The aim of this study was to examine the effect of mental fatigue on postural sway under different sensory conditions in healthy older adults and in persons with chronic stroke (PwCS). Thirty healthy older adults (> 60 years old), randomly separated into experimental and control groups, as well as 15 PwCS participated in this study. Experimental groups were asked to stand on a force platform wearing seven inertial sensors while performing the Sensory Organization Test (SOT) under two cognitive conditions (single- and dual-task) before and after a mental fatigue task (stop-signal task for 60 min). The control group performed the same protocol before and after watching a movie for 60 min. Changes in subjective fatigue was assessed by the NASA Task Load Index and psychophysiological workload was assessed by heart rate variability (HRV). Postural sway was assessed by calculating the Jerk and root mean square (RMS) of center of mass (COM). Higher Jerk and RMS of COM (p < 0.05) were observed after the mental fatigue task in both healthy older adults and PwCS during SOT, which was not observed in the control group (p > 0.05). Additionally, postural sway increased in the three groups as the SOT conditions became more challenging. Our results indicate that mental fatigue, induced by sustained cognitive activity, can impair balance during SOT in older adult and stroke populations.

Background: Exercise-based conventional training has predominantly benefited fall-associated volitional balance control domain; however, the effect on reactive balance control is under-examined. Therefore, the purpose of this study was to examine the effect of exercise-based conventional training on reactive balance control. Methods: Eleven people with chronic stroke (PwCS) underwent multi-component training for six weeks (20 sessions) in a tapering manner. Training focused on four constructs-stretching, functional strengthening, balance, and endurance. Volitional balance was measured via movement velocity on the Limits of Stability (LOS) test and reactive balance via center of mass (COM) state stability on the Stance Perturbation Test (SPT). Additionally, behavioral outcomes (fall incidence and/or number of steps taken) were recorded. Results: Movement velocity significantly increased on the LOS test (p < 0.05) post-intervention with a significant decrease in fall incidence (p < 0.05). However, no significant changes were observed in the COM state stability, fall incidence and number of recovery steps on the SPT post-intervention. Conclusion: Although volitional and reactive balance control may share some neurophysiological and biomechanical components, training based on volitional movements might not significantly improve reactive balance control for recovery from large-magnitude perturbations due to its task-specificity.

Objective: To examine the effects of a six-week body weight-support treadmill training (BWSTT) program on center-of-mass control and gait independence in chronic, incomplete spinal cord injury (iSCI) patients. Design: Descriptive. Setting: Clinica Los Coihues. Neurorehabilitation center in Santiago, Chile. Participants: 17 chronic iSCI patients and 17 healthy subjects. Outcome Measures: An instrumented sway (ISway) test was performed before and after the implementation of a six-week BWSTT program. The standing balance of participants was measured by Normalized jerk (NJ) and root mean square (RMS). These values were used to assess the standing balance of participants, and were correlated with the scores obtained on the Walking Index Spinal Cord Injury (WISCI) II test. Results: Significant differences were found in standing balance (i.e., through NJ) after the BWSTT program (P = 0.016), but no significant differences were found in RMS values for postural sway (P = 0.693). None of the patients obtained improved WISCI II scores pre- vs. post-intervention. Conclusion: While a BWSTT program can improve center-of-mass control in iSCI patients, no effects were recorded for gait independence. Trial Registration: National Clinical Trials, registry number NCT02703883.

Spinal cord injury (SCI) is a devastating event for individuals, who frequently develop motor and sensory impairment as well as autonomic dysfunction. Previous studies reported that autonomic activity plays a major role in social cognition and that difficulties in the ability to interpret social information are commonly observed in a variety of mental disorders, which in turn correlate with a poor autonomic nervous system (ANS) regulation. It is well established that subjects with SCI have an alteration in ANS regulation mechanisms. We hypothesized that subjects diagnosed with SCI, who are experiencing a period of adaptation and socio-labor insertion suffer alterations in an emotion recognition task, a component of social cognition, which correlate with poor ANS regulation. We evaluated ANS function by measuring the heart rate variability (HRV) in eighteen healthy subjects and ten subjects with SCI. A five-min baseline HRV was compared to a task period while performing The Reading the Mind in the Eyes Test (RMET). We found that while both groups have similar general performance in the test, healthy subjects responded with greater certainty during the RMET. This level of certainty during the RMET was positively correlated with baseline HRV measures in this group. Also, the group of healthy subjects exhibited higher HRV at baseline than participants with SCI. Finally, the changes in HRV between baseline and task condition were significantly higher in healthy individuals than in SCI participants. Our results show that patients with SCI have low levels of autonomic regulation mechanisms which may promote social cognition problems during their reinsertion to daily life.