Increased intensity and reduced frequency of EMG signals from feline self-reinnervated ankle extensors during walking do not normalize excessive lengthening

Abstract

Pantall A, Hodson-Tole EF, Gregor RJ, Prilutsky BI. Increased intensity and reduced frequency of EMG signals from feline selfreinnervated ankle extensors during walking do not normalize excessive lengthening. J Neurophysiol 115: 2406 -2420, 2016. First published February 24, 2016 doi:10.1152/jn.00565.2015-Kinematics of cat level walking recover after elimination of length-dependent sensory feedback from the major ankle extensor muscles induced by self-reinnervation. Little is known, however, about changes in locomotor myoelectric activity of self-reinnervated muscles. We examined the myoelectric activity of self-reinnervated muscles and intact synergists to determine the extent to which patterns of muscle activity change as almost normal walking is restored following muscle selfreinnervation. Nerves to soleus (SO) and lateral gastrocnemius (LG) of six adult cats were surgically transected and repaired. Intramuscular myoelectric signals of SO, LG, medial gastrocnemius (MG), and plantaris (PL), muscle fascicle length of SO and MG, and hindlimb mechanics were recorded during level and slope (Ϯ27°) walking before and after (10 -12 wk postsurgery) self-reinnervation of LG and SO. Mean myoelectric signal intensity and frequency were determined using wavelet analysis. Following SO and LG self-reinnervation, mean myoelectric signal intensity increased and frequency decreased in most conditions for SO and LG as well as for intact synergist MG (P Ͻ 0.05). Greater elongation of SO muscle-tendon unit during downslope and unchanged magnitudes of ankle extensor moment during the stance phase in all walking conditions suggested a functional deficiency of ankle extensors after self-reinnervation. Possible effects of morphological reorganization of motor units of ankle extensors and altered sensory and central inputs on the changes in myoelectric activity of self-reinnervated SO and LG are discussed.

Self-reinnervated muscles lose autogenic length feedback, but intermuscular feedback can recover functional connectivity

“…It is possible but less clear how preservation of intermuscular feedback could be directly responsible for such compensatory actions. During downslope walking, it has recently been reported that the mean myoelectric magnitude of the self-reinnervated SOL muscle (but not lateral G) was higher, 10 -12 wk after nerve repair, compared with before injury, but the ankle net joint moment was the same as control recordings (Pantall et al 2016). The finding of "normal" ankle net joint moment but exaggerated ankle yielding, despite the same or greater muscle activation, is best explained by a greater contribution of passive parallel elastic muscle components (i.e., ineffective muscle activation) that might stimulate Golgi tendon organs.…”

“…Table 1 are cat-identifier labels, based on which muscle nerves were cut and repaired, and subject characteristics. Signs of motor recovery identified by EMG begin around 4 wk after nerve cut and repair, and locomotor mechanics and EMG returns to presurgery levels during level and upslope walking within 10 -14 wk (Maas et al 2007;Pantall et al 2016). The data reported here were collected at a minimum of 19 wk after surgery.…”

“…However, the most salient stimulus for Golgi tendon organs is active contractile force (Houk and Henneman 1967). Thus we speculate the apparent reduction in active contractile force due to ineffective activation (Pantall et al 2016) and/or loss of the stretch reflex reduce the net Golgi tendon organ stimuli. As a result, the compensatory knee extension could result from a reduction in the relative inhibitory force feedback from the self-reinnervated ankle extensors.…”

“…In contrast to level and upslope walking, ankle yield was found to persist, even after complete motor recovery of ankle extensors during downslope walking (Abelew et al 2000;Maas et al 2007;Pantall et al 2016). Interestingly, global measures of whole-limb function, such as hip height, remain unchanged during downslope walking and accomplished by increases in knee and hip extension.…”

Effect of Parkinson’s disease and two therapeutic interventions on muscle activity during walking: a systematic review

“…Relative timing of motor activity onset may reveal dysfunction of sensorimotor integration. Spectral characteristics of the EMG signal may indicate altered motor unit recruitment strategies 22,23 and presence of fatigue 24 . Multi-muscle EMG analysis and intermuscular coherence may provide information about global control networks 25,26 .…”