Posture

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Postural System Overview

Posture can be defined as the body's position in space that maintains balance during both dynamic movements and static positions. It represents the body's automatic and unconscious reaction to the force of gravity. It is maintained through coordinated skeletal muscle contractions and continuous neuromuscular adjustments. Essentially, posture is any position that achieves balance with maximum stability, minimal energy consumption, and minimal stress on anatomical structures.

The postural system involves complex interactions between the musculoskeletal system and the central nervous system's afferent and efferent pathways. It serves to protect the body's supporting structures from injury and progressive deformity. In humans, three physiological spinal curves create balance: cervical lordosis, thoracic kyphosis, and lumbar lordosis. These curves form and stabilise in children aged around 5-6 years following foot proprioceptive maturation.

The postural system can be understood through three key concepts:

• spatiality: body position in three-dimensional space and relationships between skeletal segments
• anti-gravity response: posture as a reaction to the fundamental external force of gravity
• balance: the relationship between the subject and the environment

Balance itself can be static (maintaining a stationary position with the spinal column stretched upward along the centre of gravity) or dynamic (maintaining stability during daily activities). Both dynamic and static balance require a person to maintain their centre of gravity through anatomical structures while minimising energy consumption and using antagonistic isometric muscle contractions that create postural tone.

Posture can be categorised as either functional (characterised by the absence of pain, normal muscle tone, balanced kinetic chains, and harmonious skeletal segment relationships) or non-functional (marked by pain, muscle dystonia, abnormal tension, and kinetic chain imbalances). From a motor perspective, static posture actively resists gravitational dislocation of body segments, while dynamic posture maintains balance through synergistic interactions between active components (i.e., muscles), passive components (i.e., joints and bones), and control systems (i.e., the central nervous system, proprioceptive and exteroceptive systems, and the vestibular system).

Current Understanding of the Ideal or Optimal Posture

Optimal posture

Traditional texts and articles have long praised the virtues of optimal alignment, and rehabilitation clinicians widely assess and treat "sub-optimal" posture to improve patient function. However, modern research challenges this concept of an "optimal" posture. The literature lacks a universally accepted definition of posture, with recent research characterising it as highly individual rather than adherent to a fixed standard. Rather than striving for an arbitrarily ideal posture, the emerging view in physiotherapy and related fields is that it may be more beneficial to cultivate postural variability: the ability to comfortably change and adapt one's posture to different situations.

There is limited research to confirm strong relationships between musculoskeletal pain and postural alignment, but recent systematic reviews show mixed and contradictory evidence rather than a complete absence of correlation. Some weak correlations have emerged in specific conditions, such as forward head posture and neck pain, and lumbar lordosis in older adults with chronic low back pain. However, a 2020 umbrella review confirmed no consensus on the impact of spine posture, physical exposure, and low back pain. It stated that reviews had produced "contrasting outcomes, supporting the overall conclusion that the relationship between postural alignment and musculoskeletal dysfunction remains unclear and inconsistent."

Anatomical Landmarks for Postural Screening and Assessment

Despite questions about clinical relevance, assessing posture remains a key feature of the rehabilitation assessment.

Lateral, anterior, and posterior views with plumb line in place

The postural assessment uses anatomical landmarks to evaluate alignment, symmetry, and balance across the kinetic chain. Bony and soft tissue reference points provide standardised markers for assessing structural relationships between body segments and identifying postural deviations. This method of assessment is widely used as an initial screen because it is quick, inexpensive, and readily accessible.

The lateral view is the most commonly assessed perspective in a postural evaluation. It provides information about the spine's natural curves and the body's relationship to gravity through the line of weight-bearing joints. This view enables clinicians to assess forward head posture, thoracic kyphosis, lumbar lordosis, and overall anterior-posterior balance. It uses a plumb line reference that ideally passes through key anatomical landmarks from the head to the foot.

The anterior and posterior views complete the postural assessment by revealing asymmetries, lateral deviations, and rotational components that cannot be detected from the lateral perspective alone. The anterior view is particularly valuable for identifying shoulder height differences, pelvic obliquities, and lower extremity alignment issues, while the posterior view provides essential information about spinal scoliosis, scapular positioning, and bilateral symmetry.

Table 1. Lateral view of "ideal" posture assessment

	Lateral View
Plumb line position	Should pass through key weight-bearing joints
Landmarks that should align with plumb line	External auditory meatus (earlobe) Bodies of the cervical vertebrae Acromion process Axillary line Bodies of the lumbar vertebrae Greater trochanter Lateral epicondyle of the femur Lateral malleolus
Additional reference points	Plumb line should pass just anterior to the navicular bone Weight-bearing line through the centre of gravity

Table 2. Anterior and posterior views of "ideal" postural assessment

	Anterior View	Posterior View
Plumb line position	Midway between the feet, dividing the body into equal left and right halves	Midway between the feet, dividing the body into equal left and right halves
Landmarks that should align with or be equidistant from the plumb line	Nose/midline of the face Midline of the chin Jugular notch (suprasternal notch) Xiploid process Umbilicus Symphysis pubis	External occipital protuberance Spinal processes of the cervical vertebrae Spinal processes of the thoracic vertebrae Spinal processes of the lumbar vertebrae Median sacral crest Gluteal cleft
Structures equidistant from the plumb line	Shoulders (acromial processes) Anterior superior iliac spines (ASIS) Patellae Medial malleoli Feet (equal weight distribution)	Shoulders (acromial processes) Posterior superior iliac spines (PSIS) Greater trochanters Lateral epicondyles of the femurs Lateral malleoli Calcanei

Base of Support and Centre of Gravity

Relationship between centre of gravity, line of gravity, and base of support

The centre of gravity (COG, also called the centre of mass) represents the theoretical point where the body's entire mass is concentrated and perfectly balanced in all directions. In an average adult standing upright, this point is typically located approximately at the second sacral vertebra. However, its exact position varies based on individual anthropometric characteristics, body composition, and current posture. The COG shifts continuously as body segments move, requiring constant neuromuscular adjustments to maintain stability.

The base of support (BOS) is the area of contact between the body and the supporting surface, which in standing includes both feet and the space between them. This support polygon extends from the heel of one foot to the heel of the other, encompassing the lateral borders and toe regions. The resulting area is roughly rectangular or oval-shaped, depending on foot positioning and stance width. The size and shape of the BOS can be modified through changes in foot placement—wider stances increase the BOS and enhance stability, while narrower stances reduce the BOS and challenge balance systems.

The vertical line of gravity is an imaginary vertical line that extends downward from the COG toward the Earth's centre. For optimal postural stability, this line must remain within the boundaries of the BOS. When the line of gravity approaches or extends beyond the BOS perimeter, the body's balance systems must activate compensatory mechanisms, such as postural reflexes, muscle contractions, and movement strategies, to prevent loss of balance or falling.

This dynamic relationship is crucial for maintaining stability, as it determines the amount of muscular effort required to sustain upright posture. When the COG is centrally positioned within the BOS, minimal muscular activity is needed to maintain balance, resulting in efficient energy expenditure. However, as the line of gravity moves toward the BOS boundaries, increased muscular activation and postural adjustments become necessary to maintain equilibrium.

The Importance of the Pelvic Girdle

Pelvic tilts and associated muscle activation

The pelvis, with its anchored sacrum, serves as the foundational base for spinal alignment. Its position in the sagittal plane is determined by the equilibrium between opposing muscle groups that create either an anterior or posterior pelvic tilt. Pelvic tilt is a key component of spino-pelvic alignment and significantly affects overall posture.

According to the classical mechanical model, posterior pelvic tilt (also called retroversion) results from the coordinated activation of gluteus maximus and the hamstring muscles. These muscles effectively lower the posterior pelvic rim while elevating the anterior edge, reducing overall pelvic tilt. This movement can be enhanced synergistically through simultaneous activation of the abdominal muscles (e.g., rectus abdominis, obliques, and transversus), particularly when the sternum is stabilised.

Conversely, anterior pelvic tilt (also known as anteversion) occurs through the antagonistic action of the iliopsoas, rectus femoris, and lumbar erector spinae muscles, which collectively increase forward pelvic rotation.

However, this simplified mechanical model assumes symmetrical bilateral muscle activation patterns that may not always reflect the complex reality of human postural control.

Table 3. Muscle activity during anterior and posterior pelvic tilts

Muscle group	Anterior pelvic tilt	Posterior pelvic tilt
Hip flexors Iliopsoas Rectus femoris Tensor fasciae latae Sartorius	Active, shortened, strong and/or tight	Inactive, lengthened and/or weak
Lumbar extensors Erector spinae Multifidus Quadratus lumborum Latissimus dorsi (lower fibres)	Active, shortened, strong and/or tight	Inactive, lengthened and/or weak
Abdominal muscles Rectus abdominis External and internal obliques Transverse abdominis	Inactive, lengthened and/or weak	Active, shortened, strong and/or tight
Hip extensors Gluteus maximus Hamstrings (biceps femoris, semitendinosus, semimembranosis)	Inactive, lengthened and/or weak	Active, shortened, strong and/or tight

Traditional Muscle Imbalance Theories

The following muscle imbalance theories are important to understand from a historical perspective. However, neither represents current evidence-based practice. Instead, they provide a foundation for understanding how concepts of postural assessment and muscle balance have evolved. Modern rehabilitation practice requires a more nuanced approach. Rather than pathologising normal variation or age-related changes, clinicians should focus on functional capacity, symptom patterns, and individual presentations within the context of natural human diversity.

The Kendall Manual

The Kendall manual originated from the 1952 work "Posture and Pain" by Henry O. Kendall and physiotherapists Florence P. Kendall and Dorothy A. Boynton. It established what became the gold standard for postural assessment in rehabilitation. Their theory proposed that "ideal alignment" exists when specific anatomical landmarks align with a plumb line: the external auditory canal, midway through the shoulder, slightly posterior to the hip joint centre, slightly anterior to the knee joint axis, and slightly anterior to the lateral malleolus. This "standard posture" was considered the optimal position for minimising stress on musculature and ligaments, with deviations associated with pain and dysfunction. The underlying premise was that poor posture causes pain, and correcting postural deviations would alleviate musculoskeletal complaints.

Contemporary research demonstrates that the Kendall standard does not correspond to natural human posture or actual gravity line positioning. Studies using force platforms and three-dimensional radiographic analysis show that in natural standing, the centre of the femoral heads sits approximately 28 mm anterior to the true gravity line, whilst the line connecting the acoustic meatus to the femoral heads deviates 30 mm anteriorly from actual gravitational alignment. When healthy, asymptomatic individuals are assessed using Kendall's criteria, 66% demonstrate forward head posture, 38% show kyphosis, and over 70% exhibit forward shoulder positioning. This suggests that these variations represent normal human diversity rather than pathological deviations. This fundamentally challenges the posture-pain paradigm that has dominated rehabilitation practice for decades. While correlations between certain postural presentations and pain exist, a 2024 scoping review highlights that correlation does not establish causation, with considerable literature contradicting the assumed posture-pain relationship.

Upper and Lower Crossed Syndromes

The terms upper crossed syndrome and lower crossed syndrome have been used to describe recognised muscle imbalances that have the potential to lead to pain and dysfunction. However, they are NOT medical diagnoses and their validity is not fully supported by recent research. It is not recommended to use these terms as diagnostic labels in clinical practice. Yet despite these limitations, understanding these terms is useful in communication with patients and other healthcare professionals, as they represent patterns of muscle balance that can help guide more individualised clinical assessment.

The upper and lower crossed syndromes describe two distinct muscle imbalance patterns identified by Dr. Vladimir Janda in 1987. Janda was a Czech doctor and researcher who pioneered a muscle imbalance evaluation and treatment for chronic musculoskeletal pain. Janda observed that changes in muscular tone create muscle imbalances, leading to movement dysfunction. He found that muscles prone to tightness have a "lowered irritability threshold" and are readily activated with movement, thus creating abnormal movement patterns. Janda observed that humans tend to develop crossed syndromes at two primary levels: the shoulders (upper or proximal crossed) and the pelvis/hips (lower or distal crossed). These postures are primarily observed in the sagittal plane.

Upper crossed syndrome is characterised by tightness of the upper trapezius, levator scapulae, pectoral muscles, and suboccipitals. There is an imbalance between tight muscles, like the levator scapulae and trapezius, and weak muscles, like the deep neck flexors and lower trapezius. This theoretically creates muscular imbalances that affect postural alignment.

Lower crossed syndrome (also known as pelvic crossed syndrome) is characterised by specific patterns of muscle weakness and tightness that cross between the dorsal and ventral sides of the body. The hip flexors and lumbar extensors are purportedly overactive and tight, while the deep abdominal and gluteal muscles are weak, causing anterior pelvic tilt, increased hip flexion and compensatory lumbar spine curvature.

Common Postural Patterns

The following sections describe some common postural patterns observed clinically. These classifications are useful for communication and assessment, but should not always be considered inherently pathological, as postural variation is normal.

Flat-back posture: presents with a forward head and cervical spine extension. There is slight flexion of the upper thoracic spine and a straight or flattened appearance of the lower thoracic and lumbar spine. The pelvis is in a posterior tilt, the knees are in extension, and the ankles are plantar flexed. When considering muscle activation, the hip flexors are lengthened and/or weak. The hip extensors are shortened, strong and/or tight.

Kyphosis: there is an increased convex curve observed in the thoracic or sacral regions of the spine. The head is forward, the cervical spine is hyperextended, the scapulae are abducted, the thoracic spine has increased flexion and the lumbar spine is hyperextended. The pelvis is anteriorly tilted, the hips are flexed, the knees are in hyperextension, and the ankles are plantar flexed. When considering muscle activation, the neck flexors, thoracic paraspinals, external obliques, and middle/lower trapezius are lengthened and/or weak. The neck extensors, hip flexors, and lower back muscles are shortened, strong and/or tight.

Lordotic posture: lordosis refers to the normal inward curvature of the spine. When this curve is exaggerated, it is usually referred to as hyperlordosis. The head, neck, and thoracic spine are in neutral. The lumbar spine is hyperextended, producing an anterior tilt of the pelvis. The hips are flexed, the knees are hyperextended, and the ankles are plantar flexed. When considering muscle activation, the neck flexors, thoracic paraspinals, external obliques, and middle/lower trapezius are lengthened and/or weak. The neck extensors, hip flexors, and lower back muscles are shortened, strong and/or tight.

Scoliosis: this posture presents as a deviation of the normal vertical line of the spine, consisting of a lateral curvature and rotation of the vertebrae. Scoliosis is considered when there is at least 10° of spinal angulation on the posterior-anterior radiograph associated with vertebral rotation. This is a 3-dimensional C- or S-shaped sideways curve of the spine.

Sway back posture: presents with forward head, hyper-extension of the cervical spine, flexion of the thoracic spine, lumbar spine extension, posterior tilt of the pelvis, hip and knee hyper-extension, and slightly plantar flexed ankles. When considering muscle activation, the neck flexors, middle/lower trapezius, thoracic paraspinals, external obliques, and iliopsoas are lengthened and/or weak. The hip extensors are shortened, strong and/or tight.

Forward head posture: presents with a forward shift of the head, with the chin poking out. It is caused by increased flexion of the lower cervical spine and upper thoracic spine, with increased extension of the upper cervical spine and extension of the occiput on C1.

Additional Resources

Optional Video

This video discusses the relationship between the centre of gravity and base of support.

Optional Reading

• Barra-López ME. The standard posture is a myth: A scoping review. Journal of Rehabilitation Medicine. 2024 Oct 15;56:41899.