Clark Brian C, Issac Lailah C, Lane Jason L, Damron Leatha A, Hoffman Richard L
Dept. of Biomedical Sciences, Ohio Univ. College of Osteopathic Medicine, Athens, OH 45701, USA.
J Appl Physiol (1985). 2008 Sep;105(3):868-78. doi: 10.1152/japplphysiol.90530.2008. Epub 2008 Jul 17.
Prolonged reductions in muscle activity results in alterations in neuromuscular properties; however, the time course of adaptations is not fully understood, and many of the specific adaptations have not been identified. This study evaluated the temporal evolution of adaptations in neuromuscular properties during and following 3 wk of immobilization. We utilized a combination of techniques involving nerve stimulation and transcranial magnetic stimulation to assess changes in central activation of muscle, along with spinal (H reflex) and corticospinal excitability [i.e., motor-evoked potential (MEP) amplitude, silent period (SP)] and contractile properties in 10 healthy humans undergoing 3 wk of forearm immobilization and 9 control subjects. Immobilization induced deficits in central activation (85 +/- 3 to 67 +/- 7% ) that returned to baseline levels 1 wk after cast removal. The flexor carpii radialis MEP amplitude increased greater than twofold after the first week of immobilization and remained elevated throughout immobilization and 1 wk after cast removal. Additionally, we observed a prolongation of the SP 1 wk after cast removal compared with baseline (78.5 +/- 7.1 to 98.2 +/- 8.7 ms). The contractile properties were also altered, since the rate of evoked force relaxation was slower following immobilization (-14.5 +/- 1.4 to -11.3 +/- 1.0% peak force/ms), and remained depressed 1 wk after cast removal (-10.5 +/- 0.8% peak force/ms). These observations detail the time course of adaptations in corticospinal and contractile properties associated with disuse and illustrate the profound effect of immobilization on the human neuromuscular system as evidenced by the alterations in corticospinal excitability persisting 1 wk following cast removal.
肌肉活动的长期减少会导致神经肌肉特性的改变；然而，适应过程的时间进程尚未完全了解，许多具体的适应变化也尚未明确。本研究评估了3周固定期间及之后神经肌肉特性适应的时间演变。我们采用了包括神经刺激和经颅磁刺激在内的多种技术，以评估10名接受3周前臂固定的健康受试者和9名对照受试者的肌肉中枢激活变化，以及脊髓（H反射）和皮质脊髓兴奋性[即运动诱发电位（MEP）幅度、静息期（SP）]和收缩特性。固定导致中枢激活出现缺陷（从85±3%降至67±7%），在去除石膏后1周恢复到基线水平。桡侧腕屈肌MEP幅度在固定第一周后增加了两倍多，并在整个固定期间及去除石膏后1周保持升高。此外，我们观察到去除石膏后1周的SP与基线相比有所延长（从78.5±7.1毫秒延长至98.2±8.7毫秒）。收缩特性也发生了改变，因为固定后诱发力量松弛的速率较慢（从-14.5±1.4%峰值力/毫秒降至-11.3±1.0%峰值力/毫秒），并且在去除石膏后1周仍处于较低水平（-10.5±0.8%峰值力/毫秒）。这些观察结果详细描述了与废用相关的皮质脊髓和收缩特性适应的时间进程，并说明了固定对人类神经肌肉系统的深远影响，去除石膏后1周皮质脊髓兴奋性的改变就证明了这一点。
