Musculoskeletal assessment: why "correcting posture" is a conceptual error

The spatial configuration of the body is not an independent variable to be judged in aesthetic or normative terms. It is the observable resultant of a system of forces in dynamic equilibrium. Classifying a configuration as "correct" or "incorrect" based on visible form constitutes a methodological error. Assessment must focus on the quality of the articular sequence and on the distance between the real configuration and the model of maximum biomechanical efficiency.

The attached PDF document, available for free download, develops the complete model with images and bibliographic references.

From musculoskeletal equilibrium to articular sequence

The term "posture" is here replaced with musculoskeletal equilibrium, to highlight the dynamic and mechanical nature of the phenomenon and avoid the morphological and prescriptive connotations of everyday language.

Musculoskeletal equilibrium is the resultant of the muscular vector forces acting on the skeletal system. The mechanical action of muscle is expressed through two components: basal tone — the level of muscular tension present even at rest, necessary to guarantee articular stability — and effective muscle length — which determines the distance between bony insertions and, consequently, the angular relationships between articular segments.

Muscular shortening is not the direct effect of maintained positions or incorrect habits. It is the consequence of increased basal tone that the neuromuscular system uses to guarantee stability and control. When the increase persists, the connective tissue component adapts through tissue remodelling processes: shortening stabilises and the reduction in distance between bony insertions becomes biomechanically relevant.

The engineering reference model: measuring the distance from the ideal

The reference model is engineering-based, not statistical. As in engineering one reasons in terms of 100% efficiency knowing it is unattainable, in biomechanics one refers to an ideal physiological articular sequence — the ideal biotype — as a conceptual tool for interpreting, quantifying, and improving the mechanical organisation of the body.

The ideal biotype does not represent an achievable therapeutic goal. Muscles inevitably tend to shorten over time and it is not realistic to think this process can be eliminated. The difference between a functional equilibrium and a pathological one is not qualitative but quantitative: the body always uses the same principles of organisation and compensation; what changes is the extent of deviation from the ideal configuration and the mechanical price the system is forced to pay to maintain it.

Compensation: adaptive capacity, not dysfunction

When one or more joints lose the ability to move according to a physiological sequence, the system reorganises. Other structures are recruited to maintain function. This process — compensation — is not dysfunction but the expression of the intrinsic adaptive capacity of the biological system.

Over time, compensatory strategies stabilise through neuromuscular and connective tissue remodelling mechanisms. What initially allows movement without pain eventually further modifies the mechanical organisation, distributing loads and tensions non-physiologically. Compensation, while still ensuring function, may become an indirect source of overload and remote symptomatology.

Static assessment parameters

The patient is assessed frontally, posteriorly, laterally, and in the supine position. The constant reference is foot position: heel and first metatarsal in contact, gaze directed forward. Parameters observed include: foot and toes, lower limbs (four contact points), knees, pelvis (lateral translation, elevation, rotation), waist triangles, shoulder girdle, shoulders, clavicles, upper limbs (humeral rotation, elbow, forearm, hand), cranium.

Supine observation is the most relevant: no muscle needs to activate to maintain position, so true structural shortenings are observed. In standing, asymmetries provide information about muscular strategies for maintenance of antigravity equilibrium.

Dynamic observations

Active dynamic observations detect whether actions are performed by the anatomically assigned muscles or whether substitutive moments are present. Passive dynamic observations detect aphysiological reactions — skeletal reactions incongruent with the induced movement — and mobility restrictions consequent to muscular shortening.

Physical foundations of the model.
This article applies the AIFIMM biomechanical model.
Its physical foundations are developed in three sequential articles, best read in order:
1. How muscle shortening generates joint conflict — why muscles shorten and the Resistant Force / Working Force model
2. Do antigravity muscles really oppose gravity? — how segmental malalignment raises Resistant Force
3. Why joint conflict develops: vector analysis of muscular forces — how the responsible forces are identified and predicted