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Effect of two seating positions on upper limb function in normal subjects

November 2005
International Journal of Therapy and Rehabilitation 12(11):485-490

DOI:10.12968/ijtr.2005.12.11.20058

Authors:

Amar Gandavadi

Care Quality Commission

Jill Ramsay

University of Birmingham

Many upper limb functions are performed in a sitting position. However, if seating is inadequate and poorly designed, back pain and reduced upper limb control may result. This study investigates pelvic posture and performance in an upper limb task. In total, 15 normal healthy volunteers (aged 18–30 years) were seated in posterior and anterior pelvic tilt positions and performed a simple upper limb task. The parameters measured were electromyography of the lumbar paravertebral muscles, time taken to complete the task and the task error rate. The data were analysed by repeated measures analysis of variance (ANOVA) and post-hoc t tests. The results indicate that, when seated in an anterior pelvic tilt position, the error rate decreased (P=0.013) and the electrical activity increased (P=0.008). The time taken to complete the task was not significantly different. Since the error rate decreased when seated in the anterior pelvic tilt position, it might be concluded that this posture facilitated task skill. It is suggested that the increase in electrical activity is related to the increased load on the lumbar muscles in maintaining the posture. This study's generalizability is limited, with small subject numbers and the use of a non-functional task. It is, however, a beginning in addressing the interrelationship between the seated posture and skilled upper limb performance.

The Bambach Saddle Seat (reproduced with permission from Bambach).

…

(a) Bar chart for errors made in the two seating positions, showing mean ±2 standard error (SE) of mean; (b) error bar chart for electromyography readings in the two seating positions, showing mean ±2 SE of mean; (c) error bar chart for time taken for activity, showing mean ±2 SE of mean.

…

Figures - uploaded by Amar Gandavadi

Content may be subject to copyright.

Content uploaded by Amar Gandavadi

Content may be subject to copyright.

People are increasingly spending more time

sitting – for work, for travel and for relax-

ation. However, it is important that the

seat is comfortable, maintains a healthy

posture and facilitates task performance. The pur-

pose of this article is to describe a study investigat-

ing the effects of two different seated postures upon

the muscular activation and the ability to perform a

simple upper limb skill.

BIOMECHANICS

The seated posture changes the demands placed

on the musculoskeletal system, since there is a ten-

dency to gradually adopt a position in which the

pelvis is rotated backward to compensate for mus-

cular tightness in the Hamstring muscles (Pheasant,

1996). Such rotation at the pelvis is accompa-

nied by flexion of the lumbar spine, which may

be close to the end of the available range. In this

position the muscles relax and the body weight is

supported by passive structures such as the spinal

ligaments. Therefore, slump sitting has been noted

to be associated with higher intradiscal pressures

(Nachemson, 1975).

International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11 485

Effect of two seating

positions on upper limb

function in normal subjects

The need for good sitting posture is further rein-

forced, since prolonged sitting has been shown to

predispose individuals to the development of low

back pain (Magora, 1972; Wilder and Pope, 1996).

Electromyographic studies suggest that sitting in a

slouched or reclined posture relaxes the trunk mus-

cles and requires minimal muscle activity to support

the body weight. However, this finding is ambigu-

ous, since the reduction in muscular activity may

not be healthier in terms of minimizing the onset of

low back pain.

To sit in an anterior pelvic tilt position, the mus-

cles must be activated to achieve and maintain the

position. Further, habitual slump sitting could result

in muscle fibre imbalance with slow oxidative fibres

changing to fast twitch fibres (Cram and Vinitzky,

1995). Such fibre changes may result in loss of abil-

ity to maintain an upright seated posture for longer

than a short period before fatigue intervenes and the

person then slumps into a posteriorly tilted posture

(Garlick, 1998).

Of recent years, there have been attempts to

design seating that maintains the pelvis in a rela-

tively neutral position (i.e. neither posteriorly nor

anteriorly tilted). To achieve this position, the hips

Many upper limb functions are performed in a sitting position. However, if seating is inadequate and

poorly designed, back pain and reduced upper limb control may result. This study investigates pelvic

posture and performance in an upper limb task.

In total, 15 normal healthy volunteers (aged 18–30 years) were seated in posterior and anterior pelvic

tilt positions and performed a simple upper limb task. The parameters measured were electromyography

of the lumbar paravertebral muscles, time taken to complete the task and the task error rate. The data

were analysed by repeated measures analysis of variance (ANOVA) and post-hoc t tests. The results

indicate that, when seated in an anterior pelvic tilt position, the error rate decreased (P=0.013) and the

electrical activity increased (P=0.008). The time taken to complete the task was not significantly different.

Since the error rate decreased when seated in the anterior pelvic tilt position, it might be concluded

that this posture facilitated task skill. It is suggested that the increase in electrical activity is related to

the increased load on the lumbar muscles in maintaining the posture. This study’s generalizability is

limited, with small subject numbers and the use of a non-functional task. It is, however, a beginning in

addressing the interrelationship between the seated posture and skilled upper limb performance.

Key words: upper limb function, seating, pelvic posture, back pain

Gandavadi A, Ramsay J, James G (2005) Effect of two seating positions on upper limb function in normal subjects. Int

J Ther Rehabil 12(11): 485–490

Clinical

Amar Gandavadi

is PhD student and

Jill Ramsay and Gill

James are Lecturers in

Physiotherapy, School

of Health Sciences,

Physiotherapy, University

of Birmingham,

Edgbaston, Birmingham

B15 2TT, UK.

Correspondence to:

Amar Gandavadi

Amar Gandavadi, Jill Ramsay, Gill James

ered a suitable non-invasive method for assessing

electrical activity in muscles. A wire game was used

for quantifying the upper limb function. This is a

simple game that needs no special skill to play, and

is an easy way of measuring errors in the activity.

Ethics

The research was approved by the ethics committee

of the School of Health Sciences before commence-

ment of the research. All subjects were volunteers

recruited from an advertisement placed on a notice-

board in the university. Subjects provided informed

consent and could withdraw at any time without

explanation.

Subject selection

Participants were included in the study if they had

no low back or upper limb pain at the time of the

experiment. Participants were excluded if they had

any spinal deformities, acute or persistent back

pain or shoulder or upper limb injury, or lacked full

range upper limb movement, because the presence

of these conditions could influence the outcome of

the study.

Materials

Materials used were as follows:

■ Adjustable-height treatment couch.

■ The Bambach Saddle Seat (Figure 1).

■ The NeuroTrac dual channel electromyograph

(Verity Medical Ltd., www.veritymedical.co.uk)

■ A wire game (Figure 2): This consists of a base

with two upright arms perpendicular to the base

International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11 487

486 International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11

Clinical

must be positioned at an angle of less than 90º.

Mandel (1976, 1981) argued that a forward sloping

seat surface decreases the hip flexion requirements.

Various seats have been designed adopting these

principles – most notably, the ‘kneeling’ chair.

Evaluation of such seats has been largely confined

to examining user comfort (Drury and Flancher,

1985). Such investigations showed that users of the

kneeling chair complained of increased discomfort

in the knees, thereby limiting its usefulness.

Recently, a saddle-type seat (manufactured by

Bambach; www.bambach.co.uk) has been mar-

keted. This seat maintains the pelvis in an anteriorly

tilted posture but does not bear body weight on the

knees, and should therefore be investigated since

theoretically, it may be more user friendly and there-

fore be used more widely.

SEATING AND UPPER LIMB SKILL

One aspect of seating that has been relatively

neglected is the effect upon upper limb function.

Reissner (1972) argues that sitting in an anterior

pelvic tilt position provides pelvic stability, which

is necessary to allow for dynamic spinal move-

ments and for upper limb stability (Nwaobi, 1987).

However, he fails to explain how pelvic stability

affects upper limb function. Logically, sitting in an

anterior pelvic tilt position promotes ease of main-

tenance of the natural lumbar curve and may mini-

mize discal pressures (Keegan, 1953; Mandal, 1981;

Bridger et al, 1992).

Some work has been carried out investigating chil-

dren with disabilities such as cerebral palsy. Myhr

(1994), for example, showed greater ability to use

the upper limb when seated in an anterior pelvic tilt

position, thereby resulting in improved task qual-

ity and diversity. Biomechanically, more upper limb

effort is required to perform movements in the pos-

terior pelvic tilted position owing to the gravitational

pull, thus rendering arm and hand function non-

optimal (Ariyaratnam et al, 2000). However, there

appears to have been little work investigating the

effect of the seating posture upon skill performance

in a population of people without such disabilities.

METHODOLOGY

Research design

A same-subject experimental design was selected,

since the focus of interest is comparing the two dif-

ferent pelvic positions while performing the same

experimental task. Surface electromyography

(EMG) was used to record the electrical activity

of the paraspinal muscles. EMG has been used in

similar studies (Finsen et al, 1998; Callaghan and

McGill, 2001) and within its constraints, is consid-

Figure 1. The Bambach Saddle Seat (reproduced with

permission from Bambach).

and a sinuous metal wire connecting the arms. A

jockey is inserted into the metal wire. The jockey

consists of a hand piece with a small metal ring

in front of it and with a wire attached to it. The

metal ring of the jockey is inserted into the sinu-

ous metal wire.

■ Stopwatch.

■ Tape measure.

Pilot study

A pilot study was carried out with one subject in

order to test the methodology and to assess reliabil-

ity in measuring the parameters. The experimenter

and two physiotherapists measured all the param-

eters. No differences were observed in the results.

Task

The task involved passing a metal ring into a sinuous

wire, tracing its path to the end. A light illuminated

each time the metal ring contacted the wire. In order

to control for possible learning effects, the subject

could not see the light. All the trials were therefore

carried out under the same conditions. The wire game

was placed on a height-adjustable couch at distance

of 1.5 forearm lengths from the trunk midline of

the subject and at elbow height of the seated subject

when the subject’s hand was placed on the thigh.

The subjects were seated for 30 mins before the

task was carried out, in order to acclimatize them to

the sitting position and to standardize the condition

of the subjects before the experiment. Various time

periods have been used in similar studies – from

very short (e.g. mins) to prolonged (Callaghan and

McGill, 2001). A total of 30 mins acclimatization

was used because it was long enough to allow tis-

sues to adapt, but not so long as for fatigue to occur.

Conditions and parameters measured

Figure 3 shows the subject seated on the Bambach

Saddle Seat with the pelvis anteriorly tilted. The

back was unsupported and the feet were fully sup-

ported on the floor by adjusting the height of the

International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11 487

486 International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11

Clinical

Bambach chair. The hip was kept at an obtuse angle

from the horizontal, allowing the pelvis to fall in the

anterior tilted position.

Figure 4 shows the subject seated on a couch with

the back slumped and unsupported in a posterior

pelvic tilt position. The feet were fully supported on

the floor by adjusting the height of the couch. The

order of seated positions was counterbalanced to

control for any possible order effects.

The parameters measured were:

■EMG activity of the lumbar paravertebral mus-

cles – mean of peak amplitudes of three trials.

The peak amplitudes are sudden surges in ampli-

tude, which were critical to the task being per-

formed. The mean of these peak amplitudes was

used as it uses all the data and improved the reli-

ability of the data. Two electrodes are placed in

the back at the L1/L2 spinal level and two elec-

trodes are placed at the L4/L5 spinal level (Cram

and Vinitzky, 1995).

■Time taken for task completion. The mean of the

three trials was used.

Figure 2. The wire game.

Figure 3. Subject seated on

the Bambach Saddle Seat

in an anterior pelvic tilt

position (reproduced with

permission from Bambach).

Figure 4. Subject

seated on a couch in

a posterior pelvic tilt

position (reproduced with

permission from Bambach).

488 International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11

Clinical

■Task error rate. This was measured as the number

of times the light illuminated during the task. The

mean of the three trials was used.

Data analysis

All these hypotheses are two-tailed. Two-way, same-

subject repeated measures analyses of variance

(ANOVA) were performed to test the hypothesis that

the seated posture makes a difference to the param-

eters stated above. Post-hoc tests (the t test) were

calculated to examine significant differences where

appropriate. Throughout, a 0.05 level of significance

was used for rejection of the null hypotheses.

Procedure

■The subjects were seated for 30 mins and given a

magazine or newspaper to read.

■The height of the couch or seat was adjusted so

the feet were flat on the floor, with the thighs

fully supported.

■After 30 mins, three trials of the upper limb task

were carried out.

■The seated condition was then adjusted and a

further three trials of the upper limb task was

carried out.

■The time for completion of the task was measured

using a stop clock and the numbers of errors were

noted in accordance to the number of light glows.

Simultaneously, EMG measurements were taken.

RESULTS

A total of 15 subjects aged 18–30 years who ful-

filled the inclusion criteria were recruited to take

part in the experiment. Figure 5 shows the mean and

standard error for all three parameters. The error rate

and task time had both fallen when the subjects were

seated in the anterior pelvic tilt position (Bambach

seat), while the mean EMG measurement increased

in that condition.

The ANOVA results were significant (F=216.105,

P<0.000). Post hoc t tests were significant for errors

(t=2.863, P=0.013) and for EMG (t=–3.106,

P=0.008). The time taken to complete the task was

not significant. It is clear that both the error rate and

the EMG measurements (P=0.008) were signifi-

cantly affected by the seating posture. While the error

rate decreased when using the Bambach seat, the

mean peak EMG reading increased. In both cases,

therefore, the null hypothesis can be rejected and the

experimental hypothesis accepted.

DISCUSSION

The study shows that there was a statistically signifi-

cant difference in the subject’s upper limb function

relative to this task in the anterior pelvic tilted posi-

tion (i.e. seated on the Bambach chair). This sug-

gests that the principles of pelvic tilt and dynamic

seating enhance natural spinal curves, good seating

and upper limb function (Keegan, 1953; Mandal,

1981, Bridger et al, 1992; McClenaghan et al, 1992).

The fall in the error rate was highly significant

(P=0.013), with 12 participants improving their per-

formance in the anterior pelvic tilt position. Reissner

(1972) reported that an anteriorly tilted pelvis pro-

vides pelvic stability and is necessary to allow for

dynamic spinal movements. Such improved stabil-

ity should enable subjects to access the wire game

more easily, because movement occurs at the hip

without the characteristic slouching so often seen

Figure 5. (a) Bar chart for

errors made in the two

seating positions, showing

mean ±2 standard error

(SE) of mean; (b) error bar

chart for electromyography

readings in the two seating

positions, showing mean

±2 SE of mean; (c) error

bar chart for time taken

for activity, showing mean

±2 SE of mean.

Errors: Couch

EMG: Couch

Activity time Activity time

Errors: Bambach Saddle Seat

EMG: Bambach

Number of errors made (mean ± 2E)

Electromyography readings (mean ± 2E) (µA)

Time taken (mean ± 2E) (s)

in other positions and facilitates the pelvic stabil-

ity necessary for good upper limb movement for

desktop tasks. Conversely, poor performance by the

subjects sitting in the posterior tilted position was

noted – a finding which apparently concurs with the

study reported by Ariyaratnam et al (2000).

An increase in EMG activity was noted when

subjects were seated in the Bambach seat.

Biomechanically, in the anterior pelvic tilted posi-

tion, the line of gravity falls anterior to the axis of

rotation at the ischial tuberosities, gravity acts to

flex the head and trunk so as to pull it down. In

order to maintain a stable posture, the back and

neck muscles generate an equal torque in the oppo-

site direction (Norkin and Levangie, 1983). There is

a reflex activation of the postural muscles as well as

the order in which these muscles are recruited for

postural alignment and stability. This supports the

reason for increased EMG activity of the back mus-

cles reported in this study.

When asked to comment on the two postures, par-

ticipants indicated that they believed that their upper

limb performance was enhanced by their improved

posture. However, three of the participants reported

that they were more comfortable sitting in the pos-

terior pelvic tilt position and perceived difficulties

in performing the task in the anterior pelvic tilt posi-

tion. The reason for this might be a muscle fibre

imbalance associated with the habitual slumped

position – instead of slow oxidative fibres of postural

or antigravity muscles, the fast twitch muscle fibres

can be activated (Cram and Vinitzky, 1995).

This study should be regarded as a pilot study,

owing to its small subject numbers and the narrow

age band from which subjects were recruited. It

would be useful to replicate the study with a larger

sample drawn from a wider age range. Additionally,

it would be useful to study subjects with either low

back pain or neck or upper limb dysfunctions. The

task is unfunctional and therefore adopting a similar

methodology but using a functional work-related task

should be attempted. However, such a study would

require a method of evaluating skilled performance.

CONCLUSIONS

Within these limitations, however, it is possible to

draw several positive conclusions. It appears that the

ability to carry out upper limb tasks may be influ-

enced by the seated posture – specifically, the angle

of pelvic tilt. Interestingly, it may be that the altered

posture facilitates skilled performance, although

this aspect needs further investigation.

The increase in EMG activity, however, indicates

caution since subjects may need time to adapt to

sitting with the pelvis tilted anteriorly. Even allow-

ing for such training time, this position may not suit

everyone and in those cases, it is possible to specu-

late that performance will be adversely affected.

However, for those people whom this sitting posture

suits, it could logically create healthier working pos-

tures and may thereby decrease morbidity in those

individuals with work-related dysfunctions.

The authors gratefully acknowledge the assistance of Bambach for

the loan of a Bambach Saddle Seat. They also thank all the sub-

jects who participated in the study. This study was carried out in

part-fulfillment of the regulations for the degree of MSc in Health

Sciences at the University of Birmingham by the first author.

Conflict of interest: none.

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Drury CG, Flancher M (1985) Evaluation of a forward-sloping

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■When subjects were seated in an anterior pelvic tilt position, upper limb

task performance was significantly better than when they were seated in a

posterior pelvic tilt position.

■There was increased electrical activity in the lumbar paravertebral muscles in

the anterior pelvic tilt position.

■The decreased error rate in the anterior pelvic tilt position (using the

Bambach Saddle Seat) appears indicative of enhanced upper limb function.

■Sitting in an anterior pelvic tilt position should promote healthier working

postures and may minimize discal pressure.

Key points

490 International Journal of Therapy and Rehabilitation, November 2005, Vol 12, No 11

Clinical

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Oct 2013

Helen Westley

Musculoskeletal disorders, including repetitive motion injuries, result in painful work, lost workdays, and, in extreme cases, disability resulting in forced retirement disorders. That's why it's so important that you choose an ergonomic seat which ensures that the pelvis is properly positioned and stabilised

Trunk Restraint to Promote Upper Extremity Recovery in Stroke Patients: A Systematic Review and Meta-Analysis

Article

Feb 2014
NEUROREHAB NEURAL RE

. Many stroke patients exhibit excessive compensatory trunk movements during reaching. Compensatory movement behaviors may improve upper extremity function in the short-term but be detrimental to long-term recovery. . To evaluate the evidence that trunk restraint limits compensatory trunk movement and/or promotes better upper extremity recovery in stroke patients. . A search was conducted through electronic databases from January 1980 to June 2013. Only randomized controlled trials (RCTs) comparing upper extremity training with and without trunk restraint were selected for review. Three review authors independently assessed the methodological quality and extracted data from the studies. Meta-analysis was conducted when there was sufficient homogenous data. . Six RCTs involving 187 chronic stroke patients were identified. Meta-analysis of key outcome measures showed that trunk restraint has a moderate statistically significant effect on improving Fugl-Meyer Upper Extremity (FMA-UE) score, active shoulder flexion, and reduction in trunk displacement during reaching. There was a small, nonsignificant effect of trunk restraint on upper extremity function. . Trunk restraint has a moderate effect on reduction of upper extremity impairment in chronic stroke patients, in terms of FMA-UE score, increased shoulder flexion, and reduction in excessive trunk movement during reaching. There is insufficient evidence to demonstrate that trunk restraint improves upper extremity function and reaching trajectory smoothness and straightness in chronic stroke patients. Future research on stroke patients at different phases of recovery and with different levels of upper extremity impairment is recommended.

Appropriate seating for medical patients: An audit

Article

Aug 2011

To determine the number and types of chairs available for patient use; to establish minimum criteria of appropriate chairs; and to assess the suitability of available chairs to seat patients admitted to medical wards. Audit of chairs available in medical wards in a tertiary referral public hospital was conducted. All chairs relevant to patient use were photographed and counted. An expert panel determined minimum criteria of appropriate seating for older patients from functional, occupational health and safety, ergonomic, infection control and usability viewpoints. The number of chairs meeting the minimum criteria level was recorded and was expressed as a percentage of the number of required chairs (hospitalised patients able to be sat out of bed). A total of 270 chairs of 36 different types were identified. The majority of chairs, 231 (85%), did not meet the minimum criteria. Thirty-nine chairs met the minimum criteria for patients to sit in with 113 (66%) patients unable to sit out of bed. This study identified that there were insufficient appropriate chairs available for patients to sit out of bed in this facility. This has potential implications for functional ability of the patients, particularly for the older person.

A quantitative investigation of lumbar and pelvic postures in standing and sitting: Interrelationships with body position and hip muscle length

Article

Full-text available

May 1992
INT J IND ERGONOM

Lumbar angles, pelvic tilts and hip muscle indices of 25 female and 25 male subjects were measured in standing and in a variety of body positions in order to test hypotheses derived from the model of standing and sitting posture expounded by authors such as Keegan (1953) and later by Mandal (1991). The model emphasises the interrelationship between the anterior and posterior thigh muscles and tilt of the pelvis in determining spinal posture in different body positions. The posterior trunk-thigh muscles are held to play a major role in the flattening of the lumbar spine in sitting and the anterior trunk-thigh muscles in accentuating the lumbar curve in standing.A quantitative test of hypotheses derived from the model carried out. Spinal angles and pelvic tilts were measured using an inclinometer. An angular index of iliopsoas muscle length proved the best predictor of postural adaptation. A supplementary investigation clarified the role of the hamstrings in postural adaptation. The findings support and extend those of other recent researchers but draw attention to the effects of body position of lumbo-pelvic constraint as well as the mechanisms of loss of lumbar lordosis in sitting. Some potential problems of postural stress in standing - caused by excessive lumbar lordosis - are suggested as well as implications for research into working posture in developing countries.

EFFECTS OF SEAT-SURFACE INCLINATION ON POSTURAL STABILITY AND FUNCTION OF THE UPPER EXTREMITIES OF CHILDREN WITH CEREBRAL PALSY

Article

Jul 1992
J PEDIATR ORTHOPED

Seating Orientations and Upper Extremity Function in Children with Cerebral Palsy

Article

Aug 1987

Olunwa Mafiana Nwaobi

This study was conducted to determine the effect of body orientation on upper extremity function in children and adolescents with cerebral palsy. Thirteen children between ages 8 and 16 and diagnosed as having spastic or athetoid cerebral palsy were placed randomly in different seating orientations (30°, 15°, and 0° of posterior inclination and 15° of anterior inclination). In each seating position, the subject performed an upper extremity activity on cue. The tests were repeated in reverse sequence. Mean performance times were different at all seating orientations for both types of subjects. Performance time was lowest at the 0-degree orientation during the retest for the subjects with spasticity and highest at 15-degree anterior inclination during the retest for the subjects with athetosis. The results of this study show that orientation of the body in space affects upper extremity function and emphasizes the importance of positioning for maximizing upper extremity function.

Effects of chair design on back muscle fatigue

Article

Jun 1995
J OCCUP REHABIL

The electromyographic activity of the paraspinal muscles were examined to investigate the effects of chair sitting on muscle activation patterns and muscle fatigue. Twenty-four subjects were studied on the Balans, Back Up, and standard office chairs during a seated writing task and standing while performing a standardized muscle fatigue assessment test. The results of the study indicate that in 87.5% of the comparisons at the L3 site, the Back Up chair has lower readings of muscular effort compared to the Balans and office chair. During the muscle fatigue testing, the greatest amount of fatigue was noted in those subjects who sat in the Back Up chair last. When the Back Up chair was first or second, the least amount of fatigue was observed. The sEMG results supports a biomechanical model. The ergonomics of the Balans and office chairs give the least amount of support to the low back, while the Back Up chair provides the greatest amount of support. It is suggested that adequate pelvic girdle support during seated tasks will lower the threshold of back fatigue and thus facilitate return to work for low back pain patients.

Bodyspace: anthropometry, ergonomics, and the design of work

Book

Jan 1998

S.T. Pheasant

Towards a better understanding of low back pain: A Review of the mechanics of the lumbar disc

Article

Sep 1975
Rheumatol Rehabil

ALF NACHEMSON

By measurement of intradiscal pressure in vitro, the hydrostatic properties of the nucleus pulposus of normal lumbar intervertebral disc was established. The stress distribution within normal discs subjected to vertical load was also explained, demonstrating the high tangential strains occurring in the posterior part of the annulus fibrosus. Intravitally performed measurements of disc pressure have demonstrated how the load on the lumbar disc varies according to the position of the subject's body. Compared to the pressure or load in the upright standing position, reclining reduces the pressure by 70%, while unsupported sitting increases the load by 40% and forward leaning and weight lifting by more than 100%. Similar relatively large augmentations of the load were observed in subjects performing various commonly used muscle-strengthening exercises. Measurement of intradiscal pressure is instrumental in explaining, from a mechanical point, the occurrence of posterior ruptures in the lumbar discs, and provides a basis for the rational treatment of patients with low-back pain in so far as these exhibit increase of pain on increased mechanical loads. For the majority of patients with low-back pain, the cause is unknown, although most evidence so far presented links the lumbar intervertebral disc to the pain syndromes. Results of recent studies have shown that both chemical and mechanical factors are probably of importance. So far we cannot successfully treat the chemical part of the disc syndrome. Since all our patients exhibit more pain when the spine is mechanically loaded, knowledge gained from intravital disc-pressure measurements provides a basis for successfully treating the mechanical part of the condition. Since none of the frequently prescribed and more spectacular remedies has ever been proved statistically superior to any of the others, it is most fair to our patients and to ourselves to use simpler, less expensive, and less dangerous programmes, such as bed-rest, administration of salicylates, and proper ergonomic advice. Based on a scientific approach, the low-back-pain school is intended to help the patient to be able to cope with these back troubles, to avoid excess therapy, and to decrease the cost both for the individual and for Society.

Work-chair with Tilting Seat

Article

Apr 1976

åge C. Mandal

Despite the frequent occurrence of backache, our sitting habits have elicited strikingly little interest among doctors. In order to obtain the best support in tho lumbar region, present-day office chairs aro tilted backwards by 5° and thus render all work involving bending forwards difficult. The author has constructed a chair where the seat tilts forwards in work involving bonding forward. In this manner considerable overstretching of the muscles of the back is avoided and a comfortable, relaxed and well-balanced working position is obtained. Flexion of the hips is considerably reduced and lumbar lordosis re-established. In all, approximately 20° floxion in the spino and hip joint is avoided. It should be noted that this is tho most strenuous fraction of flexion.

Effects Of Seat‐Surface Inclination On Postural Stability And Function Of The Upper Extremities Of Children With Cerebral Palsy

Article

Feb 1992

This study investigated the effects of seat‐surface inclination on parameters of postural stability and functional use of the upper extremity. 10 non‐impaired children and 10 children with cerebral palsy, aged between four and 15 years, were studied. Seat‐suface inclinations of 0d̀, 5d̀ anteriorly and 5d̀ posteriorly were used as the experimental conditions. Significant differences were observed on most dependent measures between the two groups. The results suggest that anteriorly tilting the seats of children with cerebral palsy may disturb postural stability, without improving performance of the upper extremity. REŚUMŕ Effets de l'inclinaison de surface de siège sur la stabilitŕ poslurale el la fonction des mains chez les enfants I.M.C. Cette ŕtude analyse les effets de l'inclinaison de surface des sièges sur les paramètres de la stabilitŕ posturale et 1'usage des mains. 10 enfants indemnes et 10 enfants I.M.C, agŕs de quatre a 15 ans, ont ŕtŕ ŕtudiŕs. Des inclinaisons de la surface de siège de 0±, 5± vers 1'avant et 5± vers 1'arrière, ont dŕfini les conditions expŕrimentales. Des differences significatives ont ŕtŕ observŕes sur la plupart des variables dŕpendantes entre les deux groupes. Les rŕsultats suggèrent que l'inclinaison antŕrieure du siège des enfants I.M.C peut altŕrer leur stabilitŕ posturale, sans amŕliorer pour autant les performances manuelles. ZUSAMMENFASSUNG Einfluß der Sitzneigung auf die Haltungsstabilitat und die Funktion der oberen Extremiteit bei Kindern mit Cerebralparese In dieser Studie wird der Einfluß der Sitzneigung auf Parameter der Haltungsstabilitat und die Funktion der oberen Extremitat untersucht. 10 nicht behinderte Kinder und 10 Kinder mit cerebralparese, im Alter zwischen vier und 15 Jahren, wurden untersucht. Sitzneigungen von 0d̀, von 5d̀ nach vorne und 5d̀ nach hinten wurden getestet. Für die meisten Parameter wurden signifikante Unterschiede zwischen den beiden Gruppen gefunden. Die Ergebnisse zeigen, daß nach vorn geneigte Sitze die Haltungsstabilitat von Kindern mit Cerebralparese storen können, ohne die Funktion der oberen Extremitat zu verbessern. RESUMEN Efectos de la inclinación de la superficie del asiento sobre la estabilidad postural y la función de las extremidades superiores en nin̈os con parálisis cerebral Este estudio investigo los efectos de la inclinación de la superficie del asiento sobre los parametros de la estabilidad postural y el uso funcional de la extremidad superior. Se estudiaron 10 nin̈os no patológicos y 10 con parálisis cerebral, de edad entre cuatro y 15 an̈os. Como condiciones experimentales se utilizaron Ia inclinación de Ia superficie del asiento de 0d̀ a 5d̀ hacia adelante y 5d̀ hacia atras. Se observaron diferencias significativas en las mediciones mas dependientes entre ambos grupos. Los resultados sugieren que la inclinación hacia adelante de los asientos en nin̈os con parálisis cerebral puede alterar la estabilidad postural, sin mejoral la realización de la extremidad superior.

Investigation of the relation between low back pain and occupation. 3. Physical requirements: sitting, standing and weight lifting

Article