1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

Results
The mean normalised length changes of the GB, GT and MTU over the gait cycle are shown in
Figure 2 along with the activation patterns of the gastrocnemius muscle.
GB
MTU
Heel-toe walking
adult
(a
SS DS SS DS ) SS DS SS DS
child
GT
(
EMG
b
Figure 2: (a) Mean changes in normalised length for the MTU, GB and GT in HTW and TW
for adults and children (b) typical EMG activation pattern for HTW and TW from initial
contact to next initial contact. Periods of single support (SS) and double support (DS) are
marked.
Discussion
In a numerical model of gastrocnemius MTU action during walking, Hof et al. 3 suggested that
the GB stiffens the MTU so that GT can act to store and release energy at appropriate phases in
the gait cycle. Hof went on to predict that the muscle belly would contribute to the shortening
of the MTU in pre-swing. Our results validate the work of Hof and agree with the experimental
results of Fukunaga 1 for walking at low speeds on a treadmill.
Further, we have shown that voluntary TW alters the interaction between the GB and the GT.
Activation of the GB in late swing and loading may act to stiffen the MTU. In children, the GB
is able to withstand the large tensile forces acting upon it while the GT stretches. In adults,
possibly due to greater body mass and less compliant GT, there are periods of eccentric action
carrying the potential for muscle damage.
Our results demonstrate the sympathetic actions of GB and GT during HTW and TW in
normally developing subjects, but also suggest a mechanism that explains the deterioration of
gait in individuals limited to TW by an underlying condition such as spastic cerebral palsy
(SCP). Children with SDCP have GBs of less than half the volume of those of their weight
matched ND peers 4 . The weakened GB in SCP may not be able to resist the tensile forces in
walking resulting in eccentric muscle action and consequential damage. Progression from TW
to crouch may be caused by a requirement to offload the damaged GB.
References
1. Fukunaga T et al. Proc. R. Soc. Lond. B (2001) 268 229-233 In vivo behaviour of human muscle tendon
during walking
2. Eames NWA et al Gait & Posture (1997) 6 9-17 Defining gastrocnemius length in ambulant children
3. Hof AL. J. Biomechanics (2003) 36 1031-1038 Muscle mechanics and neuromuscular control
4. Fry et al. Dev Med Child Neurol Submitted. Changes to the volume and length of the medial gastrocnemius
after surgical recession in children with spastic diplegic cerebral palsy
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Toe walking