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Abstract
During locomotion, muscles are controlled by a network of neurones located in the
spinal cord and by supraspinal structures. Alterations in that neuromuscular system
have a functional impact, in particular on locomotion. The hindlimb unloading (HU)
model in rat has been commonly used to generate disuse since it suppresses the hindlimb
loading and limits movements. In consequence, it induces plastic mechanisms in the
muscle, the spinal cord and the sensorimotor cortex. The aim of this study was to
assess the locomotion in HU rats in two conditions: (1) on a runway and (2) in a challenging
situation involving the participation of supraspinal structures (ladder walking).
For that purpose, the motor pattern has been investigated by means of 3D motion analysis
of the right fore- and hindlimbs as well as electromyographic recording of the soleus
and tibialis anterior muscles. The 3D motion results show that HU induces a support-dependent
alteration of the kinematics: increased duration of step, stance and swing; increased
ankle flexion during stance and hyperextension at toe-off; lower protraction during
swing. The electromyographic results show that whatever the support, the flexor and
extensor burst duration was longer in HU rats. In addition, results show that ladder
exacerbates some effects of HU. As ladder walking is a situation which requires precision,
it is suggested that the control of hindlimb movement by supraspinal structures is
affected in HU rats.