This study of medial gastrocnemius (MG) muscle and motor units (MUs) after spinal cord hemisection and deafferentation (HSDA) in adult cats, asked 1) whether the absence of muscle atrophy and unaltered contractile speed demonstrated previously in HSDA-paralyzed peroneus longus (PerL) muscles, was apparent in the unloaded HSDA-paralyzed MG muscle, and 2) how ankle unloading impacts MG muscle and MUs after dorsal root sparing (HSDA-SP) with foot placement during standing and locomotion. Chronic isometric contractile forces and speeds were maintained for up to 12 months in all conditions, but fatigability increased exponentially. MU recordings at 8-11½ months corroborated the unchanged muscle force and speed with significantly increased fatigability; normal weights of MG muscle confirmed the lack of disuse atrophy. Fast MUs transitioned from fatigue resistant and intermediate to fatigable accompanied by corresponding fiber type conversion to fast oxidative (FOG) and fast glycolytic (FG) accompanied by increased GAPDH enzyme activity in absolute terms and relative to oxidative citrate synthase enzyme activity. Myosin heavy chain composition, however, was unaffected. MG muscle behaved like the PerL muscle after HSDA with maintained muscle and MU contractile force and speed but with a dramatic increase in fatigability, irrespective of whether all the dorsal roots were transected. We conclude that reduced neuromuscular activity accounts for increased fatigability but is not, in of itself, sufficient to promote atrophy and slow to fast conversion. Position and relative movements of hindlimb muscles are likely contributors to sustained MG muscle and MU contractile force and speed after HSDA and HSDA-SP surgeries.

中文翻译：

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长期脊髓半切和单侧脱胎后瘫痪的猫后肢内侧腓肠肌疲劳但不萎缩。

这项研究对成年猫脊髓半切和去脱力（HSDA）后的内侧腓肠肌（MG）的肌肉和运动单位（MUs）提出了以下要求：1）先前在HSDA瘫痪的腓骨长肌中是否表现出无肌肉萎缩和收缩速度不变（ PerL）肌肉在未加载的HSDA瘫痪的MG肌肉中很明显，以及2）在站立和运动过程中背根保留（HSDA-SP）并放置脚后，踝关节卸荷如何影响MG肌肉和MU。在所有情况下，慢性等距收缩力和速度都可以维持长达12个月，但疲劳性却呈指数增长。8-11½个月的MU记录证实了不变的肌肉力量和速度，并明显增加了易疲劳性。正常的MG肌肉重量证实缺乏废用性萎缩。快速MUs从耐疲劳和中等疲劳过渡到可疲劳，伴随着相应的纤维类型转化为快速氧化（FOG）和快速糖酵解（FG），同时绝对绝对值和相对于柠檬酸合酶的活性都增加了GAPDH酶的活性。然而，肌球蛋白重链组成不受影响。MG的行为类似于HSDA后的PerL肌肉，保持了肌肉和MU的收缩力和速度，但可疲劳性显着提高，无论是否所有背根均被横断。我们得出结论，减少的神经肌肉活动导致增加的易疲劳性，但其本身不足以促进萎缩和缓慢至快速的转化。