This work presents a framework for selection of subject-specific quasi-stiffness of hip orthoses and exoskeletons, and other devices that are intended to emulate the biological performance of this joint during walking. The hip joint exhibits linear moment-angular excursion behavior in both the extension and flexion stages of the resilient loading-unloading phase that consists of terminal stance and initial swing phases. Here, we establish statistical models that can closely estimate the slope of linear fits to the moment-angle graph of the hip in this phase, termed as the quasi-stiffness of the hip. Employing an inverse dynamics analysis, we identify a series of parameters that can capture the nearly linear hip quasi-stiffnesses in the resilient loading phase. We then employ regression analysis on experimental moment-angle data of 216 gait trials across 26 human adults walking over a wide range of gait speeds (0.75–2.63 m/s) to obtain a set of general-form statistical models that estimate the hip quasi-stiffnesses using body weight and height, gait speed, and hip excursion. We show that the general-form models can closely estimate the hip quasi-stiffness in the extension (R2 = 92%) and flexion portions (R2 = 89%) of the resilient loading phase of the gait. We further simplify the general-form models and present a set of stature-based models that can estimate the hip quasi-stiffness for the preferred gait speed using only body weight and height with an average error of 27% for the extension stage and 37% for the flexion stage.
Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.
Humans walk and run at a range of speeds. While steady locomotion at a given speed requires no net mechanical work, moving faster does demand both more positive and negative mechanical work per stride. Is this increased demand met by increasing power output at all lower limb joints or just some of them? Does running rely on different joints for power output than walking? How does this contribute to the metabolic cost of locomotion? This study examined the effects of walking and running speed on lower limb joint mechanics and metabolic cost of transport in humans. Kinematic and kinetic data for 10 participants were collected for a range of walking (0.75, 1.25, 1.75, 2.0 m s−1) and running (2.0, 2.25, 2.75, 3.25 m s−1) speeds. Net metabolic power was measured by indirect calorimetry. Within each gait, there was no difference in the proportion of power contributed by each joint (hip, knee, ankle) to total power across speeds. Changing from walking to running resulted in a significant (p = 0.02) shift in power production from the hip to the ankle which may explain the higher efficiency of running at speeds above 2.0 m s−1 and shed light on a potential mechanism behind the walk–run transition.
locomotion; speed; mechanical power; efficiency; cost of transport
Objective The aim of this study was to develop the Transition Readiness Assessment Questionnaire (TRAQ), a measure of readiness for transition from pediatric to adult healthcare for youth with special health care needs (YSHCN). Methods We administered TRAQ to 192 YSHCN aged 16–26 years in three primary diagnostic categories, conducted factor analysis, and assessed differences in TRAQ scores by age, gender, race, and primary diagnosis type. Results Factor analysis identified two TRAQ domains with high internal consistency: Skills for Self-Management and Skills for Self-Advocacy. Each domain had high internal consistency. In multivariate regression models, older age and a primary diagnosis of an activity limiting physical condition were associated with higher scores in Self-Management, and female gender and a primary diagnosis of an activity limiting physical condition were associated with higher scores in Self-Advocacy. Conclusions Our initial validation study suggests the TRAQ is a useful tool to assess transition readiness in YSHCN and to guide educational interventions by providers to support transition.
adolescents; chronic illness; health care services
To examine the relationship between illness perception, health status, and health-related quality of life (HRQOL) in a cohort of adults with cystic fibrosis (CF).
In the Project on Adult Care in Cystic Fibrosis (PAC-CF), we administered five subscales (Illness Consequences, Illness Coherence, Illness Timeline-Cyclical, Personal Control, Treatment Control) of the Illness Perception Questionnaire-Revised (IPQ-R). Multivariable linear regression analyses explored the associations between illness perception, health status, symptom burden, and physical and psychosocial HRQOL as measured by various domains of the CF Questionnaire-Revised (CFQ-R).
Among the 199 respondents (63% female, mean age 36.8±10.2 years), IPQ-R scores did not differ based on age, gender, or lung function. In multivariable regression models neither clinical characteristics nor physical or psychological symptom burden scores were associated with CFQ-R physical domains. In contrast, higher scores on Illness Consequences were associated with lower psychosocial CFQ-R scores. Higher scores on lllness Coherence and Personal Control scales were associated with higher psychosocial CFQ-R scores.
Adults with CF report a high understanding of their disease, feel that CF has significant consequences, and endorse both personal and treatment control over their outcomes. Illness perceptions did not vary with increased age or worsening disease severity, suggesting that illness perceptions may develop during adolescence. Illness perceptions were associated with psychosocial but not physical aspects of HRQOL. Efforts to modify illness perceptions as part of routine clinical care and counseling may lead to improved quality of life for adults with CF.
Cystic fibrosis; quality of life; illness perceptions
Children with food allergies often have concurrent asthma.
The authors aimed to determine the prevalence of asthma in children with food allergies and the association of specific food allergies with asthma.
Parental questionnaire data regarding food allergy, corroborated by allergic sensitization were completed for a cohort of 799 children with food allergies. Multivariate regression analysis tested the association between food allergy and reported asthma.
In this cohort, the prevalence of asthma was 45.6%. After adjusting for each food allergy, environmental allergies, and family history of asthma, children with egg allergy (odds ratio [OR] = 2.0; 95% confidence interval [CI] = 1.3–3.2; P < .01) or tree nut allergy (OR = 2.0; 95% CI = 1.1–3.6; P = .02) had significantly greater odds of report of asthma.
There is a high prevalence of asthma in the food-allergic pediatric population. Egg and tree nut allergy are significantly associated with asthma, independent of other risk factors.
asthma; food allergy; food hypersensitivity; nut allergy; nut hypersensitivity; egg allergy; egg hypersensitivity; pediatrics; allergy; asthma epidemiology
Daily controller medication use is recommended for children with persistent asthma to achieve asthma control.
To examine patterns of inhaled corticosteroid (ICS) use and asthma control in an observational study of children and adolescents with mild-to-moderate asthma (the Childhood Asthma Management Program Continuation Study).
We assessed patterns of ICS use during a 12-month period (consistent, intermittent, and none) and asthma control (well controlled vs poorly controlled). Multivariate logistic regression examined the association between pattern of ICS use and asthma control.
Of 914 patients enrolled, 425 were recommended to continue receiving ICS therapy in the Childhood Asthma Management Program Continuation Study. Of these patients, 46% reported consistent ICS use and 20% reported no ICS use during year 1. By year 4, consistent ICS use decreased to 20%, whereas no ICS use increased to 57%; poorly controlled asthma was reported in 18% of encounters. In multivariate models controlling for age, sex, forced expiratory volume in 1 second, and asthma severity assessment, patients reporting consistent ICS use during a 12-month period were more likely to report poor asthma control (odds ratio, 1.6; 95% confidence interval, 1.2–2.1) compared with those reporting no ICS use.
In this observational study of children and adolescents with mild-to-moderate asthma, most did not report continued use of ICS. Patients recommended to continue receiving ICS therapy and reporting consistent ICS use were less likely to report well-controlled asthma even after controlling for markers of asthma severity. Although residual confounding by severity cannot be ruled out, many children and adolescents may not achieve well-controlled asthma despite consistent use of ICS.
A large portion of the mechanical work required for walking comes from muscles and tendons crossing the ankle joint. By storing and releasing elastic energy in the Achilles tendon during each step, humans greatly enhance the efficiency of ankle joint work far beyond what is possible for work performed at the knee and hip joints.
Humans produce mechanical work at the ankle joint during walking with an efficiency two to six times greater than isolated muscle efficiency.
gait; locomotion; walking; energetics; exoskeleton; efficiency
More aggressive management of cystic fibrosis (CF), along with the use of new therapies, has led to increasing survival. Thus, the recommended daily treatment regimens for most CF adults are complex and time consuming.
In the Project on Adult Care in CF (PAC-CF), an ongoing longitudinal study of CF adults, we assessed self-reported daily treatment activities and perceived treatment burden as measured by the CF Questionnaire-Revised (CFQ-R), a disease-specific quality of life measure.
Among the 204 respondents, the median number of daily therapies reported was 7 (IQR 5-9) and the mean reported time spent on treatment activities was 108 minutes per day (SD 58 minutes). Respondents reported a median of 3 inhaled and 3 oral therapies on the day prior to the survey. Only 49% reported performing airway clearance (ACT) on that day. There were no differences in the number of medications or the time to complete therapies based on gender, age or FEV1. The mean CFQ-R treatment burden domain score was 52.3 (SD 22.1), with no significant differences in the treatment burden based on age or FEV1. In a multivariable model controlling for age, gender, and FEV1, using 2 or more nebulized medications and performing ACT for ≥30 minutes were significantly associated with increased treatment burden.
The level of daily treatment activity is high for CF adults regardless of age or disease severity. Increasing number of nebulized therapies and increased ACT time, but not gender, age, or pulmonary function, is associated with higher perceived treatment burden. Efforts to assess the effects of high treatment burden on outcomes such as quality of life are warranted.
Cystic fibrosis; treatment burden; quality of life
Because many patients with cystic fibrosis (CF) continue to survive into adulthood, discussion of end-of-life care decisions between clinicians and patients becomes a crucial part of CF adult care. Advance care planning (ACP) promotes alignment of patient care at the end of life with an individual's goals, however minimal research exists on ACP in CF.
We surveyed adults enrolled in the Project on Adult Care in Cystic Fibrosis (PAC-CF). We assessed experiences with ACP processes and communication and sought to identify factors associated with completion of an advance directive.
The mean age of respondents (n = 234) was 34 years and the mean forced expiratory volume in 1 second (FEV1) was 64% predicted. Seventy-four percent reported that they had spoken to someone, generally a family member, about the care they would want if they became too ill to make decisions for themselves. However, only 30% reported completing an advance directive. Although 79% reported feeling comfortable talking to their clinician about ACP, only 28% said that their CF clinicians have asked about ACP. Having specific wishes about treatment decisions (odds ratio [OR] 7.8, 95% confidence interval [CI] 1.9–32.1) and reporting that a clinician had discussed ACP (OR 4.4, 95% CI 1.5–12.6) were significantly associated with reporting the completion of an advance directive.
Though the majority of adults with CF report thinking about and communicating with family about advance care wishes, only a minority report completing an advance directive. Few adults with CF report being asked about ACP by their clinicians. Formulating specific wishes and discussing ACP with a clinician are strongly associated with completing an advance directive. Efforts to improve clinician communication with CF adults around ACP are needed to ensure that discussion of advance directives becomes an integral component of adult CF care.
The goal of this study was to test the mechanical performance of a prototype knee-ankle-foot orthosis (KAFO) powered by artificial pneumatic muscles during human walking. We had previously built a powered ankle-foot orthosis (AFO) and used it effectively in studies on human motor adaptation, locomotion energetics, and gait rehabilitation. Extending the previous AFO to a KAFO presented additional challenges related to the force-length properties of the artificial pneumatic muscles and the presence of multiple antagonistic artificial pneumatic muscle pairs.
Three healthy males were fitted with custom KAFOs equipped with artificial pneumatic muscles to power ankle plantar flexion/dorsiflexion and knee extension/flexion. Subjects walked over ground at 1.25 m/s under four conditions without extensive practice: 1) without wearing the orthosis, 2) wearing the orthosis with artificial muscles turned off, 3) wearing the orthosis activated under direct proportional myoelectric control, and 4) wearing the orthosis activated under proportional myoelectric control with flexor inhibition produced by leg extensor muscle activation. We collected joint kinematics, ground reaction forces, electromyography, and orthosis kinetics.
The KAFO produced ~22%–33% of the peak knee flexor moment, ~15%–33% of the peak extensor moment, ~42%–46% of the peak plantar flexor moment, and ~83%–129% of the peak dorsiflexor moment during normal walking. With flexor inhibition produced by leg extensor muscle activation, ankle (Pearson r-value = 0.74 ± 0.04) and knee ( r = 0.95 ± 0.04) joint kinematic profiles were more similar to the without orthosis condition compared to when there was no flexor inhibition (r = 0.49 ± 0.13 for ankle, p = 0.05, and r = 0.90 ± 0.03 for knee, p = 0.17).
The proportional myoelectric control with flexor inhibition allowed for a more normal gait than direct proportional myoelectric control. The current orthosis design provided knee torques smaller than the ankle torques due to the trade-off in torque and range of motion that occurs with artificial pneumatic muscles. Future KAFO designs could incorporate cams, gears, or different actuators to transmit greater torque to the knee.
Few empirical studies have examined the role of family caregivers in the lives of adults with CF.
As part of the Project on Adult Care in CF (PAC-CF), an on-going prospective, longitudinal panel study of adults with CF, 119 family members and friends of adults with CF completed a mail survey in which they reported the frequency of help they provide for their family member with CF during routine care, hospitalization, and home IV treatment.
The 119 caregivers were mainly spouses or unmarried partners (56%) and parents (29%). Fifteen percent of caregivers were children, friends, siblings or roommates. Family caregivers for adults with CF report assisting mainly with communication and social support during routine treatment, although one third provide some clinical care on a regular basis. Family caregivers report an increase in assistance during periods of acute illness, such as during a hospitalization and home IV treatment, especially with clinical care tasks.
The depth of commitment required of families of children with CF has been well documented for decades. Our results suggest that the responsibilities of family members diminish only moderately as those with CF reach adulthood.
Symptom burden is a key component of health-related quality of life (HRQOL) in patients with cystic fibrosis (CF). In order to examine symptom prevalence and characteristics of adults with CF, we administered the Memorial Symptom Assessment Scale (MSAS), a previously validated measure of symptom burden, to CF patients enrolled in the Project on Adult Care in CF (PAC-CF). The mean age of the 303 respondents (response rate 91%) was 32.8 years (range 19–64); 58% were female, and their mean baseline pulmonary function (FEV1 % predicted) was 69% (SD 28%). The median number of symptoms reported was 10, and there was no difference in the number of symptoms reported based on age, gender, or FEV1. The most prevalent symptoms were cough (94%), shortness of breath (77%), and lack of energy (77%). Lack of energy and irritability caused the highest level of distress. MSAS symptom subscales were only moderately correlated with symptom status domains from existing CF HRQOL measures. Factor analysis led to the development of three distinct MSAS CF-symptom subscales, each with high internal validity. These findings show that adults with CF have a high symptom burden, particularly with respiratory and psychological symptoms, and that the new MSAS CF specific subscales are a reliable measure of symptom distress in the CF population.
Cystic fibrosis; symptom burden; symptom prevalence
Bodyweight supported treadmill training has become a prominent gait rehabilitation method in leading rehabilitation centers. This type of locomotor training has many functional benefits but the labor costs are considerable. To reduce therapist effort, several groups have developed large robotic devices for assisting treadmill stepping. A complementary approach that has not been adequately explored is to use powered lower limb orthoses for locomotor training. Recent advances in robotic technology have made lightweight powered orthoses feasible and practical. An advantage to using powered orthoses as rehabilitation aids is they allow practice starting, turning, stopping, and avoiding obstacles during overground walking.
locomotion; exoskeleton; locomotor training; bodyweight support; robotics
Technological advances in robotic hardware and software have enabled powered exoskeletons to move from science fiction to the real world. The objective of this article is to emphasize two main points for future research. First, the design of future devices could be improved by exploiting biomechanical principles of animal locomotion. Two goals in exoskeleton research could particularly benefit from additional physiological perspective: 1) reduction in the metabolic energy expenditure of the user while wearing the device, and 2) minimization of the power requirements for actuating the exoskeleton. Second, a reciprocal potential exists for robotic exoskeletons to advance our understanding of human locomotor physiology. Experimental data from humans walking and running with robotic exoskeletons could provide important insight into the metabolic cost of locomotion that is impossible to gain with other methods. Given the mutual benefits of collaboration, it is imperative that engineers and physiologists work together in future studies on robotic exoskeletons for human locomotion.
biomechanics; walking; running; neural control; metabolic cost
Treadmill training with bodyweight support and manual assistance improves walking ability of patients with neurological injury. The purpose of this study was to determine how manual assistance changes muscle activation and kinematic patterns during treadmill training in individuals with incomplete spinal cord injury.
We tested six volunteers with incomplete spinal cord injury and six volunteers with intact nervous systems. Subjects with spinal cord injury walked on a treadmill at six speeds (0.18–1.07 m/s) with body weight support with and without manual assistance. Healthy subjects walked at the same speeds only with body weight support. We measured electromyographic (EMG) and kinematics in the lower extremities and calculated EMG root mean square (RMS) amplitudes and joint excursions. We performed cross-correlation analyses to compare EMG and kinematic profiles.
Normalized muscle activation amplitudes and profiles in subjects with spinal cord injury were similar for stepping with and without manual assistance (ANOVA, p > 0.05). Muscle activation amplitudes increased with increasing speed (ANOVA, p < 0.05). When comparing spinal cord injury subject EMG data to control subject EMG data, neither the condition with manual assistance nor the condition without manual assistance showed a greater similarity to the control subject data, except for vastus lateralis. The shape and timing of EMG patterns in subjects with spinal cord injury became less similar to controls at faster speeds, especially when walking without manual assistance (ANOVA, p < 0.05). There were no consistent changes in kinematic profiles across spinal cord injury subjects when they were given manual assistance. Knee joint excursion was ~5 degrees greater with manual assistance during swing (ANOVA, p < 0.05). Hip and ankle joint excursions were both ~3 degrees lower with manual assistance during stance (ANOVA, p < 0.05).
Providing manual assistance does not lower EMG amplitudes or alter muscle activation profiles in relatively higher functioning spinal cord injury subjects. One advantage of manual assistance is that it allows spinal cord injury subjects to walk at faster speeds than they could without assistance. Concerns that manual assistance will promote passivity in subjects are unsupported by our findings.
Powered lower limb orthoses could reduce therapist labor during gait rehabilitation after neurological injury. However, it is not clear how patients respond to powered assistance during stepping. Patients might allow the orthoses to drive the movement pattern and reduce their muscle activation. The goal of this study was to test the effects of robotic assistance in subjects with incomplete spinal cord injury using pneumatically powered ankle-foot orthoses.
Five individuals with chronic incomplete spinal cord injury (ASIA C-D) participated in the study. Each subject was fitted with bilateral ankle-foot orthoses equipped with artificial pneumatic muscles to power ankle plantar flexion. Subjects walked on a treadmill with partial bodyweight support at four speeds (0.36, 0.54, 0.72 and 0.89 m/s) under three conditions: without wearing orthoses, wearing orthoses unpowered (passively), and wearing orthoses activated under pushbutton control by a physical therapist. Subjects also attempted a fourth condition wearing orthoses activated under pushbutton control by them. We measured joint angles, electromyography, and orthoses torque assistance.
A therapist quickly learned to activate the artificial pneumatic muscles using the pushbuttons with the appropriate amplitude and timing. The powered orthoses provided ~50% of peak ankle torque. Ankle angle at stance push-off increased when subjects walked with powered orthoses versus when they walked with passive-orthoses (ANOVA, p < 0.05). Ankle muscle activation amplitudes were similar for powered and passive-orthoses conditions except for the soleus (~13% lower for powered condition; p < 0.05).
Two of the five subjects were able to control the orthoses themselves using the pushbuttons. The other three subjects found it too difficult to coordinate pushbutton timing. Orthoses assistance and maximum ankle angle at push-off were smaller when the subject controlled the orthoses compared to when the therapist-controlled the orthoses (p < 0.05). Muscle activation amplitudes were similar between the two powered conditions except for tibialis anterior (~31% lower for therapist-controlled; p < 0.05).
Mechanical assistance from powered ankle-foot orthoses improved ankle push-off kinematics without substantially reducing muscle activation during walking in subjects with incomplete spinal cord injury. These results suggest that robotic plantar flexion assistance could be used during gait rehabilitation without promoting patient passivity.