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BACKGROUND: Despite extensive research on falls among individuals with stroke, little is known regarding the impact of neurological conditions with comorbid diagnoses and motor functional capacity on the risk of falls in these individuals. Hence, the purpose of this study was to determine the fall risk and the contribution of reduced motor functional capacity to fall risk in individuals with stroke, dementia, and stroke plus dementia. METHODS: Data from the National Health and Aging Trends Study (NHATS), a nationally-representative sample of Medicare beneficiaries, were analyzed for this cross-sectional study. The odds of self-reported falls within the past month in three subgroups of neurological conditions [stroke (n=751), dementia (n=369), and stroke plus dementia (n=141)] were evaluated with a reference group of individuals with no stroke/dementia [i.e., controls (n=6337)] using logistic regression models. RESULTS: The prevalence of a recent fall was significantly higher (P

This study was set-up to investigate the multi-segmental organization of human postural control in a dynamic balance task. The focus was on the coupling between the center of mass (CoM) and center of pressure (CoP) as a candidate collective variable that supports maintaining balance on a sinusoidal oscillating platform in the medial-lateral (ML) plane and was continuously scaled up and then down across a frequency range from 0.2 Hz to 1.2 Hz. The CoM-CoP coordination changed from in-phase to anti-phase and anti-phase to in-phase at a critical frequency (∼0.4 Hz to 0.6 Hz, respectively) in the scaling up or down of the support surface frequency, showed hysteresis as a function of the direction of frequency change and critical fluctuations at the transition region. There was evidence of head motion independent of CoM motion at the higher platform frequencies and a learning effect on several of the dynamic indices over 2 days of practice. The findings are consistent with the hypothesis of CoM-CoP acting as an emergent collective variable that is supported by the faster time scale motions of the joints and their synergies in postural control.

The multi-joint coordination responsible for maintaining upright posture in the standing human manifests in the pattern of variation of the support-surface force (F). Assessment of both the translational and rotational kinematics in the sagittal-plane requires understanding the critical relationship between the direction and location of F. Prior work demonstrated that band-pass filtered F direction and center-of-pressure (CoP) covary in time such that the F vector lines-of-action pass near a fixed point called an intersection point (IP). The height of that IP (IPz) varies systematically with the frequency of the pass band. From F measurements in able-bodied humans (n = 17) standing on various pitched surfaces, the present study also found the emergent property of an IP, with IPz located above the center of mass (CoM) at frequencies

Background Motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) are typically recorded via surface electromyography (EMG). However, another suitable alternative may be recording torque output associated with MEPs, especially when studying multiheaded muscles (e.g. quadriceps) for which EMG may not be ideal. Methods We recorded the motor evoked torque elicited by TMS along with conventional EMG-based MEPs (MEPEMG) over a range of TMS intensities (100–140 % of active motor threshold [AMT]) from twenty healthy young adults on two different days. MEPs were normalized using different normalization procedures (raw, normalized to maximum voluntary isometric contraction [MVIC], and peak MEP). Additionally, motor evoked torque was normalized to TMS-evoked peripheral resting twitch torque. Intraclass correlation coefficients (ICCs) were determined for each of these variables to compute reliability. Results Motor evoked torque showed good to excellent reliability (ICC: 0.65-0.90) at TMS intensities ≥ 110 % AMT, except when normalized by peak MEP. The reliability of raw MEPEMG and MVIC normalized MEPEMG was fair to excellent only at ≥ 130 % AMT (ICC: 0.42-0.82) and at ≥ 120 % AMT (ICC: 0.41-0.83), respectively. The reliability of both MEPEMG and motor evoked torque generally increased with increasing TMS intensities, with motor evoked torque normalized to the resting twitch torque yielding the best ICC scores. Comparison with existing methods When compared with conventional MEPEMG, motor evoked torque offers superior and reliable estimates of corticospinal excitability, particularly when normalized to resting twitch torque. Conclusions TMS-induced motor evoked torque can reliably be used to measure corticospinal excitability in the quadriceps muscles.

Upright postural control system exhibits dynamic behavior to produce flexible adaptations to a variety of internal and external perturbations. Understanding the range of postural adaptability in healthy individuals can index the overall state of the system and needs to be defined over various environmental and task constraints. The purpose of the current investigation was to understand the role of vision and support surface angle on the multiple time scales of control that maintain upright posture. Thirteen young, healthy adults performed quiet standing tasks on flat, inclined and declined support surfaces with either eyes open or closed. The variability of the anterior-posterior center of pressure (COP) trajectory was analyzed using linear (COPlength) and non-linear (multiscale entropy - MSE) approaches to index postural dynamics. Sway magnitude - COPlength - was greater in both sloped conditions compared to the flat support surface standing and with the removal of vision. Increased irregularity was revealed during the sloped conditions compared to flat surface standing with additional increases of COP complexity when vision was removed. Overall, a similar range of postural adaptability was revealed for both the singular and combined sensory manipulations suggesting limits to the degree of change of COP dynamics.