Estimating biological age, how old the body truly is physiologically, has become a central theme in longevity science and preventive medicine. While molecular biomarkers such as DNA methylation clocks and blood-based composites are frequently discussed, evidence increasingly points to functional capacity, particularly in cardiorespiratory, musculoskeletal, and neuromotor domains as a more direct and actionable insight into the ageing process.
VO₂max: A Powerful Predictor of Survival
Cardiorespiratory fitness (CRF), measured via VO₂max, is one of the strongest independent predictors of all-cause mortality.
- In a cohort of 122,007 adults, each 1 estimated metabolic equivalents (MET) increase in CRF was linked to a 12% reduction in mortality (Mandsager et al., JAMA Netw Open, 2018).
- The highest fitness quintile had a fivefold lower mortality risk than the least fit, with no observed ceiling effect.
Strength and Neuromotor Function
Other performance metrics also show strong, independent associations with ageing and survival:
- Grip strength – In the PURE study (Leong et al., Lancet, 2015; N=139,691), each 5 kg decrement was associated with a 16% increased risk of all-cause mortality.
- Single-leg balance (eyes closed) – Inability to maintain posture for 10 s in midlife predicted higher mortality risk (Araújo et al., BJSM, 2022).
- Push-up capacity – In a 10-year study of male firefighters, those performing >40 push-ups had a 96% lower incidence of cardiovascular events than those doing <10 (Yang et al., JAMA Netw Open, 2019).
These tests integrate neuromuscular, cardiovascular, and metabolic performance—unlike single biomarkers that typically reflect isolated biological pathways.
Evidence-Based Functional Testing
At STILL, we prioritise validated, repeatable measures of functional capacity in our biological age testing, including:
- VO₂max testing
- Grip strength
- Single-leg balance (eyes closed)
- Maximal push-up endurance
This approach reflects ageing at the functional system level, where meaningful differences in healthspan and lifespan emerge. Whilst DNA methylation clocks and biochemical composite testing offer promising insights into biological ageing, current evidence suggests:
- Their associations with functional outcomes (mobility, strength, VO₂max) are modest to moderate at best.
- Their sensitivity to lifestyle interventions remains under investigation and often lag behind changes in functional capacity
Thus, while valuable in research and long-term monitoring, they may be less useful to inform individualised diet, exercise and lifestyle interventions.
At STILL. we continue to prioritise functional testing as primary indicators of biological age due to their strong predictive value.
If you can run, lift, balance, and recover like someone 20 years younger, that’s a powerful indicator of true biological youth.
If you’re curious where your biological age really stands, we’d love to show you!