Title The relationship between posture, muscle tone and arm

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Title The relationship between posture, muscle tone and arm Powered By Docstoc

FR. BAJERS VEJ 7D3 •          DK-9220 AALBORG         • DENMARK                    PHONE: +45 96 35 88 27
                                                                                  TELEFAX: +45 98 15 40 08
                                Dario G. Liebermann, Ph.D.
                                  Hemda Rotem & Michal Katz-Leurer
                                     Physical Therapy Department
                                      Sackler Faculty of Medicine
                                        University of Tel Aviv

Time: Monday 24th April at 14:00-15:00

Place: Aalborg University, Fredriks Bajers Vej 7D in room D2-106

Title: The relationship between posture, muscle tone and arm motor function in
       children with cerebral palsy (CP) and traumatic brain injury (TBI): Myths
       versus evidence in clinical settings.

Background: Practitioners in motor rehabilitation often suggest that upper-limb function of spastic children
with CP or TBI may benefit from performing in erect standing position. Such an effect is attributed to a
reduction in muscle tone, which is assumed to result from the change in postural set. In the present study, we
assessed the relationship between arm motor function, standing posture and muscle tone using behavioral
and electrophysiological measures. Methods: A group of 20 children (Patient Group; 10 children with TBI
and 10 with CP) participated in the experiment. Their performances were compared to a group of 20 healthy
children (Control Group). Upper limb motor functioning was assessed in the affected and unaffected arms
using the Box & Blocks test (B&B: i.e., maximal number of blocks moved from side to side in 60 sec) in
sitting and standing conditions. EMG was recorded (60 sec) bilaterally from the Gastrocnemius (GA) and the
Tibialis Anterior (TA) muscles while subjects were active (B&B task) and passive (no upper limb action
while sitting or standing). The EMG amplitudes and frequencies were used to assess changes in muscle
activity (standing\sitting, passive\active conditions). Results: A robust influence of posture on upper limb
motor function was observed. In patients and controls, the hand motor performance was superior during
standing as compared to sitting (p<0.01). A similar effect of postural configuration was observed for the
affected and the unaffected arm. However, the EMG analyses did not fully account for the effect of posture
on motor behavior. In the leg contra-lateral to the affected arm (i.e., the most affected leg), the mean EMG
amplitude for the GA muscle tended to decrease during passive standing. For the TA muscle, the mean EMG
amplitude significantly increased during standing (p<0.01) either in active and passive conditions. At first
glance, the spectral analyses for both muscles (i.e., the power of the Fourier decomposition as a % of first
harmonic) appeared to be similar in different postural configurations. However, comparisons of the averaged
spectrograms of the GA and TA (expressed as a proportion of the EMG spectrograms obtained for the
control group) showed different and complex patterns of muscle activation in the CP and TBI subgroups.
The contribution of fibers firing at >300 Hz was proportionally smaller in CP children as compared to
Controls during passive, but not in active movement conditions during sitting or standing. In the TBI group,
the firing pattern of the TA was nearly reversed in sitting conditions but not during standing. In the same
subgroup, the GA muscle presented a lower activation at all firing frequencies. Conclusions: Changes in
postural set affect arm performance, but the underlying mechanisms could not simply be attributed to a
general reduction of muscle tone. Different postural configurations result in complex patterns of motor unit
activation that may be subtly divergent for different pathological conditions. As shown here in TBI and CP
patients, muscle spasticity should not be regarded as one common phenomenon in spite of similarities in the
observed motor outcomes. Finally, practical experience may not always lead to myths but the underlying
explanations for common therapeutic practices may not be based on evidence.