The research team set out to compare how three fundamental properties of the neuromuscular system — mass, force, and power — track against age, and whether those trajectories differ between men and women. Muscle mass was quantified using dual-energy X-ray absorptiometry, the gold-standard imaging technique that distinguishes lean tissue from fat and bone, yielding the appendicular skeletal muscle mass index that underpins most sarcopenia diagnoses. Muscle force was assessed in two ways: handgrip dynamometry, the familiar squeeze test performed in clinics worldwide, and maximal isometric contraction of the knee extensors, which captures the peak force the quadriceps can produce against an immovable resistance. Power, the product of force and velocity, was measured through isokinetic dynamometry — a motorized apparatus that holds limb movement at fixed angular speeds, allowing researchers to separate the torque a muscle generates from the speed at which it can generate it — and through sit-to-stand testing, which converts the mechanics of rising from a chair into a direct wattage estimate of lower-limb explosive capability.

The statistical verdict was unambiguous. In regression models, lower-limb muscle power showed a standardized association with age of β = −0.433, substantially stronger than the association for muscle force (β = −0.303) and dramatically stronger than that for muscle mass (β = −0.119), with all three reaching statistical significance at p < 0.001. In practical terms, for every additional year of age, power declined at a rate far out of proportion to the modest shrinkage of the muscle itself. This dissociation is physiologically revealing. Muscle mass is a structural quantity; force reflects the contractile capacity of that structure under static conditions; but power demands that the neuromuscular system recruit motor units rapidly, coordinate them precisely, and sustain high firing frequencies. It is the most computationally demanding task a muscle performs, and it appears to be the first to falter.

The study’s authors are careful about one crucial limitation: because the design is cross-sectional, comparing different people of different ages at a single moment, it cannot establish whether power actually begins to decline earlier in life than force or mass. The steeper age gradient for power is consistent with that hypothesis, and it aligns with a growing body of evidence that has led some researchers to coin the term powerpenia for the age-related loss of muscular power, but longitudinal confirmation remains outstanding. What the cross-sectional data do establish is that at any given moment in the aging process, the gap between what a person’s muscles can do slowly and what they can do quickly widens in ways that conventional strength testing entirely misses.

Perhaps the most clinically consequential result concerns timing. When the researchers stratified their sample by decade, the strongest negative associations with age clustered between 71 and 80 years — the window in which power, force, and mass all deteriorated most sharply. After age 80, the pattern changed strikingly: fewer significant associations survived, and handgrip strength was the only measure that continued to show a clear relationship with age. This plateau effect after 80 has several possible interpretations. It may reflect a survivor effect, in which individuals who reach very old age with intact neuromuscular function represent a biologically selected group. It may also reflect a floor effect, in which so much function has already been lost by the ninth decade that the remaining variance is compressed. Either way, the finding suggests that the eighth decade of life is the critical battleground for interventions aimed at preserving mobility and independence.

Sex differences added a second layer of complexity. For several measured variables, the age associations were stronger in men than in women, with this pattern appearing most consistently for lower-limb power. Yet when the team ran age-stratified analyses, these sex-by-age interactions were not systematically reproduced across all subgroups, leaving the picture deliberately nuanced rather than definitive. The authors interpret this cautiously: sex may genuinely contribute to variability in how muscle power declines with age, but the evidence is not yet strong enough to declare that men and women age neuromuscularly along fundamentally different trajectories. What the finding does challenge is the assumption that any single definition or threshold of muscle power decline can be applied universally across sexes — a question the researchers explicitly flag as warranting further confirmation.

The implications for clinical practice are difficult to overstate. Current diagnostic frameworks for sarcopenia — the age-related loss of muscle mass and function — lean heavily on grip strength, gait speed, and DXA-derived mass. If power is the variable most tightly coupled to functional deterioration, then a patient whose grip strength and muscle mass look acceptable on paper may nonetheless be well along a trajectory toward mobility impairment, simply because their capacity for rapid force production has collapsed. Sit-to-stand power testing is particularly attractive in this regard: it requires no expensive dynamometer, translates directly into a task every older adult performs dozens of times daily, and its reference values have already been linked to adverse outcomes such as falls and hospitalization in independent studies. The French team’s results, generated under a protocol approved by the French Ethics Committee and prospectively registered as NCT05343286, give that argument fresh quantitative weight.

There is also a mechanistic story worth telling. The preferential loss of power over force is thought to reflect the selective vulnerability of type II fast-twitch muscle fibers, which are recruited precisely during high-velocity movements and are known to atrophy faster with age than slow-twitch type I fibers. Add to this the well-documented age-related slowing of motor unit firing rates, the decline in neural drive from the central nervous system, and the stiffening of tendons that changes how force is transmitted to bone, and a coherent picture emerges: aging dismantles the speed machinery of movement before it dismantles the strength machinery. Resistance training programs that emphasize velocity — lifting loads explosively rather than slowly — have shown promise in targeting exactly this deficit, and the new findings suggest such approaches deserve priority in preventive strategies for adults entering their seventies.

The study is not without caveats beyond its cross-sectional design. The sample, while large for a single-center investigation of this kind, was drawn from community-dwelling adults in southeastern France, and the oldest participants were necessarily survivors of their birth cohort. The measurement battery, though comprehensive, captures lower-limb function at fixed laboratory conditions rather than in the variable environments of daily life. And the authors themselves note that the sex-interaction results were inconsistent across analytical approaches, meaning any clinical tailoring by sex would be premature. Still, the core message survives these qualifications intact: of all the ways we currently quantify the aging muscle, power is the one that tracks most closely with the loss of the capabilities that actually matter — getting up, getting going, and staying independent.

As populations across the developed world age, the search for early biomarkers of physical decline has become something of a holy grail in geriatric research. This study makes a strong case that the grail has been sitting in plain sight, measurable with a chair, a stopwatch, and a bit of physics. Muscle power, the researchers conclude, should be treated as a key biomarker of neuromuscular aging and incorporated systematically into strategies designed to preserve independence in older adults. For the 319 volunteers who powered this study — some of them in their tenth decade — and for the billions who will follow them into old age, the fastest-moving target may also be the most important one to hit.

Subject of Research: Age-related decline in lower-extremity muscle mass, force, and power in older adults and associated sex differences

Article Title: Age-associated differences in lower-extremity muscle mass, force, and power in older adults: a cross-sectional analysis of sex differences

Article References: Piche, E., Zory, R., Michel, E., Guerin, O., Colson, S. S., & Chorin, F. (2026). Age-associated differences in lower-extremity muscle mass, force, and power in older adults: a cross-sectional analysis of sex differences. BMC Geriatrics. https://doi.org/10.1186/s12877-026-08274-0

Image Credits: AI Generated

DOI: 10.1186/s12877-026-08274-0

Keywords: aging, sarcopenia, muscle power, muscle strength, neuromuscular decline, older adults, sit-to-stand, DXA, isokinetic dynamometry, sex differences, powerpenia, mobility