Browsing by Author "Lee, Beom-Chan"
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Item A New Robot-Assisted Therapy for Stroke Survivors: Effects of Long-Term Stretching Exercises on Ankle Range of Motion, Balance and Gait(2017) Yoo, Dongyual; Lee, Beom-Chan; Son, YounsunOur study has demonstrated that stroke survivors received ankle stretching exercises with the MAS for 4 weeks improved ankle range of motion, balance, and gait ability. These improvements remained relatively constant through the retention period (i.e., 1 month after the completion of the exercises). The findings have two important clinical implications: 1) stroke survivors could use the MAS in clinical or home environments, and 2) physical therapists could prescribe or adapt the MAS exercise sessions as needed.Item A Systematic Review of the Effects of Interactive Telerehabilitation with Remote Monitoring and Guidance on Balance and Gait Performance in Older Adults and Individuals with Neurological Conditions(2024-05-06) Park, Catherine; Lee, Beom-ChanRecognizing the growing interests and benefits of technology-assisted interactive telerehabilitation in various populations, the aim of this review is to systematically review the effects of interactive telerehabilitation with remote monitoring and guidance for improving balance and gait performance in older adults and individuals with neurological conditions. The study protocol for this systematic review was registered with the international prospective register of systematic reviews (PROSPERO) with the unique identifier CRD42024509646. Studies written in English published from January 2014 to February 2024 in Web of Science, Pubmed, Scopus, and Google Scholar were examined. Of the 247 identified, 17 were selected after initial and eligibility screening, and their methodological quality was assessed with the National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross-sectional Studies. All 17 studies demonstrated balance and gait performance improvement in older adults and in individuals with stroke, Parkinson’s disease, and multiple sclerosis following 4 or more weeks of interactive telerehabilitation via virtual reality, smartphone or tablet apps, or videoconferencing. The findings of this systematic review can inform the future design and implementation of interactive telerehabilitation technology and improve balance and gait training exercise regimens for older adults and individuals with neurological conditions.Item Adaptive Changes in Gait and Balance Control to Unloading(2018-12) Kabbaligere, Rakshatha; Layne, Charles S.; Lee, Beom-Chan; Thrasher, Timothy Adam; Pollonini, Luca; Mulavara, Ajitkuma P.Adaptive motor learning is a process that enables us to modify and maintain accurate movements to changes of both the body and the environment. Spaceflight provides a unique opportunity to study sensorimotor adaptation since astronauts must adapt to microgravity and readapt back to Earth’s gravity upon return. Within the sensorimotor system, both peripheral (functional or structural) and central adaptive changes are reported to occur, which produces gait and balance impairments. Thus, there is a need to understand the mechanisms underlying sensorimotor adaptation to prolonged unloading. Ground based models such as bed rest and dry immersion are helpful in isolating the sensorimotor impairments unique to modifications in the somatosensory system. However, since the participants are inactive and their limb movements are constrained while being unloaded in these models, the changes observed could be due to “passive unloading”. Given that astronauts are constantly moving and actively interacting with the environment while in space, studying the changes produced by “active unloading” may provide additional insights into the adaptation process. To date, there is no systematic research conducted to study motor adaptation to active unloading or unloaded walking. This dissertation was conducted with the main goal of evaluating and understanding the mechanism of motor adaptation to unloaded walking. The primary focus was to evaluate the adaptive changes in dynamic balance control and locomotion produced by prolonged vertical unloaded walking. Secondly, to determine the role of plantar cutaneous receptors’ sensitivity and body weight perception in balance and locomotor adaptation to unloaded walking. Changes in dynamic balance control were evaluated by measuring body sway response and lower limb muscle activity to repeated forward support surface translations in the absence of vision. Changes in locomotion were evaluated by measuring temporal gait parameters, lower limb joint kinematics and muscle activity during treadmill-walking at normal body weight before and after 30 minutes of both loaded (control condition) and unloaded walking (experimental condition) at 38% body weight. Changes in foot sensitivity was assessed by measuring vibration perception threshold and touch detection threshold at the great toe, heel and 5th metatarsal head and correlated with changes in balance and gait performance. Perception of body weight was assessed by using a custom-made weight perception scale. The results indicate that 1) the postural control system learns to efficiently restore balance with repeated forward support surface translations by attenuating the postural and neuromuscular responses when body weight is unaltered, and fails to do so after 30 minutes of unloaded walking; 2) there are alterations in lower limb kinematics and neuromuscular activation patterns during walking at normal body weight after 30 minutes of unloaded walking; 3) unloaded walking does not affect foot sensitivity measures; and 4) there is a reduction in perceived body weight during unloaded walking, which returns to baseline or increases after unloaded walking depending on the movement context. These findings indicate that behavioral changes in balance and gait performance produced by unloading are not produced by changes in foot sensitivity nor by changes in conscious percept of body weight; instead due to central reinterpretation and recalibration of load related inputs. This study provides insights about the effects of active unloading on gait and balance control, which will aid in developing effective sensorimotor countermeasures against the deleterious effect of prolonged unloading.Item EFFECTS OF SIMULATED GRAVITATIONAL LOADING AND UNLOADING ON KINEMATIC AND ELECTROMYOGRAPHIC VARIABLES DURING WALKING(2022-12-15) Malaya, Chris; Layne, Charles S.; Lee, Beom-Chan; Parikh, Pranav J.; Smith, Dean L.Gravity is a major factor in human gait and movement. Changes in body weight have been shown to drive adaptations in leg swing speed, foot placement and pressure distribution, as well as affect joint angles and muscle activity during walking. However, it is unclear how quickly the body adapts to new gravitational environments and, in particular, if the adaptations seen are consistent and robust at certain gravitational levels, or if they are influenced by previous gravitational loads. This project was composed of two complementary studies that examined kinematic and electromyographic adaptations to simulated gravitational environments both greater than (hyper-gravitational) and less than (hypo gravitational) standard earth conditions. In this project, 15 healthy, young adults were asked to walk in two treadmill-based loading and unloading systems. These systems allowed for investigators to manipulate the weight of each participant without changing their mass. Each individual was asked to walk under normal loading conditions for 5 minutes to allow time for their gait to stabilize. In the loading protocol, each individual walked for 1 minute each at 110%, 120% and 130% of their body weight before unloading to 120%, 110% and 100%, in that order. In the unloading protocol, individuals were unloaded from 100% down to 20% of their normal body weight, in 20% increments, before returning to 100% of body weight in the same way. Each individual spent 1 minute walking at each level of unloading. Lower body kinematics were collected by an array of inertial measurement units; muscle activity was evaluated with four surface electromyography sensors. This dissertation project found that kinematic and electromyographic responses differed with both loading and unloading during walking. Furthermore, not all levels of load elicited changes in both kinematics and electromyography, but often one or the other, regardless of whether these responses were driven by hyper- or hypo-gravitational environmental stimuli. Though coordinative movement patterns remained largely stable across levels of load, phase analysis revealed marked expansion and contraction of available states in the hip and knee with gravitational changes. These results imply that previous studies utilizing the addition of external mass to simulate increased load should not be generalized to encompass environments in which weight is increased or decreased without additional mass. Similarly, evidence of hysteretic adaptations suggest that rehabilitation protocols should not assume that the increasing or decreasing of effective weight are equivalent phenomena, even if they result in the same externally measured level of load.Item Effects of Tendon Vibration, Light Touch, and Mechanical Noise on Postural Control: Implications for Somatosensory Reweighting(2019-12) Temple, David Rick; Layne, Charles S.; Thrasher, Timothy Adam; Lee, Beom-Chan; Leung, PatrickIn order to maintain balance equilibrium, the body relies on sensory feedback from the visual, vestibular, and somatosensory systems. It is hypothesized that postural control is maintained by dynamically weighting the contributions of afferents from these systems based upon the relevance and accuracy of their inputs, a concept known as sensory reweighting. The reweighting of sensory afferents for balance is more commonly explained holistically as entire sensory systems being up-weighted or down-weighted based on their appropriateness; however, all three sensory modalities utilized in balance (visual, vestibular, and somatosensory) have various types of sensory receptors whose inputs could be reweighted accordingly within a modality, as opposed to reweighting the entire modality as a whole for postural control. This study investigated contributions from various receptor types specifically within somatosensation to postural control. Tactile and muscle spindle receptors from both the upper- and lower-body were manipulated by utilizing combinations of tendon vibration, fingertip light touch (FLT), and small amounts of mechanical noise intended to induce stochastic resonance (SR), a phenomenon where weak sensory inputs may be enhanced by the addition of noise. Three separate experiments were conducted to assess interaction effects on balance among: 1) mechanical noise delivered to the bottom of the feet and Achilles tendon vibration (Aim 1), 2) FLT conditions and Achilles tendon vibration (Aim 2), and 3) FLT and arm tendon vibration conditions (Aim 3). Results revealed that combinations of somatosensory stimuli produced differing postural effects than the individual stimuli themselves. It was inferred that these effects during interactions were evidence of reweighting occurring within the somatosensory system itself. This study provides further insight into how the sensory reweighting hypothesis accounts for human postural control and how such forms of somatosensory manipulation might be utilized in the development of countermeasures to combat balance deficits in a multitude of populations at greater fall risk.Item Exploring the Relationship between Postural Control and Brain Activity using Dual-Task Methodology(2019) Shams-ul-hooda, Akeil B.; John, Isaac; Young, D. R.Understanding how attention is allocated during a balance task, when paired with competing cognitive tasks, can be used to develop therapeutic protocols for elderly individuals as well as those with particular disease conditions requiring a higher efficacy of balance control. Using dual-task methodology, a balance task was paired with a cognitive distractor task. Attention tradeoff between the two tasks was monitored using functional near-infrared spectroscopy (fNIRS), which measured oxygen utilization in various regions of the brain to determine how oxygen use patterns varied in single and dual-tasks. It was hypothesized that participants will prioritize balance/posture and cognitive task scores will drop, and that this performance pattern will be associated with particular patterns of frontal lobe oxygen utilization that can be detected with fNIRS. There were three test conditions, all while the subjects stood. The first condition was a cognitive task that required subjects to listen and identify the number of times they heard the ‘probe’ sound. The second condition was a balance control task that required the participant to sway about the ankles in response to light vibration applied to the abdomen and lower back. If the participant accurately responded to the vibration by swaying either forward or backward, they followed the programmed pattern. A sensor determined the subject’s error of movement. The third condition combined the two tasks. It was found that the dual-task condition resulted in extreme decline of cognitive task accuracy, suggesting that the balance task was prioritized in the non-threatening environment of the study.Item Leveraging Sensorimotor Adaptive Generalizability to Minimize Dynamic Fall Risk(2016-12) Madansingh, Stefan Ishan; Layne, Charles S.; Lee, Beom-Chan; Laughlin, Mitzi S.; Bloomberg, Jacob J.; Paloski, William H.Post-flight balance control disturbances have long been a focus for the human spaceflight program and recently an effort to identify predictors of sensorimotor adaptation to microgravity has been proposed to customize and enhance the efficacy of space flight countermeasures. Balance related changes due to sensorimotor adaptation in the microgravity environment are of particular interest due to increased locomotor dysfunction and risk of falls – real risks for astronauts returning home or embarking on discovery missions. Unfortunately, there is no single technique or countermeasure to address these issues, and their severity is highly individualized. This dissertation explored within-individual sensorimotor adaptation performance during manual and locomotor control tasks, as well as recovery responses to whole-body gait perturbations, such as slips and trips. It was hypothesized that individuals adept at achieving motor adaptation during manual control would show improved adaptation performance during a locomotor adaptation task, as a result of effective forward model updating in the cerebellum. By better understanding motor adaptation performance within individuals, it was further hypothesized that whole-body postural recovery to locomotor challenges would be related to this performance, predicting trip and slip recovery step reaction time, recovery step force and time to recover to normal gait. Finally, this dissertation assessed the effectiveness of a novel split-belt treadmill slip and trip perturbation system to produce challenging and unpredictable locomotor stressors, for which practice and training of opposing tasks would show minimal transfer effects. A population of 58 healthy, college-aged participants (30 female) performed two sensorimotor adaptation tasks: a rotated-input joystick matching task and a 3:1 split-belt walking protocol, and navigated a block-randomized set of 10 trip and 10 slip perturbations to characterize postural recovery during locomotion. A pair of exponential curve fits were used to estimate adaptation performance in the two sensorimotor tasks. Whole-body motion capture and treadmill force-plates captured postural recovery kinematics and kinetics. The results of this dissertation identified a strong relationship among manual and locomotor adaptation performance (r = 0.799), suggesting adaptation performance may be centrally mediated by a common mechanism, likely located within the cerebellum. Individual split-belt adaptation performance was also observed to be predictive of slip recovery time after a bout of training (r = 0.338), as well as trip (r = 0.427) and slip (r = 0.312) recovery time improvement (% change) after a bout of 10 perturbations. This suggests a level of strategic motor adaptation related to plastic adaptation performance, within-individuals, in a set of very challenging discrete motor tasks. Finally, all participants were observed to improve significantly in recovery step force and time to recover after repeated slip or trip perturbations, but there were no meaningful transfer effects of a bout of trip training (10 perturbations) upon a novel slip, nor a bout of slip training (10 perturbations) upon a novel trip. Taken together, these results are the first to show a strong individualized link among manual and locomotor adaptation tasks, and significant correlations between adaptation performance and whole-body postural recovery during slips and trips. It is suggested that these relationships represent a deeper, generalizable connection among short-term strategic adaptation and traditional plastic adaptation observed during a simple motor adaptation task, bridging a previously unobserved gap between discrete and continuous motor control tasks.Item Mechanisms of Sensory Integration During Postural Adaptation(2020-05) Young, David R.; Layne, Charles S.; Parikh, Pranav J.; Lee, Beom-Chan; Tamber-Rosenau, Benjamin J.The body schema is an internal representation of the position of one’s body in relationship to the environment. Adaptation of the body schema involves an update of this internal model in response to changes in the task or the environment. Plasticity of the body schema during postural control allows for one to adapt to changes or hazards in their environment. The level of plasticity is related to the efficiency of integration of sensory feedback in the cortex. This investigation sought to improve the understanding of postural adaptation by identifying the impact of sensory reweighting during a postural adaptation task. Additionally, this investigation sought to identify the effects of bilateral neuromodulation of the posterior parietal cortex (PPC) using transcranial direct current stimulation (tDCS) on postural adaptation. We proposed three experiments to accomplish these goals. During the first experiment, we presented tendon vibration during an incline-intervention, which results an adaptation consisting of an anterior shift in position known as lean after-effect (LAE). During the second experiment, we presented tendon vibration after an incline-intervention. During the third experiment, we performed tDCS prior to an incline-intervention. Primary analyses of the data collected during this investigation revealed that an inclined support surface altered subjects’ response to vibration. We also found that vibration during an inclined stance did not alter the development of LAE, but vibration during the after-effect period had direction specific effects. Last, we found that neuromodulation of the PPC led to alterations in LAE. Results of this dissertation identified effects of proprioceptive reliability on the development of postural adaptation induced by an incline-intervention. Furthermore, this dissertation identified the direction specific results of altered support surface inclination on the effects of tendon vibration, providing new insights to this line of research. Results also help to improve the understanding of the role of the PPC in postural adaptation associated with adaptation of the body schema. These insights may lead to improvements in understanding of the role of the body schema in postural control, which may lead to improvements in strategies for the maintenance and rehabilitation of postural control in aging and disabled populations.Item Modeling Torso Shape and Assessing Lumbar Kinematics with Flexible Strain Sensors(2018-05) Vu, Linh Q.; Schulze, Lawrence; Chung, Christopher A.; Lee, Beom-Chan; Kim, HanAstronauts that are exposed to long-term microgravity and perform functional tasks in a spacesuit are at high risk for low back pain and injury. To understand and mitigate injury risks, it is necessary to evaluate the lumbar kinematics. This evaluation can be achieved using fabric-based strain sensors. Therefore, the purpose of this study was to develop and test a method to assess the torso shape deformation and lumbar motion with fabric-based strain sensors that were adhered on the body. Twelve male study participants performed lumbar articulation postures while 3D body scans and sensor measurements were collected. A multilayer principal component and regression-based model was constructed to estimate torso shape and lumbar kinematics. The model demonstrated good lumbar kinematics estimation (< 15°), fairly accurate torso (RMSE < 4.5 cm), and lumbar (RMSE < 1.2 cm) geometry estimation. This method may become a useful tool for measuring suited lumbar motion.Item The Effect of Age, Cognition and Context on Human Responses to Tendon Vibration(2016-12) Chelette, Amber; Layne, Charles S.; Lee, Beom-Chan; Thrasher, Timothy Adam; Hernandez, Arturo E.High-frequency vibration applied to the musculotendinous junction of a joint induces an illusory perception of the stimulated joint’s position. Historically, the illusory perception of movement during tendon vibration was described as a certain outcome, but more recently has been reportedly difficult to elicit in many instances. This poses problems for researchers who have expressed interest in manipulating human responses to tendon vibration for the purpose of neurorehabilitation. The purpose of this dissertation was to investigate factors that may influence the perception of the movement illusions induced by tendon vibration.The first experiment examined the influence of one’s knowledge and expectations about the illusion, as well as, whether directing attention to or away from the tendon vibration stimulation influenced the magnitude of movement illusions experienced. Providing instructions about the expected direction of movement illusions during tendon vibration, irrespective of their accuracy, reduced the magnitude of movement illusions perceived. Directing the attention to the external aspects of the joint positioning task, reduced the magnitude of the illusions the greatest extent, while the addition of a 1-back cognitive task meant to dilute attention resources was not challenging enough to alter the movement illusions perceived.The second experiment compared movement illusions induced by tendon vibration in a group of young and older adults. Participants experienced tendon vibration while performing both a continuous and discrete contralateral matching task, at both the elbow and knee, on both sides of the body. Older adults experienced a larger magnitude of movement illusions at the elbow and in the continuous contralateral matching task, while no differences between young and old were observed in the discrete matching task, at the knee or between the left and right limbs. A positive correlation was observed in movement illusions experienced between the continuous and discrete matching tasks, and between the left and right side of the body. In the second experiment, we also observed a weak but positive correlation between motor imagery ability and the magnitude of movement illusions perceived in the continuous contralateral matching task and at the elbow. Together, these outcomes suggest that the perception of movement illusions during tendon vibration results from the integration of both central and peripheral neural processes. Instructions about the illusions and the task can bias the outcome of experiments regarding tendon vibration and researchers should carefully consider their instructions and maintain consistency across participants and conditions. Elderly individuals and those who experience more vivid motor imagery experience greater movement illusions during tendon vibration stimulation, although the duration and location of stimulation would also influence the extent to which someone would experience movement illusions. These factors may be used to improve future investigations into human responses to tendon vibration. Future investigations should examine movement illusions in additional joints and a broader age range of participants before using these factors to identify individuals for the use of tendon vibration in neurorehabilitation.Item The Influence of Dopaminergic Medication on Gait and Balance Automaticity and Nonlinear Regularity in Parkinson’s Disease(2018-12) Workman, Craig D.; Thrasher, Timothy Adam; Arellano, Christopher J.; Lee, Beom-Chan; Bryant, Monthaporn S.Dual-tasking studies have shown that gait and balance automaticity in Parkinson’s disease (PD) is significantly diminished. It is also well accepted that dopaminergic medication improves single-task gait and some aspects of balance. Yet, how dopaminergic medication influences gait and balance automaticity in PD is not well understood. Additionally, gait and balance automaticity studies in PD have almost exclusively employed linear measures to describe outcomes. Unlike linear measures, nonlinear analyses like Approximate Entropy and Recurrence Quantification Analysis account for the regularity of the entire signal and can help determine the automaticity of the intended movement pattern. Therefore, this study aimed to determine how dopaminergic medication influenced the automaticity of gait and balance via linear and nonlinear analyses of joint angle and center of pressure (COP) path signals while single and dual-tasking in PD. Sixteen subjects with PD completed single- and dual-task walking and standing (eyes open and eyes closed) for 3 minutes off and on medication. Gait velocity, cadence, and stride length were measured, as well as kinematic variables (mean, maximum, and SD angles of bilateral hip, knee, and shoulder joint) were calculated to describe gait performance. For balance, 95% confidence ellipse area, anterior-posterior sway velocity, medial-lateral sway velocity, and integrated time to boundary were calculated. For the nonlinear analyses, approximate entropy and percent determinism were calculated for bilateral hip, knee, and shoulder joints, as well as the COP path. Data were statistically analyzed with a series of repeated measures ANOVAs and linear mixed effects models controlling for gait velocity for the linear and nonlinear analyses of joint angle data. For gait, the analysis indicated that dopaminergic medication significantly improved gait velocity (p = 0.007) and several kinematic variables. Dualtasking significantly interfered with cadence (p = 0.042), stride length (p < 0.001), and some kinematic measures, despite medication state. Dopaminergic medication mostly impacted the less PD-affected hip and knee joints, while dual-tasking primarily affected the less-PD affected hip joints. For balance, dopaminergic medication significantly increased ellipse area (p = 0.002) and decreased the performance on the secondary task (p = 0.004), while dual-tasking significantly increased sway velocity in both directions (anterior-posterior = p < 0.001, medial-lateral = p < 0.004) and integrated time to boundary (p < 0.001). There were also several medication*task interactions among the balance variables. Overall, both dopaminergic medication and dual tasking seemed to hinder balance performance, when analyzed using traditional interpretations. However, because medication only increased sway area, we propose that PD medication improved balance maneuverability without a decrease in stability. For the nonlinear analyses, there were significant medication effects on the Approximate Entropy of the more-PD affected knee while dual tasking (p = 0.014) and the less-PD affected knee while dual-tasking (p = 0.004), both of which indicated that off medication dual-tasking was more regular than on-medication dual tasking. The analysis also revealed that balance task complexity, specifically eyes open vs. eyes closed, was reflected in the analysis of the COP path, with more complex tasks eliciting significantly less regular/deterministic results. Overall, the significant gait differences in dual tasking between off- and on medication states indicated motor improvements from taking dopaminergic medication improved dualtasking. However, the lack of significant interactions and secondary task effects did not support a medication-induced improvement in gait automaticity. Lastly, the nonlinear characteristics of gait and balance in PD seemed to be differently affected by medication and task complexity. The medication-induced decreases in regularity, coupled with accepted improvements in gait performance with medication, may indicate that PD patients are too regular in their joint movements off medication.Item Understanding the body’s kinematic/kinetic responses and motor adaptation to unpredictable gait perturbation induced by a split-belt treadmill in young and older adults(2020-12) Yoo, Dongyual; Lee, Beom-Chan; Layne, Charles S.; Thrasher, Timothy Adam; Martin, Bernard J.Falls are one of the major leading causes of death for the elderly, and the number of fall-related deaths has been increasing with a steadily increased older population in the USA. Falls result in physical injuries and psychological injuries, which affect the quality of life in older adults. Unexpected gait perturbations (e.g., slips and trips) are the major leading cause of falls, and it makes up approximately 59% of falls in the community-dwelling elders. Age-related changes (e.g., decline in muscle strength and the function of the neuromuscular system) affect balance control in older adults, which contributes to higher fall rates. Although physical exercises (e.g., balance, ambulatory, and resistance training) have been utilized to enhance muscle strength and balance control, which may help to decrease fall rates, the effects of physical exercises on improving fall rates are still controversial. Instead, fall-inducing systems using external mechanisms such as slippery contaminants, external obstacles, and split-belt treadmills have been developed to investigate the response mechanisms of gait perturbations (e.g., kinematics, kinetics, and muscles responses) in young and older adults. Furthermore, fall-inducing systems have been used to improve the body’s responses to gait perturbations depending on motor adaptation principles (e.g., decreased forward center of mass (COM) velocity and trunk forward rotation after repeated exposure to the perturbations), which is more task-specific than physical exercises. However, some limitations were not fully addressed in previous studies. First, although the compensatory limb’s stepping response (i.e., the opposite side of the perturbed limb) is typical for unexpected gait perturbations, most previous studies have evaluated the perturbed limb’s joint moments. Second, although trip perturbations cause greater fall-related injuries than slip perturbations in the older population, most previous studies investigated the differences of muscle responses and joint moments between young and older adults for slip perturbations, not for trip perturbations. Third, no studies have quantitatively investigated young and older groups’ trial-to-trial adaptations based on the kinematic responses after the repetitive trip perturbations induced by a split-belt treadmill. The first study of this dissertation examined joint moments of the compensatory limb during the first stepping response after an unexpected trip or slip gait perturbations and compared the results to normal walking in the young adults. The results of the first study showed that the ankle, knee, and hip joint moments of the compensatory limb were higher after gait perturbations than during normal walking, and the joint moments were greater with the slip than the trip perturbations. The second study investigated joint moments and muscle responses of the compensatory limb to trip perturbations in young and older adults to determine whether joint moments and muscle responses differ significantly with ages. The results indicated that joint moments and muscle activations were higher for young adults than older adults after trip perturbations, and muscle co-contractions were higher for older adults. The third study assessed trial-to-trial adaptations of the reactive kinematic responses to repetitive trip perturbations in young and older adults. The result showed that adaptation took place with both young and older adults, however, the rate of adaptation was faster in young adults. The results of this dissertation will contribute to understanding the mechanisms of joint moments and muscle responses of the compensatory limb to unexpected gait perturbations and motor adaptation abilities in young and older adults. This will help develop a better strategy of therapeutic regimens utilizing fall-inducing technologies for young and older adults to improve the compensatory responses to gait perturbations, which may help reduce fall rates.