The role of load-dependent sensory input in the control of balance during gait in rats

Abstract

Locomotor activity requires fine balance control that strongly depends on the afferent input from the load receptors. Following hindlimb unloading (HU), the kinematic and EMG activity of the hindlimbs is known to change significantly. However, the effects of HU on the integrative control mechanisms of posture and locomotion are not clear. The goal of the present study was to evaluate the center of mass (CoM) dynamic stabilization and associated adaptive changes in the trunk and hindlimb muscle activity during locomotion after 7 days of HU. The EMG signals from the muscles of the low lumbar trunk (m. longissimus dorsi [VERT]) and the hind limb (m. tibialis anterior [TA], m. semitendinosus [ST], m. soleus [SOL]) were recorded together with the hindquarter kinematics during locomotion on a treadmill in 6 rats before and after HU. The CoM lateral shift in the step cycle significantly increased after HU and coincided with the enhanced activity of VERT. The mean EMG of the TA and the ST flexor activity increased significantly with reduction of their burst duration. These data demonstrate the disturbances of body balance after HU that can influence the basic parameters of locomotor activity. The load-dependent mechanisms resulted in compensatory adjustments of flexor activity toward a faster gait strategy, such as a trot or gallop, which presumably have supraspinal origin. The neuronal underpinnings of these integrative posture and locomotion mechanisms and their possible reorganization after HU are discussed.

Effect of Hindlimb Unloading on Hamstring Muscle Activity in Rats

“…Changes in the locomotor activity of ST and BFp after HU were even more complex. In the previous study [36], we suggested that HU changed the ST activity differently throughout the step cycle during treadmill locomotion. Although the knee joint angle in the late stance was in hyperextension after HU [24], which theoretically led to the ST lengthening, the increase in the ST burst activity after HU is not likely to be associated with an increased activity of its I-a afferents.…”