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Introduction: The ability to scale anticipatory postural adjustments (APAs) according to the predicted size of the upcoming movement is reduced with aging. While age-related changes in central set may be one reason for this effect, an individual's emotional state might also contribute to changes in anticipatory postural control. Therefore, the purpose of this study was to determine whether an altered emotional state, as elicited through postural threat, alters the scaling of APAs during a handle pull movement in young and older adults. It was hypothesized that the presence of postural threat would lead to more homogenous APAs (i.e., less scaling of APAs) across a range of pulling forces.Methods: Young (n=23) and older adults (n=16) stood on top of a force plate that was mounted to a motorized platform. From this position, participants performed a series of handle pull trials without (no threat) or with (threat) the possibility of receiving a postural perturbation in the form of an unpredictable surface translation. Handle pulls were performed at force levels between 50% and 90% of maximum force. For each trial, the magnitude and timing of the APA were quantified from center of pressure (COP) recordings as well as electromyographic (EMG) activity of the soleus and medial gastrocnemius. The scaling of APAs with respect to force exertion was then determined through regression analyses and by comparing APAs during pulls of lower versus higher force.Results and Discussion: As evidenced by their smaller slope of the regression line between various dependent measures (i.e., COP velocity, soleus EMG onset latency, and soleus EMG amplitude) and the pulled forces, older adults demonstrated less scaling of APAs than the young. However, increases in arousal, anxiety and fear of falling due to postural threat, only minimally altered the scaling of APAs. Regardless of age, the slope of the regressions for none of the measures were affected by threat while only the soleus and medial gastrocnemius EMG onsets demonstrated significant force x threat interaction effects. These results suggest that the decreased ability to scale APAs with aging is unlikely to be due to changes in emotional state.

The goal of this work was to develop an adaptive rehabilitation technique using a haptic wrist robot that would induce cross-education to an untrained limb. Fourteen individuals with Multiple Sclerosis (MS) and eight non-affected adults completed an eight-week intervention. MS participants were placed into two groups, training their more affected limb (direct training), and training their less affected limb (indirect training). The purpose of the intervention was to improve wrist and grip strength (measured via maximal grip and isometric wrist strength) and motor control (measured via robotic assessments). Participants trained with the robotic device three times per week for eight consecutive weeks. Training consisted of eccentric contractions as the participant resisted a force elicited from the robotic device as it moved in flexion, extension, and radial-ulnar deviation. The MS group reported significant increases in wrist strength. The indirect training group significantly improved in flexion, extension, radial and ulnar deviation in the trained limb, and flexion and radial deviation in the untrained limb. The direct training group showed improvements in extension and ulnar deviation in both limbs. The control group improved in radial and ulnar deviation, with radial deviation improving in the untrained limb. Grip force remained unchanged for all groups. MS participants significantly decreased tracking and figural error post-intervention suggesting evidence that motor control adaptations occurred following an adaptive and resistive robotic intervention of the upper limb. Results of this work provide evidence that eight-week robotic rehabilitation can elicit cross-education effects to the untrained limb.

When an electrical stimulus is applied to perturb the vestibular system, a postural response is generated orthogonal to head orientation. It has previously been shown that there is a convergence of neck proprioceptive and vestibular input within the cerebellum to provide a head-on-body reference frame (Manzoni et al. in Neuroscience 93:1095–1107, 1999 ). The objective of this experiment was to determine whether the direction of the postural response to a vestibular perturbation is modulated when function of the cerebellar vermis is temporarily depressed. Twenty participants were randomly assigned to a SHAM group (paired-pulse transcranial magnetic stimulation) or a TEST group (continuous theta burst stimulation). Stochastic vestibular stimulation (SVS) was applied to standing subjects with their head facing forward or over their left shoulder. Cumulant density traces were established between the SVS and shear force over 180°, and the peak amplitude determined the direction of sway. There were no significant changes in sway direction when the head was facing forward for either stimulation (TEST or SHAM; p  = 0.889) or when the head was facing over the shoulder for the SHAM condition ( p  = 0.954). There was, however, a significant change in sway direction when the head was turned with a depressed cerebellum ( p  = 0.018); from the expected antero-posterior direction, orthogonal to head orientation, to one slightly more mediolateral with respect to the feet. These results suggest the cerebellum plays a role in the integration of input to generate an appropriately directed postural response relative to the head position.

Background and Purpose. People with stroke are at risk for falls. The purpose of this study was to estimate the strength of the relationship of balance and mobility to falls. Subjects. The participants were 99 community-dwelling people with chronic stroke. Methods. An interview was used to record fall history, and physical performance assessments were used to measure balance (Berg Balance Scale [BBS]) and mobility (gait speed). Results. No differences were found between subjects who fell once and subjects who did not fall or between subjects who fell more than once and subjects who did not fall. Neither balance nor mobility was able to explain falls in people with chronic stroke. Discussion and Conclusion. Clinicians should be cautious when using the BBS or gait speed to determine fall risk in this population. Falls occurred frequently during walking; it may be necessary to focus on reactive balance and environmental interaction when assessing individuals for risk of falls and devising fall prevention programs for individuals with chronic stroke. The authors' observations suggest that the prescription of 4-wheel walkers for individuals with a low BBS score (≤45) may be a mobility aid that could reduce the risk of falls.

Introduction Galvanic vestibular stimulation (GVS) is able to evoke distinct responses in the muscles used for balance. These reflexes, termed the short (SL) and medium latency (ML) responses, can be altered by sensory input; decreasing in size when additional sensory cues are available. Although much is known about these responses, the origin and role of the responses are still not fully understood. It has been suggested that the cerebellum, a structure that is involved in postural control and sensory integration, may play a role in the modulation of these reflexes. Methods The cerebellar vermis was temporarily depressed using continuous theta burst stimulation and SL, ML and overall vestibular electromyographic and force plate shear response amplitudes were compared before and after cerebellar depression. Results There were no changes in force plate shear amplitude and a non‐significant increase for the SL muscle response (p = .071), however, we did find significant increases in the ML and overall vestibular muscle response amplitudes after cerebellar depression (p = .026 and p = .016, respectively). No changes were evoked when a SHAM stimulus was used. Discussion These results suggest that the cerebellar vermis plays a role in the modulation of vestibular muscle reflex responses to GVS. The amplitude of the medium latency electromyographic reflex response, evoked from a square wave vestibular perturbation, is significantly increased with synaptic depression of the cerebellar vermis. The short latency response and the shear force responses are not significantly modulated with cerebellar depression.

Individuals report directing attention toward and away from multiple sources when standing under height-related postural threat, and these changes in attention focus are associated with postural control modifications. As it is unknown whether these changes generalize to other types of threat situations, this study aimed to quantify changes in attention focus and examine their relationship with postural control changes in response to a direct threat to stability. Eighty young adults stood on a force plate fixed to a translating platform. Three postural threat conditions were created by altering the expectation of, and prior experience with, a postural perturbation: no threat of perturbation, threat without perturbation experience, and threat with perturbation experience. When threatened, participants were more anxious and reported directing more attention to movement processes, threat-related stimuli, and self-regulatory strategies, and less to task-irrelevant information. Postural sway amplitude and frequency increased with threat, with greater increases in frequency and smaller increases in amplitude observed with experience. Without experience, threat-related changes in postural control were accounted for by changes in anxiety; larger changes in anxiety were related to larger changes in sway amplitude. With experience, threat-related postural control changes were accounted for by changes in attention focus; increases in attention to movement processes were related to greater forward leaning and increases in sway amplitude, while increases in attention to self-regulatory strategies were related to greater increases in sway frequency. Results suggest that relationships between threat-related changes in anxiety, attention focus, and postural control depend on the context associated with the threat.

PurposeIn adults, low-load resistance training with blood flow occlusion (BFO) mimics strength increases that occur from high-load training, without the need to experience high mechanical stress. In view of child–adult differences in exercise responses, this study examined whether BFO during exercise elicits differential changes in maximal voluntary contraction (MVC) and electromyographical (EMG) activity in children and adults.MethodsSixteen men (24.4 ± 2.5 years) and 14 boys (10.7 ± 2.0 years) performed low-load resistance exercise (25 repetitions at 35% MVC) of the wrist flexors with and without BFO. MVC wrist flexor force and EMG activity of the flexor carpi radialis (FCR) were obtained at the beginning and end of the exercise.ResultsBoth groups demonstrated a larger decrease in MVC force following BFO (− 18.6 ± 12.5%) than the control (without BFO) condition (− 6.2 ± 15.0%; p < 0.001). Whereas the men’s EMG amplitude increased 16.3 ± 20.5% (p = 0.005) during BFO, the boys’ EMG amplitude did not change over time or between conditions. In both groups, the mean power frequency (MPF) of the EMG signal decreased more during BFO (− 20.1 ± 9.6%; p < 0.001) than the control condition (− 5.6 ± 9.7%; p = 0.002).ConclusionsLow-load exercise with BFO resulted in similar neuromuscular responses between boys and men, except for an observed increase in the EMG amplitude in men but not boys. While this result might suggest that men relied on a greater activation of higher-threshold motor units during BFO, it does not explain why there were similar decreases in MPF between groups. Therefore, it remains unclear whether the effectiveness of BFO training is similar for children and adults.

Previous research has shown that the postural configuration adopted by a subject, such as active leaning, influences the postural response to an unpredictable support surface translation. While those studies have examined large differences in postural conditions, it is of additional interest to examine the effects of naturally occurring changes in standing posture. Thus, it was hypothesized that the normal postural sway observed during quiet standing would affect the responses to an unpredictable support surface translation. Seventeen young adults stood quietly on a moveable platform and were perturbed in either the forward or backward direction when the location of the center of pressure (COP) was either 1.5 standard deviations anterior or posterior to the mean baseline COP signal. Postural responses, in the form of electromyographic (EMG) latencies and amplitudes, were recorded from lower limb and trunk muscles. When the location of the COP at the time of the translation was in the opposite, as compared to the same, direction as the upcoming translation, there was a significantly earlier onset of the antagonists (10-23%, i.e. 15-45 ms) and a greater EMG amplitude (14-39%) in four of the six recorded muscles. Stepping responses were most frequently observed during trials where the position of the COP was opposite to the direction of the translation. The results support the hypothesis that postural responses to unpredictable support surface translations are influenced by the normal movements of postural sway. The results may help to explain the large variability of postural responses found between past studies.

The current study aimed to understand how deep and superficial abdominal muscles are coordinated with respect to activation onset times and amplitudes in response to unpredictable support-surface translations delivered in multiple directions. Electromyographic (EMG) data were recorded intra-muscularly using fine-wire electrodes inserted into the right rectus abdominis (RA), obliquus externus (OE), obliquus internus (OI) and transversus abdominis (TrA) muscles. Twelve young healthy male subjects were instructed to maintain their standing balance during 40 support surface translations (peak acceleration 1.3 m s −2 ; total displacement 0.6 m) that were counter-balanced between four different directions (forward, backward, leftward, rightward). Differences between abdominal muscles in EMG onset times were found for specific translation directions. The more superficial RA (backward translations) and OE (forward and leftward translations) muscles had significantly earlier EMG onsets compared to TrA. EMG onset latencies were dependent on translation direction in RA, OE and OI, but independent of direction in TrA. EMG amplitudes in RA and OE were dependent on translation direction within the first 100 ms of activity, whereas responses from the two deeper muscles (TrA and OI) were independent of translation direction during this interval. The current results provide new insights into how abdominal muscles contribute to postural reactions during human stance. Response patterns of deep and superficial abdominal muscles during support surface translations are unlike those previously described during upper-body perturbations or voluntary arm movements, indicating that the neural mechanisms controlling individual abdominal muscles are task-specific to different postural demands.