Shaved chimpanzee muscles1/14/2024 ![]() This increase in MTU length might have several advantages for promoting ankle extension including: (1) slack in the passive structures of the muscles could be taken up, and thus, the passive tissue (possibly including denervated muscles) would contribute more to the ankle extension moment (2) longer lengths of MTUs of two-joint muscles during stance could enhance the so-called tendon action of these muscles, i.e. A greater ankle yield and smaller knee flexion in stance permit a greater length of the muscle tendon unit (MTU) at which intact and denervated multi-joint MG, LG and plantaris (PL) operate. There is another possible explanation for the documented kinematic changes at the ankle and knee joints immediately after partial denervation of ankle extensors, which is also consistent with purposeful enhancement of EMG in intact synergists. According to previous observations, the above kinematic changes enable the animal to maintain pre-injury trajectories of limb orientation and limb length and hip height and limb orientation at paw contact and paw off, permitting a more symmetric gait. The reduction in knee flexion after partial denervation of ankle extensors resulting in additional ankle yield does not appear to be functionally useful at a first glance. ![]() The emergence of a second EMG burst of MG at the stance-swing transition after partial denervation of the hamstrings in the cat appears functionally appropriate in assisting knee flexion. The rise in stance-related activity of intact medial gastrocnemius (MG) muscle after denervation of its ankle synergists may help preserve the peak magnitude of the ankle extensor moment. In the previous studies, relatively little attention has been paid to the question as to whether the observed locomotor changes in response to paralysis of selected muscles have any meaningful compensatory significance. These immediate changes in motor pattern were suggested to be mediated by proprioceptive afferent signals, modifications of central drive to the muscles and changes in feedback gains. ankle dorsiflexion) and a decrease in the knee flexion during stance of level and slope walking. This enhancement in muscle activity is accompanied by a marked increase in the ankle angle yield (i.e. For instance, denervation of selected ankle extensors in the cat – e.g., soleus (SO) and lateral gastrocnemius (LG) – led to an increase in activity of the remaining intact major ankle extensors. Studies in animals have demonstrated that within days after peripheral nerve injury there are changes in electromyographic (EMG) activity of intact synergists and movement kinematics. These patients must rely on muscle redundancy (the existence of synergists with similar functions) and neural plasticity permitting alternative motor strategies to accomplish everyday tasks. 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.Ībout 2.5% of peripheral nerve injuries are unrepairable which leads to paralysis of injured muscles. ![]() 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. 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). ![]() 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. 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. We tested this hypothesis by comparing joint moments and power patterns during walking before and after denervation of soleus and lateral gastrocnemius muscles. 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. These changes have been suggested to permit preservation of global kinematic characteristics of the hindlimb during stance. Denervation of selected ankle extensors in animals results in locomotor changes. ![]()
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