Upper body contributions to pitched ball velocity in elite high school pitchers using an induced velocity analysis.

Interest in joint and segment contributions to pitched ball velocity has been dominated by inverse dynamic solutions, which is limited in ascertaining complex muscle/joint interactions. Our purpose was to use induced velocity analysis to investigate which joint(s) made the largest contribution to the velocity of a pitched ball. Pitching data were collected from six elite high school-aged pitchers with no history of arm injury. Participants threw a fastball pitch from the windup on flat ground. Data were collected using seven Vicon 612 cameras (250 Hz) and three AMTI force platforms (1000 Hz). A 14-segment biomechanical model (feet, legs, thighs, pelvis, a combined thorax-abdomen-head, i.e., trunk, upper arms, forearms, and hands) was implemented in Visual3D as a dynamic link library built using SD/Fast (PTC) software. Model-generated induced velocity of the ball was validated against ball velocity obtained from a calibrated radar gun. Velocity induced torques at the shoulder just prior to release, and elbow during the cocking phase, contributed 31.0% and 18.1%, respectively, to forward ball velocity. The centripetal/Coriolis effects from the upper arm and forearm velocities made the largest contribution to ball velocity (average 57.8%), but the source of these effects are unknown. The lower extremities and trunk made little direct contribution to pitched ball velocity. These results may have implications with regard to pitching performance enhancement and rehabilitation.

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking.

An objective understanding of human foot and ankle function can drive innovations of bio-inspired wearable devices. Specifically, knowledge regarding how mechanical force and work are produced within the human foot-ankle structures can help determine what type of materials or components are required to engineer devices. In this study, we characterized the combined functions of the foot and ankle structures during walking by synthesizing the total force, displacement, and work profiles from structures distal to the shank. Eleven healthy adults walked at four scaled speeds. We quantified the ground reaction force and center-of-pressure displacement in the shank's coordinate system during stance phase and the total mechanical work done by these structures. This comprehensive analysis revealed emergent properties of foot-ankle structures that are analogous to passive springs: these structures compressed and recoiled along the longitudinal axis of the shank, and performed near zero or negative net mechanical work across a range of walking speeds. Moreover, the subject-to-subject variability in peak force, total displacement, and work were well explained by three simple factors: body height, mass, and walking speed. We created a regression-based model of stance phase mechanics that can inform the design and customization of wearable devices that may have biomimetic or non-biomimetic structures.

Using a Real-Time Locating System to Measure Walking Activity Associated with Wandering Behaviors Among Institutionalized Older Adults.

A real-time locating system (RTLS) can be used to track the walking activity of institutionalized older adults in long-term care who are at risk for wandering behaviors. The benefits of a RTLS are objective and continuous measurements of activity. Self-report methods of activity, especially wandering, by health care staff are vulnerable to floor effects and recall bias, and continuous clinical or research observation over the long-term can be time-consuming and expensive. Health care staff also fail to recognize the onset and/or duration of wandering behaviors, which are associated with a variety of adverse health outcomes in this population but amenable to intervention. RTLS technologies can measure the walking activity of institutionalized residents with cognitive impairment over time with a high degree of accuracy. This is particularly useful for the study of wandering, defined as walking for at least 60 seconds with few (if any) breaks in activity. Wandering is associated with disease progression, hospitalizations, falls and death. Previous work suggests older adults with poor balance ability and high sustained walking activity may be particularly susceptible to poor health outcomes. RTLS's are used to assess cognitive impairment and factors associated with gait and balance; however, supplemental paper and pencil gait/balance tools may be used to further refine risk profiles. This project discusses the use of a RTLS to measure walking activity and also gait quality and balance ability measures on this population.

Balance ability and cognitive impairment influence sustained walking in an assisted living facility.

PURPOSE OF STUDY: The purpose of this study was to determine the influence of cognitive impairment (CI),1 gait quality, and balance ability on walking distance and speed in an assisted living facility. MATERIALS AND METHODS: This was a longitudinal cohort study of institutionalized older adults (N = 26; 555 observations) followed for up to 8 months. Hierarchical linear modeling statistical techniques were used to examine the effects of gait quality and balance ability (using the Tinetti Gait and Balance Test) and cognitive status (using the Montreal Cognitive Assessment) on walking activity (distance, sustained distance, sustained speed). The latter were measured objectively and continuously by a real-time locating system (RTLS). RESULTS: A one-point increase in balance ability was associated with an 8% increase in sustained walking distance (p = 0.03) and a 4% increase in sustained gait speed (p = 0.00). Gait quality was associated with decreased sustained gait speed (p = 0.03). Residents with moderate (ERR = 2.34;p = 0.01) or severe CI (trend with an ERR = 1.62; p = 0.06) had longer sustained walking distances at slower speeds when compared to residents with no CI. CONCLUSIONS: After accounting for cognitive status, it was balance ability, not gait quality, that was a determinant of sustained walking distances and speeds. Therefore, balance interventions for older adults in assisted living may enable sustained walking activity. Given that CI was associated with more sustained walking, limiting sustained walking in the form of wandering behavior, especially for those with balance impairments, may prevent adverse events, including fall-related injury.

A mathematical analysis to address the 6 degree-of-freedom segmental power imbalance.

Segmental power is used in human movement analyses to indicate the source and net rate of energy transfer between the rigid bodies of biomechanical models. Segmental power calculations are performed using segment endpoint dynamics (kinetic method). A theoretically equivalent method is to measure the rate of change in a segment's mechanical energy state (kinematic method). However, these two methods have not produced experimentally equivalent results for segments proximal to the foot, with the difference in methods deemed the "power imbalance." In a 6 degree-of-freedom model, segments move independently, resulting in relative segment endpoint displacement and non-equivalent segment endpoint velocities at a joint. In the kinetic method, a segment's distal end translational velocity may be defined either at the anatomical end of the segment or at the location of the joint center (defined here as the proximal end of the adjacent distal segment). Our mathematical derivations revealed the power imbalance between the kinetic method using the anatomical definition and the kinematic method can be explained by power due to relative segment endpoint displacement. In this study, we tested this analytical prediction through experimental gait data from nine healthy subjects walking at a typical speed. The average absolute segmental power imbalance was reduced from 0.023 to 0.046 W/kg using the anatomical definition to ≤0.001 W/kg using the joint center definition in the kinetic method (95.56-98.39% reduction). Power due to relative segment endpoint displacement in segmental power analyses is substantial and should be considered in analyzing energetic flow into and between segments.

Constituent Lower Extremity Work (CLEW) approach: A novel tool to visualize joint and segment work.

Work can reveal the mechanism by which movements occur. However, work is less physically intuitive than more common clinical variables such as joint angles, and are scalar quantities which do not have a direction. Therefore, there is a need for a clearly reported and comprehensively calculated approach to easily visualize and facilitate the interpretation of work variables in a clinical setting. We propose the Constituent Lower Extremity Work (CLEW) approach, a general methodology to visualize and interpret cyclic tasks performed by the lower limbs. Using six degree-of-freedom power calculations, we calculated the relative work of the four lower limb constituents (hip, knee, ankle, and distal foot). In a single pie chart, the CLEW approach details the mechanical cost-of-transport, the percentage of positive and negative work performed in stance phase and swing phase, and the individual contributions of positive and negative work from each constituent. This approach can be used to compare the constituent-level adaptations occurring between limbs of individuals with impairments, or within a limb at different gait intensities. In this article, we outline how to generate and interpret the CLEW pie charts in a clinical report. As an example of the utility of the approach, we created a CLEW report using average reference data from eight unimpaired adult subjects walking on a treadmill at 0.8 statures/s (1.4m/s) compared with data from the intact and prosthetic limbs of an individual with a unilateral amputation walking with an above-knee passive prosthesis.

Changes in relative work of the lower extremity joints and distal foot with walking speed.

The modulation of walking speed results in adaptations to the lower limbs which can be quantified using mechanical work. A 6 degree-of-freedom (DOF) power analysis, which includes additional translations as compared to the 3 DOF (all rotational) approach, is a comprehensive approach for quantifying lower limb work during gait. The purpose of this study was to quantify the speed-related 6 DOF joint and distal foot work adaptations of all the lower extremity limb constituents (hip, knee, ankle, and distal foot) in healthy individuals. Relative constituent 6 DOF work, the amount of constituent work relative to absolute limb work, was calculated during the stance and swing phases of gait. Eight unimpaired adults walked on an instrumented split-belt treadmill at slow, moderate, and typical walking speeds (0.4, 0.6, and 0.8 statures/s, respectively). Using motion capture and force data, 6 DOF powers were calculated for each constituent. Contrary to previously published results, 6 DOF positive relative ankle work and negative relative distal foot work increased significantly with increased speed during stance phase (p<0.05). Similar to previous rotational DOF results in the sagittal plane, negative relative ankle work decreased significantly with increased speed during stance phase (p<0.05). Scientifically, these findings provide new insight into how healthy individuals adapt to increased walking speed and suggest limitations of the rotational DOF approach for quantifying limb work. Clinically, the data presented here for unimpaired limbs can be used to compare with speed-matched data from limbs with impairments.

The Bridging Advanced Developments for Exceptional Rehabilitation (BADER) Consortium: Reaching in Partnership for Optimal Orthopaedic Rehabilitation Outcomes.

The Bridging Advanced Developments for Exceptional Rehabilitation (BADER) Consortium began in September 2011 as a cooperative agreement with the Department of Defense (DoD) Congressionally Directed Medical Research Programs Peer Reviewed Orthopaedic Research Program. A partnership was formed with DoD Military Treatment Facilities (MTFs), U.S. Department of Veterans Affairs (VA) Centers, the National Institutes of Health (NIH), academia, and industry to rapidly conduct innovative, high-impact, and sustainable clinically relevant research. The BADER Consortium has a unique research capacity-building focus that creates infrastructures and strategically connects and supports research teams to conduct multiteam research initiatives primarily led by MTF and VA investigators.BADER relies on strong partnerships with these agencies to strengthen and support orthopaedic rehabilitation research. Its focus is on the rapid forming and execution of projects focused on obtaining optimal functional outcomes for patients with limb loss and limb injuries. The Consortium is based on an NIH research capacity-building model that comprises essential research support components that are anchored by a set of BADER-funded and initiative-launching studies. Through a partnership with the DoD/VA Extremity Trauma and Amputation Center of Excellence, the BADER Consortium's research initiative-launching program has directly supported the identification and establishment of eight BADER-funded clinical studies. BADER's Clinical Research Core (CRC) staff, who are embedded within each of the MTFs, have supported an additional 37 non-BADER Consortium-funded projects. Additional key research support infrastructures that expedite the process for conducting multisite clinical trials include an omnibus Cooperative Research and Development Agreement and the NIH Clinical Trials Database. A 2015 Defense Health Board report highlighted the Consortium's vital role, stating the research capabilities of the DoD Advanced Rehabilitation Centers are significantly enhanced and facilitated by the BADER Consortium.

Loaded Vertical Jumping: Force-Velocity Relationship, Work, and Power.

The aims of the current study were to explore the pattern of the force-velocity (F-V) relationship of leg muscles, evaluate the reliability and concurrent validity of the obtained parameters, and explore the load associated changes in the muscle work and power output. Subjects performed maximum vertical countermovement jumps with a vest ranging 0-40% of their body mass. The ground reaction force and leg joint kinematics and kinetics were recorded. The data revealed a strong and approximately linear F-V relationship (individual correlation coefficients ranged from 0.78-0.93). The relationship slopes, F- and V-intercepts, and the calculated power were moderately to highly reliable (0.67 < ICC < 0.91), while the concurrent validity F- and V-intercepts, and power with respect to the directly measured values, was (on average) moderate. Despite that a load increase was associated with a decrease in both the countermovement depth and absolute power, the absolute work done increased, as well as the relative contribution of the knee work. The obtained findings generally suggest that the loaded vertical jumps could not only be developed into a routine method for testing the capacities of leg muscles, but also reveal the mechanisms of adaptation of multijoint movements to different loading conditions.

Passive-dynamic ankle-foot orthosis replicates soleus but not gastrocnemius muscle function during stance in gait: Insights for orthosis prescription.

BACKGROUND: Passive-dynamic ankle-foot orthosis characteristics, including bending stiffness, should be customized for individuals. However, while conventions for customizing passive-dynamic ankle-foot orthosis characteristics are often described and implemented in clinical practice, there is little evidence to explain their biomechanical rationale. OBJECTIVES: To develop and combine a model of a customized passive-dynamic ankle-foot orthosis with a healthy musculoskeletal model and use simulation tools to explore the influence of passive-dynamic ankle-foot orthosis bending stiffness on plantar flexor function during gait. STUDY DESIGN: Dual case study. METHODS: The customized passive-dynamic ankle-foot orthosis characteristics were integrated into a healthy musculoskeletal model available in OpenSim. Quasi-static forward dynamic simulations tracked experimental gait data under several passive-dynamic ankle-foot orthosis conditions. Predicted muscle activations were calculated through a computed muscle control optimization scheme. RESULTS: Simulations predicted that the passive-dynamic ankle-foot orthoses substituted for soleus but not gastrocnemius function. Induced acceleration analyses revealed the passive-dynamic ankle-foot orthosis acts like a uniarticular plantar flexor by inducing knee extension accelerations, which are counterproductive to natural knee kinematics in early midstance. CONCLUSION: These passive-dynamic ankle-foot orthoses can provide plantar flexion moments during mid and late stance to supplement insufficient plantar flexor strength. However, the passive-dynamic ankle-foot orthoses negatively influenced knee kinematics in early midstance. CLINICAL RELEVANCE: Identifying the role of passive-dynamic ankle-foot orthosis stiffness during gait provides biomechanical rationale for how to customize passive-dynamic ankle-foot orthoses for patients. Furthermore, these findings can be used in the future as the basis for developing objective prescription models to help drive the customization of passive-dynamic ankle-foot orthosis characteristics.

Comparison of mechanical energy profiles of passive and active below-knee prostheses: a case study.

BACKGROUND: With the recent technological advancements of prosthetic lower limbs, there is currently a great desire to objectively evaluate existing prostheses. Using a novel biomechanical analysis, the purpose of this case study was to compare the mechanical energy profiles of anatomical and two disparate prostheses: a passive prosthesis and an active prosthesis. CASE DESCRIPTION AND METHODS: An individual with a transtibial amputation who customarily wears a passive prosthesis (Elation, Össur) and an active prosthesis (BiOM, iWalk, Inc.) and 11 healthy subjects participated in an instrumented gait analysis. The total mechanical power and work of below-knee structures during stance were quantified using a unified deformable segment power analysis. FINDINGS AND OUTCOMES: Active prosthesis generated greater peak power and total positive work than passive prosthesis and healthy anatomical limbs. CONCLUSION: The case study will enhance future efforts to objectively evaluate prosthetic functions during gait in individuals with transtibial amputations. CLINICAL RELEVANCE: A prosthetic limb should closely replicate the mechanical energy profiles of anatomical limbs. The unified deformable (UD) analysis may be valuable to facilitate future clinical prescription and guide fine adjustments of prosthetic componentry to optimize gait outcomes.

Passive-dynamic ankle-foot orthoses substitute for ankle strength while causing adaptive gait strategies: a feasibility study.

Bending stiffness of passive-dynamic ankle-foot orthoses (PD-AFOs) is a functional characteristic thought to restore lost ankle function due to weakened plantar flexors. However, lower extremity impairment profiles of patients are seldom limited to plantar flexion weakness, and PD-AFO characteristics often influence gait in other ways. Combined, all PD-AFO characteristics and patient impairments likely mask the main effect of PD-AFO bending stiffness and complicate the PD-AFO bending stiffness prescription process. In this study, we propose a biomechanical probing paradigm, where customized PD-AFOs with a range of precise stiffness values are worn by healthy subjects, to experimentally test a PD-AFO strength substitution hypothesis while simultaneously documenting gait adaptations to PD-AFO use. Two healthy subjects walked at a scaled velocity while wearing a series of three PD-AFOs that ranged in bending stiffness levels. Supporting the strength substitution hypothesis, peak ankle plantar flexion moments remained unchanged across PD-AFO stiffness conditions. Further biomechanical analyses documented a complex series of ankle related kinematic and kinetic adaptive movement strategies due to PD-AFO use. This study demonstrated the utility of the biomechanical probing paradigm to help understand the contribution of PD-AFO stiffness to ankle strength and its secondary effects on ankle biomechanics.

Assessment of a virtual functional prototyping process for the rapid manufacture of passive-dynamic ankle-foot orthoses.

Passive-dynamic ankle-foot orthosis (PD-AFO) bending stiffness is a key functional characteristic for achieving enhanced gait function. However, current orthosis customization methods inhibit objective premanufacture tuning of the PD-AFO bending stiffness, making optimization of orthosis function challenging. We have developed a novel virtual functional prototyping (VFP) process, which harnesses the strengths of computer aided design (CAD) model parameterization and finite element analysis, to quantitatively tune and predict the functional characteristics of a PD-AFO, which is rapidly manufactured via fused deposition modeling (FDM). The purpose of this study was to assess the VFP process for PD-AFO bending stiffness. A PD-AFO CAD model was customized for a healthy subject and tuned to four bending stiffness values via VFP. Two sets of each tuned model were fabricated via FDM using medical-grade polycarbonate (PC-ISO). Dimensional accuracy of the fabricated orthoses was excellent (average 0.51 ± 0.39 mm). Manufacturing precision ranged from 0.0 to 0.74 Nm/deg (average 0.30 ± 0.36 Nm/deg). Bending stiffness prediction accuracy was within 1 Nm/deg using the manufacturer provided PC-ISO elastic modulus (average 0.48 ± 0.35 Nm/deg). Using an experimentally derived PC-ISO elastic modulus improved the optimized bending stiffness prediction accuracy (average 0.29 ± 0.57 Nm/deg). Robustness of the derived modulus was tested by carrying out the VFP process for a disparate subject, tuning the PD-AFO model to five bending stiffness values. For this disparate subject, bending stiffness prediction accuracy was strong (average 0.20 ± 0.14 Nm/deg). Overall, the VFP process had excellent dimensional accuracy, good manufacturing precision, and strong prediction accuracy with the derived modulus. Implementing VFP as part of our PD-AFO customization and manufacturing framework, which also includes fit customization, provides a novel and powerful method to predictably tune and precisely manufacture orthoses with objectively customized fit and functional characteristics.

Mechanical energy profiles of the combined ankle-foot system in normal gait: insights for prosthetic designs.

Over the last half-century, the field of prosthetic engineering has continuously evolved with much attention being dedicated to restoring the mechanical energy properties of ankle joint musculatures during gait. However, the contributions of 'distal foot structures' (e.g., foot muscles, plantar soft tissue) have been overlooked. Therefore, the purpose of this study was to quantify the total mechanical energy profiles (e.g., power, work, and work-ratio) of the natural ankle-foot system (NAFS) by combining the contributions of the ankle joint and all distal foot structures during stance in level-ground steady state walking across various speeds (0.4, 0.6, 0.8 and 1.0 statures/s). The results from eleven healthy subjects walking barefoot indicated ankle joint and distal foot structures generally performed opposing roles: the ankle joint performed net positive work that systematically increased its energy generation with faster walking speeds, while the distal foot performed net negative work that systematically increased its energy absorption with faster walking speeds. Accounting for these simultaneous effects, the combined ankle-foot system exhibited increased work-ratios with faster walking. Most notably, the work-ratio was not significantly greater than 1.0 during the normal walking speed of 0.8 statures/s. Therefore, a prosthetic design that strategically exploits passive-dynamic properties (e.g., elastic energy storage and return) has the potential to replicate the mechanical energy profiles of the NAFS during level-ground steady-state walking.

Sensitivity of joint moments to changes in walking speed and body-weight-support are interdependent and vary across joints.

We investigated the effect of simultaneous changes in body-weight-support level and walking speed on mean peak internal joint moments at the ankle, knee and hip. We hypothesized that observed changes in these joint moments would be approximately linear with both body-weight-support and walking speed and would be similar across joints. Kinematic and kinetic data were collected from 8 unimpaired adult subjects walking on an instrumented treadmill while wearing a dynamically controlled overhead support harness. Subjects walked with four levels of body-weight-support (0%, 20%, 40%, and 60% of bodyweight) at three walking speeds (0.4, 0.6, and 0.8 statures/s, ranging on average from 0.7 to 1.4m/s). Data were used to calculate mean peak joint moments across subjects for each condition. In general, subjects' mean peak joint moments decreased linearly with decreasing walking speed and with increasing body-weight-support, except the knee extension moment, which showed a quadratic relationship with walking speed and no significant change with body-weight-support. All joint moments, with the exception of knee extension, showed a significant interaction effect between walking speed and body-weight-support, indicating that the sensitivity of these joint moments to changes in these variables was interdependent. In most cases, the ankle and hip extension moments showed the largest sensitivity to walking speed. The ankle moment was observed to have the greatest sensitivity to body-weight-support. This finding, that altering walking speed and body-weight-support level results in non-uniform changes in peak moments across joints, suggests that further research is warranted to establish the set of combined speed and support conditions that produce motor patterns supportive of normal gait retraining.

A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait.

Anatomically-relevant (AR) biomechanical models are traditionally used to quantify joint powers and segmental energies of lower extremity structures during gait. While AR models contain a series of rigid body segments linked together via mechanical joints, prosthetic below-knee structures are often deformable objects without a definable ankle joint. Consequently, the application of AR models for the study of prosthetic limbs has been problematic. The purpose of this study was to develop and validate a unified deformable (UD) segment model for quantifying the total power of below-knee structures. Estimates of total below-knee power derived via the UD segment model were compared to those derived via an AR model during stance in gait of eleven healthy subjects. The UD segment model achieved similar results to the AR model. Differences in peak power, total positive work, and total negative work were 1.91±0.31%, 3.97±0.49%, and 1.39±0.33%, relative to the AR model estimates. The main advantage of the UD segment model is that it does not require the definition of an ankle joint or foot structures. Therefore, this technique may be valuable for facilitating direct comparisons between anatomical and disparate prosthetic below-knee structures in future studies.

Dimensional accuracy of ankle-foot orthoses constructed by rapid customization and manufacturing framework.

Passive-dynamic ankle-foot orthoses (PD-AFOs) constitute a class of ankle braces that rely on material properties and physical features to establish functional characteristics such as bending or rotational stiffness. We have developed a novel framework that combines a fully parameterized PD-AFO computer-aided design (CAD) model and free-form fabrication to rapidly manufacture customized PD-AFOs. The three-dimensional locations of select anatomic landmarks serve to fit customize the PD-AFO CAD model. A virtual orthopedic alignment process and selection of discrete design parameter values further customize the orthosis, which is fabricated via selective laser sintering. CAD models were customized and full-scale orthoses were manufactured for two nondisabled subjects. The surface of one half-scale CAD model was marked with 3 mm hemispherical dimples, and four orthoses were manufactured in different build orientations and positions. Dimensional accuracy was determined by calculating discrepancies between corresponding CAD and fabricated orthoses interdimple distances. Subjective evaluations of the full-scale PD-AFOs following use in gait were positive. Dimension discrepancies were well under a 2 mm tolerance for the four half-scale orthoses. Mean foot plate, strut, and cuff component discrepancies were 0.31 +/- 0.28, 0.34 +/- 0.08, 0.52 +/- 0.39 mm, respectively, and 0.29 +/- 0.23 mm for the overall orthosis. Dimensional accuracy of the rapid customization and manufacturing framework was well within tolerances suggested in the literature.

Strength asymmetry and osteoarthritis risk factors in unilateral trans-tibial, amputee gait.

Persons with a unilateral, trans-tibial amputation have an increased risk of developing osteoarthritis (OA) in the knee of their intact limb. Between-side strength discrepancies observed in individuals with an amputation may indicate overuse of the intact limb and increased osteoarthritis risk; however, the relationship between lower extremity strength and gait mechanics has not been addressed in previous literature. It was hypothesized that amputee subjects' strength and gait would be more asymmetrical than controls, and that strength asymmetry would positively correlate with gait variable asymmetry and intact side gait variables associated with osteoarthritis risk. Eight persons with unilateral, trans-tibial amputation and eight able-bodied control subjects participated. Three gait variables related to osteoarthritis risk (knee external adduction moment, knee adduction moment load rate, and vertical ground reaction force load rate) were measured bilaterally, along with three strength measures (hip abductors, knee extensors, and knee flexors). Four of the six variables were more asymmetrical in the amputee group than the control group (p<0.05 and/or effect size greater than 0.70). Knee extension strength asymmetry was significantly related to knee adduction moment load rate asymmetry (rho=0.714), and knee flexion strength asymmetry was moderately related to the vertical ground reaction force on the intact limb (rho=0.643). Results suggest that strength asymmetry in unilateral trans-tibial amputees has a moderate relationship with osteoarthritis risk, and may be a useful way to assess gait ability and the need for rehabilitation in this population.

Visuomotor adaptation of voluntary step initiation in older adults.

It has been suggested that feedforward planning of gait and posture is diminished in older adults. Motor adaptation is one mechanism by which feedforward commands can be updated or fine-tuned. Thus, if feedforward mechanisms are diminished in older adults, motor adaptation is also likely to be limited. The purpose of the study was to compare the ability of healthy older versus young adults in generating a voluntary stepping motor adaptation in response to a novel visual sensory perturbation. We recorded stepping movements from 18 healthy older and 18 young adults during baseline and adaptation stepping blocks. During baseline, the stepping target remained stationary; in adaptation, a visual perturbation was introduced by shifting the target laterally during mid-step. We compared adaptation between groups, measured by improvements in endpoint accuracy and movement duration. Older adults adapted stepping accuracy similarly to young adults (accuracy improvement: 29.7 + or - 27.6% vs. 37.3 + or - 22.9%, older vs. young group respectively, p = 0.375), but showed significant slowness during movement. Thus older adults were able to achieve accuracy levels nearly equivalent to younger adults, but only at the expense of movement speed, at least during the early adaptation period (movement duration: 1143.7 + or - 170.6 ms vs. 956.0 + or - 74.6 ms, p < 0.001). With practice, however, they were able to reduce movement times and gain speed and accuracy to levels similar to young adults. These findings suggest older adults may retain the ability for stepping adaptations to environmental changes or novel demands, given sufficient practice.

Using two palpable measurements improves the subject-specific femoral modeling.

Subject-specific musculoskeletal models are essential to biomedical research and clinical applications, such as customized joint replacement, computer-aided surgical planning, gait analysis and automated segmentation. Generating these models from CT or magnetic resonance imaging (MRI) is time and resource intensive, requiring special skills. Therefore, in many studies individual bone models are approximated by scaling a generic template. Thus, the primary goal of this study was to determine a set of clinically available parameters (palpable measures and demographic data) that could improve the prediction of femoral dimensions, as compared to predicting these variables using uniform scaling based on palpable length. Similar to previous non-homogenous anthropometric scaling methods, the non-homogenous scaling method proposed in this study improved the prediction over uniform scaling of five key femoral measures. Homogenous scaling forces all dimensions of an object to be scaled equally, whereas non-homogenous scaling allows the dimensions to be scaled independently. The largest improvement was in femoral depth, where the coefficient of determination (r(2)) improved from 0.22 (homogenous) to 0.60 (non-homogeneous). In general, the major advantage of this non-homogenous scaling method is its ability to support the accurate and rapid generation of subject-specific femoral models since all parameters can be collected clinically, without imaging or invasive methods.