Meyer Peter F, Oddsson Lars I E, De Luca Carlo J
Department of Biomedical Engineering, Boston University, MA 02215, USA.
Exp Brain Res. 2004 Jun;156(4):505-12. doi: 10.1007/s00221-003-1804-y. Epub 2004 Feb 14.
Considerable evidence shows that sensation from the feet and ankles is important for standing balance control. It remains unclear, however, to what extent specific foot and ankle sensory systems are involved. This study focused on the role of plantar cutaneous sensation in quasi-static balance control. Iontophoretic delivery of anesthesia was used to reduce the sensitivity of the forefoot soles. In a follow-up experiment, subjects received intradermal injections of local anesthetic into the entire weight-bearing surface of the foot soles. Properties of the center-of-foot-pressure (COP) trajectories and ground reaction shear forces were analyzed using stabilogram-diffusion analysis and summary statistics. Effects of foot-sole anesthesia were generally small and mostly manifested as increases in COP velocity. Magnitude of COP displacement was unaffected by foot-sole anesthesia. Forefoot anesthesia mainly influenced mediolateral posture control, whereas complete foot-sole anesthesia had an impact on anteroposterior control. During bipedal stance, statistically significant effects of foot-sole anesthesia on COP were present only under eyes-closed conditions and included increases in COP velocity (11-12%) and shear force root-mean-square (13%), the latter indicating increases in body center-of-mass accelerations due to the foot-sole anesthesia. Similar effects were seen for unipedal stance in addition to an increase in anteroposterior COP median frequency (36%). Changes in stabilogram-diffusion parameters were confined to the short-term region suggesting that sensory information from the foot soles is mainly used to set a relevant background muscle activity for a given posture and support surface characteristic, and consequently is of little importance for feedback control during unperturbed stance. In general, this study demonstrates that plantar sensation is of moderate importance for the maintenance of normal standing balance when the postural control system is challenged by unipedal stance or by closing of the eyes. The impact of reduced plantar sensitivity on postural control is expected to increase with the loss of additional sensory modalities such as the concomitant proprioceptive deficits commonly associated with peripheral neuropathies.
大量证据表明，足部和脚踝的感觉对于站立平衡控制至关重要。然而，具体的足部和脚踝感觉系统在多大程度上参与其中仍不清楚。本研究聚焦于足底皮肤感觉在准静态平衡控制中的作用。采用离子导入法给予麻醉剂以降低前脚掌底部的敏感性。在后续实验中，受试者在整个足底负重表面接受皮内注射局部麻醉剂。使用稳定图扩散分析和汇总统计数据来分析足底压力中心（COP）轨迹和地面反作用力剪切力的特性。足底麻醉的影响通常较小，主要表现为COP速度增加。COP位移幅度不受足底麻醉影响。前脚掌麻醉主要影响内外侧姿势控制，而完全足底麻醉对前后控制有影响。在双足站立期间，足底麻醉对COP的统计学显著影响仅在闭眼条件下出现，包括COP速度增加（11 - 12%）和剪切力均方根增加（13%），后者表明由于足底麻醉导致身体质心加速度增加。除了前后COP中频增加（36%）外，单足站立时也观察到类似效果。稳定图扩散参数的变化局限于短期区域，这表明来自足底的感觉信息主要用于为给定姿势和支撑表面特征设定相关的背景肌肉活动，因此在无干扰站立期间对反馈控制的重要性不大。总体而言，本研究表明，当姿势控制系统受到单足站立或闭眼挑战时，足底感觉对于维持正常站立平衡具有中等重要性。预计随着其他感觉模态的丧失，如通常与周围神经病变相关的伴随本体感觉缺陷，足底敏感性降低对姿势控制的影响会增加。
