This informal CPD article ‘The Muscle as Final Effector: Three Converging Systems’, was provided by Dr. Mauro Lastrico, Physiotherapist at AIFiMM Formazione, an organisation recognised by the Italian Ministry of Health as an authorised CME provider. They offer organised training courses in the Mézières Method, a rehabilitative and postural approach.
Neurophysiological, biomechanical and psychosomatic models of muscle shortening
Previous contributions in this series have analysed the vectorial dominances of individual anatomical districts, demonstrating how muscle shortening, understood as viscoelastic deformation of connective components [1,11], alters the physiological joint sequence and the equilibrium between the weight force and the ground reaction force [2]. Vector analysis [3,4] provided the tool for identifying the dominances responsible for these alterations. The upstream question remains: why do muscles tend to shorten. The present article identifies three systems that use the muscle as a common final effector: the neurophysiological system, the biomechanical system and the psychosomatic system.
1. The Muscle as Final Effector
Muscle shortening is not a random phenomenon but the result of precise physiological mechanisms that lead to an increase in basal tone [5,6,7]. When this increase in tension persists over time, it progressively involves the connective tissue component of the muscle fibre, producing the permanent residual shortening observed in segmental analysis [1,11]. The increase in basal tone may be induced by three distinct systems that converge on the muscle as a common final pathway: the neurophysiological system, the biomechanical system and the psychosomatic system [5,6]. Each may act independently or in synergy with the others, producing the clinical complexity observed in daily practice. This distinction guides therapeutic strategies, discriminating cases in which the intervention must be predominantly directed at the muscular system from those in which it must be directed primarily at other systems [5,6,17].
2. The Neurophysiological Model
2.1 Cortical and Subcortical Control of Tone
Muscular tone is the resultant of a complex series of psycho-neurophysiological processes within the tonic postural system [5,6,8]. This system receives information from specific receptors — the foot, the eye, the stomatognathic apparatus, the skin and the musculoskeletal system — and its output, muscular tone, is conditioned both by the sensory inputs and by the processing of the central nervous system [5,8,9,20].
The cortical centres are involved in planning motor objectives, while the subcortical centres, using a mapping known as the “body schema”, modulate the execution of motor strategies through neural patterns automated by evolution and modulated by experience [5,8,10,21]. Since motor planning is hierarchically prioritised over execution, the neural representation of the body schema influences the quality of muscular activation [5,8]. The less accurately the body schema is represented at the neural level, the more the muscular system will be activated with excessive tension, in co-contraction of muscles not necessary for the action, to the point of generating substitutive patterns [5,8,19,29].
2.2 Protective Mechanisms of the Subcortical Centres
The subcortical centres modulate muscular tone through the gamma circuit as a function of protective mechanisms for safeguarding physical integrity, distinguishable into physiological and functional mechanisms [5,6,7]. Physiological mechanisms are muscular contractions that the nervous system activates automatically as a stereotyped response to an event: for example, following an ankle sprain, the subcortical centres send a contraction message to all the peri-articular muscles to immobilise the joint until the damaged structures have been repaired [5,6,24]. The duration of the sustained contraction will be proportional to the damage, and consequently so will the residual muscular shortening [1,5].
Muscular contraction, as a function of the variables of magnitude and duration, produces residual shortening: the lesser the time and force of contraction, the lesser the shortening; the greater the force, but above all the time, the greater the residual shortening [1,11,15].
2.3 The Posterior Antalgic Reflex
Functional mechanisms are muscular contractions sustained over time, constituted by a more or less substantial increase in basal tone, activated by the subcortical centres via the gamma motor neurone, whose purpose is to attenuate and/or eliminate present pain [5,6,16]. The subcortical centres, in their work of safeguarding, respond to a single time frame: the “here and now” [5]. Pain and/or functional limitation are processed with the meaning of threat, and avoidance strategies are therefore adopted [5,6].
The posterior antalgic reflex thus represents the ultimate defensive strategy: sustained muscular contraction, as long as it does not provoke structural conflicts, has an antalgic effect [5,6]. This strategy proves useful in the immediate term but, if it persists over time, itself becomes a cause of further mechanical conflicts, establishing a circuit in which the local mechanical conflict activates the reflex, which produces contraction and residual shortening, which alters the local and systemic joint sequence, generating new conflicts [5,6,12].
2.4 The Pre-emptive Antalgic Reflex
The physiological mechanisms and the posterior antalgic reflex intervene only at certain moments in life and alone are not sufficient to explain the summation of shortenings and asymmetries present in the body [5]. Their true cause is principally the pre-emptive antalgic reflex [5,6].
This is a perpetually active reflex whose purpose is to prevent latent pain and mechanical conflicts from manifesting [5,6]. Progressive muscular shortening, as long as it does not create conflicts, prevents the unmasking of musculoskeletal discomforts [5]. The subcortical centres use the muscular system by distributing shortenings so as to systemically alter all joint sequences, precisely in order to avoid, for as long as possible, local conflicts [5,6].
This reflex also manifests through the adoption of specific bodily configurations or through movement, compelling the person to make non-random motor choices [5,21]. Such compulsions are initially unconscious: one “feels” the need to move or to position oneself in a given way. If the shortening modifications of the musculature become more significant, the motor compulsions become consciously aimed at avoiding the onset of discomfort [5,6].
2.5 Self-Perpetuating Circuits
If the mechanism of systemic muscular shortening persists over time, local conflicts may develop, giving rise to a self-perpetuating circuit in which the two antalgic reflexes coexist [5,6]. When the pre-emptive reflex dominates, the preventive shortening, originally distributed to avoid potential conflicts, itself generates a local mechanical conflict that activates the posterior reflex, which produces further contraction and shortening, feeding the cycle [5]. When the posterior reflex dominates, the local mechanical conflict in progress activates sustained contraction which, through residual shortening, alters the joint sequence until potential conflicts are generated at other sites, activating the pre-emptive reflex as a preventive mechanism [5,6].
Musculoskeletal system
3. The Biomechanical Model
The biomechanical model, extensively developed in previous contributions of the series [3,4], analyses the modalities through which the musculoskeletal system organises itself following precise physical laws [2,15,18]. Vectorial equilibrium at low intensity of muscular forces ensures the coexistence of good stability and good joint mobility, positioning the system “at the edge of chaos” [5,25,30]. If forces act at high intensity, skeletal axiality remains possible, but movement requires greater energy expenditure, becoming disharmonious: the system acquires rigidity [5,15,22].
When vectorial imbalance at high intensity is maintained over time, the dominant forces prevail over the antagonists and the system reorganises at the cost of segmental misalignments [3,5,23]. The altered alignment of the individual centres of gravity compels the increase in basal tone, which produces connective tissue shortening, which further misaligns the centres of gravity: a self-perpetuating circuit in which skeletal misalignment and muscular contraction feed each other reciprocally [2,5,15].
4. The Psychosomatic Model
The psychosomatic model, in the original formulations of Reich and developed by Lowen in the therapeutic procedure of Bioenergetic Analysis, describes the functional identity between psychic and somatic processes [5,13,14,27]. The tensions accumulated in the body and the adoption of attitudes aimed at blocking emotions give rise to a dual armour: a character armour, understood as the set of psychic and behavioural attitudes, which has a somatic counterpart in a muscular armour [5,13,14]. The formation of the bodily armour occurs through the increase in basal tone in the contractile portion of the muscle fibre; if this condition persists over time, the connective tissue portion is also involved, producing the residual shortening that will alter the physiological joint sequence [1,5,11]. The psychosomatic model does not attribute an exclusive causal role to the psychic origin, but describes one of the modalities through which a chronic increase in basal tone may become established, which in any case follows the same mechanical laws inherent to the musculoskeletal system [5,27].
5. The Integration of Systems
The three systems — neurophysiological, biomechanical and psychosomatic — are interacting and interdependent [5,25,28]. Whichever system is primarily implicated in the imbalance, the others must implement adaptive strategies to allow the safeguarding of function. The overall system reacts by raising basal tone and activating regional and systemic muscular contractions [5,6]. When contraction and/or increase in basal tone persist for a sufficient time, the connective tissue portion of the muscle fibre becomes involved, with residual shortening and loss of the physiological joint sequence [1,5,11]. This misalignment in turn becomes a cause of muscular contraction and increase in basal tone, establishing the general self-perpetuating circuit that perpetuates and amplifies the initial imbalance, regardless of the primary causal system [5,6,15,26].
Conclusions
Understanding these mechanisms provides the scientific basis for interpreting the alterations of the physiological skeletal axes, regardless of the therapeutic approach used for their correction [5,6]. The physical analysis of muscular shortenings demonstrates that, whichever causal system is primarily involved, the final result follows the same mechanical laws [1,3,15]: the increase in basal tone and the consequent connective tissue shortening modify the vectorial relationships, alter the distribution of forces G and R, and shift the system from optimal equilibrium toward rigidity [2,5,30].
The coherent therapeutic sequence involves the reduction of Resistant Force in shortened dominant muscles, followed by strengthening to consolidate the correction obtained [1,3,17]. The identification of the primarily involved system guides the intervention: in cases where the neurophysiological or psychosomatic component is predominant, intervention on the muscular system alone may prove insufficient if the upstream cause of the imbalance is not addressed [5,6,23].
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