Brief bouts of hard effort with easy recovery raise the body's peak ability to take in and use oxygen — among the strongest markers of how long people live. Lower blood pressure, better blood sugar handling, less abdominal fat, better mood and thinking follow, in far less time than gentler exercise. Injuries are common; stopping is the likeliest failure. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Maximal oxygen uptake | Above the 75th percentile for age and sex | Primary target; a strong survival predictor |
| Resting heart rate | 50–65 beats per minute | Falls as stroke volume rises; a cheap daily proxy |
| Heart rate variability | No universal target; 7-day trend vs own baseline | Earliest signal of excessive interval load |
| Blood pressure | 110–120 / 70–80 mmHg | Improved by training; contraindicated above 200/110 mmHg |
| HbA1c | 4.8–5.3% | Tracks the glycaemic benefit |
| Fasting insulin | 2–5 µIU/mL | More sensitive than glucose to the effect |
| High-sensitivity C-reactive protein | Below 1.0 mg/L | Tracks inflammation; flags unresolved stress |
| Apolipoprotein B | Below 80 mg/dL; below 60 at high cardiovascular risk | The lipid measure least distorted by exercise |
| Creatine kinase | 40–200 U/L at rest, 72 h after hard training | Detects excessive muscle breakdown |
| Estimated glomerular filtration rate | Above 90 mL/min/1.73 m² | The organ at risk if muscle breakdown occurs |
Cadence: Baseline before starting; fitness test and blood pressure at 12 weeks, then every 6–12 months; metabolic panel and inflammation marker at 3 months, then annually. Resting heart rate and heart rate variability tracked continuously by wearable.