Age-related adaptation of the body's kinematic responses to unpredictable trip perturbations induced by a split-belt treadmill.

This study quantitatively investigated motor adaptations to unpredictable trip perturbations repeatedly induced by a commercially available split-belt treadmill. Using a motion capture system, three outcome measures (i.e., maximum trunk flexion angle, maximum right hip flexion angle, and minimum whole-body center of mass (COM) position) quantified the kinematics of 10 healthy young (YG) and 10 healthy older adult (OG) groups. In each of the five trials, random trip perturbations were induced between the 31st and 40th steps. The three outcome measures were computed for the pre-trip period (from the baseline gait to the five steps before the trip perturbation) and the recovery period (after the trip perturbation to the baseline gait). The results showed that both groups progressively adapted the body's kinematic responses to the repetitive trip perturbations. The findings suggest that our trip-inducing technology may train young and older adults to improve the body's kinematic responses and reduce the risk of falling.

Visual guidance can help with the use of a robotic exoskeleton during human walking.

Walking is an important activity that supports the health-related quality of life, and for those who need assistance, robotic devices are available to help. Recent progress in wearable robots has identified the importance of customizing the assistance provided by the robot to the individual, resulting in robot adaptation to the human. However, current implementations minimize the role of human adaptation to the robot, for example, by the users modifying their movements based on the provided robot assistance. This study investigated the effect of visual feedback to guide the users in adapting their movements in response to wearable robot assistance. The visual feedback helped the users reduce their metabolic cost of walking without any changes in robot assistance in a given time. In a case with the initially metabolic expensive (IMExp) exoskeleton condition, both training methods helped reduce the metabolic cost of walking. The results suggest that visual feedback training is helpful to use the exoskeleton for various conditions. Without feedback, the training is helpful only for the IMExp exoskeleton condition. This result suggests visual feedback training can be useful to facilitate the use of non-personalized, generic assistance, where the assistance is not tuned for each user, in a relatively short time.

Aging Affects Lower Limb Joint Moments and Muscle Responses to a Split-Belt Treadmill Perturbation.

Age-related changes cause more fall-related injuries and impede the recoveries by older adults compared to younger adults. This study assessed the lower limb joint moments and muscle responses to split-belt treadmill perturbations in two groups (14 healthy young group [23.36 ± 2.90 years] and 14 healthy older group [70.93 ± 4.36 years]) who performed two trials of unexpected split-belt treadmill perturbations while walking on a programmable split-belt treadmill. A motion capture system quantified the lower limb joint moments, and a wireless electromyography system recorded the lower limb muscle responses. The compensatory limb's (i.e., the tripped limb's contralateral side) joint moments and muscle responses were computed during the pre-perturbation period (the five gait cycles before the onset of a split-belt treadmill perturbation) and the recovery period (from the split-belt treadmill perturbation to the baseline gait relying on the ground reaction forces' profile). Joint moments were assessed by maximum joint moments, and muscle responses were quantified by the normalization (%) and co-contraction index (CCI). Joint moments and muscle responses of the compensatory limb during the recovery period were significantly higher for the YG than the OG, and joint moments (e.g., knee flexion and extension and hip flexion moments) and muscle responses during the recovery period were higher compared to the pre-perturbation period for both groups. For CCI, the older group showed significantly higher co-contraction for biceps femoris/rectus femoris muscles than the young group during the recovery period. For both groups, co-contraction for biceps femoris/rectus femoris muscles was higher during the pre-perturbation period than the recovery period. The study confirmed that older adults compensated for muscle weakness by using lower joint moments and muscle activations and increasing muscle co-contractions to recover balance after split-belt treadmill perturbations. A better understanding of the recovery mechanisms of older adults who train on fall-inducing systems could improve therapeutic regimens.

The Effects of Technology-Assisted Ankle Rehabilitation on Balance Control in Stroke Survivors.

Many stroke survivors have impaired balance control. This study assesses the effects of ankle stretching exercising with our recently developed Motorized Ankle Stretcher (MAS) technology compared to exercising with a stretching board, on stroke survivors' balance control. Sixteen stroke survivors were randomly assigned to a control group (CG) and an intervention group (IG). The CG and IG performed ankle stretching exercises with the stretching board and MAS, respectively, two days per week for four consecutive weeks. Balance performance was assessed by a Sensory Organization Test (SOT) at the beginning of week 1 (pre-assessment), at the end of week 4 (post-assessment), and 1 month after week 4 (retention-assessment). Balance performance was quantified by a root-mean-square (RMS), range, and area of body's center of pressure (COP) data obtained by the SOT. The IG significantly improved COP RMS and COP range in the anterior-posterior direction at the post- and retention-assessments compared to the pre-assessment. The IG also significantly improved COP area at the retention-assessment compared to the pre-assessment. The improvements were not observed in the CG. The findings of this study have clinical implications since the MAS potentially could be used in both domestic and clinical settings.

The effect of the most common gait perturbations on the compensatory limb's ankle, knee, and hip moments during the first stepping response.

BACKGROUND: Trips and slips, the two most common gait perturbations, often cause falls. Multiple studies have focused mainly on the kinematics of multiple body segments in response to an unexpected trip or slip induced by mechanical obstacles, cables, treadmills, and slippery agents or contaminants on a floor. Few studies have examined the joint moments of the compensatory limb following an unexpected trip on an obstacle. RESEARCH QUESTION: This proof-of-concept study sought to assess the ankle, knee, and hip moments of the compensatory limb during normal walking and the first stepping response following the two most common gait perturbations. METHODS: Eighteen healthy young adults completed 4 trials (2 trials with a random trip perturbation and 2 trials with a random slip perturbation) while walking on a split-belt treadmill. In each trial, the motorized treadmill induced either an unexpected trip or slip perturbation to the left foot between the 31 st and 40th step randomly. A motion capture system recorded the positions of body segments, the joint moments (i.e., ankle, knee, and hip moments) of the compensatory limb were quantified, and the maximum joint moments were assessed during normal walking and the first stepping response. RESULTS: Compensatory limb's ankle plantarflexion, knee flexion, hip flexion, and hip extension moments were significantly higher for a slip perturbation than for a trip perturbation during the first stepping response. Compensatory limb's knee flexion, hip flexion, and hip extension moments were also significantly higher during the first stepping response to a slip perturbation compared to normal walking. SIGNIFICANCE: This proof-of-concept study is the first to investigate the ankle, knee, and hip moments of the compensatory limb during the first stepping response following unexpected gait perturbations induced by a split-belt treadmill. The findings are expected to improve the gait perturbation paradigms developed for training balance-impaired individuals.

Electrocortical activity changes in response to unpredictable trip perturbations induced by a split-belt treadmill.

This study explored the contributions of cortical activity in the primary sensorimotor cortex (SMC) and the posterior parietal cortex (PPC) to recovery responses following unpredictable trip perturbations. A technology platform equipped with a programmable split-belt treadmill induced unpredictable trip perturbations while walking. 128-channel non-invasive electroencephalography (EEG) signals were collected. Power spectral analysis was performed to quantify the electrocortical activity of two clusters in the SMC and PPC during quiet standing, steady state walking, and recovery periods. Alpha (8-13 Hz) power of the SMC and PPC was significantly suppressed during the recovery period compared to the standing and walking periods. The main finding of this study could inform the future development gait perturbation paradigms that facilitate the recovery responses in different populations, based on motor learning by repetition.

Technology-Assisted Ankle Rehabilitation Improves Balance and Gait Performance in Stroke Survivors: A Randomized Controlled Study With 1-Month Follow-Up.

Many stroke survivors have limited ankle range of motion (ROM) caused by weak dorsiflexors and stiff plantarflexors. Passive ankle stretching exercises with physical therapists or a stretching board are usually recommended, but these treatments have some limitations (e.g., cost and availability of physical therapists). In this paper, we assessed the results of ankle stretching exercises delivered by a robotic ankle stretching system called motorized ankle stretcher (MAS) that we developed or by a stretching board on ankle ROM, balance control, and gait performance. The 16 stroke survivors were randomly assigned to an intervention group (IG) or a control group (CG) and participated in seven sessions of dorsiflexion stretching exercises for three-and-a-half consecutive weeks. Laboratory assessments included pre-assessment (baseline at the beginning of the first exercise session), post-assessment (at the end of the seventh exercise session), and retention assessment (one month after the seventh exercise session). All assessments included ankle ROM for the affected side, static/dynamic balance control with a sensory organization test (SOT), walking speed, walking cadence, and step length for the affected and unaffected sides. During seven sessions of ankle stretching exercises, the IG performed them using the MAS, and the CG used a stretching board. The IG significantly improved ankle ROM, SOT scores (i.e., static/dynamic balance control), walking speeds, walking cadences, and step lengths for the unaffected side after completing the seven exercise sessions of ankle stretching exercises and maintained the enhancements at the retention assessment. The CG did not significantly improve across the majority of outcome measures except for the SOT scores between the pre-assessment and retention assessment. Future work will investigate the ideal intensity, frequency, and duration of exercising with the MAS. Our research on technology-assisted ankle rehabilitation, which can ascertain the level of persistent improvement, long-term performance retention, and carry-over effects in stroke survivors, can be used to inform future designs.