ESTADO ACTUAL DEL DESARROLLO DE LA PLANIFICACIÓN

Standing from sitting is an activity which is per- formed frequently in daily life. In a review of the

literature, Kerr et al (1991) categorised the research relating to rising from a chair into four major areas:

• biomechanical investigations • kinematic studies

• investigations of muscle activity

• general studies of the functional aspects of seating for disabled people.

Many variables have been shown to influence getting up from a chair. These include the height of the chair, use of the arms, speed of movement, the direction of movement, placement of the feet and the age and sex of the individual. An example of the complexity of analysis of this movement sequence may be found in a study which demonstrated that in a sample of 10 young adults, five different arm patterns, three different head and trunk patterns and three different leg patterns were found to occur (Francis et al 1988 as cited by VanSant 1990b).

While producing definitive numerical data on moments of force generated at the joints and muscles of the lower extremity during rising, many of the biomechanical studies have demon- strated substantial complexity in study design, involving highly sophisticated technical equip- ment and considerable manipulation of subjects. This may preclude the application of such proce- dures to large samples of disabled subjects (Kerr et al 1991). The following analysis discusses the key components of sitting to standing and their significance to clinical practice.

The initial base of support is relatively large and includes the surface area of the chair with which the body is in contact, the floor area within the base of the chair and the area within and pos- terior to the foot position. A key component of this movement is the transference of weight from a relatively large base of support to one which is significantly smaller - the feet alone.

Many studies identify two distinct phases in moving from sitting into standing - initial for- ward trunk lean and upward extension (Nuzik et al 1986, Schenkman et al 1990).

On clinical observation, the movement for- wards of the trunk varies. In some individuals the trunk moves forwards on the pelvis prior to

the pelvis tilting anteriorly, whereas in others the trunk is held more rigidly extended and the trunk and pelvis move forwards simultaneously. This trunk and pelvic movement enables the weight to be transferred forwards over the feet. It may also be necessary for the individual to move the buttocks forwards, depending upon the initial position in the chair.

As the trunk and pelvis move forwards, the head extends and the knees move forwards over the feet so as to facilitate the transference of weight during upward extension. The knees move for- wards over the feet producing dorsiflexion at the ankle, the maximum range of dorsiflexion occur- ring as the buttocks are lifted from the seat of the chair. The legs extend as the individual moves into the upright position with a decreasing amount of activity in quadriceps as the knee angle approaches zero (Schuldt et al 1983). The anterior tilt of the pelvis is at its maximum as the buttocks are lifted off the chair and reduces as the sequence progresses, with extension of the hips on com- pletion of the movement. Similarly, the position of the head adjusts relative to the trunk throughout the sequence, moving from a more extended posi- tion at the beginning of the movement to one of relative flexion.

Clinical application

Many people with neurological disability have difficulty with this complex movement sequence. Treatment strategies vary depending on the dif- ferent reasons for the problem. Such problems may include restricted joint range at the foot and ankle or abnormal tone within the trunk and pelvis, both of which may preclude or impair the initial forward lean.

In clinical practice, the height of the chair or plinth is seen to be a critical factor in performance of the activity. Increasing seat height and the use of arms decreases muscle and joint forces at the hips and knees (Burdett et al 1985, Arborelius et al 1992) and also decreases energy expenditure (Didier et al 1993). Many patients benefit from first practising the movement from a higher seat and gradually reducing the height as they become more proficient.

Walking

The purpose of this analysis is to consider aspects of normal gait in relationship to patho- logical gait of neurological origin. Throughout this section the terms 'walking' and 'gait' are used interchangeably, although Whittle (1991) defines gait as the manner or style of walking rather than the walking process itself. There are many definitions of gait, which include:

• a series of controlled falls (Rose et al 1982) • a method of locomotion involving the use of

the two legs, alternately, to provide both support and propulsion, at least one foot being in contact with the ground at all times (Whittle 1991)

• a highly coordinated series of events in which balance is being constantly challenged and regained continuously (Galley & Forster 1987). There are numerous studies which have described aspects of gait in detail. These include Saunders et al (1953), Murray et al (1964) and Whittle (1991). Saunders et al (1953) identified the primary determinants of human locomotion in respect of the behaviour of the centre of gravity of the body. In normal level walking, this follows a smooth, regular sinusoidal curve in the plane of progression which enables the human body to conserve energy.

Murray et al (1964) recorded the displacements associated with locomotion and established the ranges of normal values for many components of the walking cycle. These were considered in respect of the speed and timing of gait and stride dimensions, sagittal rotation of the pelvis, hip, knee and ankle and vertical, lateral and forward movement of the trunk and the transverse rotation of the pelvis and thorax.

The gait cycle

The gait cycle is the time interval between two successive occurrences of one of the repetitive events of walking (Whittle 1991). The cycle com- prises two component parts, the stance and swing phases. The stance phase is the portion of the cycle where the foot is in contact with the

floor and the swing phase is where the leg is off the ground moving forwards to take a step. There are two periods during the cycle when both feet are in contact with the ground. The pro- portion as a percentage of the walking cycle is 60% stance and 40% swing. The duration of the supportive phases of the walking cycle decreases with increased walking speeds (Smidt 1990).

Common characteristics of gait

Step and stride length. The step length is the distance between successive points of floor-to- floor contact of alternate feet; the stride length is the linear distance between successive points of floor-to-floor contact of the same foot. The step and stride length are related to the height of the individual, shorter subjects taking shorter steps and taller subjects longer steps, and to age, sub- jects over 60 having a shorter step length than those of a younger age group (Murray et al 1964, Prince et al 1997).

The stride width or walking base. This is the side-to-side distance between the line of the two feet, usually measured at the midpoint of the heel (Whittle 1991). It is directly related to the lateral displacement of the pelvis produced by the hori- zontal shift of the pelvis or relative adduction of the hip (Saunders et al 1953). This allows the stride width to remain within the pelvic circum- ference throughout the gait cycle, and Murray et al (1964) observed that the midpoint of one foot may even cross over the other. The stride width is not related to age or height nor does it correlate significantly with foot length, bi- acromial or bi-iliac measures (Murray et al 1964). Murray identified an increase in the foot angle (outward placement) of subjects over 60 years of age and suggested this to be their means of achieving additional lateral stability as the neuromuscular system begins to decline. The foot angle is also increased at slower walking speeds. An increase in the stride width is a notable feature in people with impaired balance. The degree to which it occurs depends on the extent of the damage to the CNS.

Cadence and velocity. The cadence is the number of steps taken in a given time and the

velocity of walking is the distance covered in a given time. The normal ranges for gait para- meters are given in Table 3.2.

Greater velocities of locomotion are achieved by the lengthening of the stride rather than by an increase in cadence (Saunders et al 1953) and this depends to a great extent on the functional ob- jective. For example, strolling along the pro- menade is more leisurely than walking quickly knowing one is late for an appointment. Balance modification is directly related to speed; enforced reduction in the natural cadence will require increased postural adaptation.

The muscle activity required to step forwards differs in accordance with the speed of move- ment. For example, a step from a standing posi- tion requires greater hip flexor activity than a step taken as part of the gait cycle at the individ- ual's natural cadence. Similarly, the initiation of a step from a standing position produces a back- ward displacement of the body to counter the extended lever anteriorly, whereas the body is more upright in the natural gait cycle. These are important considerations for the physiotherapist when re-educating gait. In many instances, treat-

ment of necessity takes the form of re-education of the component parts, but it must be appre- ciated that fluidity and economy of movement are dependent upon the many factors associated with the gait cycle, not least cadence and speed. Re-education of gait at slow speeds often makes performance more difficult (Mauritz & Hesse 1996).

Rotation. The pelvis and thorax rotate simul- taneously in the transverse plane during each cycle of gait, the pelvis and shoulders rotating in opposite directions. Murray (1967) suggested that one of the functions of arm swing is to coun- teract excessive trunk rotation in the transverse plane. Maximum rotation occurs at the time of heel contact and the greater the speed, the greater the degree of rotation and subsequent arm swing. The enhanced amplitude of rotation is achieved mainly by increased shoulder extension on the backward end of the arm swing (Murray 1967). There is a decreased amplitude of rotation in the elderly which may be related to a more flexed posture (Elble et al 1991).

With increasing speed, either walking as quickly as possible or when running, the arm swing becomes more vigorous to help in both generating pace and in maintaining balance. An example is that of a sprinter in action. As the speed increases, so too does the pumping action of the arms combined with increased extension of the thoracic spine, perfectly illustrated as the athlete crosses the finishing line.

Disability resulting in an imbalance of the inter-reaction between flexor and extensor activ- ity may impair rotation. An example of this is illustrated in the person with Parkinson's disease (Rogers 1991). The main observable features are those of increased flexion and lack of rotation with the characteristic shuffling gait. In the past, therapists were taught to work for improved rotation by facilitating arm swing. Little attention was paid to the inherent loss of extensor activity. It is now widely accepted in clinical practice that rotation can only be facilitated on the basis of appropriate inter-reaction between flexion and extension within the trunk. Hence, in this instance, improving extension must occur before rotation is possible.

Vertical displacement. This occurs twice during the gait cycle and is approximately 50 mm (Whittle 1991). The summit of these oscillations occurs during the middle of stance phase and the centre of gravity falls to its lowest level during double stance when both feet are in contact with the ground (Saunders et al 1953). The magnitude of the vertical excursion correlates with the length of stride because when the step lengths are longer the lower limbs are more obliquely situated (Murray et al 1964). This characteristic ascent and descent of the body mass is altered in patients with hemiplegia. The movement is dependent upon sufficient muscle activity to maintain stabil- ity of the pelvis and hip joint during stance phase. Patients with hemiplegia often have inadequate or inappropriate activity to provide this stability. This gives rise to the characteristic unilateral Trendelenburg gait whereby the vertical dis- placement occurs only during stance phase of the unaffected leg (Wagenaar & Beek 1992).

Muscle activity and joint range associated with gait

Normal walking is dependent upon the continual interchange between mobility and stability (Perry 1992) with more than 1000 muscles moving over 200 bones around 100 movable joints (Prince et al 1997). Box 3.1 provides a summary of normal muscle activity and function during gait. These muscles do not have one single action but may work concentrically, eccentrically or isometrically at different stages of the gait cycle.

This is of particular relevance when con- sidering the use of muscle (botulinum toxin) or nerve (phenol) blocks. For example, the role of the plantar flexors is to contribute to knee stabil- ity, provide ankle stability, restrain the forward movement of the tibia on the talus during stance phase and minimise the vertical oscillation of the whole body centre of mass (Sutherland et al 1980). Therefore, while muscle or nerve blocks may reduce excessive or poorly timed calf muscle activation (Hesse et al 1994, Richardson et al 2000), they may also lead to knee and ankle instability and increased energy expenditure.

The foot and ankle

Efficient transfer of weight from one leg to the other is partly dependent upon the ability of the feet to respond and adjust effectively to the base of support, be it a firm surface or over rough ground. The ankle and intrinsic foot musculature make constant adjustments to adapt appro- priately to provide the dynamic stability essen- tial for this acceptance of, and movement over, the base of support. The mobility of the foot and ankle is therefore essential for effective transfer of weight. The total range of dorsiflexion and plantar flexion varies between about 20 and 35 degrees, with foot clearance being only 0.87 cm in mid-swing (Gage 1992). Any restric- tion in this mobility will necessitate com- pensatory adjustments - for example, increased knee flexion or hip hitching.

The muscle action occurring at the ankle is primarily that of dorsiflexion controlling the placing of the foot on the supporting surface fol- lowing heel strike and plantar flexion to propel the body forwards (Winter 1987, Kameyama et al 1990).

The knee

The range of movement at the knees is between approximately 70 degrees during the swing phase and full extension at the moment of heel strike and in mid-stance (Whittle 1991). In normal locomotion, the body moves forwards over the leg while the knee joint is flexed, the knee extending during stance and then once more flexing to carry the non-weight-bearing limb forwards. Saunders et al (1953) refer to the knee being locked in extension' during heel strike and during mid-stance but, on clinical observation, it would seem that this only occurs with pathology.

The hip

Movement at the hip is between approximately 30 degrees flexion and 20 degrees extension (Whittle 1991). The predominant activity during stance phase is that of extension and abduction as the

body moves forwards over the supporting foot. Prior to initiation of swing phase, the extended position at the hips is dependent upon the ability of the hip flexors to lengthen, thereby allowing this transference of weight. During swing phase, the primary activity is again that of extension acting as a deceleration force as the leg moves for- wards through momentum prior to heel strike (Whittle 1991). The leg initially flexes, with adduc-

tion and medial rotation at the hips. As the knee begins to extend in preparation for heel contact, the leg becomes more laterally rotated.

The pelvis

The pelvis provides the dynamic stability essen- tial for coordinating the activity of the lower limbs and the control and alignment of the trunk.

Many authors refer to rotation of the pelvis although it may be more appropriate, as the pelvis is a rigid structure, to consider rotation in relation to the hips and the thoracolumbar spine. Palpating the anterior superior iliac spines while walking at one's natural pace reveals little dis- cernible movement, the rotational movement being approximately 4 degrees on either side of the central axis, the lateral movement approxi- mately 5 degrees (Saunders et al 1953) and the anterior/posterior movement approximately 3 degrees (Murray et al 1964).

As the body moves forwards over the sup- porting leg, the pelvis maintains its stability predominantly through the action of gluteus maximus and medius. The maintenance of a neutral or slight posterior tilt of the pelvis is also determined by this activity.

Neural control

Control of locomotion is extremely complex. Leonard (1998) highlights this complexity in his analysis of human gait:

the CNS somehow must generate the locomotor pattern; generate appropriate propulsive forces; modulate changes in centre of gravity; coordinate multi-limb trajectories; adapt to changing conditions and changing joint positions; coordinate visual, auditory, vestibular and peripheral afferent information; and account for the viscoelastic properties of muscles. It must do all of this within milliseconds and usually in conjunction with coordinating a multitude of other bodily functions and movements.

Central pattern generators (CPGs) within the spinal cord generate the locomotor rhythm, but whereas cats with totally transected spinal cords still maintain the ability to walk, humans depend upon supraspinal control. It is suggested that descending systems integrate with spinal cord circuitry to fractionate lower limb movement and provide greater adaptability to changing afferent conditions (Dietz 1997, Leonard 1998).

Clinical application

For normal subjects, walking is goal-oriented and automatic with no consideration given to the component parts necessary to propel them on

their way. In contrast, many patients with neuro- logical impairment may have to consider every aspect of movement in walking. Conscious thought about how to put one foot forward in front of the other and maintain balance in order to achieve a functional goal is both physically and mentally demanding.

There are many assumptions within physio- therapy regarding the re-education of gait, the majority of which are unsubstantiated. Quality of movement is considered to be of the essence and yet, with a damaged nervous system, is it poss- ible to regain normal activity (Latash & Anson 1996)? There is widespread reluctance by physio- therapists to recommend the use of walking aids (Sackley & Lincoln 1996). However, Tyson (1999) found that these did not adversely affect walking ability and, although Hesse et al (1998) reported a more balanced walking pattern immediately following gait facilitation by Bobath therapists as opposed to walking with or without an aid, no carry-over could be demonstrated 1 hour after treatment. Hesse et al (1998) concluded that 'hesitant prescription' of walking aids for hemiplegic patients was not justified.