Trimble M H
Department of Physical Therapy, University of Florida, Gainesville 32610-0154, USA.
Int J Neurosci. 1998 Jul;95(1-2):85-100. doi: 10.3109/00207459809000652.
This purpose of this study was to clarify the relationship between segmental reflex excitability and posture and to investigate potential mechanisms responsible for modulation of the H-reflex (HR) in unsupported standing. Soleus (S) and lateral gastrocnemius (LG) HRs were recorded from subjects (N=12S, N=11LG) while their static posture was altered from supine to vertical (5 positions). This was compared to an unsupported standing position in which the subjects naturally underwent a small degree of postural sway, a dynamic posture condition. Although individual profiles suggested varied relationships between the S and LGHR and the angle of body tilt, the group data did not reveal significant differences. There was, however, a significant (p < .01) decrease in the S (43% 49%) and LG (34%-46%) HR when subjects stood without support compared to all static postures. This decrease occurred even though the tonic or background activity of the S and LG was present only when subjects were free standing. To determine whether weight-bearing was responsible for the HR depression, 3 additional conditions were compared (N=3), supported standing without weight-bearing (90 degrees NWB), supported standing with weight-bearing (90 degrees WB), and free standing. Again, S and LGHRs were depressed only when subjects were free standing. Presynaptic inhibition presumably accounts for the depression of the HR in unsupported standing. Data from 8 of the subjects were collected under the same 6 conditions using a shorter interstimulus interval (1 Hz stimulus instead of 0.1 Hz) which produced low frequency depression (LFD) of the S and LG HR. LFD reduced the amplitude of the S HR an average of 43% (p < .05) when subjects were in a supported static position but only 21% when subjects were free standing. Although tonic activity of the S was present only when subjects were free standing, in 2 (of 8) individuals the EMG in free standing was not measurably different from static conditions. In these individuals, free standing still depressed the SHR by 35%; however, the shorter stimulus interval now produced the same degree of LFD when subjects were free standing (35%) as when they were standing with support (37%). The data suggest that 2 presynaptic mechanisms, although independent, interact to control spindle afferent feedback when subjects are free standing. Postural sway appears to be necessary to reduce the gain of the HR when subjects are standing, whereas, LFD is influenced by the degree of muscle activation.
本研究的目的是阐明节段性反射兴奋性与姿势之间的关系，并探究无支撑站立时H反射（HR）调制的潜在机制。在受试者（比目鱼肌组N = 12，外侧腓肠肌组N = 11）的静态姿势从仰卧位改变为垂直位（5个姿势）时，记录比目鱼肌（S）和外侧腓肠肌（LG）的HR。将其与受试者自然发生小程度姿势摆动的无支撑站立姿势（一种动态姿势条件）进行比较。尽管个体情况表明S和LGHR与身体倾斜角度之间存在不同的关系，但组数据并未显示出显著差异。然而，与所有静态姿势相比，受试者无支撑站立时S肌（43% - 49%）和LG肌（34% - 46%）的HR显著降低（p < .01）。即使仅在受试者自由站立时S和LG才有紧张性或背景活动，这种降低仍会发生。为了确定负重是否是HR降低的原因，比较了另外3种情况（N = 3）：无负重支撑站立（90度非负重）、负重支撑站立（90度负重）和自由站立。同样，仅在受试者自由站立时S和LGHR才降低。推测突触前抑制是造成无支撑站立时HR降低的原因。使用更短的刺激间隔（1Hz刺激而非0.1Hz），在相同的6种条件下收集了8名受试者的数据，这会导致S和LG HR的低频抑制（LFD）。当受试者处于支撑静态姿势时，LFD使S HR的幅度平均降低43%（p < .05），而当受试者自由站立时仅降低21%。尽管仅在受试者自由站立时S才有紧张性活动，但在8名受试者中有2名，自由站立时的肌电图与静态条件下没有明显差异。在这些个体中，自由站立仍使S HR降低35%；然而，现在更短的刺激间隔在受试者自由站立时（35%）和支撑站立时（37%）产生相同程度的LFD。数据表明，两种突触前机制虽然相互独立，但在受试者自由站立时相互作用以控制肌梭传入反馈。当受试者站立时，姿势摆动似乎是降低HR增益所必需的，而LFD受肌肉激活程度的影响。
