Longevity depends on systems, not just mass

Healthy aging requires more than maintaining muscle mass; it demands systemic energetic efficiency. Researchers now argue that sarcopenia, the age-related decline in muscle, is better understood as a breakdown in how the body supplies and uses energy (Built to Move, Born to Heal). While muscle mass is a common metric, it fails to capture functional decline because it ignores how nerves recruit fibers and how mitochondria convert fuel into ATP, the cellular energy currency (Built to Move, Born to Heal). Studies show that interventions increasing lean body mass, such as testosterone or myostatin antibodies, often fail to improve physical performance in older adults. Instead, true fitness relies on metabolic flexibility, the ability of muscle to switch between burning fat and glucose depending on demand. When this coordination fails, people first experience fatigue and slow recovery after exertion, which serves as a warning sign long before strength tests show a decline.

“Your future does not have to be a smaller version of your past. It can be a different chapter, shaped by the knowledge you have gained.”

Human health

Cardiovascular health and sleep are the primary pillars of a long life, often outweighing diet and exercise in predictive power. A study using county-level data found that insufficient sleep, defined as less than seven hours per night, had a stronger association with lower life expectancy than physical inactivity or educational level (Intelsense). Only smoking and, in some models, obesity and diabetes ranked higher in their negative impact. Cardiovascular health also requires monitoring beyond how you feel, as masked hypertension can lead to functional decline. For the brain, hearing loss is a major modifiable risk factor; data from over 60,000 adults showed that those using hearing aids had significantly lower all-cause and cardiovascular mortality than those with untreated hearing loss (Forever Young). Prioritizing these foundational systems is more effective than chasing individual anti-aging trends.

Functional longevity is best assessed by your ability to move independently, such as standing up from the floor without assistance. A study of over 4,000 adults found that a simple floor-rising test predicted survival more accurately than most standard medical checkups (Paulina Cee). Those who required hands or knees to stand had six times the risk of dying from heart disease compared to those who performed the movement perfectly. To improve this, you must train both ends of your aerobic fitness and maintain strength. A balanced weekly routine includes one to two sessions of easy aerobic work, one session of harder intervals, and two to three full-body strength sessions (Ashley’s Substack, Ashley’s Substack). This approach builds the necessary base for energy metabolism while providing the high-intensity stimulus needed to improve cardiovascular capacity. Age does not dictate your fitness, as evidenced by athletes who improve their VO2 max and power well into their second century.