Department of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, MD, USA; Department of Kinesiology and Health Education, University of Texas at Austin, Austin, TX, USA.
Department of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, MD, USA; Department of Exercise Science, Lebanon Valley College, Annville, PA, USA.
Hum Mov Sci. 2020 Dec;74:102715. doi: 10.1016/j.humov.2020.102715. Epub 2020 Nov 20.
Falls contribute to injuries and reduced level of physical activity in older adults. During falls, the abrupt sensation of moving downward triggers a startle-like reaction that may interfere with protective response movements necessary to maintain balance. Startle reaction could be dampened by sensory pre-stimulation delivered immediately before a startling stimulus. This study investigated the neuromodulatory effects of pre-stimulation on postural/startle responses to drop perturbations of the standing support surface in relation to age. Ten younger and 10 older adults stood quietly on an elevated computer-controlled moveable platform. At an unpredictable time, participants were dropped vertically to elicit a startle-like response. Reactive drop perturbation trials without a pre-stimulus (control) were alternated with trials with acoustic pre-stimulus tone (PSI). A two-way mixed design analysis of variance comparing condition (control vs. PSI) X group (younger vs. older) was performed to analyze changes in muscle activation patterns, ground reaction force, and joint angular displacements. Compared to younger adults, older adults showed lower neck muscle electromyography amplitude reduction rate and incidence of response. Peak muscle activation in neck, upper arm, and hamstring muscles were reduced during PSI trials compared to control trials in both groups (p < 0.05). In addition, knee and hip joint flexion prior to ground contact was reduced in PSI trials compared to control (p < 0.05). During post-landing balance recovery, increased knee and hip flexion displacement and time to peak impact force were observed in PSI trials compared to control condition (p < 0.05). PSI reduced startle-induced muscle activation at proximal body segments and likely decreased joint flexion during abrupt downward vertical displacement perturbations of the body. Older adults retained the ability to modulate startle and postural responses but their neuromodulatory capacity was reduced compared with younger adults. Further research on the potential of applying PSI as a possible therapeutic tool to reduce the risk of fall-related injury is needed.
跌倒会导致老年人受伤和身体活动水平降低。在跌倒过程中，突然向下移动的感觉会引发类似惊吓的反应，这可能会干扰维持平衡所需的保护性反应动作。通过在令人惊讶的刺激之前立即提供感觉预刺激，可以抑制惊吓反应。本研究调查了预刺激对与年龄相关的站立支撑面突然垂直下降引起的姿势/惊吓反应的神经调节作用。10 名年轻成年人和 10 名老年成年人安静地站在一个升高的计算机控制的可移动平台上。在不可预测的时间，参与者被垂直下降以引起类似惊吓的反应。没有预刺激（对照）的反应性下降扰动试验与具有声预刺激音（PSI）的试验交替进行。采用条件（对照与 PSI）X 组（年轻与年老）的两因素混合设计方差分析比较分析肌肉激活模式、地面反力和关节角度位移的变化。与年轻成年人相比，老年成年人的颈部肌肉肌电图幅度降低率和反应发生率较低。与对照试验相比，两组的 PSI 试验中颈部、上臂和腿筋肌肉的峰值肌肉激活均降低（p < 0.05）。此外，与对照相比，PSI 试验中膝关节和髋关节在接触地面之前的屈曲减少（p < 0.05）。在落地后平衡恢复期间，与对照条件相比，PSI 试验中观察到膝关节和髋关节的屈曲位移和达到峰值撞击力的时间增加（p < 0.05）。PSI 降低了近端身体部位的惊吓诱导肌肉激活，并且可能在身体突然垂直向下位移扰动期间降低了关节屈曲。老年人仍然能够调节惊吓和姿势反应，但与年轻成年人相比，他们的神经调节能力降低。需要进一步研究 PSI 作为一种可能的治疗工具的应用潜力，以降低与跌倒相关的伤害风险。
