Non-VO2max Fitness Markers: Thinking Beyond VO2max

Approximate Read Time: 10 minutes

“Cardiorespiratory fitness is more than a single number; non-VO2max fitness markers offer a practical, multidimensional view of healthspan and performance for clinicians and athletes alike.”

The Gold Standard Trap

In the world of high-performance physical therapy and sports science, we often obsess over the “gold standard.” We chase the perfect MRI, the precise force plate data, and, when it comes to aerobic capacity, the elusive VO2max. While VO2max remains the benchmark for cardiorespiratory fitness, relying on it exclusively creates a significant blind spot.

It is expensive, requires maximal exertion that isn’t safe for every population, and it doesn’t tell the whole story. I have seen athletes with sky-high VO2max scores struggle with recovery, and I have seen general population clients with “average” numbers display incredible resilience.

This realization forces us to ask a better question: What else matters?

Recent evidence suggests that non-VO2max fitness markers such as resting heart rate, ventilatory thresholds, and peripheral oxygen extraction are not just “consolation prizes” for those who can’t afford a metabolic cart. They are powerful, independent predictors of both healthspan and athletic performance¹.

As we navigate the gray space between rehabilitation and performance, understanding these metrics allows us to build more robust, accessible, and data-driven plans for our athletes.

Resting Heart Rate: The Silent Sentinel

If VO2max is the size of your engine, resting heart rate (RHR) is your idle speed. It is one of the most accessible non-VO2max fitness markers.

The research is compelling: RHR is inversely associated with fitness and serves as a strong predictor of longevity and cardiovascular outcomes². Lower rates typically indicate better conditioning, reflecting a heart that is efficient, strong, and capable of maintaining homeostasis with minimal effort³.

Large-scale studies have demonstrated that this correlation holds true even after adjusting for confounding variables like body composition and physical activity levels⁴. For the clinician, this means RHR is more than a vital sign to check off at the start of a session; it is a longitudinal data point. A rising RHR in an athlete can signal under-recovery, impending illness, or detraining long before performance metrics drop. Conversely, a gradually lowering RHR is a tangible sign that your aerobic conditioning blocks are taking root.

Ventilatory Thresholds and Heart Rate Variability

Moving beyond the resting state, we must look at how the body manages stress during movement. This is where ventilatory thresholds (VT) and heart rate variability (HRV) come into play.

VO2max tells us the ceiling of aerobic power, but VT tells us about the usable floor. It marks the intensity at which metabolism shifts, lactate accumulates, and sustainability drops. Research highlights that ventilatory thresholds are strongly linked to aerobic capacity and endurance performance, often providing more practical training zones than maximal numbers⁵.

Similarly, HRV during exercise, specifically the rate of its decline—offers a window into the autonomic nervous system. It reflects the body’s ability to transition from parasympathetic dominance (rest and digest) to sympathetic drive (fight or flight)⁶.

For the rehab professional, these non-VO2max fitness markers are invaluable. They allow us to prescribe exercise intensity with precision without needing a mask and a treadmill test. If we can improve an athlete’s VT, we push back the point of fatigue, allowing them to operate at higher intensities for longer, a critical factor in return-to-play scenarios for sports like soccer or basketball⁷.

Peripheral Oxygen Extraction: The Local Hero

While the heart and lungs (central adaptations) get all the glory, the muscles (peripheral adaptations) are doing the heavy lifting. Peripheral oxygen extraction, often measured as muscle oxygen saturation (SmO2), reflects how efficiently your muscles pull oxygen out of the blood.

You can have a massive heart that pumps blood, but if your mitochondria or hemoglobin are not efficient enough to use that oxygen, performance stalls. This is a fantastic example of how peripheral adaptations may be the keystone variable, not improving global VO2 numbers.

Studies indicate that improvements in peripheral oxygen extraction are often the unsung heroes behind gains in aerobic performance, particularly following high-intensity interval training (HIIT)⁸. These adaptations are linked to increased mitochondrial content, capillary density, and nitric oxide bioavailability⁹.

In a rehab context, this validates the use of local muscular endurance work such as extensive isometrics. When we prescribe high-volume, low-load circuits or blood flow restriction training, we aren’t just building muscle size; we are upgrading the local metabolic machinery. We are improving the muscle’s ability to “drink” the oxygen the heart delivers.

Clinical Application: From Lab to Court

Understanding the science of non-VO2max fitness markers is useless if we cannot apply it. In my experience across professional sports, the integration of these metrics follows the 3P Framework: Principles, Process, and Plans.

Principles (The “Why”)

We believe that fitness is a buffer against injury. Therefore, we must assess it frequently and accurately. Since maximal testing is taxing and infrequent, submaximal markers like RHR and HRV become our daily compass. When I was working in Major League Soccer, we routinely would do a sub-max Yo-Yo Intermittent Recovery Test and evaluate Heart Rate Recovery (HRR) throughout the season.

Process (The “How”)

We don’t need a metabolic cart to track progress.

• Daily: Monitor RHR and morning HRV. A trend of rising RHR requires a conversation about load management or sleep hygiene.
• Weekly: Use submaximal field tests (like a standardized warm-up run) to monitor heart rate response to a fixed load. If the heart rate at the same speed drops over time, peripheral and central adaptations are occurring.
• Rehab: Early stage rehab often limits maximal exertion. Here, we focus on peripheral extraction through local muscular endurance (e.g., BFR or density circuits) to maintain metabolic fitness without stressing the injured joint.

Plans (The “What”)

• Assessment: Screen every athlete during intake to establish a baseline.
• Intervention: If RHR is high, prioritize Zone 2 aerobic development. If VT is low relative to sport demands, implement threshold intervals.
• Re-evaluation: Track these markers monthly. They should improve alongside your performance metrics.

By shifting our focus from a single “gold standard” number to a dashboard of non-VO2max fitness markers, we gain a higher-resolution picture of the athlete. We see the engine, the fuel lines, and the exhaust system all at once.

Conclusion: A Multidimensional View of Fitness

The reliance on VO2max as the sole arbiter of aerobic fitness is an incomplete picture in the world of high performance. In the world of everyday fitness – sure, this is a fantastic starting point. In its place, a more nuanced understanding is emerging, one that values efficiency, recovery, and metabolic flexibility.

Non-VO2max fitness markers like resting heart rate, ventilatory thresholds, and peripheral oxygen extraction offer us independent and collective insights. They are practical, scalable, and deeply relevant to the day-to-day reality of the human body.

For the clinician or coach, this is a call to not get lost in the longevity hype an Vo2max craze. We must look beyond the max effort test and start reading the subtle, daily signals the body sends us.

The Fab Five

1. Large-scale studies confirm RHR is inversely associated with fitness and independently predicts longevity, rivaling more complex metrics.
2. While markers like RHR are well-established, areas like CO2 tolerance and resting metabolic rate require further investigation to fully understand their independent predictive value.
3. Use heart rate recovery (HRR) after a standardized warm-up drill as a proxy for fitness. Faster recovery (dropping >12-15 bpm in the first minute) generally correlates with better aerobic conditioning.
4. Don’t just track your steps; track your resting heart rate trends. A consistent drop over weeks indicates your cardio routine is working, even if the scale hasn’t moved.
5. Deepening your understanding of these physiological markers is a core component of the Performance Therapy Mentorship, where we teach clinicians to navigate the data that drives elite performance.

Read More Like This

• Complete Guide to Staying Fit During Rehab
• Rethinking Fitness: Beyond Conditioning Alone
• General vs. Specific Adaptations: Conditioning Strategies for Return to Play

Related Podcasts

• The Role of Breath Work and Respiration in Pro Sports Physical Therapy ft. Andrew Hauser
• Tactical Periodization in Practice with David Tenney
• Load Management Redefined ft. Matt Tuttle

Trusted Partners

References

1. Gonzales, T., Jeon, J., Lindsay, T., Westgate, K., Perez-Pozuelo, I., Hollidge, S., Wijndaele, K., Rennie, K., Forouhi, N., Griffin, S., Wareham, N., & Brage, S. (2023). Resting heart rate is a population-level biomarker of cardiorespiratory fitness: The Fenland Study. PLOS ONE, 18.
2. Böhm, M., Reil, J., Deedwania, P., Kim, J., & Borer, J. (2015). Resting heart rate: risk indicator and emerging risk factor in cardiovascular disease. The American journal of medicine, 128(3), 219-28.
3. Mongin, D., Chabert, C., Extremera, M., Hue, O., Courvoisier, D., Carpena, P., & Galvan, P. (2021). Decrease of heart rate variability during exercise: An index of cardiorespiratory fitness. PLoS ONE, 17.
4. Mazaheri, R., Schmied, C., Niederseer, D., & Guazzi, M. (2021). Cardiopulmonary Exercise Test Parameters in Athletic Population: A Review. Journal of Clinical Medicine, 10.
5. Maufroy, E., Senterre, J., & Deboeck, G. (2025). Central versus peripheral adaptation to explain improvement in aerobic exercise capacity by moderate-intensity continuous training or high-intensity interval training. European Journal of Preventive Cardiology.
6. Stamatakis, E., Hamer, M., O’Donovan, G., Batty, G., & Kivimaki, M. (2013). A non-exercise testing method for estimating cardiorespiratory fitness: associations with all-cause and cardiovascular mortality in a pooled analysis of eight population-based cohorts. European heart journal, 34(10), 750-8.
7. Chaliki, K., Sharma, A., Sharma, A., Yee, C., Chaliki, H., & Reddy, S. (2025). Key Resting Echocardiographic Parameters for the Estimation of Exercise Parameters of Peak VO2, Heart Rate Recovery, and Ventilatory Efficiency. Journal of Clinical Medicine, 14.
8. Shushan, T., Lovell, R., McLaren, S., Buchheit, M., Iacono, A., Arguedas-Soley, A., & Norris, D. (2024). Assessing criterion and longitudinal validity of submaximal heart rate indices as measures of cardiorespiratory fitness: A preliminary study in football. Journal of science and medicine in sport.
9. Qiu, S., Cai, X., Sun, Z., Wu, T., & Schumann, U. (2021). Is estimated cardiorespiratory fitness an effective predictor for cardiovascular and all-cause mortality? A meta-analysis. Atherosclerosis, 330, 22-28.
10. Schumacher, B., Di, C., Bellettiere, J., LaMonte, M., Simonsick, E., Parada, H., Hooker, S., & LaCroix, A. (2022). Validation, Recalibration, and Predictive Accuracy of Published VO2max Prediction Equations for Adults Ages 50-96 Yr. Medicine & Science in Sports & Exercise, 55, 322-332.