Effects of Walking Speed and Added Mass on Hip Joint Quasi-Stiffness in Healthy Young and Middle-Aged Adults.

Joint quasi-stiffness has been often used to inform exoskeleton design. Further understanding of hip quasi-stiffness is needed to design hip exoskeletons. Of interest are wearer responses to walking speed changes with added mass of the exoskeleton. This study analyzed hip quasi-stiffness at 3 walking speed levels and 9 added mass distributions among 13 young and 16 middle-aged adults during mid-stance hip extension and late-stance hip flexion. Compared to young adults, middle-aged adults maintained a higher quasi-stiffness with a smaller range. For a faster walking speed, both age groups increased extension and flexion quasi-stiffness. With mass evenly distributed on the pelvis and thighs or biased to the pelvis, both groups maintained or increased extension quasi-stiffness. With mass biased to the thighs, middle-aged adults maintained or decreased extension quasi-stiffness while young adults increased it. Young adults decreased flexion quasi-stiffness with added mass but not in any generalizable pattern with mass amounts or distributions. Conversely, middle-aged adults maintained or decreased flexion quasi-stiffness with even distribution on the pelvis and thighs or biased to the pelvis, while no change occurred if biased to the thighs. In conclusion, these results can guide the design of a hip exoskeleton's size and mass distribution according to the intended user's age.

Characterization of Upper Extremity Kinematics Using Virtual Reality Movement Tasks and Wearable IMU Technology.

Task-specific training has been shown to be an effective neuromotor rehabilitation intervention, however, this repetitive approach is not always very engaging. Virtual reality (VR) systems are becoming increasingly popular in therapy due to their ability to encourage movement through customizable and immersive environments. Additionally, VR can allow for a standardization of tasks that is often lacking in upper extremity research. Here, 16 healthy participants performed upper extremity movement tasks synced to music, using a commercially available VR game known as Beat Saber. VR tasks were customized to characterize participants' joint angles with respect to each task's specified cardinal direction (inward, outward, upward, or downward) and relative task location (medial, lateral, high, and/or low). Movement levels were designed using three common therapeutic approaches: (1) one arm moving only (unilateral), (2) two arms moving in mirrored directions about the participant's midline (mirrored), or (3) two arms moving in opposing directions about the participant's midline (opposing). Movement was quantified using an XSens System, a wearable inertial measurement unit (IMU) technology. Results reveal a highly engaging and effective approach to quantifying movement strategies. Inward and outward (horizontal) tasks resulted in decreased wrist extension. Upward and downward (vertical) tasks resulted in increased shoulder flexion, wrist radial deviation, wrist ulnar deviation, and elbow flexion. Lastly, compared to opposing, mirrored, and unilateral movement levels often exaggerated joint angles. Virtual reality games, like Beat Saber, offer a repeatable and customizable upper extremity intervention that has the potential to increase motivation in therapeutic applications.

How Does Added Mass Affect the Gait of Middle-Aged Adults? An Assessment Using Statistical Parametric Mapping.

To improve exoskeleton designs, it is crucial to understand the effects of the placement of such added mass on a broad spectrum of users. Most prior studies on the effects of added mass on gait have analyzed young adults using discrete point analysis. This study quantifies the changes in gait characteristics of young and middle-aged adults in response to added mass across the whole gait cycle using statistical parametric mapping. Fourteen middle-aged and fourteen younger adults walked during 60 s treadmill trials under nine different loading conditions. The conditions represented full-factorial combinations of low (+3.6 lb), medium (+5.4 lb), and high (+10.8 lb) mass amounts at the thighs and pelvis. Joint kinematics, kinetics and muscle activations were evaluated. The young and middle-aged adults had different responses to added mass. Under pelvis loading, middle-aged adults did not adopt the same kinematic responses as younger adults. With thigh loading, middle-aged adults generally increased knee joint muscle activity around heel strike, which could have a negative impact on joint loading. Overall, as age may impact the user's response to an exoskeleton, designers should aim to include sensors to directly monitor user response and adaptive control approaches that account for these differences.

How Do Joint Kinematics and Kinetics Change When Walking Overground with Added Mass on the Lower Body?

Lower-limb exoskeletons, regardless of their control strategies, have been shown to alter a user's gait just by the exoskeleton's own mass and inertia. The characterization of these differences in joint kinematics and kinetics under exoskeleton-like added mass is important for the design of such devices and their control strategies. In this study, 19 young, healthy participants walked overground at self-selected speeds with six added mass conditions and one zero-added-mass condition. The added mass conditions included +2/+4 lb on each shank or thigh or +8/+16 lb on the pelvis. OpenSim-derived lower-limb sagittal-plane kinematics and kinetics were evaluated statistically with both peak analysis and statistical parametric mapping (SPM). The results showed that adding smaller masses (+2/+8 lb) altered some kinematic and kinetic peaks but did not result in many changes across the regions of the gait cycle identified by SPM. In contrast, adding larger masses (+4/+16 lb) showed significant changes within both the peak and SPM analyses. In general, adding larger masses led to kinematic differences at the ankle and knee during early swing, and at the hip throughout the gait cycle, as well as kinetic differences at the ankle during stance. Future exoskeleton designs may implement these characterizations to inform exoskeleton hardware structure and cooperative control strategies.

Surface Electromyography of the Internal and External Oblique Muscles During Isometric Tasks Targeting the Lateral Trunk.

CONTEXT: Tasks that activate the lateral trunk muscles are clinically relevant in athletic and rehabilitation programs. However, no electromyography studies have compared tasks aimed at lateral trunk muscle activation. OBJECTIVE: To compare the activation magnitudes of the internal and external obliques between 4 tasks targeting recruitment of the lateral trunk muscles, including the proposal of a novel assessment. DESIGN: Comparative laboratory study. SETTING: University-based biomechanics laboratory. PARTICIPANTS: Sixty-three participants (35 females, age = 23.6 [2.0] y, height = 1.72 [0.10] m, mass = 70.7 [14.4] kg, body mass index = 23.6 [2.86] kg/m2). INTERVENTION(S): Surface electromyography data were recorded bilaterally from the internal and external obliques while the participants performed 2 maximum voluntary contraction tasks followed by 4 isometric tasks. The isometric tasks included feet-elevated side-supported, trunk-elevated side-unsupported, lateral plank, and side-lying hip abduction. MAIN OUTCOME MEASURES: Maximum voluntary contraction-normalized and integrated muscle activities were calculated for targeted and nontargeted muscles in each task. A side-by-task analysis of variance with Bonferroni correction was conducted. RESULTS: The trunk-elevated side-unsupported task strongly activated the internal (199% maximum voluntary contraction) and external (103%) oblique muscles. The feet-elevated side-supported task strongly activated the internal obliques (205%) but not the external obliques (55%). The lateral plank task successfully activated the internal (107%) and external (72%) obliques, but not at the highest levels of the tested tasks. The side-lying hip abduction task was the least effective at activating either the internal (48%) or external (20%) obliques. CONCLUSIONS: We recommend the novel trunk-elevated side-unsupported task for assessing lateral trunk muscle performance. For independent exercise, we recommend the lateral plank task, unless arm or shoulder pathologies are present, whereby the feet-elevated side-supported task may be favorable.

Facilitating Partner Support for Lifestyle Change Among Adults with Serious Mental Illness: A Feasibility Pilot Study.

The purpose of this pilot study was to explore the feasibility of an intervention designed to facilitate partner support for lifestyle change among overweight and obese adults with serious mental illness (SMI). Fifteen adults with SMI enrolled in a lifestyle intervention at community mental health centers participated with a self-selected partner in an additional 12-week intervention component designed to facilitate social support for health behavior change. Participants reported that the program was useful, convenient, and helped them reach their goals. Approximately two-thirds (66%) of participants were below their baseline weight at follow-up, including 27% achieving clinically significant weight loss. Participants reported significant increases in partner support for exercise and use of persuasive social support strategies. Partner support interventions that promote exercising together and positive communication may be effective for helping individuals with SMI initiate and sustain health behavior change necessary to reduce cardiovascular risk.

Age Stratification and Sample Entropy Analysis Enhance the Limits of Stability Tests for Older Adults.

The objective of this study was to determine if a foam testing condition and/or nonlinear analysis methods can be used to identify differences between age stratified subgroups of older adults when conducting the Limits of Stability assessment. Ninety older adults participated in this study. A force plate was used to record center of pressure data during Limits of Stability testing on a firm and foam surface. Participants were grouped into age-stratified subgroups: young-old (60-69 years), middle-old (70-79 years), and old-old (80+ years). Anterior-posterior (A/P) and medial-lateral (M/L) sway ranges and sample entropy values were calculated. The young-old group had significantly larger A/P and M/L sway ranges than the old-old group on both surfaces. A/P sample entropy increased significantly with age. M/L sample entropy increased significantly with age between the young-old and old-old and the middle-old and old-old groups. Sample entropy values between surfaces significantly differed for all groups. These results indicate Limits of Stability differences occur between older adults of different age groups and should be taken into consideration for clinical and research testing. Nonlinear analysis may help further identify differences in Limits of Stability performance while use of a foam surface is of limited additional value.

Neuromusculoskeletal Model Calibration Significantly Affects Predicted Knee Contact Forces for Walking.

Though walking impairments are prevalent in society, clinical treatments are often ineffective at restoring lost function. For this reason, researchers have begun to explore the use of patient-specific computational walking models to develop more effective treatments. However, the accuracy with which models can predict internal body forces in muscles and across joints depends on how well relevant model parameter values can be calibrated for the patient. This study investigated how knowledge of internal knee contact forces affects calibration of neuromusculoskeletal model parameter values and subsequent prediction of internal knee contact and leg muscle forces during walking. Model calibration was performed using a novel two-level optimization procedure applied to six normal walking trials from the Fourth Grand Challenge Competition to Predict In Vivo Knee Loads. The outer-level optimization adjusted time-invariant model parameter values to minimize passive muscle forces, reserve actuator moments, and model parameter value changes with (Approach A) and without (Approach B) tracking of experimental knee contact forces. Using the current guess for model parameter values but no knee contact force information, the inner-level optimization predicted time-varying muscle activations that were close to experimental muscle synergy patterns and consistent with the experimental inverse dynamic loads (both approaches). For all the six gait trials, Approach A predicted knee contact forces with high accuracy for both compartments (average correlation coefficient r = 0.99 and root mean square error (RMSE) = 52.6 N medial; average r = 0.95 and RMSE = 56.6 N lateral). In contrast, Approach B overpredicted contact force magnitude for both compartments (average RMSE = 323 N medial and 348 N lateral) and poorly matched contact force shape for the lateral compartment (average r = 0.90 medial and -0.10 lateral). Approach B had statistically higher lateral muscle forces and lateral optimal muscle fiber lengths but lower medial, central, and lateral normalized muscle fiber lengths compared to Approach A. These findings suggest that poorly calibrated model parameter values may be a major factor limiting the ability of neuromusculoskeletal models to predict knee contact and leg muscle forces accurately for walking.

How sensitive is the deltoid moment arm to humeral offset changes with reverse total shoulder arthroplasty?

BACKGROUND: Reverse total shoulder arthroplasty commonly treats cuff-deficient or osteoarthritic shoulders not amenable to rotator cuff repair. This study investigates deltoid moment arm sensitivity to variations in the joint center and humeral offset of 3 representative reverse total shoulder arthroplasty subjects. We hypothesized that a superior joint implant placement may exist, indicated by muscle moment arms, compared with the current actual surgical implant configuration. METHODS: Moment arms for the anterior, lateral, and posterior aspects of the deltoid muscle were determined for 1521 perturbations of the humeral offset location away from the surgical placement in a subject-specific musculoskeletal model with motion defined by subject-specific in vivo abduction kinematics. The humeral offset was varied from its surgical position ±4 mm in the anterior/posterior direction, ±12 mm in the medial/lateral direction, and -10 to 14 mm in the superior/inferior direction. RESULTS: The anterior deltoid moment arm varied in humeral offset and center of rotation up to 20 mm, primarily in the medial/lateral and superior/inferior directions. The lateral deltoid moment arm varied in humeral offset up to 20 mm, primarily in the medial/lateral and anterior/posterior directions. The posterior deltoid moment arm varied up to 15 mm, primarily in early abduction, and was most sensitive to humeral offset changes in the superior/inferior direction. DISCUSSION: High variations in muscle moment arms were found for all 3 deltoid components, presenting an opportunity to dramatically change the deltoid moment arms through surgical placement of the reverse shoulder components and by varying the overall offset of the humerus. LEVEL OF EVIDENCE: Basic Science Study; Computer Modeling.

Manual and Cognitive Dual Tasks Contribute to Fall-Risk Differentiation in Posturography Measures.

Falls occur in 33% of older adults each year, some leading to moderate to severe injuries. To reduce falls and fall-related injuries, it is important to identify individuals with subtle risk factors elevating their likelihood of falling. The objective of this study was to determine how postural sway measures differed between fallers and nonfallers under standard and dual-task conditions. Quietstanding posturography measures were collected from 150 older adults during standard, cognitive, manual, and cognitive+manual tasks, and analyzed through traditional and nonlinear analyses. Of the traditional measures, M/L sway range and 95% confidence ellipse sway area showed statistically significant differences in all 4 test conditions between fallers and nonfallers. Although the manual dual task showed the most stable balance, effect sizes demonstrated larger differences between fallers and nonfallers. Nonlinear analysis revealed M/L sample entropy and M/L α-scaling exponent differentiating between fallers and nonfallers, with the cognitive task demonstrating larger differences. Based on the results, it is recommended to: (1) apply M/L sway range and 95% confidence ellipse area, (2) use the manual task to differentiate between fallers and nonfallers when using traditional analyses, and (3) use the cognitive task and M/L alpha and M/L sample entropy when using nonlinear analyses.

Muscle synergies may improve optimization prediction of knee contact forces during walking.

The ability to predict patient-specific joint contact and muscle forces accurately could improve the treatment of walking-related disorders. Muscle synergy analysis, which decomposes a large number of muscle electromyographic (EMG) signals into a small number of synergy control signals, could reduce the dimensionality and thus redundancy of the muscle and contact force prediction process. This study investigated whether use of subject-specific synergy controls can improve optimization prediction of knee contact forces during walking. To generate the predictions, we performed mixed dynamic muscle force optimizations (i.e., inverse skeletal dynamics with forward muscle activation and contraction dynamics) using data collected from a subject implanted with a force-measuring knee replacement. Twelve optimization problems (three cases with four subcases each) that minimized the sum of squares of muscle excitations were formulated to investigate how synergy controls affect knee contact force predictions. The three cases were: (1) Calibrate+Match where muscle model parameter values were calibrated and experimental knee contact forces were simultaneously matched, (2) Precalibrate+Predict where experimental knee contact forces were predicted using precalibrated muscle model parameters values from the first case, and (3) Calibrate+Predict where muscle model parameter values were calibrated and experimental knee contact forces were simultaneously predicted, all while matching inverse dynamic loads at the hip, knee, and ankle. The four subcases used either 44 independent controls or five synergy controls with and without EMG shape tracking. For the Calibrate+Match case, all four subcases closely reproduced the measured medial and lateral knee contact forces (R2 ≥ 0.94, root-mean-square (RMS) error < 66 N), indicating sufficient model fidelity for contact force prediction. For the Precalibrate+Predict and Calibrate+Predict cases, synergy controls yielded better contact force predictions (0.61 < R2 < 0.90, 83 N < RMS error < 161 N) than did independent controls (-0.15 < R2 < 0.79, 124 N < RMS error < 343 N) for corresponding subcases. For independent controls, contact force predictions improved when precalibrated model parameter values or EMG shape tracking was used. For synergy controls, contact force predictions were relatively insensitive to how model parameter values were calibrated, while EMG shape tracking made lateral (but not medial) contact force predictions worse. For the subject and optimization cost function analyzed in this study, use of subject-specific synergy controls improved the accuracy of knee contact force predictions, especially for lateral contact force when EMG shape tracking was omitted, and reduced prediction sensitivity to uncertainties in muscle model parameter values.

Update on grand challenge competition to predict in vivo knee loads.

Validation is critical if clinicians are to use musculoskeletal models to optimize treatment of individual patients with a variety of musculoskeletal disorders. This paper provides an update on the annual Grand Challenge Competition to Predict in Vivo Knee Loads, a unique opportunity for direct validation of knee contact forces and indirect validation of knee muscle forces predicted by musculoskeletal models. Three competitions (2010, 2011, and 2012) have been held at the annual American Society of Mechanical Engineers Summer Bioengineering Conference, and two more competitions are planned for the 2013 and 2014 conferences. Each year of the competition, a comprehensive data set collected from a single subject implanted with a force-measuring knee replacement is released. Competitors predict medial and lateral knee contact forces for two gait trials without knowledge of the experimental knee contact force measurements. Predictions are evaluated by calculating root-mean-square (RMS) errors and R(2) values relative to the experimentally measured medial and lateral contact forces. For the first three years of the competition, competitors used a variety of methods to predict knee contact and muscle forces, including static and dynamic optimization, EMG-driven models, and parametric numerical models. Overall, errors in predicted contact forces were comparable across years, with average RMS errors for the four competition winners ranging from 229 N to 312 N for medial contact force and from 238 N to 326 N for lateral contact force. Competitors generally predicted variations in medial contact force (highest R(2 )= 0.91) better than variations in lateral contact force (highest R(2 )= 0.70). Thus, significant room for improvement exists in the remaining two competitions. The entire musculoskeletal modeling community is encouraged to use the competition data and models for their own model validation efforts.

A qualitative study of social facilitators and barriers to health behavior change among persons with serious mental illness.

This qualitative focus group study was conducted to explore social facilitators and barriers to health behavior change in persons with serious mental illness engaged in a healthy lifestyle intervention. Six focus group interviews were conducted with a total of 30 clients stratified by "high" and "low" achievers in the program based on clinically significant weight loss or significant increase in fitness. Thematic analysis of focus group discussions revealed that emotional, practical, and mutual support from family members and significant others were social facilitators to health behavior change, while unhealthy social environments was a barrier. Participants in the "high" achiever group reported more mutual support for health behavior change than participants in the "low" achiever group. Results highlight the need for researchers and clinicians to consider the potential role of family and significant others as health supporters for persons with mental illness who could encourage healthy behavior in the social environment.

Spatiotemporal and muscle activation adaptations during overground walking in response to lower body added mass.

BACKGROUND: Lower-extremity exoskeletons have been used in rehabilitation and performance augmentation for the past two decades. An exoskeleton adds a significant load to certain segments of the user's body and the underlying science about the effects of adding mass to the different lower-body segments is limited. RESEARCH QUESTION: What are the adaptive changes that occur when mass is placed on three lower body segments (pelvis, thigh, and shank)? METHODS: Healthy adults (n = 24) completed 5 overground walking trials for 7 added mass conditions. The seven added mass conditions included a Baseline (no-load) condition, + 2 and + 4 lb on either the shanks or the thighs, and + 8 and + 16 lb on the pelvis. Spatiotemporal metrics, surface electromyography (EMG) data from 5 lower-limb muscles, and ground reaction force data were analyzed and compared between conditions. RESULTS: Pelvis mass of 16 lb increased the double support time (p < 0.001) and decreased the single support time (p < 0.001) from the Baseline. Loading rate for none of the added mass conditions were significantly different from the Baseline. The highest activation of the considered thigh muscles and gastrocnemius generally occurred when High Mass was added either to the pelvis or the thigh. SIGNIFICANCE: The results demonstrate how added mass affects muscle activity, which could inform design of EMG-based exoskeleton controllers. With respect to spatiotemporal changes, results indicate that adding masses equal to or greater than 16 lb on the pelvis can cause significant differences when compared to unloaded walking. This finding implies that all other mass loadings in this study, regardless of location, are regulated. Thus, as a guideline to exoskeleton design, we recommend mass distributions over the pelvis and the thigh to take advantage of the larger muscle groups in adapting to the added mass.

Impact of an ankle foot orthosis on reactive stepping in young adults.

BACKGROUND: Ankle-foot orthoses (AFOs) have been shown to improve gait and static balance in individuals with lower extremity weakness and instability. However, the effects of AFOs on dynamic balance reactions including reactive stepping responses are not well known. Therefore, the purpose of this study was to determine the effects of an AFO on reactive stepping responses in healthy young adults. RESEARCH QUESTION: Does an AFO alter reactive stepping responses in healthy young adults? METHODS: Twenty healthy young adults completed 10 reactive stepping trials using a lean-and-release system for each of three AFO conditions: 1) no AFO, 2) AFO on left leg and 3) AFO on right leg. Trials were recorded using 3D motion capture and force plates. Stepping limb preference and temporal, spatial, and kinematic variables were measured. Differences between conditions were determined by a one-way ANOVA with a Tukey post-hoc. RESULTS: With no AFO, participants demonstrated a preference for stepping with the right leg, 7.0 ± 3.9 of 10 trials. With an AFO on the right leg, this preference decreased to 5.7 ± 4.4 (p = 0.03). With an AFO on the left leg, this preference increased to 8.1 ± 3.3 (p = 0.03). Reaction times were not significantly different between conditions, but participants took a significantly shorter reactive step with the leg wearing the AFO. Peak ankle, knee, and hip joint angles were significantly less with the AFO on the stepping limb compared to the stance limb. SIGNIFICANCE: This study shows that AFO use can influence reactive stepping limb preference and stepping limb kinematics in healthy young adults. These results can inform future research on AFO users with gait impairments. These finding may also be helpful in developing interventions to address the specific effects of an AFO on reactive stepping responses.

Influence of musculoskeletal model parameter values on prediction of accurate knee contact forces during walking.

Treatment design for musculoskeletal disorders using in silico patient-specific dynamic simulations is becoming a clinical possibility. However, these simulations are sensitive to model parameter values that are difficult to measure experimentally, and the influence of uncertainties in these parameter values on the accuracy of estimated knee contact forces remains unknown. This study evaluates which musculoskeletal model parameters have the greatest influence on estimating accurate knee contact forces during walking. We performed the evaluation using a two-level optimization algorithm where musculoskeletal model parameter values were adjusted in the outer level and muscle activations were estimated in the inner level. We tested the algorithm with different sets of design variables (combinations of optimal muscle fiber lengths, tendon slack lengths, and muscle moment arm offsets) resulting in nine different optimization problems. The most accurate lateral knee contact force predictions were obtained when tendon slack lengths and moment arm offsets were adjusted simultaneously, and the most accurate medial knee contact force estimations were obtained when all three types of parameters were adjusted together. Inclusion of moment arm offsets as design variables was more important than including either tendon slack lengths or optimal muscle fiber lengths alone to obtain accurate medial and lateral knee contact force predictions. These results provide guidance on which musculoskeletal model parameter values should be calibrated when seeking to predict in vivo knee contact forces accurately.

Multi-segment foot model reveals distal joint kinematic differences between habitual heel-toe walking and non-habitual toe walking.

Toe walking is observed in pathological populations including cerebral palsy, stroke, and autism spectrum disorder. To understand pathological toe walking, previous studies have analyzed non-habitual toe walking. These studies found sagittal plane deviations between heel-toe and toe walking at the hip, knee, and ankle. Further investigation is merited as toe walking may involve altered biomechanics at more distal joints, such as the midtarsal joint. The purpose of this study was to examine biomechanical differences between rearfoot strike walking (RFSW) and non-rearfoot strike walking (NRFSW) in the midfoot and ankle. We hypothesized that during NRFSW, midtarsal kinematics would diverge from those during RFSW in all three cardinal planes and ankle kinematics would display increased supination. Twenty-four healthy females walked overground with both walking patterns. Motion capture, electromyography (EMG), and force plate data were collected. A validated multi-segment foot model was used with mean difference waveform analyses to compare walking conditions during stance. Significantly different kinematics were found in all three planes for the midtarsal and ankle joint during NRFSW. The NRFSW midtarsal joint exhibited increased plantarflexion, eversion, and adduction with the largest differences occurring at initial contact and in the sagittal plane. The NRFSW ankle exhibited increased supination at initial contact and during early stance. These findings indicate that toe walking alters both distal and proximal foot joint kinematics in multiple planes. This may further the understanding of altered biomechanics during toe walking while providing a basis for future analyses of pathological gait.

Simulation on the Effect of Gait Variability, Delays, and Inertia with Respect to Wearer Energy Savings with Exoskeleton Assistance.

Exoskeletons are human-robot interfaces that have enormous potential to assist people with everyday tasks. To improve the design of exoskeletons for use in clinical populations, it is important to further our understanding of how exoskeleton design and control parameters lead to sub-optimal effectiveness. Here we simulated the effect of three factors, gait variability, wearer-exoskeleton delays, and exoskeleton inertia, have on the predicted energy assistance provided by an exoskeleton with a finite-state controller trained on a set of stroke survivors' free walking gait data. Results indicate that larger errors between the wearer's desired ankle trajectory and the exo's estimated ankle trajectory result in statistically large reductions in the actual assistance provided. Specifically lags on the order of even 10 ms can illustrate statistically sub-optimal performance. Likewise subjects that exhibit large gait variability will have a statistical reduction in actual assistance. However, reasonably low exoskeleton inertias are not significant as a factor in terms of sensitivity to wearer assistance. Therefore, to improve cooperative control algorithms for exoskeletons and achieve true assistance based on wearer induced motion, this work implies that designers should prioritize minimizing delays and wearers should train to reduce variability in order to maximize energy savings.

Adolescents' Use of Digital Technologies and Preferences for Mobile Health Coaching in Public Mental Health Settings.

Objective: Youth with mental illnesses often engage in unhealthy behaviors associated with early mortality from physical diseases in adulthood, but interventions to support positive health behaviors are rarely offered as part of routine mental health care for this group. Digital health technology that is desirable, accessible, and affordable has the potential to address health behaviors in public mental health settings where many adolescents with severe mental health problems receive care. The aims of this study were to examine how adolescents receiving public mental health services use digital technology and social media and to explore their preferences using technology to support health and wellness. Methods: Using a convergent parallel mixed methods design, we surveyed adolescents ages 13-18 from four community mental health centers in one state and conducted focus group interviews to explore their perspectives on using digital technology and social media to receive health coaching and connect with peers to support healthy behaviors. The survey and focus group data were merged to inform the future development of a digital health intervention for adolescents receiving public mental health services. Results: Of 121 survey respondents (mean age 15.2, SD = 1.5), 92% had a cell phone, 79% had a smartphone, 90% used text messaging, and 98% used social media. Focus group interviews revealed that adolescents were interested in receiving strengths-based mobile health coaching, and they preferred structured online peer-to-peer interactions in which a professional moderator promotes positive connections and adherence to privacy guidelines. Conclusions: Adolescents receiving public mental health services in this study had access to smartphones and were frequent social media users. These data suggest that digital health interventions to promote health and wellness among adolescents may be scalable in community mental health settings. Adolescent participants suggested that digital health interventions for this group should focus on strengths and online peer support for health promotion should include a professional moderator to foster and manage peer-to-peer interactions.

A virtual learning collaborative to implement health promotion in routine mental health settings: Protocol for a cluster randomized trial.

BACKGROUND: Despite widespread use of learning collaboratives in health care, few randomized trials have evaluated their effectiveness. The primary aim of this cluster randomized implementation trial is to evaluate the effectiveness of a virtual learning collaborative (VLC) in the implementation of a lifestyle intervention for persons with serious mental illness (SMI) in routine mental health settings, compared to standard individual technical assistance. METHODS: Forty-eight mental health provider organizations from across the United States will be recruited to participate in the trial. The evidence-based practice to be implemented is the InSHAPE health promotion intervention for persons with SMI. Sites will be stratified by size and randomized to receive an 18-month intensive group-based VLC with monthly learning sessions or individual technical assistance with four scheduled conference calls over 18 months. Sites will be enrolled in three blocks of 16 sites each. The primary outcomes are InSHAPE program participation and fidelity, and participant weight loss; secondary outcomes are program operation, program uptake, participant health behaviors of physical activity and nutrition, organizational change, and program sustainment. Implementation outcomes are measured at 3, 6, 12, 18, and 24 months after the program start-up. Participant-level outcomes are measured at fixed intervals every 3 months after each participant enrolls in the study. DISCUSSION: This study will determine whether VLCs are an effective implementation strategy among resource-limited providers when the new practice necessitates a shift in mission, scope of practice, type of services delivered, and new financing. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03891368 Registered 25 March 2019, retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT03891368?term=NCT03891368&rank=1.