Rheumatology 1999;38:267–274
Forces measured during spinal manipulative
procedures in two age groups
M. C. Harms1,2, S. M. Innes1 and D. L. Bader2
1Camden and Islington Community Trust, The Middlesex Hospital, Mortimer
Street, London and 2Department of Materials and IRC in Biomedical Materials,
Queen Mary and Westfield College, University of London, UK
Abstract
Objective. Manipulation techniques have a prominent, yet controversial, role in the
treatment of back pain. Their use varies widely between the professional groups and between
individual therapists, with no accurate method of standardizing or quantifying the treatment
administered.
Methods. An instrumented mobilization couch was developed to measure and characterize
typical forces used during spinal manipulative therapy. The couch was used to measure the
forces applied to the lumbar spine of 30 young healthy subjects during five mobilization
techniques, and to a clinical sample of 31 patients, aged between 45 and 65 yr.
Results. The magnitudes of the mobilization forces were found to be similar for the young
and the older groups. Median forces of 164 and 168 N, respectively, were recorded during a
Grade III procedure. However, the forces applied to the older group exhibited a smaller
amplitude and higher frequency of oscillation than those applied to the young group
(P < 0.001).
Conclusion. Objective measurements can be used to characterize manipulative forces for
both evaluative and teaching purposes.
K : Spinal manipulation, Mobilization, Force, Measurement.
The impact of back pain on the general population is
often estimated [1]. Aside from the personal cost to the
sufferer, back pain results in financial costs to the health
service amounting to approximately £700 million per
annum. The incidence of disability due to back pain is
rising exponentially, a trend thought to be the result of
increasingly sedentary lifestyles and a lower tolerance
of illness within the population [1, 2].
Seventy-two per cent of patients with back pain will
be treated with spinal manipulative procedures, yet little
is known of their effects or efficacy [3, 4]. To date, there
are no validated methods of measuring the characteristics of the mobilization force, making it impossible to
quantify or standardize the treatment [3, 5]. At best,
procedures are described in semi-quantitative terms, e.g.
‘high-velocity, low-amplitude thrusts’ [6 ]. Of the few
studies that attempted to monitor force characteristics,
Triano et al. [7] recorded the forces applied by a spinal
manipulator. Two procedures were defined: a highvelocity, low-amplitude thrust and a high-velocity, lowforce mimic. The relatively high variability associated
with the mean forces measured, 1008 N (.. 501 N )
and 212 N (.. 109 N ), respectively, suggested that
there was little standardization of the techniques used.
Previous studies by the authors reported that whilst
some individuals are able to repeat applied forces with
reasonable accuracy, many demonstrate considerable
variation, and there are substantial differences between
individuals [8]. Their use also varies widely between the
professional groups including physiotherapists, physicians, osteopaths and chiropractors. Consequently,
manual therapy has often been evaluated as a global
treatment for back pain without sufficient control or
definition of the treatment protocol [4]. Two recent
reviews of randomized controlled trials on manipulation
for low back pain conclude that the efficacy of manipulation has not been demonstrated. The methodological
quality of many commonly cited studies is also brought
into question [4, 9].
Manipulation can be categorized into the two techniques of mobilization and high-velocity manipulative
thrust [4, 10]. The former is a passive, rhythmical
oscillation of the vertebra that can be resisted by the
patient at any time and is performed within or at the
limit of physiological joint range.
During postero-anterior central vertebral mobilization, the therapist rhythmically applies a force to the
spinous process. This results in translation and rotation
of the vertebral body with respect to adjacent vertebrae
[11], which affects the surrounding soft tissues.
Submitted 9 June 1998; revised version accepted 11 November 1998.
Correspondence to: M. Harms, Camden and Islington Community
Trust, Physiotherapy Office, North East Building, 4 St Pancras Way,
London NW1 0PE, UK.
267
© 1999 British Society for Rheumatology
268
M. C. Harms et al.
Generally, mobilization procedures aim to restore
normal structure and function to scar tissue, to encourage removal of the by-products of inflammation, and
improve tissue rehabilitation by improving the flow of
nutrients and tissue metabolism. The rhythmical movement is thought to modulate pain and muscle spasm by
stimulating receptors within the mobilized structures.
The soft tissues demonstrate hysteresis, which is likely
to occur during mobilization procedures, generating
thermal energy within the soft tissues [12], and increasing the rate of tissue metabolism and the flow of tissue
fluids [13].
The range of movement, and hence the force used for
mobilization, is dependent on the patient’s condition
and whether spinal pain, stiffness or muscle spasm
predominates. The techniques are graded subjectively
from one to four, which reflect both their range and
amplitude and hence the force used for mobilization
(Fig. 1). The grades are defined according to the resistance encountered and the amplitude of oscillation.
Grades I and II are performed before resistance is
detected in the joint excursion. Grades III and IV are
performed in the resisted range, and may reach the end
of available joint range [14]. The irritability, severity
and nature of the patient’s symptoms will dictate the
frequency and rate of force application. When pain
predominates, a low frequency of oscillation is recommended, with smooth changes in force. If stiffness is the
dominant sign, treatment aims to increase joint range
using a greater force to stretch the tissues and at a
higher frequency [14, 15]. The End Feel is a sustained
force, thought to result in displacement of the joint
through the full range of translatory movement
available.
Before developing a rationale for the use of these
techniques, manipulative forces need to be defined and
characterized. Previous attempts at measuring these
forces used flexible pressure mats under the hands of
the therapist [16, 17]. However, palpatory feedback is
essential for the successful use of mobilization and
manipulative techniques, and any measuring device that
F. 1. A typical force–time profile for one therapist.
is interposed between the therapist and patient is likely
to interfere with the therapist’s perception of the quality
and quantity of joint movement. Matyas and Bach [18]
report on a series of studies in which the therapist stood
on a force platform during manipulation. However, the
large separation between the point of force application
and the plane of measurement would be likely to introduce substantial error. Further limitations of these
approaches are discussed in previous reports [19, 20].
Force application during mobilization will undoubtedly
comprise components along vertical, longitudinal and
horizontal axes. Therefore, any measuring technique
should allow measurement of forces along these three
axes of movement.
System description and characteristics
An alternative approach involves the instrumentation
of a couch on which the subject lies during spinal
manipulation [7, 19]. The authors have previously
detailed the development of an instrumented mobilization couch to measure the magnitude of the applied
force (F
), the orthogonal component forces (F , F ,
total
x y
F ), the peak-to-peak range and the temporal variation
z
in force application during common procedures [8, 19].
A standard mobilization couch (Akron Therapy
Products Ltd, Ipswich, UK ) was modified to allow the
couch top to be removed from the tubular steel frame.
Six bending beam load cells (Model No. SHBxM,
Revere Transducers Europe, Breda, The Netherlands)
were mounted between the base and the couch top
(Fig. 2). Three of the load cells were positioned in a
triangular arrangement with vertical primary sensing
axes. The three remaining load cells were mounted with
horizontal sensing axes in an arrangement which allowed
the calculation of forces directed along X- and Y-axes
(Fig. 3). This arrangement also minimized the distance
between the plane of measurement and force application,
avoiding unnecessary signal attenuation and inertial
error. In addition, a stand-off bar was attached to the
lower frame to allow the therapist to lean against the
Force measurement during spinal manipulation
269
therapists during every technique, ranging from 63 to
347 N for a Grade IV procedure [8].
Degenerative lumbar disc disease and osteoarthritis
of the zygapophyseal joints increase with age, progressing steadily from the second decade [21, 22]. It is
estimated that 97% of lumbar discs will show some
degree of degeneration by the age of 50 yr [23]. These
changes will influence both the mechanical loading of
the spine and the viscoelastic properties of the associated
soft tissues. Loss of extensibility of collagenous vertebral
tissue and reduced facet joint excursion caused by these
degenerative changes can reduce the available range of
movement [24]. However, degeneration that results in
disc narrowing will tend to reduce the stabilizing effects
of the ligaments and may increase the range of movement available within the neutral zone [25, 26 ]. The
objectives of the current study were to define the characteristics of a typical mobilization force used on an
asymptomatic lumbar spine in two subject groups of
different age ranges.
Method
F. 2. One transducer unit incorporating two load cells
mounted on the couch frame.
side of the couch to gain stability, without affecting the
forces measured.
Extensive calibration procedures allowed the measuring system to be characterized. Linearity was found to
be high (r2 = 0.99), and with sustained loading of forces
equating to body weight, minimal drift was observed
over a 10 min period (<0.07%). Cross effects, expressed
as a percentage of the signal in the primary axis, were
generally <2%. The variability of signal in response to
changes in the point of load application was considered
to be within acceptable limits of 2%. The sensitivity of
the couch was found to be better than 1 N along the
Z-axis, and 2 N along X- and Y-axes, well within the
requirements necessary to record the smallest peak
mobilization forces. The resonant frequencies of the
couch were found to be significantly higher than the
frequencies associated with mobilizations. Further calibration data demonstrating the characteristics of the
instrumentation system have been described in a previous report [19].
The reliability with which mobilization techniques are
performed will affect both the assessment of tissue
compliance and their ultimate clinical success. If different
forces are used, at different rates, the apparent joint
compliance will change. Therefore, using the instrumented couch, a study was undertaken to examine the
characteristics of the mobilization forces used by 30
experienced therapists on a single spinal model.
Although many of the therapists were consistent in their
force application over replications, there was considerable variation between the forces exerted by different
One female superintendent therapist of average build
(height 1.68 m, weight 59 kg), qualified for 5 yr and
with 3 yr experience working in an out-patient department, performed all the techniques in this study. In a
previous study, forces applied by this therapist had been
shown to be representative of a group of 30 experienced
therapists. The therapist was also able to repeat mobilization procedures consistently [8].
Two groups of Caucasian female subjects were
selected. The first were a young group who were in good
general health and with no previous back problems
requiring medical attention. The peak age for low back
pain has been reported to be between 45 and 64 yr [1];
therefore, an older group within this age range, who
were attending a standard out-patient physiotherapy
department, with an asymptomatic third lumbar vertebra (L3) level formed the second group. Exclusion
criteria were based on the recommended contraindications for manipulation [27]. The previous study provided
an approximation of the number of subjects required
[8]. For an experimental design with a power of 80% to
detect a clinically important difference, at a 5% level of
significance, at least 26 subjects in each group were
required.
The modified Schober method [28] was used to provide an estimate of the spinal mobility of the subjects
prior to performing the mobilization protocol. The
repeatability of this method was calculated using the
analysis technique of Bland and Altman, and found to
be adequate for the purposes of this study [20, 29].
Each subject was then required to lie prone on the
instrumented couch where the therapist pre-conditioned
the Functional Spinal Unit (FSU ) by performing each
mobilization grade 10 times before the start of the
recording. This was followed by one set of mobilizations
performed over 50 s, which included an End Feel technique, and a Grade I, II, III and IV postero-anterior
270
M. C. Harms et al.
F. 3. The Instrumented Mobilization Couch, with couch top and stand-off bar removed for clarity.
technique on the spinous process of the L3 of each
subject. Identical procedures were adopted for both
subject groups. The therapist was screened from the
computer VDU to avoid any influence resulting from
visual feedback on either the magnitude of the forces or
the rate of application.
A separate investigation examined whether the position of the vertebra, within the lumbar curve, affected
the application of these techniques. Therefore, in five
subjects within the young group, one technique was
performed on the first lumbar vertebra (L1), in addition
to the full set of techniques performed on L3.
The mobilization force was characterized by its magnitude, amplitude and frequency of oscillation. The force
amplitude was defined as the difference between the
minimum and maximum force applied, and represented
the peak-to-peak range of the mobilization cycle. The
non-linear load-displacement response of the vertebra
[26 ], which demonstrates a toe-in region, implies that
the amplitude of the mobilization force does not provide
information on the amplitude of the resulting joint
movement. Thus, a significantly greater force is necessary to displace the joint through 10% of its available
range at the end of joint range than to move it a similar
amount at the beginning of joint range. Therefore, a
normalization procedure was adopted where the force
amplitude was expressed as a percentage of the maximum force applied by the therapist for each grade of
mobilization.
Data analysis
The load cells were sampled at 40 Hz for periods of 20 s
during the application of each technique. The resulting
Force measurement during spinal manipulation
signals were fed into a personal computer using a data
acquisition package (Labtech Notebook, Boston, MA,
USA). Data files were translated into a format suitable
for input into Excel (Microsoft, Redmond, WA, USA).
Unless stated, the results were based on the magnitude
of the total force vector (F
), calculated as:
total
F
= √F2 + F2 + F2
x
y
z
total
Data were checked for normality using the Shapiro–
Wilks W∞ statistic. This led to the selection of nonparametric or parametric statistical testing methods, as
appropriate. For comparisons between groups, the
Mann–Whitney U-test, a non-parametric test for comparing data for two independent groups, was selected.
Analysis of variance or its non-parametric equivalent,
the Friedman two-way analysis of variance, was used to
compare the characteristics of the grades of mobilization. Because force magnitude increased through the
grades, comparisons between sequential pairs were performed. However, for force amplitude and frequency,
all combinations of grades were compared. Where the
results were significant, Tukey’s post hoc analysis and
the Wilcoxon matched pairs, signed rank sum test, with
the Bonferroni correction for multiple comparisons were
used. Correlations were performed using a Spearman
rank order correlation analysis.
271
F. 4. The distribution of maximum forces used for each
grade of mobilization performed on groups of young and
older subjects, indicating median, upper and lower quartile,
and extreme values.
Results
The demographic data for the two subject groups are
given in Table 1. The ranges of maximum force used
during each grade of mobilization are illustrated in
Fig. 4. The differences between the forces used for each
grade were found to be statistically significant for both
groups of subjects (young subjects: H = 102.2,
P < 0.001; older subjects: H = 106.4, P < 0.001). There
were no differences between the maximum forces applied
to the younger and older groups of subjects during
Grades III, IV and End Feel. However, for Grades I
and II, the forces used on the older subject group were
significantly higher (Grade I: U = 2.5, Grade II:
U = 3.0; both grades P < 0.05).
There was a demonstrable relationship between the
forces used during Grades III, IV and End Feel for both
groups of subjects. This indicated that the spines, which
were subjected to the higher forces at one grade, were
also subjected to higher forces during the other two
procedures (Fig. 5).
The association between the physical characteristics
T 1. Physical characteristics and range of movement of the
lumbar spine of the subjects participating in the study
Young group
(n = 30)
Older group
(n = 31)
Age (yr)
Height (m)
Weight (kg)
Lumbar spine
mobility (mm)
26 (4)a
1.66 (0.06)
61 (7)
84 (11)
55 (6)
1.64 (0.05)
68 (11)
74 (14)
aMean values with standard deviation in parentheses.
F. 5. The relationship between the forces measured during
Grades III and IV.
of the subject, including their range of movement, age,
weight and height, and the maximum forces used during
each grade of mobilization was assessed. There was a
significant relationship between the range of movement
recorded in the lumbar spine and the forces used for
Grades III and IV in the young group (rho = 0.35 and
0.45, respectively, P < 0.05). The weight of the older
group also demonstrated a significant positive correlation with the forces used during Grades I and II
(rho = 0.4, P < 0.05).
Figure 6 illustrates that there were significant differences in the amplitude of the mobilization force between
all grades for both subject groups (H = 61.0, P < 0.01),
with the exception of the comparison between Grades
II and III for the older subjects. In both groups, it was
clear that Grades II and III were associated with a
greater force amplitude than Grades I and IV. It was
also evident that the force amplitude was significantly
smaller in the older group for mobilization Grades I,
III and IV (U = 3.6–5.1, P < 0.001).
The frequency of oscillation associated with Grade
272
M. C. Harms et al.
between the characteristics of the forces applied to L1
and L3 with respect to the maximum force, force amplitude, frequency and direction.
Discussion
F. 6. The normalized force amplitude used for each grade
of mobilization performed on groups of young and older
subjects, indicating median, upper and lower quartile, and
extreme values.
IV mobilization was substantially higher than that associated with the other three grades (Fig. 7). All six
comparisons between grades in the young group, and
five of the six comparisons in the older group, were
statistically significant (P < 0.001). The only exception
being the comparison between Grades I and III in the
older group, where the values were clearly similar. The
frequencies recorded for the older group were higher for
Grades I, III and IV than for the young group
(U = 2.5–4.5, P < 0.01). In contrast, the frequency associated with a Grade II procedure was lower in the older
group (U = 2.6, P < 0.01).
When the ranges of force directed along each of the
three principal axes were assessed, the vertical force was
found to account for 81–100% of the total force. For
the higher grades of mobilization, the median values
were between 98.5 and 99.8% of the total force. The
results confirmed that the horizontal force components
were relatively small.
Results associated with the Grade III mobilization on
L1 of five young subjects indicated no differences
F. 7. The frequency of oscillation used for each grade of
mobilization performed on groups of young and older subjects,
indicating median, upper and lower quartile, and extreme
values.
The use of an instrumented couch has confirmed that
each mobilization technique has individual characteristics that can be described by magnitude, amplitude
and the temporal variation in the force applied. The
relatively small forces measured of between 9 and 17 N
suggest that Grades I and II are carried out within the
neutral zone of the joint, or the toe region of the load
displacement curve [30]. These grades are therefore
unlikely to stretch the fibres of the surrounding soft
tissues to any significant extent. Conversely, the high
forces of between 165 and 190 N experienced during
Grades III and IV suggest that the soft tissues offer
resistance to vertebral displacement during these procedures. This implies that the joints were moving within
the linear region of the load displacement curve of the
FSU with the soft tissues stretching to resist displacement of the vertebra.
Grades II and III, regarded as large-amplitude movements [14], were performed with a proportionally
greater force amplitude than Grade I and IV, in line
with conventional theory. The frequencies of oscillation
recorded for Grade I and III mobilization procedures
were similar, while Grade IV was performed at a significantly higher frequency. The known viscoelastic properties of the FSU suggest that the rate of loading during
mobilization will affect the tissue response. A previous
study by Lee and Evans [31] demonstrated that a force
delivered to the spine at a low frequency achieved
greater vertebral displacement than when the same force
was delivered at a high frequency.
It had been hypothesized that the nature of the
resistance of the spinal tissues to movement, determined
by the therapist during palpation, would influence the
characteristics of the mobilization force. If so, for those
subjects who exhibited stiffness of the FSU, higher forces
would be recorded for every grade of mobilization. The
significant association between the forces applied during
each of the higher grades supports this hypothesis and
suggests that the characteristics of joint movement were
interpreted by the therapist in a consistent manner.
The lack of a consistent association between the
physical characteristics of the subject and the force
applied to their spine indicated that neither the weight
nor height of the subject could account for the variation
of up to 90 N in the magnitude of the mobilization force.
A relationship between the range of movement of the
FSU and the applied force during mobilization, which
had been predicted, was not consistently observed within
the data. This suggests that the sagittal mobility measured by Schober’s method may not reflect mobility at a
segmental level. The relationship between the posteroanterior translatory range of the vertebral joints and the
physiological sagittal range, with which it is thought to
be coupled [32], may be more complex than generally
Force measurement during spinal manipulation
described, highlighting the limitations of using physiological movements to monitor changes in the spine
following treatment at a segmental level.
The profile of the postero-anterior mobilization force
was measured on two lumbar vertebrae, L1 and L3, to
determine whether their relative positions within the
lumbar lordosis affected the force characteristics. A
postero-anterior mobilization force is thought to result
in anterior translation of one vertebra with respect to
adjacent vertebrae. To achieve comparable results at L1
with those reported at L3, the force would need to be
angled towards the head of the subject. However, no
increase in the horizontal component along the X-axis
was noted. The position of the vertebra within the
lumbar curve had little influence on the direction of the
force applied.
Age markedly influences the biomechanical properties
of the disc, and indeed all ligaments, rendering them
less compliant and less able to recover from deformation
[33]. Yet the similarities between Grades III, IV and
End Feel applied to the two groups suggest that the
therapist may have been influenced more by the magnitude of the force applied than by the amount of joint
movement occurring, which is normally thought to guide
treatment.
The higher recorded forces in the older group during
the Grade I and II procedures (Fig. 4) may have been
the result of changes in the nature of the soft tissues
overlying the spine, where a greater force was required
to achieve a similar degree of displacement to that
occurring in the young group. Alternatively, the forces
may have been influenced by an increase in the initial
resistance to movement due to age-related changes in
the nucleus of the disc or in the synovial fluid within
the zygapophyseal joint. As this increase is not common
to the higher grades and involves relatively small forces,
it is unlikely to be of great clinical significance.
The reduced amplitude of the mobilization force in
the older group (Fig. 6) may have been a direct result
of a reduction in segmental range of movement, which
also resulted in a higher frequency of oscillation. Indeed,
there was an inverse relationship between amplitude and
frequency for both groups during the Grade IV procedure (P < 0.001).
Previous work on spinal kinematics suggests that a
force directed anteriorly is likely to result in extension
of the lumbar spine, anterior translation and posterior
sagittal rotation of the vertebral body at which the force
is directed [11]. These movements will all affect the
intervertebral joints and soft tissues. However, whilst
the movement of the spinal components under this force
can be estimated, further imaging studies are now
required to measure the displacement of the vertebrae
during mobilization procedures.
Conclusion
The instrumented couch has been shown to provide a
valuable method of measuring the characteristics of the
mobilization forces used during treatment of the lumbar
273
spine. This is the first system reported where the modus
operandi of the therapist has not been affected by the
measuring system. Its successful use in the clinical
situation is an important advance with considerable
potential in both research and teaching applications.
The results of the comparison between the young and
older subject groups demonstrate that although the
characteristics of the forces applied differ in many
respects, these differences are not as great as would have
been expected, given the alterations in the constitution
of the disc nucleus and the reduction in compliance of
the soft tissues associated with the ageing process. The
dearth of basic information on the most fundamental
and frequently used techniques has impeded the development of a scientific basis for the professions who use
manipulative techniques, and has hindered evaluation
of the efficacy of treatment practices. The instrumented
couch promises to be a versatile tool, with many applications in the field of manual therapy, an important
advance in an area where the use of these techniques
and their efficacy remain controversial.
Acknowledgements
This work was supported by a grant from the Arthritis
and Rheumatism Council for Research and the bequest
of Mrs P. O’Shaughnessy Lorant. The authors would
also like to thank V. Hackett, Physiotherapy Services
Manager, Camden & Islington Community Trust, members of the departments of physiotherapy of Camden &
Islington Community Trust, University College London
Hospitals Trust and patients who were involved in
the study.
References
1. Rosen M, Breen A, Hamann W et al. Report of a Clinical
Standards Advisory Group Committee on Back Pain; May
1994. London: HMSO, 65–71.
2. Frymoyer JW, Mooney V. Occupational orthopaedics.
J Bone Joint Surg 1986;68A:469–73.
3. Meade TW, Dyer S, Browne W, Frank AO. Randomised
comparison of chiropractic and hospital outpatient management for low back pain: results from extended follow
up. Br Med J 1995;311:349–51.
4. Koes BW, Assendelfe WJJ, van der Heijden GJMG,
Bouter LM. Spinal manipulation for low back pain: An
updated systematic review of randomised controlled trials.
Spine 1996;21:2860–73.
5. Meade TW, Dyer S, Browne W, Townsend J, Frank AO.
Low back pain of mechanical origin: Randomised comparison of chiropractic and hospital outpatient treatment. Br
Med J 1990;300:1431–7.
6. MacDonald RS, Bell CMJ. An open controlled assessment
of osteopathic manipulation in nonspecific low-back pain.
Spine 1990;15:364–70.
7. Triano JJ, McGregor M, Hondras MA, Brennan PC.
Manipulative therapy versus education programs in
chronic low back pain. Spine 1995;20:948–55.
8. Harms MC, Bader DL. Variability of forces applied by
experienced therapists during spinal mobilisation. Clin
Biomech 1997;12:393–9.
274
M. C. Harms et al.
9. Van Tulder MW, Koes BW, Bouter LM. Conservative
treatment of acute and chronic nonspecific low back pain.
Spine 1997;22:2128–56.
10. Maitland GD. Vertebral manipulation, 5th edn. London:
Butterworth & Co., 1986.
11. Lee R, Evans J. An in vivo study of the intervertebral
movements produced by posteroanterior mobilisation.
Clin Biomech 1997;12:400–8.
12. McGill SM, Brown S. Creep response of the lumbar spine
to prolonged full flexion. Clin Biomech 1992;7:43–6.
13. Collins K. Thermal effects. In Kitchen S, Bazin S, eds.
Clayton’s electrotherapy 10E. London: WB Saunders Co.,
1996:104.
14. Magarey M. Selection of passive treatment techniques.
4th Biennial Conference, Manipulative Therapists
Association of Australia, 22–25 May 1985.
15. Blake R. The Maitland concept. Organisation of Chartered
Physiotherapists in Private Practice, Autumn Seminar,
Leicester, 1984.
16. Jull GA. Monitoring aspects of the development of undergraduate student skills in manual techniques. International
Federation of Orthopaedic Manipulative Therapists,
4–9 September 1988, Cambridge.
17. Herzog W, Conway PJ, Kawchuk GN, Zhang Y, Hasler
EM. Forces exerted during spinal manipulative therapy.
Spine 1993;18:1206–12.
18. Matyas TA, Bach TM. The reliability of selected techniques in clinical arthrometrics. Aust J Physiother
1985;31:175–99.
19. Harms MC, Milton AM, Cusick G, Bader DL.
Instrumentation of a mobilisation couch for dynamic load
measurement. J Med Eng Tech 1995;19:119–22.
20. Harms MC. Force measurement during spinal mobilisation. PhD Thesis, University of London, 1996.
21. Butler D, Trafimow JH, Andersson G, McNeill TW,
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
Huckman MS. Discs degenerate before facets. Spine
1990;15:111–3.
Eisenstein SM, Parry C. The lumbar facet arthrosis syndrome. J Bone Joint Surg 1987;69B:3–7.
Miller JA, Schmatz C, Schultz AB. Lumbar disc degeneration: Correlation with age, sex and spine level in 600
autopsy specimens. Spine 1988;13:173–8.
Fitzgerald GK, Wynveen KJ, Rheault W, Rothschild B.
Objective assessment with establishment of normal values
for lumbar spinal range of motion. Phys Ther
1983;63:1776–81.
Burton AK, Tillotson KM. Is recurrent low-back trouble
associated with increased lumbar sagittal mobility.
J Biomed Eng 1989;11:245–8.
White AA, Panjabi M. Clinical biomechanics of the spine,
2nd edn. Philadelphia: JB Lippincott, 1990.
Grieve GP. Mobilisation of the spine, 3rd edn. London:
Churchill Livingstone, 1975:114.
Macrea IF, Wright V. Measurement of back movement.
Ann Rheum Dis 1969;28:584–9.
Bland M, Altman D. Statistical method for assessing
agreement between two methods of clinical assessment.
Lancet 1986;8:307–10.
Lee RYW, Evans JH. Towards a better understanding of
spinal postero-anterior mobilisation. Physiotherapy
1994;80:68–73.
Lee RYW, Evans JH. Load-displacement-time characteristics of the spine under postero-anterior mobilisation.
Aust J Physiother 1992;38:115–23 (erratum).
Panjabi M, Krag M, White A, Southwick W. Effect of
preload on load displacement curves of the lumbar spine.
Orthop Clin North Am 1977;8:181–92.
Kasra M, Shirazi-Adl A, Drouin G. Dynamics of human
lumbar intervertebral joints: Experimental and finite element investigations. Spine 1992;17:93–102.