Cardiorespiratory fitness
Cardiorespiratory fitness
Cardiorespiratory fitness (CRF) describes the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity. It is commonly quantified by maximal oxygen uptake (VO2max) and is a robust predictor of cardiovascular health and all-cause mortality.
Why it matters
- Higher CRF is associated with lower risk of cardiovascular disease, stroke, type 2 diabetes and premature death.
- CRF correlates with improved cognitive function, better mood, improved sleep and physical independence with age.
How it's measured
- VO2max: gold-standard measurement obtained during graded exercise testing with gas analysis (treadmill or cycle ergometer).
- Field estimates and submaximal tests (walk tests, step tests, predictive equations) are often used in clinical and community settings when CPET is not available.
How to improve CRF
- Regular aerobic (cardio) exercise increases VO2max and CRF. Typical public-health guidance (150 min/week moderate or 75 min/week vigorous) is a practical target.
- High-intensity interval training (HIIT) reliably improves CRF in less time than longer steady-state programmes for many populations; however, progression and medical screening are important for people with chronic disease.
Practical notes for writers
- Use CRF as a concrete, measurable concept when describing a character's stamina, endurance or recovery time.
- Sensory cues to imply higher CRF: controlled breathing under exertion, faster recovery of heart rate after sprinting, easy conversational pace during long activity, minimal post-exertion soreness.
- Low CRF can be portrayed through breathlessness at low effort, lingering fatigue or long recovery periods—useful for character contrast across life stages or illness.