🟠 Moderate Evidence
Age-related muscle loss, or sarcopenia, has long been attributed primarily to declining muscle mass. However, new research published in the Journal of Cachexia, Sarcopenia and Muscle reveals that the neural system controlling muscle—not muscle tissue itself—is the critical factor differentiating frailty from strength in older adults. The findings suggest that preserving motoneuron function through exercise may be as important as building muscle.
Key takeaways
- Motoneuron excitability, not muscle mass alone, determines strength capacity in aging
- Older adults with sarcopenia show reduced persistent inward currents (PICs), indicating weaker neural amplification of movement signals
- Master athletes retain higher motoneuron excitability and motor unit discharge rates even at advanced ages, demonstrating that decline is not inevitable
- Long-term resistance and high-intensity exercise preserve neural function alongside muscle, suggesting a dual mechanism of strength maintenance
Study at a Glance
| Source | Journal of Cachexia, Sarcopenia and Muscle |
| Study type | Comparative observational analysis |
| Population | Older adults: sarcopenic, nonsarcopenic, and master athletes |
| Key measure | Motoneuron intrinsic excitability, persistent inward currents (PICs), motor unit discharge rates |
| Published | 2025, DOI: 10.1002/jcsm.70126 |
Motoneuron Excitability Across Aging Phenotypes
Persistent inward currents (PICs) and motor unit discharge rates by phenotype, relative units
Source: Orssatto et al., Journal of Cachexia, Sarcopenia and Muscle, 2025 | Georgian Medical Journal News
Motoneuron Excitability, Not Muscle Mass Alone, Drives Strength
The neural architecture that controls muscle contraction determines how powerfully and how long muscle fibers can fire, according to research led by researchers including Dr. David Scott and Dr. Roger M. Daly at the Monash University Institute for Physical Activity and Nutrition. The study compared three aging phenotypes—sarcopenic older adults, nonsarcopenic older adults, and master athletes—and measured intrinsic motoneuron excitability, including persistent inward currents (PICs) and motor unit discharge rates. The findings indicate that older adults with sarcopenia display significantly reduced persistent inward currents, which represent weaker neural amplification of motor commands from the central nervous system to the muscles.
This neural deficit explains why some older adults remain strong while others, despite maintaining reasonable muscle mass, become functionally weak. The motoneuron sets the ceiling for force production—no amount of muscle can generate more force than the neural signal driving it allows.
Master Athletes Preserve Neural Function With Age
A striking contrast emerges when examining master athletes—older individuals who maintain regular high-intensity and resistance training. According to the Journal of Cachexia, Sarcopenia and Muscle study, master athletes retain significantly higher motoneuron excitability, stronger persistent inward currents, and higher motor unit discharge rates compared to age-matched sedentary older adults, even when chronological age is advanced.
This finding challenges the notion that aging inevitably causes neural decline. Rather, it suggests that physical activity patterns determine whether the nervous system degrades. The data imply that inactivity, not chronological age itself, is the primary driver of motoneuron dysfunction in aging.
Intrinsic motoneuron excitability differentiates sarcopenic, nonsarcopenic, and athletic aging phenotypes, suggesting that strength in older age is fundamentally a neural trait before it is a muscular one.
— Orssatto LBR et al., Journal of Cachexia, Sarcopenia and Muscle (2025)
Long-Term Exercise Protects Both Muscle and the Nervous System
The implication of these findings extends beyond muscle physiology. Long-term resistance training and high-intensity movement appear to preserve motoneuron function itself—not simply by enlarging muscle fibers, but by maintaining the neural drive that activates them. This dual protective mechanism means that exercise offers a two-pronged defense against age-related weakness: it preserves muscle tissue and protects the nervous system controlling that tissue.
For older adults seeking to maintain strength and function, this suggests that the type and consistency of exercise matter. High-intensity and resistance-based activities appear more effective at maintaining motoneuron excitability than sedentary or light activity alone.
Reframing Sarcopenia as a Neural Problem
Sarcopenia—age-related muscle loss and weakness—has traditionally been understood as primarily a muscular disorder. This research repositions it as partly a problem of neural signal degradation. Lower motoneuron excitability correlates directly with poorer physical performance, strength, and functional capacity, independent of muscle volume alone.
This reframing has practical consequences for how aging and weakness are approached clinically. Rather than focusing exclusively on muscle-building interventions, clinicians might consider that preserving nervous system function is equally critical. This aligns with emerging evidence in gerontology and exercise physiology that emphasizes the integration of neural and muscular systems in maintaining functional capacity with age.
What this means
Frequently asked questions
Is motoneuron excitability the same as muscle strength?
No. Motoneuron excitability is the neural capacity to drive muscle contraction. It sets the ceiling for strength, but muscle quality, fiber type, and coordination also contribute. Low motoneuron excitability guarantees weakness; high excitability creates the potential for strength only if muscle is adequately developed and coordinated.
Can someone build muscle without improving motoneuron excitability?
Partially. Muscle can be enlarged through resistance training, but functional strength gains are limited if motoneuron excitability remains low. The study suggests that high-intensity and varied-intensity exercise is more effective at preserving neural function than low-intensity muscle building alone.
Is it too late to preserve motoneuron function in very old age?
The data from master athletes—some of whom compete in their 70s and 80s—suggest that consistent training throughout life maintains neural function. The critical factor appears to be sustained activity, not age per se. However, research on the reversibility of neural decline in sedentary very old adults remains limited.
The findings published in the Journal of Cachexia, Sarcopenia and Muscle represent a paradigm shift in understanding age-related weakness. By identifying motoneuron excitability as a critical determinant of strength that can be preserved with exercise, the research offers a mechanistic basis for why some older adults maintain power and function while others decline. The message is clear: protecting the nervous system through consistent physical training may be as important as, if not more important than, muscle building alone in the quest to maintain strength and independence with age.
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Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD. Spotted an error? Contact the editorial team.
