Although the control group included slightly younger volunteers compared with the LBP group, the stability index of the core spine significantly decreased in RHT and RST, especially when visual feedback was blocked for subjects with LBP. The interaction between visual feedback and trunk rotation indicated that core spine stability is critical in coordinating balance control. A trunk muscle imbalance may contribute to unbalanced postural activity, which could prompt a decreased, uncoordinated bracing effect in subjects with LBP. As a result, core spine training could be used in the prevention of postural instability in such subjects.

Polarization of cells by extracellular fields is relevant to neural stimulation, cardiac pacing, cardiac defibrillation, and electroporation. The electric field generated by an extracellular electrode may be nonuniform, and highly nonuniform fields are produced by microelectrodes and near the edges of larger electrodes. We solved analytically for the transmembrane voltage (phi(m)) generated in a spherical cell by a nonuniform extracellular field, as would arise from a point electrode. Phi(m) reached its steady state value with a time constant much shorter than the membrane time constant in both uniform and nonuniform fields. The magnitude of phi(m) generated in the hemisphere of the cell toward the electrode was larger than in the other hemisphere in the nonuniform field, while symmetric polarization occurred in the uniform field. The transmembrane potential in oocytes stained with the voltage sensitive dye Di-8-ANEPPS was measured in a nonuniform field at three different electrode-to-cell distances. Asymmetric biphasic polarization and distance-dependent patterns of membrane voltage were observed in the measurements, as predicted from the analytical solution. These results highlight the differences in cell polarization in uniform and nonuniform electric fields, and these differences may impact excitation and poration by extracellular fields.

Even though a number of studies have evaluated postural adjustments based on kinematic changes in subjects with low back pain (LBP), kinematic stability has not been examined for abnormal postural responses during the one leg standing test. The purpose of this study was to evaluate the relative kinematic stability of the lower extremities and standing duration in subjects with and without chronic LBP. In total, 54 subjects enrolled in the study, including 28 subjects without LBP and 26 subjects with LBP. The average age of the subjects was 37.8 ± 12.6 years and ranged from 19 to 63 years. The outcome measures included normalized holding duration and relative kinematic stability. All participants were asked to maintain the test position without visual input (standing on one leg with his/her eyes closed and with the contra lateral hip flexed 90°) for 25 s. The age variable was used as a covariate to control confounding effects for the data analyses. The control group demonstrated significantly longer holding duration times (T = -2.78, p = 0.007) than the LBP group (24.6 ± 4.2 s vs. 20.5 ± 6.7 s). For the relative kinematic stability, there was a difference in dominance side (F = 9.91, p = 0.003). There was a group interaction between side and lower extremities (F = 11.79, p = 0.001) as well as an interaction between age and dominance side (F = 7.91, p = 0.007). The relative kinematic stability had a moderate negative relationship with age (r = -0.60, p = 0.007) in subjects without LBP. Clinicians need to understand the effects of age and relative stability, which decreased significantly in the single leg holding test, in subjects with LBP in order to develop effective rehabilitation strategies.

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