Iterated Insights

Jared Edward Reser Ph.D.

Abstract

Chronic muscle hypertonicity and its downstream sequelae, including adaptive shortening, myofascial contracture, reduced range of motion, postural collapse, and diminished movement variability, are conventionally framed as pathological or degenerative phenomena. This article proposes an alternative interpretation: that these effects, considered in aggregate rather than individually, may constitute an evolutionarily conserved strategy for reducing whole-organism energy expenditure. While individual components of this syndrome carry local metabolic costs, their collective result is a structural reorganization of the musculoskeletal system that reduces dynamic muscle recruitment, offloads postural maintenance onto passive connective tissue, and constrains the organism to a lower-movement, lower-energy behavioral mode. The phylogenetic universality of this pattern across aging mammals is consistent with evolutionary conservation rather than coincidental degeneration. This is presented here as an explicit hypothesis, and will outline the logic of the selective argument, address major objections, and propose testable predictions intended to motivate empirical investigation.

1. Introduction

Chronic muscle hypertonicity is among the most common musculoskeletal findings in aging mammals, yet it occupies an ambiguous position in the biomedical literature. Its local manifestations — myofascial trigger points, taut bands, adaptive shortening, and reduced joint excursion — are well characterized at the tissue level and are consistently framed as dysfunction: the product of injury, disuse, repetitive strain, or neuromuscular dysregulation. The organism, on this view, is doing something wrong, and the clinical imperative is correction.

We suggest this framing is incomplete. It focuses analytical attention on the local and the pathological while largely ignoring the aggregate and the functional. When the sequelae of chronic hypertonicity are considered together — reduced range of motion across multiple joints, progressive postural reorganization toward flexion, diminished movement variability, offloading of structural load onto passive connective tissue, and a systematic narrowing of the accessible movement repertoire — a different picture emerges. The organism is not simply accumulating local failures. It is converging on a structural configuration that is mechanically stable, neurally simple, and metabolically inexpensive to maintain.

This pattern is not idiosyncratic. It is observed across all studied mammalian species as a consistent feature of aging: progressive stiffening, postural collapse, reduced spontaneous movement, and declining metabolic rate co-occur reliably and in a consistent sequence. The juvenile phenotype — high movement variability, full range of motion, high metabolic throughput — gives way across the lifespan to a phenotype defined by constraint, rigidity, and metabolic conservation. That this transition occurs across divergent mammalian lineages, in animals with vastly different ecologies and life histories, is not easily explained by coincidental degeneration. It is more parsimoniously interpreted as an evolutionarily conserved program.

We propose, as an explicit and testable hypothesis, that the sequelae of chronic hypertonicity serve a conserved energy-conservation function. The argument is not that individual trigger points or taut bands are designed to save energy — the local physiology does not support this — but that their aggregate structural and behavioral consequences reduce whole-organism energy expenditure in ways that may carry selective advantage, particularly in the post-peak-reproductive period. This hypothesis reframes a familiar clinical phenomenon as a potential life-history strategy, and in doing so opens new questions at the intersection of muscle physiology, evolutionary biology, and gerontology. The following correlates are implicated here:

• Hypertonicity
• Tonic contraction
• Muscle guarding and bracing
• Partial contraction
• Adaptive shortening
• Knotting
• Myofascial trigger points
• Taut bands
• Local contracture
• Myofascial pain syndrome
• Central sensitization
• Neuromuscular dysregulation

2. The Aggregate Effect Problem

A central obstacle to interpreting chronic hypertonicity as an energy-conservation strategy is the local physiology of its most studied manifestation: the myofascial trigger point. Within these regions, sustained cross-bridge cycling, impaired calcium reuptake, and failed motor unit relaxation produce a state of persistent low-level contractile activity. Blood flow is reduced through capillary compression, creating a local environment characterized by ischemia, metabolite accumulation, and insufficient ATP resynthesis — what the trigger point literature describes as an energy crisis. On this basis, it is tempting to conclude that chronically hypertonic tissue is metabolically costly rather than conserving, and that no energy-saving interpretation can survive contact with the physiology.

This conclusion, however, conflates the wrong units of analysis. The energy crisis model describes conditions within a small cluster of motor units — a microscopic region of dysfunctional tissue embedded in a much larger system. The relevant question for an evolutionary argument is not whether that region is locally efficient, but what the aggregate effect of chronic hypertonicity is on whole-organism energy expenditure. These are distinct questions, and the answer to the first does not determine the answer to the second.

When the unit of analysis is shifted to the whole organism, a different picture emerges. The primary energetic consequence of chronic hypertonicity is not the metabolic cost of dysfunctional motor units but the systematic reduction in dynamic muscle recruitment that accompanies it. A musculoskeletal system characterized by adaptive shortening, reduced joint excursion, and diminished movement variability is one in which large muscle groups are recruited less frequently, through smaller ranges of motion, and with lower peak force demands. The energetic cost of movement scales with range, velocity, and recruitment; a system that constrains all three burns substantially less energy in the course of ordinary behavior.

A second consequence compounds this effect. As chronic shortening progresses, the structural maintenance of posture is increasingly offloaded from active contractile tissue to passive connective tissue — thickened fascia, remodeled extracellular matrix, shortened tendons, and altered viscoelastic properties of the muscle-tendon unit. Active postural maintenance requires continuous motor unit firing and ATP consumption. Passive structural support does not. The transition from an actively maintained posture to one supported primarily by connective tissue remodeling represents a genuine reduction in ongoing metabolic demand, independent of movement.

The local inefficiency of trigger points and taut bands is therefore real but peripheral to the aggregate argument. Biology routinely tolerates local inefficiency in service of global function. The relevant claim is not that every component of the hypertonic syndrome is metabolically optimal, but that the system-level consequence of the full syndrome is a structural reorganization that reduces total energy expenditure. It is at this level that the evolutionary argument must be evaluated. Here are some of the associated factors.

Behavioral correlates

– Reduced spontaneous movement

– Reduced overall activity levels

– Reduced movement variability

– Narrowed motor repertoire

– Fewer high-amplitude movements

– Increased time in static or low-intensity postures

Kinematic / motor correlates

– Reduced range of motion (ROM)

-Joint stiffness / reduced compliance

-Increased co-contraction (agonist and antagonist together)

-Simplified movement patterns

-Loss of fine motor control

Neuromuscular activation correlates

-Chronic low-level motor unit activation in some fibers

-Under-recruitment of other fibers

-Reduced peak activation capacity

– Less full contraction–relaxation cycling Increased baseline muscle tone

Structural / tissue correlates

-Adaptive muscle shortening

– Reduced muscle length

– Loss of sarcomeres in series

-Increased passive stiffness (titin, fascia, ECM) – Fibrosis / connective tissue thickening

-Altered muscle architecture

Circulatory / local metabolic correlates

– Reduced local blood perfusion

– Reduced oxygen delivery

– Impaired capillary exchange

– Accumulation of metabolic byproducts

– Altered local metabolic signaling

Systemic metabolic correlates

– Lower resting metabolic rate

– Reduced total daily energy expenditure

– Reduced mitochondrial activity in underused muscle

– Shift toward lower metabolic throughput

Neurobehavioral / motivational correlates

– Reduced dopaminergic drive

– Reduced movement initiation

– Reduced exploratory behavior

– Increased perceived effort cost of movement

– Increased fatigue or low-energy subjective state

It is worth noting that the transition toward these factors is not instantaneous. In the early stages of chronic hypertonicity, sustained low-level contractile activity does carry a genuine local metabolic cost, consistent with the energy crisis model of myofascial trigger point formation. The hypothesis advanced here applies primarily to the chronic, structurally consolidated state — one characterized by fibrosis, serial sarcomere deletion, and reduced motor unit recruitment — in which postural load is increasingly borne by passive connective tissue rather than active cross-bridge cycling. The front-loaded metabolic cost of reaching this configuration is analogous to other biological remodeling programs that accept early expenditure in order to establish a durable lower-energy steady state.

3. Phylogenetic Universality as Evidence of Conservation

The strongest prima facie case for interpreting chronic hypertonicity as an evolved program rather than accumulated pathology is its phylogenetic distribution. Progressive musculoskeletal stiffening, postural reorganization toward flexion, reduced spontaneous movement, and declining metabolic rate are not features of any particular species or ecological niche. They are consistent features of mammalian aging observed across carnivores, primates, rodents, and ungulates alike. Animals as ecologically and morphologically divergent as domestic cats, chimpanzees, horses, and humans undergo recognizably similar transitions across the lifespan: from a juvenile phenotype characterized by high movement variability, full articular range of motion, and high metabolic throughput, to an aged phenotype defined by stiffness, postural collapse, movement restriction, and metabolic conservation.

This universality carries evidential weight. In evolutionary biology, a trait that appears consistently across divergent lineages is presumed, as a default, to reflect shared ancestry or shared selective pressure rather than independent coincidence. Degenerative processes, by contrast, tend to show greater inter-species variability, reflecting differences in body plan, tissue composition, repair mechanisms, and ecological context. The stereotyped nature of the mammalian aging transition — its consistent direction, its consistent sequence, and its consistent metabolic correlates — is more consistent with a conserved program than with the independent accumulation of similar errors across unrelated species.

The contrast between juvenile and aged phenotypes is particularly instructive. Young mammals across species share a recognizable motor profile: broad exploration of the available movement repertoire, high spontaneous activity, frequent transitions between postures, and full articular range of motion under normal conditions. Aged mammals across species share an equally recognizable profile in the opposite direction. The transition between these profiles is gradual, progressive, and remarkably consistent in its character. Postural flexion increases. Movement episodes become shorter and less varied. Ranges of motion narrow. Connective tissue stiffens. Metabolic rate declines. That this sequence recapitulates itself across the mammalian clade suggests it is not noise but signal.

It is worth being explicit about what this argument does and does not establish. Phylogenetic universality does not prove that a trait is directly selected. Universally shared features can reflect ancestral constraint, developmental coupling, or unavoidable byproducts of other selected processes. We do not claim that universality alone settles the question. What it does is shift the prior. A pattern this consistent, this directional, and this metabolically coherent across divergent lineages is more likely to reflect evolutionary conservation than coincidental degeneration. That shifted prior motivates the stronger selective argument developed in the following section.

4. The Case for Direct Selection

If the sequelae of chronic hypertonicity reduce whole-organism energy expenditure in the ways described, the question becomes whether this reduction carries sufficient selective value to explain the conservation of the underlying program. We argue that it does, and that the selective logic becomes clear once the phenomenon is situated within life-history theory and compared to other conserved energy-conservation programs in mammals.

Life-history theory holds that organisms face fundamental trade-offs in the allocation of energy between competing demands: growth, reproduction, somatic maintenance, and survival. These trade-offs are not solved once and fixed; they are dynamically regulated across the lifespan in response to changes in reproductive value, resource availability, and physiological capacity. In many species, the post-peak-reproductive period is characterized by a systematic shift in allocation away from energetically expensive activities — exploration, competition, reproduction — and toward metabolic conservation and survival. This shift has clear selective value under resource limitation, and mechanisms that enforce it reliably and structurally, without depending on behavioral volition, would be favored over those that do not.

Chronic hypertonicity, on this view, functions as a structural enforcer of reduced energy expenditure. Unlike behavioral strategies for energy conservation, which require ongoing neural regulation and can be overridden, the musculoskeletal reorganization associated with chronic hypertonicity is self-maintaining and progressive. Adaptive shortening, connective tissue remodeling, and postural collapse create a physical substrate that constrains movement independently of motivational state. The organism cannot easily choose to move through ranges it no longer possesses. This structural robustness is precisely what would be expected of a selected program rather than a facultative behavioral response.

The analogy to other conserved energy-conservation programs is instructive. Torpor, hibernation, and sickness behavior are well-recognized examples of coordinated physiological states that reduce metabolic demand in response to resource scarcity or somatic challenge. Each involves the suppression of energetically expensive activities, redistribution of metabolic resources, and acceptance of local tissue costs in service of whole-organism conservation. Chronic hypertonicity shares the key functional features of these programs: it is progressive rather than acute, it operates across multiple systems simultaneously, it reduces behavioral energy expenditure structurally rather than just neurally, and it accepts local inefficiency — dysfunctional trigger points, ischemic tissue — in exchange for a globally lower-energy configuration. The parallel is not identity but analogy: a family of conserved strategies that solve the same evolutionary problem by related means.

A possible mechanistic pathway for selection deserves brief consideration. The neuromodulatory systems that regulate muscle tone — dopaminergic, serotonergic, and noradrenergic — decline in activity with age across mammals. This decline reduces spontaneous movement, lowers exploratory behavior, and increases baseline muscle tone through reduced inhibition of spinal motor circuits. If even modest reductions in whole-organism energy expenditure resulting from this shift improved survival under resource-limited conditions — conditions that were the norm rather than the exception across most of mammalian evolutionary history — selection would have favored alleles that promoted earlier or more pronounced neuromodulatory decline. The musculoskeletal consequences of that decline, including hypertonicity and its sequelae, would then be selected indirectly but reliably. The structural changes that follow — adaptive shortening, connective tissue remodeling, postural reorganization — would consolidate and extend the initial neuromodulatory shift, creating a self-reinforcing program that deepens over time.

This account does not require that every feature of the hypertonic syndrome be directly selected. It requires only that the aggregate energetic consequence of the syndrome was sufficiently beneficial under ancestral conditions to favor the neuromodulatory and musculoskeletal architecture that produces it. The local costs — painful trigger points, reduced mobility, impaired tissue perfusion — are consistent with a program selected for net energetic benefit rather than local tissue optimization, just as the muscle wasting of sickness behavior or the metabolic suppression of torpor carry local costs that are tolerated for their systemic benefits.

Further support for situating chronic hypertonicity within a family of conserved energy-conservation programs comes from molecular comparisons with hibernation, starvation, and sickness behavior. During torpor in hibernating mammals, skeletal muscle myosin undergoes a conformational shift toward the super-relaxed state (SRX), in which ATP turnover rate is five to ten times lower than in the normally active disordered-relaxed state. Modeling studies suggest that a 20% shift of myosin heads from active to super-relaxed conformation reduces whole-body energy expenditure by approximately 16%. The researchers who characterized this mechanism explicitly called for investigation of whether analogous myosin conformational changes occur in human sarcopenia and chronic immobilization models — a gap that the present hypothesis directly addresses. A second molecular parallel involves AMP-activated protein kinase (AMPK), the cell’s master energy-conservation switch, which is activated by starvation, hibernation initiation, hypoxia, and the ischemic conditions characteristic of myofascial trigger point tissue. Under metabolic stress, AMPK activation directly suppresses myosin light chain phosphorylation in smooth muscle, reducing contractile force and ATP demand — a cellular-level mechanism for enforcing reduced muscular energy expenditure when supply is threatened. A third parallel is provided by sickness behavior, now recognized as an evolutionarily conserved motivational program that enforces immobility and whole-organism energy conservation through proinflammatory cytokine signaling. Chronic myofascial trigger points produce local accumulation of the same cytokines — IL-1β, TNF-α, bradykinin, and substance P — that drive sickness behavior centrally. This raises the question of whether widespread chronic hypertonicity involves a form of distributed, low-grade cytokine signaling that biases the organism toward immobility and reduced energy expenditure through the same pathways that mediate sickness behavior, without requiring a discrete infectious trigger. None of these parallels constitutes proof of shared mechanism. Taken together, however, they suggest that chronic hypertonicity and its sequelae operate in molecular territory already occupied by established energy-conservation programs, and that the relevant cellular machinery exists and is conserved across mammalian species.

The parallel with sickness behavior deserves elaboration because it illuminates the mechanism by which chronic hypertonicity may enforce its behavioral consequences. Sickness behavior is now well established as an evolutionarily conserved motivational program rather than a passive consequence of physiological weakness. When the immune system detects infection, proinflammatory cytokines signal the brain and body to enforce a coordinated low-energy configuration: movement becomes aversive, posture collapses, range of motion narrows, appetite diminishes, and the organism withdraws from social and exploratory activity. The organism feels heavy, achy, and stiff. These are not side effects of illness — they are active outputs of a program whose function is to redirect metabolic resources toward immune defense and tissue repair by shutting down energetically expensive behavior. The program is conserved across all studied mammals and birds, and its molecular mediators — principally IL-1β, TNF-α, and IL-6 — are among the best-characterized cytokines in biology.
Chronic myofascial trigger points produce the same biochemical environment at the tissue level. Microdialysis studies have demonstrated local accumulation of IL-1β, TNF-α, bradykinin, substance P, and protons at active trigger point sites — the same signaling molecules that drive sickness behavior when they appear systemically. The critical difference between acute illness and chronic hypertonicity is not the identity of the signals but their distribution and duration: in acute infection the cytokine signal is strong, centralized, and temporary; in chronic widespread hypertonicity it is weak, distributed across many tissue sites throughout the body, and indefinitely sustained.
This raises a hypothesis that has not, to our knowledge, been previously articulated: a person with widespread chronic hypertonicity may be running a perpetual, low-grade, distributed analog of sickness behavior. Their musculoskeletal tissue continuously broadcasts the molecular signals that the nervous system interprets as a call for immobility, energy conservation, and behavioral withdrawal — not because they are fighting an infection, but because their myofascial tissue has become a chronic source of the same cytokine environment that sickness behavior evolved to respond to. The stiffness, the achiness, the reluctance to move, the fatigue, the postural collapse, and the low mood that characterize chronic hypertonicity may not be incidental features of a dysfunctional state. They may be the intended behavioral outputs of a system reading those distributed cytokine signals and responding precisely as it was designed to: by enforcing a lower-energy, lower-movement configuration across the whole organism.
If this interpretation is correct, it has implications beyond the energy-conservation hypothesis. It suggests that the psychological sequelae of chronic hypertonicity — the background negativity, the social withdrawal, the reduced motivation — are not merely the emotional consequences of living in pain. They are part of the same conserved program, driven by the same molecular signals, producing the same behavioral phenotype that sickness behavior produces in an acutely ill animal. Chronic hypertonicity, on this view, does not merely cause suffering. It imposes a physiological state.

5. Objections and Responses

Any hypothesis proposing that a widely recognized pathological phenomenon is in fact an evolved adaptation must engage seriously with the objections it will face. We address the three most significant here.

Objection 1: The local physiology is hypermetabolic, not hypometabolic, so the energy-conservation interpretation cannot be correct.

This is the most common and superficially compelling objection, and it rests on a category error. The energy crisis model of myofascial trigger points accurately describes conditions within dysfunctional motor unit clusters: sustained contractile activity, impaired ATP resynthesis, ischemia, and metabolite accumulation. None of this is disputed. The error is in treating local tissue metabolism as the relevant quantity for evaluating an organismal-level hypothesis. A program selected for its effect on whole-organism energy expenditure need not be locally efficient in every component. Sickness behavior reduces total energy expenditure while producing local inflammatory activity that is itself metabolically costly. Hibernation preserves organismal energy while involving periodic arousal episodes that are energetically expensive. The relevant question is always net effect at the level of selection, not local efficiency at the level of tissue. At the organismal level, the aggregate consequences of chronic hypertonicity — reduced movement, reduced dynamic recruitment, passive postural support — reduce total energy expenditure. The local hypermetabolism of trigger points does not negate this.

Objection 2: This pattern looks like pathology and degeneration, not adaptation. The distinction matters.

The distinction between pathology and adaptation is real but not as clean as this objection implies. Many conserved biological programs produce tissue-level damage as an accepted cost of their systemic function. The inflammatory response causes collateral tissue destruction. Apoptosis eliminates viable cells. Bone remodeling involves deliberate osteoclastic resorption. In each case, local damage is the mechanism by which a selected program achieves its systemic effect. The presence of painful, dysfunctional tissue within the hypertonic syndrome does not preclude adaptive interpretation; it is consistent with a program that accepts local costs for global benefit. Furthermore, the distinction between pathology and adaptation is complicated by the fact that traits selected under ancestral conditions may produce outcomes that are genuinely harmful under modern conditions — abundant food, sedentary behavior, medical extension of lifespan — while remaining adaptations in the evolutionary sense. The hypertonic syndrome may be both a selected program and a source of suffering under contemporary conditions. These are not mutually exclusive.

Objection 3: Natural selection weakens after reproductive peak, so post-reproductive traits cannot be directly selected.

This objection draws on the well-established principle that selection pressure declines with age as residual reproductive value decreases. It is a serious constraint on adaptationist arguments about aging, and we do not dismiss it. However, several considerations limit its force here. First, the hypertonic program, if real, does not begin at post-reproductive age. Chronic hypertonicity develops across the adult lifespan, often well within the reproductive period, suggesting that selection could act on its early expression. Second, inclusive fitness extends the reach of selection beyond direct reproduction. In social mammals, post-reproductive individuals contribute to offspring and grandoffspring survival through resource provisioning, knowledge transfer, and cooperative behavior. A program that reduces the metabolic demands of post-reproductive individuals — allowing them to survive longer on fewer resources and compete less with younger relatives — could be favored through kin selection. Third, resource competition between generations is a genuine selective force. An aged individual that occupies a lower metabolic niche places less demand on shared resources, potentially improving the fitness of related younger individuals. Selection need not operate only through direct reproduction to shape post-reproductive physiology.

6. Testable Predictions

A hypothesis that cannot generate testable predictions is not a scientific contribution. We offer three predictions that follow directly from the proposed framework and that are addressable with existing or feasible methodology. Confirmation of any one of these would not verify the hypothesis, but would provide meaningful support; disconfirmation would constrain or refute it.

Prediction 1: Passive tissue stiffness should correlate with resting metabolic rate independently of muscle mass.

If the sequelae of chronic hypertonicity reduce whole-organism energy expenditure through structural reorganization rather than simply through loss of muscle mass, then passive mechanical stiffness — measured via elastography or range-of-motion assessment across multiple joints — should predict resting metabolic rate over and above what is accounted for by lean mass, age, and activity level. Current gerontological research attributes metabolic decline in aging primarily to sarcopenia and reduced activity. If passive stiffness independently predicts metabolic rate, this would support the hypothesis that connective tissue remodeling contributes causally to metabolic downregulation rather than merely co-occurring with it.

Prediction 2: Interventions that restore full range of motion and movement variability should attenuate metabolic decline beyond what increased activity alone predicts.

If structural constraint is a driver of metabolic downregulation rather than a passive correlate of it, then restoring the structural substrate — through sustained flexibility training, myofascial release, or similar interventions that specifically target range of motion and movement variability — should produce metabolic effects that exceed what would be predicted from the associated increase in activity alone. This prediction distinguishes the hypothesis from a simpler account in which reduced movement causes both stiffness and metabolic decline independently. If removing the structural constraint restores metabolic rate beyond the activity effect, the constraint itself was doing causal work.

Prediction 3: Species with greater post-reproductive lifespan should show earlier onset or more pronounced musculoskeletal constraint programs.

Life-history theory predicts that species in which post-reproductive individuals make larger contributions to inclusive fitness — through grandoffspring provisioning, resource sharing, or knowledge transfer — should show stronger selection on post-reproductive phenotypes generally. If the hypertonic program is selected in part through inclusive fitness mechanisms, species with extended post-reproductive lifespan and strong inter-generational resource dynamics, such as elephants, cetaceans, and humans, should show earlier onset, greater magnitude, or more stereotyped expression of the musculoskeletal constraint program relative to species with negligible post-reproductive lifespan. Comparative biomechanical and metabolic data across mammalian species, controlling for body size and activity level, could test this prediction directly.

7. Conclusion

The sequelae of chronic hypertonicity — adaptive shortening, myofascial contracture, reduced range of motion, postural reorganization, and diminished movement variability — are among the most familiar features of mammalian aging. Their familiarity has perhaps obscured their theoretical interest. Framed as pathology, they invite clinical correction. Framed as the aggregate output of an evolved program, they invite a different set of questions: what selective pressures shaped this transition, through what mechanisms is it implemented, and what does its universality tell us about the energy economics of mammalian life history.

We have argued that the aggregate effect of this syndrome is a structural reorganization of the musculoskeletal system that reduces whole-organism energy expenditure by constraining dynamic recruitment, offloading postural maintenance onto passive connective tissue, and enforcing a lower-movement behavioral mode. We have argued that the phylogenetic universality of this pattern across divergent mammalian lineages is more consistent with evolutionary conservation than coincidental degeneration. And we have argued that the selective logic is coherent: a structurally enforced reduction in energy expenditure, operating across the post-peak-reproductive period and potentially reinforced through inclusive fitness mechanisms, would have carried genuine adaptive value under the resource-limited conditions that characterized most of mammalian evolutionary history.

We do not claim this hypothesis is established. The evidence reviewed here is circumstantial and the predictions offered are largely untested. What we claim is that the hypothesis is coherent, that it is consistent with available evidence, and that it reframes a clinically familiar phenomenon in a way that generates new empirical questions. The intersection of muscle physiology, evolutionary biology, and gerontology remains underdeveloped, and the energetic consequences of musculoskeletal constraint across the lifespan have not been rigorously isolated from the confounding effects of sarcopenia and reduced activity. That gap is where the hypothesis lives, and where its resolution will be found.

More broadly, the framework proposed here suggests that biological systems may share a general principle: the progressive compression of operational state space as a conserved response to reduced capacity or resource availability. The narrowing of the movement repertoire in the aging musculoskeletal system may be one instance of a pattern that appears elsewhere — in the reduced associative exploration of the aging brain, in the behavioral simplification of chronically stressed animals, in the metabolic suppression of resource-limited organisms more generally. Whether these parallels reflect shared mechanisms or convergent solutions to a shared problem is an open question. It is, we suggest, a productive one.

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