Posture, Gait and Movement

Posture and movement are where the spine meets everyday life: how we stand at a counter, walk to the car, lift a child or spend eight hours at a desk. Clinicians have long tried to read health from posture, yet the research shows that how a person looks standing still predicts surprisingly little, while how they walk and move tells a great deal. This chapter teaches what normal posture and gait look like, which abnormal patterns carry real diagnostic meaning, how to assess movement and motor control, and what the evidence actually says about ergonomics and healthy movement habits.

Section 1Static posture and its limits as a diagnostic tool

The ideal alignment

Posture is the position of the body and the relationship of its segments at any moment. Clinicians usually start with static standing posture viewed from the side, from behind and from the front. The traditional reference for side view is a vertical plumb line, imagined as a weighted string hanging from above. In the commonly taught ideal alignment, the line passes:

• through the earlobe (external auditory meatus);
• through the bodies of the cervical vertebrae;
• through the acromion (tip of the shoulder);
• roughly through the bodies of the lumbar vertebrae;
• through or just behind the hip joint, near the greater trochanter;
• slightly in front of the center of the knee joint;
• slightly in front of the lateral malleolus (ankle).

This alignment is thought of as efficient because the line of gravity falls close to the joint axes, so little muscle effort is needed to stay upright. Because the line falls just in front of the knee, the knee is held in extension by gravity and its ligaments; because it falls just behind the hip, the hip is pushed into extension and restrained by the strong iliofemoral ligament; and because it falls in front of the ankle, the calf muscles work at a low level to stop the body tipping forward. This is why a person standing quietly sways gently, with calf muscle activity rising and falling.

Classic postural types

Physical therapists in the mid twentieth century described several common deviations from the ideal, and these categories are still taught because they provide a shared vocabulary.

From behind, clinicians look for asymmetries in the level of the shoulders, scapulae, iliac crests and gluteal folds, and for lateral curves of the spine. From the front, they note head tilt, shoulder level, pelvic level, knee alignment (genu valgum or varum) and the arches of the feet.

Why static posture predicts so little

For much of the twentieth century, clinicians assumed that deviations from ideal posture caused pain by overloading tissues, and that correcting posture would relieve it. The evidence has been humbling. Large studies and systematic reviews have generally found that sagittal spinal curves, such as the degree of lordosis or kyphosis, are weakly or not at all associated with back pain in the general population. Adolescents with "slumped" posture do not reliably develop more back pain than their upright peers. People with and without neck pain overlap so much in head posture that measuring it cannot tell them apart. Several reasons explain this:

• Normal variation is wide. Healthy, pain-free people show a broad range of curve sizes, pelvic tilts and shoulder positions.
• Posture is not static. People shift position constantly. A single snapshot in the clinic may not represent how a person sits or stands through the day.
• Tissues adapt. Bones, joints and muscles remodel to the loads they habitually bear, so a long-standing posture is usually well tolerated.
• Pain is multifactorial. As Chapter 6 showed, pain depends on the nervous system's interpretation of threat as much as on mechanical load.
• Measurement is unreliable. Visual posture rating shows only modest agreement between clinicians.

Posture is still worth observing. A marked change can signal pathology: a new list to one side (an antalgic lateral shift) often accompanies acute disc irritation; a rigid, flexed posture may reflect stenosis or spondyloarthritis; a progressive hump may reflect osteoporotic fractures. What posture does not do well is explain ordinary pain or predict who will develop it. A modern summary often taught to students is that "the best posture is the next posture": variety and movement matter more than holding any single position.

Forward head posture and "text neck"

Forward head posture describes a head positioned in front of the trunk, usually measured by the craniovertebral angle: the angle between a horizontal line through C7 and a line from C7 to the tragus of the ear. Smaller angles mean a more forward head. Biomechanical models estimate that flexing the head forward greatly increases the moment the neck extensors must resist; one widely quoted model suggested the effective load rises from about 5 kg in neutral to about 27 kg at 60 degrees of flexion. These calculations are physically reasonable, but the leap from load to injury is not. Neck tissues are designed to tolerate flexion, and studies comparing people with and without neck pain show only small and inconsistent differences in head posture. Long periods without changing position, rather than the angle itself, may matter more for comfort.

Crossed syndromes and muscle imbalance

The Czech neurologist Vladimir Janda proposed that certain muscles tend to become tight and others inhibited in predictable patterns. In the upper crossed syndrome, tight upper trapezius, levator scapulae and pectoral muscles cross with weak deep neck flexors and lower and middle trapezius and serratus anterior, producing forward head, rounded shoulders and scapular winging. In the lower crossed syndrome, tight hip flexors and lumbar extensors cross with weak abdominals and gluteal muscles, producing anterior pelvic tilt and increased lordosis. These models are useful clinical descriptions and have shaped much exercise practice. However, direct evidence that these imbalances cause pain, or that correcting them is the reason patients improve with exercise, is limited.

Leg length inequality and scoliosis screening

Leg length inequality may be anatomical (a true difference in bone length) or functional (an apparent difference from pelvic rotation, muscle tightness, foot pronation or joint contracture). Small differences of a few millimeters are almost universal and are not linked to pain. Larger differences, often cited as greater than about 20 mm, may be associated with back and hip problems. Measurement matters: tape measure methods have only moderate accuracy, and imaging is the reference standard for anatomical difference. Clinicians who identify a small "short leg" during supine leg checks should be cautious about attributing symptoms to it.

Scoliosis is a lateral curvature of the spine combined with vertebral rotation, defined radiographically as a Cobb angle of 10 degrees or more. The most common form is adolescent idiopathic scoliosis, which affects roughly 2 to 3 percent of adolescents, with larger, progressive curves much more common in girls. The Adams forward bend test reveals rotation as a rib hump or lumbar prominence when the patient bends forward; a reading of about 7 degrees or more on a scoliometer is a common threshold for radiographic referral. Curves tend to progress during growth, so skeletal maturity and curve size guide monitoring, bracing or surgery.

Section 2The gait cycle

Defining the cycle

Gait is the manner of walking. Walking is a repeating pattern, so it is described by its basic unit, the gait cycle: the interval from one event of one foot to the next occurrence of the same event in the same foot. By convention the cycle starts at initial contact of one foot (usually the heel in healthy walking) and ends at the next initial contact of the same foot. One gait cycle equals one stride. A step is the interval from initial contact of one foot to initial contact of the other, so one stride contains two steps.

Each limb alternates between two phases:

• Stance phase: the foot is on the ground. In normal walking speed it occupies about 60 percent of the cycle.
• Swing phase: the foot is in the air, moving forward. It occupies about 40 percent of the cycle.

Because each stance phase is longer than half the cycle, there are two periods when both feet are on the ground, called double limb support, each lasting about 10 percent of the cycle (20 percent in total). The rest of stance is single limb support, about 40 percent of the cycle, which exactly matches the swing time of the other leg. As walking speed increases, double support shrinks; at the transition to running it disappears and is replaced by a flight phase when neither foot touches the ground. The presence of double support is the defining feature of walking, and the presence of flight defines running.

The eight phases

The standard terminology used in clinical gait analysis divides the cycle into eight functional phases, five in stance and three in swing. Each has a job.

Spatiotemporal measures

Simple measures of time and distance describe gait well and are easy to collect with a stopwatch and tape.

Speed equals step length times cadence, so a person can walk faster by taking longer steps, quicker steps, or both. Many conditions shorten step length first.

Gait speed is so strongly linked to health that it is sometimes called the "sixth vital sign." In older adults, slower usual gait speed predicts falls, hospitalization, loss of independence and mortality. Values often cited are below about 0.6 m/s associated with dependence in daily activities, below about 0.8 m/s with limited community walking and greater risk, and at least about 1.0 m/s with independent community walking. Crossing a typical street before the signal changes needs about 1.2 m/s.

The three rockers

During stance the body rolls forward over the foot through three pivot points, called rockers, which keep forward motion smooth.

1. Heel rocker (first rocker), in loading response: the body rolls over the rounded heel. The ankle dorsiflexors (tibialis anterior and the toe extensors) contract eccentrically to lower the forefoot gently instead of letting it slap down.
2. Ankle rocker (second rocker), in midstance: the foot is flat and the tibia rotates forward over the ankle. The soleus and gastrocnemius contract eccentrically to control the speed of tibial advance.
3. Forefoot rocker (third rocker, also called the toe rocker), in terminal stance: the heel lifts and the body rolls over the metatarsal heads. The calf muscles now generate the largest burst of power in walking, and the toes extend at the metatarsophalangeal joints, tightening the plantar fascia (the windlass mechanism) to stiffen the foot into a lever.

What the muscles do

Much of walking relies on momentum and gravity, with muscles acting in short bursts, often eccentrically to control and decelerate motion rather than to drive it.

Trunk, pelvis and arms

The body's center of mass rises and falls about 4 to 5 cm in a smooth wave with each step, highest in midstance and lowest in double support, and shifts a few centimeters side to side toward each stance limb. The pelvis rotates forward on the side of the swinging leg, tilts slightly downward on the swing side, and the thoracic spine rotates in the opposite direction. The arms swing opposite to the legs, which helps to counterbalance the rotation of the pelvis and reduces the energy cost of walking. Reduced arm swing, reduced trunk rotation, or a stiff, blocked lumbar spine are all visible clues in gait observation.

Section 3Common gait patterns and what they mean

How to observe gait

Observing gait is part of every musculoskeletal and neurological examination, and it often starts before the formal examination, as the patient walks from the waiting room. A systematic approach helps. Watch from the front, the back and the side, ideally over a long enough distance to see several cycles, and ask the patient to turn, to walk on heels and toes, and to walk heel to toe in a line (tandem gait). Look at:

• the overall impression: speed, symmetry, smoothness, use of aids, and whether the patient looks steady;
• the base of support: narrow, normal or wide;
• step length and timing on each side;
• each joint in turn: foot contact, ankle, knee, hip, pelvis, trunk and arm swing;
• turning, starting and stopping.

Gait abnormalities arise from four broad causes: pain (the body shortens loading on the painful side), weakness (muscles cannot perform their job and the body substitutes another strategy), restricted joint motion (stiffness or contracture forces compensation), and neurological control problems (spasticity, rigidity, incoordination or sensory loss). Recognizing the pattern often localizes the problem quickly.

Antalgic gait

An antalgic gait (from the Greek for "against pain") is a limp in which the patient spends as little time as possible on the painful limb. The stance phase on the affected side is shortened, so the opposite leg swings through quickly and the step taken with the sound leg is short. The pattern is the same whatever the painful structure, from a sprained ankle to an arthritic hip or an irritated lumbar disc. With a painful hip, patients may also lean the trunk over the painful hip during stance, which moves the center of mass closer to the joint and reduces the compressive force the hip abductors must produce.

Trendelenburg gait

In single limb stance, the hip abductors of the stance leg, chiefly the gluteus medius and gluteus minimus, keep the pelvis level. These muscles are supplied by the superior gluteal nerve (L4 to S1). If they are weak, the pelvis drops on the opposite, swinging side: an uncompensated Trendelenburg gait. More often, patients compensate by leaning the trunk over the stance leg, which shifts the center of mass over the hip and reduces the abductor force needed: a compensated Trendelenburg gait (sometimes called a gluteus medius lurch). When the weakness is bilateral, the trunk sways side to side with every step, producing a waddling gait, typical of muscular dystrophies, other myopathies and bilateral hip dysplasia.

The Trendelenburg test examines the same mechanism in the clinic. The patient stands on one leg. Normally the pelvis on the lifted side stays level or rises slightly. If it drops, the test is positive, and the weakness is in the abductors of the stance leg, not the side that drops. Causes include superior gluteal nerve injury, L5 radiculopathy, hip osteoarthritis, hip dysplasia and gluteal tendinopathy.

Steppage gait and foot drop

If the ankle dorsiflexors are weak, the toes cannot be lifted in swing and the forefoot slaps down after heel strike. To clear the hanging foot, the patient lifts the knee and hip unusually high, as if climbing stairs: a steppage gait. Initial contact may be made with the forefoot or the whole foot instead of the heel. Common causes are common fibular (peroneal) nerve palsy at the fibular neck (from leg crossing, casts, prolonged squatting or knee injury), L5 radiculopathy, peripheral neuropathy and some motor neuron diseases. A milder dorsiflexor weakness produces only an audible foot slap in loading response.

Distinguishing fibular nerve palsy from L5 radiculopathy is a classic exercise in localization. Both weaken dorsiflexion and great toe extension. In L5 radiculopathy, ankle inversion (tibialis posterior, a tibial nerve muscle with L5 contribution) and hip abduction (gluteus medius, superior gluteal nerve) are often weak too, because they share the L5 root but not the fibular nerve. In fibular nerve palsy, inversion and hip abduction are spared, and back pain is usually absent.

Central nervous system gaits

The Romberg test separates the two ataxias. The patient stands with feet together, first with eyes open and then closed. Someone with cerebellar ataxia is unsteady even with eyes open. Someone with sensory ataxia can compensate with vision and is fairly steady with eyes open, but sways or falls with eyes closed: a positive Romberg sign. The test therefore assesses proprioception, not the cerebellum.

Mechanical and musculoskeletal patterns

Section 4Movement assessment and motor control

From posture to movement

Because static posture predicts so little, clinicians have increasingly turned to how people move: how they bend, squat, rise from a chair, balance and walk. Movement assessment serves three purposes. It measures function in a way that matters to patients (can they get out of a chair, climb stairs, walk to the shop?), it identifies specific impairments that can be trained, and it provides an outcome measure that can be repeated to track progress. The best movement tests are simple, standardized, reliable and have known normal values.

Functional performance tests

Movement screens

Several standardized screens observe fundamental movement patterns. The Functional Movement Screen scores seven tasks (deep squat, hurdle step, in-line lunge, shoulder mobility, active straight leg raise, trunk stability push-up and rotary stability) from 0 to 3, for a total out of 21. A total of 14 or below was proposed as a marker of increased injury risk in athletes, but later studies have found that the screen predicts injury poorly. The Y Balance Test measures how far a person can reach with one leg in three directions while balancing on the other; asymmetry between sides has been associated with lower limb injury in some sports populations. These screens are useful for describing movement and setting training goals, but they should not be treated as precise injury predictors.

Motor control of the spine

Motor control is the way the nervous system plans and coordinates muscle activity to produce movement and maintain stability. For the spine, a key idea came from studies in the 1990s showing that in healthy people the transversus abdominis contracts slightly before the arm or leg muscles during rapid limb movements: a feedforward (anticipatory) response that prepares the trunk for the coming disturbance. In some people with low back pain this activation was delayed. Other studies found that the lumbar multifidus can show reduced size and altered activity on the painful side after an episode of back pain, sometimes persisting after pain resolves.

Researchers divided trunk muscles into a local (deep) system of muscles attached directly to the vertebrae, such as the transversus abdominis, deep multifidus and pelvic floor, thought to control segmental motion, and a global (superficial) system, such as the rectus abdominis, external obliques and long erector spinae, that moves the trunk and handles large loads. From this model came motor control exercise, often called core stability training, which first teaches isolated activation of deep muscles and then integrates them into functional tasks.

The evidence has refined this story. Changes in muscle timing in back pain are real but vary between individuals: some people with back pain show too little trunk muscle activity, while many show too much, bracing and co-contracting as a protective strategy that may itself become a problem. Systematic reviews have found that motor control exercise reduces pain and disability in chronic low back pain about as much as other forms of exercise, but not more. The practical message is that exercise helps, the specific type matters less than consistency and patient preference, and teaching people to move with confidence rather than with constant bracing is often valuable.

Other movement observations

• Lumbopelvic rhythm: forward bending combines lumbar flexion with hip flexion (anterior pelvic rotation). Early in the movement the lumbar spine contributes more, and later the hips contribute more. People with back pain often move more slowly and with less lumbar motion.
• Flexion relaxation phenomenon: in healthy people, the lumbar erector spinae fall electrically silent near full forward flexion, as passive tissues take over the load. This silence is absent in many people with chronic back pain, reflecting protective guarding, and it often returns with successful rehabilitation.
• Directional preference: in the mechanical diagnosis approach associated with Robin McKenzie, repeated movements in one direction (often extension) may cause symptoms to retreat from the limb toward the spine, called centralization. Centralization is a favorable prognostic sign.
• Cervical joint position error: the patient, blindfolded, returns the head to a neutral starting point after rotating; errors greater than about 4.5 degrees suggest impaired cervical proprioception, common after whiplash.
• Scapulohumeral rhythm: during arm elevation, the glenohumeral joint and scapula move in roughly a 2 to 1 ratio over the full range.

Motor learning

Changing how someone moves is a learning process. The classic model describes three stages: a cognitive stage, when the learner thinks hard about the task and performance is variable; an associative stage, when errors decrease and movement becomes more consistent; and an autonomous stage, when the skill is performed with little conscious attention. Research on motor learning suggests several practical principles:

• An external focus of attention (on the effect of the movement, such as "push the floor away") usually produces better performance and learning than an internal focus on body parts ("tighten your glutes").
• Variable practice, in which the task is practiced in different ways and contexts, transfers better to real life than repeating one exact pattern.
• Feedback helps early but should fade over time so that the learner develops internal control.
• Specificity: improvements are greatest in the tasks actually practiced, so rehabilitation should include the activities the patient wants to return to.

Section 5Ergonomics and movement habits

What ergonomics tries to do

Ergonomics is the study of fitting tasks, tools and environments to the people who use them. In spinal health it covers how workstations, lifting tasks, vehicles and daily routines distribute load on the body. Good ergonomics reduces unnecessary strain and fatigue, but it is important to be honest about the evidence: most single ergonomic changes have modest effects on back and neck pain, and no workstation setup can compensate for staying in one position for hours. The most consistent message from research is that movement variety, regular breaks, overall physical activity and confidence in the body matter more than finding one perfect posture.

Intradiscal pressure: what the numbers say

Much traditional advice about sitting and lifting grew from measurements of pressure inside the lumbar disc. Pioneering studies in the 1960s measured pressure in the L3 disc with needle transducers and reported that sitting produced considerably higher pressure than standing, which led to decades of advice that sitting is especially harmful to the spine. A later study in the late 1990s used a pressure sensor implanted in the L4 to L5 nucleus of a healthy volunteer and measured many everyday positions over a full day. Several of its findings differed from the older work.

Three lessons follow. First, relaxed sitting is not dramatically worse for the disc than standing; the old claim that sitting is "the worst position for your back" is not supported by these measurements. Second, bending forward and lifting, especially with the load held away from the body, produce the highest pressures, which fits with the common experience that bending aggravates disc pain. Third, lying down unloads the disc substantially, and discs absorb fluid overnight, which is why people are slightly taller in the morning and why the disc may be more sensitive to bending early in the day.

It is important not to turn these numbers into fear. Discs are designed to bear load, and loading is necessary for disc nutrition and health. High pressure during a lift does not mean harm. Pressure data explain why some positions feel worse during an episode of disc pain; they do not mean that bending or lifting should be avoided for life.

Sitting and workstation setup

For people who work at a desk, a reasonable workstation reduces awkward sustained positions. Commonly recommended features include:

Sit-stand desks reduce sitting time, and some trials report small improvements in discomfort, but standing still for long periods has its own problems, including leg fatigue and venous pooling. The goal is alternation, not replacing hours of sitting with hours of standing. High total sedentary time is associated with poorer cardiometabolic health independent of exercise, which is another reason to build movement into the working day.

Lifting

Generations of workers have been taught to "lift with your legs, not your back." Biomechanically, keeping the load close to the body is the single most effective way to reduce spinal load, because the moment arm of the load about the lumbar spine shrinks. The posture of the back during lifting is less clear cut. Squat lifting reduces lumbar flexion but brings the knees forward, which can push the load farther from the body and requires more energy; stoop lifting with a rounded back is often more efficient. Systematic reviews have found no convincing evidence that lumbar flexion during lifting, on its own, causes back pain, and no evidence that training workers in "correct" lifting technique prevents back pain. Back belts likewise do not prevent back pain in workers.

What does matter is load tolerance. Tissues adapt to loads they are exposed to regularly and gradually. A person who lifts often and is strong and conditioned tolerates heavy lifting well; problems arise when load exceeds current capacity, as when a sedentary person moves house over a weekend. Occupational guidelines address the task rather than technique alone. The lifting equation published by a United States occupational safety agency uses a load constant of 23 kg as the recommended weight limit under ideal conditions and reduces it for factors such as distance from the body, height of the lift, twisting, frequency and poor grip. Reducing these task factors with lifting aids, team lifts and better layout is the most effective workplace strategy.

Movement habits across the day

• Physical activity: adult guidelines recommend at least 150 to 300 minutes of moderate aerobic activity per week, or 75 to 150 minutes of vigorous activity, plus muscle-strengthening on two or more days. Regular activity is associated with lower risk of recurrent back pain, and exercise is among the best supported treatments for chronic back pain.
• Sleep: no single sleeping posture is proven best for the spine. Medium-firm mattresses have modest support for comfort in people with back pain. Good sleep quality matters more, because poor sleep increases pain sensitivity.
• Backpacks: guidance often suggests keeping school bags below about 10 to 15 percent of body weight and using both straps. The evidence linking backpack weight to lasting spinal problems is weak, but heavy loads can cause discomfort.
• Driving: adjust the seat so the knees are slightly bent with pedals fully pressed, support the lumbar curve, and take breaks on long journeys.
• Variety: the healthiest habit is to change positions often, mix sitting, standing and walking, and stay physically confident. A useful phrase for patients is that "motion is lotion": joints and discs depend on movement for nutrition.

Words worth knowing