Department of Physiology and Biophysics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4.
J Neurosci. 2011 Apr 13;31(15):5579-88. doi: 10.1523/JNEUROSCI.6641-10.2011.
Extra forces or torques are defined as forces or torques that are larger than would be expected from the input or stimuli, which can be mediated by properties intrinsic to motoneurons and/or to the muscle. The purpose of this study was to determine whether extra forces/torques evoked during electrical stimulation of the muscle or its nerve with variable frequency stimulation are modulated by muscle length/joint angle. A secondary aim was to determine whether extra forces/torques are generated by an intrinsic neuronal or muscle property. Experiments were conducted in 14 able-bodied human subjects and in eight adult decerebrate cats. Torque and force were measured in human and cat experiments, respectively. Extra forces/torques were evoked by stimulating muscles with surface electrodes (human experiments) or by stimulating the nerve with cuff electrodes (cat experiments). In humans and cats, extra forces/torques were larger at short muscle lengths, indicating that a similar regulatory mechanism is involved. In decerebrate cats, extra forces and length-dependent modulation were unaffected by intrathecal methoxamine injections, despite evidence of increased spinal excitability, and by transecting the sciatic nerve proximal to the nerve stimulations. Anesthetic nerve block experiments in two human subjects also failed to abolish extra torques and the length-dependent modulation. Therefore, these data indicate that extra forces/torques evoked during electrical stimulation of the muscle or nerve are muscle length-dependent and primarily mediated by an intrinsic muscle property.
额外的力或力矩被定义为大于输入或刺激所预期的力或力矩，可以由运动神经元和/或肌肉的固有特性介导。本研究的目的是确定在肌肉或其神经的电刺激期间，通过可变频率刺激诱发的额外力/力矩是否受到肌肉长度/关节角度的调节。次要目的是确定额外的力/力矩是否由内在神经元或肌肉特性产生。实验在 14 名健康的人体受试者和 8 只成年去大脑猫中进行。在人体实验中测量扭矩，在猫实验中测量力。通过表面电极刺激肌肉（人体实验）或通过袖带电极刺激神经（猫实验）来诱发额外的力/力矩。在人和猫中，在较短的肌肉长度下，额外的力/力矩更大，表明涉及到类似的调节机制。在去大脑猫中，尽管脊髓兴奋性增加，但鞘内注射甲氧胺和在神经刺激近端切断坐骨神经，额外的力和长度依赖性调节不受影响。在两名人体受试者的麻醉神经阻滞实验中，也未能消除额外的转矩和长度依赖性调节。因此，这些数据表明，在肌肉或神经的电刺激期间诱发的额外力/力矩与肌肉长度有关，主要由内在的肌肉特性介导。
