Denervation of selected ankle extensors in animals results in locomotor changes. These changes have been suggested to permit preservation of global kinematic characteristics of the hindlimb during stance. The peak ankle joint moment is also preserved immediately after denervation of several ankle extensors in the cat, suggesting that the animal’s response to peripheral nerve injury may also be aimed at preserving ankle mechanical output. We tested this hypothesis by comparing joint moments and power patterns during walking before and after denervation of soleus and lateral gastrocnemius muscles. Hindlimb kinematics, ground reaction forces and electromyographic activity of selected muscles were recorded during level, downslope (–50%) and upslope (50%) walking before and 1–3 weeks after nerve denervation. Denervation resulted in increased activity of the intact medial gastrocnemius and plantaris muscles, greater ankle dorsiflexion, smaller knee flexion, and the preservation of the peak ankle moment during stance. Surprisingly, ankle positive power generated in the propulsion phase of stance was increased (up to 50%) after denervation in all walking conditions (p < 0.05). The obtained results suggest that the short-term motor compensation to denervation of lateral gastrocnemius and soleus muscles may allow for preservation of mechanical output at the ankle. The additional mechanical energy generated at the ankle during propulsion can result, in part, from increased activity of intact synergists, the use of passive tissues around the ankle and by the tendon action of ankle two-joint muscles and crural fascia.

Farrell BJ, Bulgakova MA, Beloozerova IN, Sirota MG, Prilutsky BI. Body stability and muscle and motor cortex activity during walking with wide stance. J Neurophysiol 112: 504 -524, 2014. First published April 30, 2014 doi:10.1152/jn.00064.2014.-Biomechanical and neural mechanisms of balance control during walking are still poorly understood. In this study, we examined the body dynamic stability, activity of limb muscles, and activity of motor cortex neurons [primarily pyramidal tract neurons (PTNs)] in the cat during unconstrained walking and walking with a wide base of support (wide-stance walking). By recording three-dimensional full-body kinematics we found for the first time that during unconstrained walking the cat is dynamically unstable in the forward direction during stride phases when only two diagonal limbs support the body. In contrast to standing, an increased lateral between-paw distance during walking dramatically decreased the cat's body dynamic stability in doublesupport phases and prompted the cat to spend more time in threelegged support phases. Muscles contributing to abduction-adduction actions had higher activity during stance, while flexor muscles had higher activity during swing of wide-stance walking. The overwhelming majority of neurons in layer V of the motor cortex, 82% and 83% in the forelimb and hindlimb representation areas, respectively, were active differently during wide-stance walking compared with unconstrained condition, most often by having a different depth of striderelated frequency modulation along with a different mean discharge rate and/or preferred activity phase. Upon transition from unconstrained to wide-stance walking, proximal limb-related neuronal groups subtly but statistically significantly shifted their activity toward the swing phase, the stride phase where most of body instability occurs during this task. The data suggest that the motor cortex participates in maintenance of body dynamic stability during locomotion.body dynamic stability; motor cortex activity; pyramidal tract neurons; locomotion; cat THE ABILITY TO CONTROL body balance and stability during locomotion is essential to prevent falls and recover from perturbations. Maintenance of stable standing and locomotion is complicated by injury (Day et al. 2012;Duong et al. 2004;Holder-Powell and Rutherford 2000), aging (Schrager et al. 2008), fear of falling (Chamberlin et al. 2005;Dunlap et al. 2012), and other factors. Several motor strategies have been found to help maintain stability while walking on complex terrain. They include 1) reducing walking velocity (Chamberlin et al. 2005;Dingwell et al. 2000;Gálvez-López et al. 2011; Maki 1997), 2) reducing stride length and increasing stance width (Dunlap et al. 2012; Maki 1997;Misiaszek 2006), and 3) lowering the center of mass (Gálvez-López et al. 2011;Schmidt and Fischer 2010) and prolonging the double-support phase (Chamberlin et al. 2005; Maki 1997). While stability of the human body during locomotion has been analyzed in detail, little is known ab...