rate is running too high for too long, you’ll tire out in the middle of the second half, and that’s when your opponent takes advantage.

If you’re focusing only on strength or skill training and ignoring the aerobic side, you’re missing out on a huge part of the equation. It’s not just about lifting more weight or being faster for 30 seconds—what counts is your ability to keep going. Below is a tip on how to improve your foundation and how to check the accuracy of your tracker.

How to Boost Your VO2 Max (and Test It Right)

If you want to improve your VO2 max, you need to train at intensities that push your body to its limit. That means spending time near your max effort, but in a way that’s structured and repeatable.

How to Improve Your VO2 Max

• Interval Training – Short bursts of high-intensity work with controlled rest. Think 3-5 minutes at 90-95% effort, followed by equal or slightly shorter rest. Repeat 4-6 times.

• Longer Tempo Efforts – Sustained efforts just below max (80-90% effort) for 10-20 minutes. This helps build endurance and efficiency.

• Hill Sprints – Short, explosive efforts (20-30 seconds) with full recovery. Builds power and oxygen uptake capacity.

Test Your Training Zones: The MAS Test

To train in the right zones, you need accurate data. Your fitness tracker’s estimates aren’t always precise, so test it yourself.

MAS (Maximal Aerobic Speed) Test

• Warm up properly.

• Run as far as possible in 5 minutes.

• Divide the total distance by 300 (seconds) to get your MAS in m/s (or convert to km/h or mph).

• Use your MAS to set training zones:

  • 60-70% MAS → Easy endurance runs

  • 80-90% MAS → Threshold/tempo work

  • 100-120% MAS → High-intensity VO2 max training

Compare these with the zones your fitness tracker gives you. If they’re way off, adjust. The goal? Train smarter, not just harder.

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Thank you for reading.

Next Monday we are back with a new athlete portrait. This time we will feature an athlete that has shattered speed records as the fastest man alive.

Have a question of your own? We’d love to hear it! Just send it to [email protected], and you might see it featured here in a future edition.

And if you missed last month’s Q&A Edition on how you can get fast as a slow athlete, read it here.

Until next week,
Paco Raven, Editor & Founder
The Stoiclete

DISCLAIMER: None of the content provided in this newsletter constitutes medical, training, or performance advice. This newsletter is strictly educational and is not intended to be a substitute for professional guidance or personalized coaching. Please be mindful of your limitations and perform exercises at your own risk.