Cardio Performance & Cardio Fitness Guide

Understand the science behind your cardiopulmonary data and uncover the meaning behind every breath and heartbeat.

What Is Cardio Performance?

In PeakWatch, we introduce Cardio Performance as a concept to evaluate your cardiopulmonary output during a single workout. To better understand its difference from VO₂ Max, imagine your body as a sports car:

• VO₂ Max = Engine Displacement (e.g., 3.0T):
  It represents the theoretical upper limit of your physical capacity. This is a relatively stable long-term indicator that does not change easily.

• Peak VO₂ = Current RPM during the workout:
  It reflects how high the engine revs during this particular session, showing how much potential you tapped into for that workout.

How to Interpret Cardio Performance?

• Low values:
  Like cruising with a light tap on the gas. This indicates aerobic endurance training with moderate intensity—good for building base endurance or recovery.

• Values near the upper limit:
  Like full-throttle acceleration. This indicates high-intensity, lactate-tolerance training.

• Values above the upper limit:
  Like a tuned engine breaking past its previous performance ceiling. Congratulations! This often means your cardiopulmonary capacity has improved, and your VO₂ Max may soon update.

What Is Cardio Fitness?

Cardio fitness refers to the body’s ability to intake, transport, and utilize oxygen to generate energy during continuous aerobic activities such as running, swimming, or cycling. It is a core indicator of overall health and athletic performance.

Research shows that higher VO₂ Max is associated with lower cardiovascular disease risk, longer life expectancy, and better athletic performance.

How Is Cardio Fitness Measured?

VO₂ Max is the gold standard for evaluating cardio fitness. It represents the maximum amount of oxygen the body can utilize during maximal exercise.
Higher values indicate stronger cardiopulmonary function—like a bigger engine.

How to Obtain VO₂ Max

Laboratory gold standard:
In a sports science lab, athletes wear a mask for gas analysis and perform an incremental treadmill test to exhaustion. Oxygen intake and output are measured directly for accurate results.

Apple Watch estimates VO₂ Max based on the relationship between heart rate and pace during exercise.

Although Apple does not disclose the exact process, based on PeakWatch’s experience and the scientific principles behind VO₂ Max estimation, you may follow this guideline:

Workout protocol:
Perform continuous exercise for more than 20 minutes, maintaining a steady intensity (typically around 70% of your max heart rate, or steady workload on flat terrain).
If these conditions are met, the algorithm can estimate VO₂ Max based on your heart-rate–pace relationship.

VO₂ Max & Athletic Performance

VO₂ Max is the foundation of athletic success.
According to research by world-renowned Professor Michael J. Joyner: athletes in running, cycling, triathlon, and similar endurance sports require high VO₂ Max to win at the elite level. Olympic marathon champions typically have VO₂ Max values above 70 ml/kg/min, roughly twice that of the average person (30–40 ml/kg/min).

Joyner, M. J., & Coyle, E. F. (2008). Endurance exercise performance: The physiology of champions. The Journal of Physiology, 586(1), 35–44. https://doi.org/10.1113/jphysiol.2007.143834

VO₂ Max, Health, and Longevity

Beyond athletic performance, VO₂ Max (cardiorespiratory fitness) is one of the strongest independent predictors of all-cause mortality—more significant than smoking, hypertension, or high cholesterol.
The American Heart Association (AHA) recommends adding cardiorespiratory fitness as the “fifth vital sign” alongside blood pressure, temperature, and others.

Research consistently shows that individuals with higher cardio fitness have significantly lower mortality risk and longer “healthspan.”

Why Does the Value Fluctuate or Decrease?

VO₂ Max is usually stable, but can fluctuate short-term or decline long-term due to:

• Inconsistent training effort (most common for Apple Watch users):
  If you perform mostly easy runs for a period, the heart-rate/pace ratio may change or fail to stimulate your cardiopulmonary system.
  The estimated value may drop temporarily—like a blade that needs sharpening, not replacement.

• Overtraining:
  Insufficient recovery stresses the autonomic nervous system, elevating heart rate and lowering the estimate.

• Undertraining:
  Stopping aerobic training for 2+ weeks can cause real physiological decline.

• Other factors:
  Age, heat, humidity, and altitude can all reduce VO₂ Max.

Strategies to Improve VO₂ Max

To expand your body’s “engine,” you must challenge your comfort zone and deliver stronger stimuli to the cardiopulmonary system.

• High-Intensity Interval Training (HIIT):
  The most efficient way to improve VO₂ Max.
  Example: sprint hard for 2–3 minutes, jog for 2 minutes, repeat 4–6 sets.
  Near-maximal stress pushes your limits effectively.

Reference

American College of Sports Medicine, Gary Liguori, Yuri Feito, Charles Fountaine和Brad Roy, 编. ACSM’s guidelines for exercise testing and prescription. Eleventh edition. Wolters Kluwer, 2021年.

• Tempo Run:
  Run at a “comfortably hard” pace (you can talk, but not fluently) for 20–40 minutes.
  This raises your lactate threshold and improves performance near VO₂ Max.

• Long Slow Distance (LSD):
  Although low in intensity, long-duration sessions build capillary density and mitochondria—your aerobic foundation.

• Weight loss:
  VO₂ Max is often expressed in ml/kg/min.
  With oxygen consumption constant, reducing body weight (the denominator) increases the value.