Buck Institute perspective positions energy as a measurable signal of healthspan decline – linking biology, behavior and early intervention.
For too long, we have treated the creeping erosion of our vitality – that nagging sense that effort costs more and recovery takes longer – as a subjective, dismissible complaint. It’s the classic “I’m just getting older” narrative that gets brushed aside during a standard checkup because the blood panels look “just fine.” Dr Noa Rappaport’s new keynote for the Buck Institute’s Healthspan Horizons flips this script. Rather than just validating the experience, she is framing energy as a coherent and quantifiable signal – a biological precursor that shifts across our internal systems long before the clinical tests start tipping into the red zone [1].
This isn’t a hunt for a single, magic biomarker. Instead, “Energy Span” captures the entire, integrated machinery of our vitality: mitochondrial output, metabolic flexibility, circadian rhythm and autonomic regulation, all operating in concert. It is, as Rappaport points out in Energy Span: An Early Signal of Healthspan Decline, one of the earliest dimensions of health to slide, yet paradoxically, it remains the least rigorously measured [1]. We are witnessing a biological drift that predates overt disease by years, a subtle fading that marks the true beginning of the descent – assuming, of course, we are paying enough attention to read the signal.
Longevity.Technology: If the longevity field has spent the past decade searching for earlier and subtler signals of decline, then “energy” – long dismissed as irredeemably subjective – may be staging a quiet return as something far more quantifiable and, crucially, actionable. The notion of an “Energy Span” reframes fatigue not as an inconvenient symptom but as an early warning system – a kind of biological whisper that heralds the clinical shout – reflecting coordinated shifts across mitochondrial function, metabolic flexibility, autonomic balance and more. It is an appealing idea, not least because it bridges the persistent gap between how patients actually experience aging and how medicine chooses to measure it; after all, few people present to their physician complaining of “subclinical mitochondrial inefficiency,” but many will recognize the creeping sense that effort costs more and recovery delivers less.
The challenge, as ever, lies in translation – turning this diffuse, systems-level signal into something robust enough to guide intervention without collapsing into yet another layer of wellness abstraction. Wearables, continuous monitoring and AI-driven longitudinal models promise to make energy legible as a trajectory rather than a moment, shifting the emphasis from population thresholds to personal baselines, but the question remains whether this emerging signal can move beyond lifestyle optimization into the realm of clinically meaningful endpoints. If it can, Energy Span may offer a rare convergence – an early, intuitive metric that is both biologically grounded and societally relevant, with implications not only for how we age, but for how we work, recover and ultimately design systems that either sustain or erode human vitality.
From symptom to system signal
Energy, in this framing, is neither a vague feeling nor a diagnostic label – instead, it is an emergent property of interacting biological systems. Mitochondria sit at the center, governing ATP production and metabolic signaling, but they are operating within a wider network that includes hormonal rhythms, inflammatory tone and neural energy demand. No single measure captures this complexity – instead, Energy Span reflects how well these systems coordinate under real-world conditions. This systems view aligns with a broader shift in geroscience away from single-pathway explanations toward network-level understanding. Declines in energy, the report suggests, often represent a loss of adaptive capacity rather than overt pathology; “effort costs more than it used to, recovery takes longer, focus fades earlier in the day,” writes Dr Rappaport, describing a pattern that many will recognise long before laboratory values shift.
Drift, disruption and decline
Crucially, the trajectory of Energy Span is not linear. The keynote introduces a dual model of gradual “drift” punctuated by more abrupt “cliff events” – episodes such as illness, psychological stress or hormonal transition that accelerate decline. These inflection points can produce lasting changes in mitochondrial function and systemic resilience, sometimes with incomplete recovery.
Such a model resonates with emerging data on aging as a dynamic process, shaped by both cumulative wear and discrete insults. It also raises a practical implication: if early deviations can be detected, there may be a window in which intervention remains tractable. Timing matters. Earlier still.
Measuring the intangible
For decades, the difficulty has been measurement. Energy has traditionally sat outside the domain of quantification, relegated to subjective reporting. That boundary is now shifting. Advances in wearable technology and continuous monitoring are making it possible to track proxies of energy regulation – heart rate variability as a marker of autonomic balance, glucose dynamics as a reflection of metabolic stability, sleep architecture as a proxy for recovery.
We’ve reached a point where consumer tech is actually good enough to hold up under scrutiny. It’s not just about counting steps anymore. Think of digital phenotyping – letting your sensors and phone silently aggregate the messy, real-world data of your daily life – as the missing piece. When you pair that constant stream with machine learning, the math changes. You stop chasing isolated snapshots and start watching a trajectory. You can see the patterns of your own resilience, the subtle declines, the way you actually recover. It turns the noise of living into a map you can finally read.
This is a different paradigm and it’s one that is less episodic and more continuous… less population-based and more personal. Within-person change becomes the signal of interest.
Intervention in familiar territory
Despite the keynote’s systems framing, the interventions proposed remain strikingly conventional [1]. Exercise, particularly when combining endurance and resistance modalities, is presented as a primary driver of mitochondrial health. Sleep, with attention to both duration and architecture, regulates circadian and endocrine rhythms. Nutrition, through glycemic control and metabolic flexibility, shapes energy stability. Stress regulation, often indexed via HRV, influences recovery capacity.
There is little novelty in these components individually. The shift lies in their integration – and in the attempt to link them to a measurable, longitudinal outcome. Energy becomes not simply something to be “boosted,” but something to be trained, stabilized and tracked.
Beyond the individual
Rappaport shifts the lens to the structural, where the misalignment of our work schedules with human physiology becomes undeniable. We aren’t just looking at individual health choices; we’re looking at a structural erosion of vitality – a societal design that treats human recovery as a luxury rather than a requisite. You can’t ‘biohack’ your way out of an environment fundamentally built to drain you. After all, many of us are essentially living in a state of perpetual social jetlag, where the demands of the clock are at odds with our internal metabolic and hormonal rhythms. Once you start measuring energy properly, you realize this isn’t a private, personal struggle – it’s a public health issue. Aggregating this data forces a reckoning with how we design our workplaces, because an aging society simply cannot function on chronic fatigue.
A signal still taking shape
Whether Energy Span will emerge as a widely adopted metric remains to be seen. Its appeal lies in its intuitiveness – everyone understands energy – and in its potential to bridge molecular biology and lived experience. As with most things, translating that appeal into clinical utility will require rigorous validation, standardization and, perhaps most challenging, integration into existing healthcare frameworks.
For now, Energy Span sits somewhere between concept and tool; promising, plausible, not yet proven. Still, the direction is clear. Biology whispers first. The question is whether we are ready to listen.
READ MORE: Healthspan Horizons aims to map healthy aging
Photograph of Dr Noa Rappaport courtesy of The Buck Institute for Research on Aging
[1] https://healthspanhorizons.org/energy-span-an-early-signal-of-healthspan-decline/
