Cardiorespiratory fitness (CRF) refers to the efficiency of the heart, lungs, and muscles in using oxygen during physical activity. The best measure of CRF is VO₂ max, the maximum amount of oxygen the body can utilize during exercise. Higher VO₂ max scores are linked to less chronic disease and longer, healthier lives.
In this blog we will cover:
- The connection between CRF and longevity
- How to test VO₂ max
- What factors influence VO₂ max
- How to improve VO₂ max
- The role of physical therapy in optimizing your VO₂ max
How Does CRF Impact Longevity?
How Does CRF Impact Longevity?
A study of over 122,000 people found that higher levels of CRF significantly reduced all-cause mortality—in other words, individuals with lower CRF scores had a higher risk of early death.
To assess CRF, the study used METs (metabolic equivalents), measured through a standardized exercise treadmill test rather than direct VO₂ max testing. VO₂ max is considered the gold standard for measuring CRF, but it is expensive and impractical for large-scale studies. Instead, METs provide a reliable estimate of CRF based on performance during graded treadmill protocols.
The study grouped individuals into five fitness levels based on their treadmill test performance:
- Low: Bottom 25%
- Below Average: 25-49 percentile
- Above Average: 50-74 percentile
- High: 75-97.6 percentile
- Elite CRF: Top 2.4%
Researchers then analyzed how CRF levels correlated with all-cause mortality risk compared to other known risk factors.
How Low CRF Increases Mortality Risk Compared to Other Health Factors
Compared to individuals with higher CRF, having low CRF was a stronger predictor of early death than many well-known health risks:
Traditional Risk Factors
- Smoking: 41% increased risk
- Coronary Artery Disease (CAD): 29% increased risk
- Diabetes: 40% increased risk
- Hypertension: 21% increased risk
CRF Levels Compared to Low CRF
- Elite: 5x lower risk
- High: 3.9x lower risk
- Above Average: 2.75x lower risk
- Below Average: 1.95x lower risk
This study reinforces that CRF is one of the strongest predictors of longevity. Improving fitness—even by moving from a low CRF category to a moderate level—can significantly reduce the risk of premature death.
How VO₂ Max Testing Measures CRF
VO₂ max is typically measured in a lab setting using a treadmill or cycle ergometer while wearing a mask that analyzes oxygen intake and carbon dioxide output. This test gradually increases intensity until exhaustion, providing the most accurate measure of maximal oxygen uptake. Many sports performance centers and medical clinics offer VO₂ max testing, but it can be expensive and requires specialized equipment.
At Home Testing
For those who want an accessible alternative, the 1.5-mile run test is a well-validated method for estimating VO₂ max. The test involves running 1.5 miles as fast as possible on a flat surface while recording total time. VO₂ max can then be estimated using a specific formula.
Key Factors that Influence VO₂ Max
Several key physiological factors influence VO₂ max. The items below directly contribute to improving and are the primary drivers of VO₂ max:
- Stroke Volume – The amount of blood the heart pumps per heartbeat.
- Mitochondrial & Capillary Density – The ability of muscles to utilize and transport oxygen.
- Hemoglobin & Red Blood Cell Count – The oxygen-carrying capacity of the blood.
The following factors don’t raise VO₂ max directly but impact performance. If they’re suboptimal, your muscles may burn out before you can fully utilize your VO₂ max.
- Lactate Threshold & Buffering Capacity – The ability to sustain high-intensity efforts before local fatigue.
- Movement Economy & Efficiency – How efficiently the body moves in a sustained pattern.
How to Improve VO₂ Max with HIIT and Long Slow Distance (LSD) Training
VO₂ max can be improved through a combination of high-intensity interval training (HIIT) and long slow distance (LSD) training, both of which challenge the cardiovascular system in different ways. HIIT improves stroke volume and oxygen delivery, while LSD training builds aerobic efficiency and endurance over time. Below are several examples of how to train each item. Note that this is not all encompassing, there are many ways to train each system.
Stroke Volume
- HIIT – Four-minute high-intensity efforts (90-95% max HR), four-minute recovery, repeat four times.
- LSD – 45-90 min continuous endurance work at moderate intensity (Zone 2).
Mitochondrial & Capillary Density
- LSD – 45-90 min Zone 2
- Threshold Training – Two 20-minute efforts at 85-90% max HR
Hemoglobin & Red Blood Cell Count
- LSD – 45-90 min Zone 2
- Iron Supplementation – If deficient, supplementation may support hemoglobin production for oxygen delivery.
- Altitude Training – Live high, train low to stimulate EPO and red blood cell production.
A combination of endurance training and HIIT ensures sustained improvements in VO₂ max. For the average person, starting with one HIIT session and two sessions of moderate sustained cardio per week is a good start.
How Physical Therapy Can Help Improve CRF & VO₂ Max
Jumping into the intricacies of improving your CRF can be overwhelming, but there is where your Physical Therapist (PT) can help. Your Physical Therapist can help you with:
Customized Training Plans
- Personalized Progressions – A PT can assess your current fitness level and create a structured plan that gradually improves VO₂ max without risking overtraining.
- Frequency & Intensity Guidelines – Knowing how often to train and at what intensity can make a big difference.
Training Modifications for Injuries & Limitations
- Low-Impact Alternatives – Running is one of the best ways to improve VO₂ max, but it’s not for everyone. A PT can suggest alternatives like cycling, rowing, swimming, or elliptical training to build aerobic capacity while reducing joint stress.
- Rehabilitation-Focused Adjustments – If you’re recovering from an injury, a PT can modify workouts to maintain cardiovascular fitness while protecting the affected area.
- Preventing Overuse Injuries – A PT can identify early signs of overuse and adjust your training before it leads to pain or dysfunction.
Addressing Limiting Factors
- Mobility & Flexibility – Restrictions in joint movement can reduce efficiency in activities like running or cycling. A PT can incorporate mobility drills to improve range of motion.
- Pain & Stiffness Management – If discomfort or chronic stiffness is interfering with your training, a PT can provide manual therapy, targeted exercises, and movement corrections to help.
- Strength & Muscle Imbalances – Weakness in key muscle groups can make it harder to train effectively. A PT can guide strength work to support better endurance and performance.
Boost Your VO₂ Max for Better Health and Longevity with Physical Therapy
VO₂ max is one of the strongest indicators of long-term health and longevity. By incorporating the right mix of training, you can boost endurance, improve overall fitness, and lower your risk of early death. Don’t let injuries, poor training plans, or inefficiency hold you back. Book a visit with a Physical Therapist today to get started.