PERFORMANCE OF REACHING TASKS IN INDIVIDUALS WITH AND WITHOUT A HISTORY OF LOW BACK PAIN' James S' T

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PERFORMANCE OF REACHING TASKS IN INDIVIDUALS WITH
AND WITHOUT A HISTORY OF LOW BACK PAIN. James S.
Thomas and Christopher R. France
Introduction Starting from an upright standing
posture and reaching for a target that requires
some forward bending of the trunk can be
accomplished in many different configurations of
the trunk and limb segments due to the large
number of joints involved in these reaching
tasks. According to Bernstein 1, when there
are more mechanical degrees of freedom than are
strictly required to complete a task, the central
nervous system (CNS) must choose a movement
pattern from an infinite set of choices. The CNS
may resolve the problem by reducing the
independent degrees of freedom in a coordinated
task. For example despite the fact that full body
reaching tasks can be completed using an infinite
number of movement patterns, investigations of
healthy subjects performing these tasks reveal
remarkably similar movement patterns of the
lumbar spine and pelvis 2,3. However, when
motion is restricted at one joint due to pain, or
fear of pain, the movement task can usually be
completed, but the movement pattern will change
(i.e. a change in inter-joint coordination). For
example, when an individual with low back pain
needs to perform a functional task that requires
some motion of the lumbar spine, they can
compensate for reduced lumbar spine motion by
increased excursions at the legs and the reaching
arm. While this means that function can be
retained even with impairments, changes in motor
coordination may prevent full recovery and
precipitate re-injury. Methods Participants
included 15 women and 14 men with (n13) and
without (n16) a history of low back pain. Mean
age for the sample was 22 years. At the time of
testing, back pain sufferers reported no more
than mild pain on the McGill Pain Questionnaire
and no restriction of activity due to back pain.
Participants performed reaching tasks to four
targets located around a clock face such that the
subject could, in theory, reach them by flexing
the pelvis 20?, 40?, 60?, and 80? with the
shoulder flexed 90? and the elbow extended
(Figure 1). The target locations progressively
challenged the participant with larger excursions
of the trunk. However, all target locations could
be reached using a variety movement patterns.
Participants performed three reaching trials to
each target location at a comfortable movement
speed and were told to reach the target in the
manner that felt most natural to them. We define
comfortable speed as the time from movement
initiation until target contact. Following the
comfortable speed reaches, participants were
paced to perform fast reaches at movement times
which were approximately one half the movement
time of the comfortable reaches (i.e., 350-500
ms).
Results For each group, the changes in angle
(from initial posture to target contact) of the
lumbar spine and pelvis were analyzed by repeated
measures ANOVAs. Figure 2 illustrates how
participants with low back pain altered their
movement pattern to limit the amount of flexion
of the spine by increasing pelvic excursions.
Specifically, during fast paced reaches,
individuals with a history of low back pain used
less lumbar spine flexion, F(1,27)7.7, plt.05,
and less lumbar spine rotation, F(1,27)8.0,
plt.05, than did participants without a history of
low back pain. To complete the reaching task,
participants with a history of low back pain
compensated for reduced lumbar spine motion by
using increased pelvic motion, F(1,27)7.0,
plt.05.
Results, continued Using the same reaching
paradigm we compared the movement patterns of a
small sample of back pain sufferers who scored
above and below the median on the Tampa Scale of
Kinesiophobia. Our preliminary data on these two
groups reveal that participants with high
kinesiophobia avoid motion of the lumbar spine
and pelvis as compared to participants with low
kinesiophobia (See Figure 3). Specifically, they
accomplish the reaching tasks by compensating
with increasing knee flexion and full extension
of the elbow.
Conclusion The results from our study support
the notion of an alteration in movement strategy
amongst individuals with low back pain.
Specifically, at fast-paced movement speeds
individuals with low back pain used less lumbar
spine motion compared to healthy controls. The
data suggest that individuals with a history of
low back pain who have returned to normal levels
of functioning display restrictions of lumbar
motion, which may increase risk for re-injury.
Based on our preliminary data, we expect that
this reaching paradigm will further differentiate
individuals with low back pain who display
varying levels of kinesiophobia. Years of
research on low back pain have demonstrated that
a complete understanding of this condition will
require a consideration of multiple perspectives,
including psychological and physical contributors
to pain and disability. From a psychological
perspective, low back pain sufferers are
differentially susceptible to chronic disability
based in part upon their cognitive appraisals of
their painful injury 4. Specifically, those
with high levels of fear of movement and
re-injury (i.e., kinesiophobia) are more likely
to develop behavioral adaptations designed to
avoid or escape potentially painful situations.
From a physical perspective there is also
compelling evidence that low back pain lead to
changes in motor coordination, and that these
changes persist even after recovery from pain
symptoms 5. Based on the existing research as
well as our own preliminary data, we propose that
changes in multi-joint coordination are moderated
by individual differences in level of
kinesiophobia, and that this interaction helps to
determine why some people with acute
musculoskeletal pain go on to develop chronic or
recurrent back pain while others do not.
References 1. Bernstein N. The Co-ordination
and Regulation of Movements. First ed. 1967,
Oxford Pergamon Press. 2. Hasan Z and JS
Thomas. Kinematic redundancy. Prog Brain Res
1999 123 379-87. 3.
Thomas JS, DM Corcos, and Z Hasan. Kinematic
rules underlying multi-joint reaching movements.
in 30th Annual Meeting. Society for Neuroscience.
2000. New Orleans, LA. 4. Vlaeyen JW and SJ
Linton. Fear-avoidance and its consequences in
chronic musculoskeletal pain a state of the art.
Pain 2000 85(3) 317-32. 5. Ferguson SA, WS
Marras, and P Gupta. Longitudinal quantitative
measures of the natural course of low back pain
recovery. Spine 2000 25(15) 1950-6.
Figure 3 Stick figures illustrating posture at
contact with the 80? target in individual
participants with low back pain who are high and
low in kinesiophobia. Pelvic angle at target
contact is defined by ?Pelvis and lumbar spine
angle at target contact is defined by ?Lumbar.
Mean data for lumbar spine and pelvic motion
(changes from initial posture to target contact)
are provided in the table.
Figure 2 Stick figures illustrating posture at
contact with the 80? target in individual
participants with and without low back pain.
Pelvic angle at target contact is defined by
?Pelvis and lumbar spine angle at target contact
is defined by ?Lumbar. Mean data for lumbar spine
and pelvic motion (changes from initial posture
to target contact) are provided in the table.
Figure 1. Target locations were determined from
the participant's arm length, hip-to-shoulder
length, and hip height.
This work was supported in part by an Ohio
University Baker Award