Effects of increasing walking cadence on gait biomechanics in adults with knee osteoarthritis.

Gait retraining is a strategy to manage altered loading patterns and pain characteristic of knee osteoarthritis. Lower walking cadence is associated with higher knee joint loading, vertical ground reaction forces, and risk for cartilage worsening. Therefore, we determined the acute effects of increasing walking cadence on measures of lower extremity loading and knee pain in knee osteoarthritis.

Induced discomfort promotes executive function while walking with(out) an artificial neuromuscular impairment.

Neuromotor disorders can degrade one's ability to locomote and attend to salient stimuli in the environment. Many disorders are physiologically complex, making it difficult to tease apart interactions between motor adaptation and executive function processes. We address this challenge by giving participants a controlled artificial impairment, using electrical stimulation to produce an uncomfortable disruption in normal muscular coordination during locomotion.

Neurorehabilitation robotics: how much control should therapists have?

Robotic technologies for rehabilitating motor impairments from neurological injuries have been the focus of intensive research and capital investment for more than 30 years. However, these devices have failed to convincingly demonstrate greater restoration of patient function compared to conventional therapy. Nevertheless, robots have value in reducing the manual effort required for physical therapists to provide high-intensity, high-dose interventions.

Recurrence Quantification Analysis of Ankle Kinematics During Gait in Individuals With Chronic Ankle Instability.

Purpose: An investigation of the ankle dynamics in a motor task may generate insights into the etiology of chronic ankle instability (CAI). This study presents a novel application of recurrence quantification analysis (RQA) to examine the ankle dynamics during walking. We hypothesized that CAI is associated with changes in the ankle dynamics as assessed by measures of determinism and laminarity using RQA.

Visual programming for accessible interactive musculoskeletal models.

Objective: Musculoskeletal modeling and simulation are powerful research and education tools in engineering, neuroscience, and rehabilitation. Interactive musculoskeletal models (IMMs) can be controlled by muscle activity recorded with electromyography (EMG). IMMs are typically coded using textual programming languages that present barriers to understanding for non-experts.

Exploiting telerobotics for sensorimotor rehabilitation: a locomotor embodiment.

Background: Manual treadmill training is used for rehabilitating locomotor impairments but can be physically demanding for trainers. This has been addressed by enlisting robots, but in doing so, the ability of trainers to use their experience and judgment to modulate locomotor assistance on the fly has been lost. This paper explores the feasibility of a telerobotics approach for locomotor training that allows patients to receive remote physical assistance from trainers.

Visual dynamics cues in learning complex physical interactions.

This study investigated the role of visual dynamics cues (VDCs) in learning to interact with a complex physical system. Manual gait training was used as an exemplary case, as it requires therapists to control the non-trivial locomotor dynamics of patients. A virtual analog was developed that allowed naïve subjects to manipulate the leg of a virtual stroke survivor (a virtual patient; VP) walking on a treadmill using a small robotic manipulandum.

Magnetic resonance images and measurements of the volume, proportion, and longitudinal distribution of contractile and non-contractile tissue in the dorsi- and plantar flexor muscles of healthy young and older adults.

Objective: This paper presents magnetic resonance images of the dorsi- and plantar flexor muscles for individual young and older healthy adults. Also included are measurements of the volume, proportion, and longitudinal distribution of contractile and non-contractile tissue. This dataset was previously used to quantify age-related differences in these measures, constrain subject- and muscle-specific estimates of dorsi- and plantar flexor maximal isometric force capability, and quantify the degree to which maximal isometric force capability explains the age-related variance in postural control.

Learning to shape virtual patient locomotor patterns: internal representations adapt to exploit interactive dynamics.

This work aimed to understand the sensorimotor processes used by humans when learning how to manipulate a virtual model of locomotor dynamics. Prior research shows that when interacting with novel dynamics humans develop internal models that map neural commands to limb motion and vice versa. Whether this can be extrapolated to locomotor rehabilitation, a continuous and rhythmic activity that involves dynamically complex interactions, is unknown.

Elucidating Sensorimotor Control Principles with Myoelectric Musculoskeletal Models.

There is an old saying that you must walk a mile in someone's shoes to truly understand them. This mini-review will synthesize and discuss recent research that attempts to make humans "walk a mile" in an artificial musculoskeletal system to gain insight into the principles governing human movement control. In this approach, electromyography (EMG) is used to sample human motor commands; these commands serve as inputs to mathematical models of muscular dynamics, which in turn act on a model of skeletal dynamics to produce a simulated motor action in real-time (i.

An Interactive Simulator for Imposing Virtual Musculoskeletal Dynamics.

Objective: disease processes are often marked by both neural and muscular changes that alter movement control and execution, but these adaptations are difficult to tease apart because they occur simultaneously. This is addressed by swapping an individual's limb dynamics with a neurally controlled facsimile using an interactive musculoskeletal simulator (IMS) that allows controlled modifications of musculoskeletal dynamics. This paper details the design and operation of the IMS, quantifies and describes human adaptation to the IMS, and determines whether the IMS allows users to move naturally, a prerequisite for manipulation experiments.

Predictability and Robustness in the Manipulation of Dynamically Complex Objects.

Manipulation of complex objects and tools is a hallmark of many activities of daily living, but how the human neuromotor control system interacts with such objects is not well understood. Even the seemingly simple task of transporting a cup of coffee without spilling creates complex interaction forces that humans need to compensate for. Predicting the behavior of an underactuated object with nonlinear fluid dynamics based on an internal model appears daunting.

Neuromotor Noise Is Malleable by Amplifying Perceived Errors.

Variability in motor performance results from the interplay of error correction and neuromotor noise. This study examined whether visual amplification of error, previously shown to improve performance, affects not only error correction, but also neuromotor noise, typically regarded as inaccessible to intervention. Seven groups of healthy individuals, with six participants in each group, practiced a virtual throwing task for three days until reaching a performance plateau.

Neural Control Adaptation to Motor Noise Manipulation.

Antagonistic muscular co-activation can compensate for movement variability induced by motor noise at the expense of increased energetic costs. Greater antagonistic co-activation is commonly observed in older adults, which could be an adaptation to increased motor noise. The present study tested this hypothesis by manipulating motor noise in 12 young subjects while they practiced a goal-directed task using a myoelectric virtual arm, which was controlled by their biceps and triceps muscle activity.

An arm for a leg: Adapting a robotic arm for gait rehabilitation.

The purpose of this study was to adapt a multipurpose robotic arm for gait rehabilitation. An advantage of this approach is versatility: a robotic arm can be attached to almost any point on the body to assist with lower- and upper-extremity rehabilitation. This may be more cost-effective than purchasing and training rehabilitation staff to use several specialized rehabilitation robots.

A reinforcement learning approach to gait training improves retention.

Many gait training programs are based on supervised learning principles: an individual is guided towards a desired gait pattern with directional error feedback. While this results in rapid adaptation, improvements quickly disappear. This study tested the hypothesis that a reinforcement learning approach improves retention and transfer of a new gait pattern.

Effects of kinematic vibrotactile feedback on learning to control a virtual prosthetic arm.

Background: After a limb is lost a prosthesis can restore function. For maximum utility, prosthetic limbs should accept movement commands and provide force and motion feedback, which can be conveyed with vibrotactile feedback (VIBF). While prior studies have shown that force-based VIBF benefits control, the merits of motion-based VIBF are unclear.

Rhythmic manipulation of objects with complex dynamics: predictability over chaos.

The study of object manipulation has been largely confined to discrete tasks, where accuracy, mechanical effort, or smoothness were examined to explain subjects' preferred movements. This study investigated a rhythmic manipulation task, which involved continuous interaction with a nonlinear object that led to unpredictable object behavior. Using a simplified virtual version of the task of carrying a cup of coffee, we studied how this unpredictable object behavior affected the selected strategies.

Safety margins in older adults increase with improved control of a dynamic object.

Older adults face decreasing motor capabilities due to pervasive neuromuscular degradations. As a consequence, errors in movement control increase. Thus, older individuals should maintain larger safety margins than younger adults.

Balance decrements are associated with age-related muscle property changes.

In this study, a comprehensive evaluation of static and dynamic balance abilities was performed in young and older adults and regression analysis was used to test whether age-related variations in individual ankle muscle mechanical properties could explain differences in balance performance. The mechanical properties included estimates of the maximal isometric force capability, force-length, force-velocity, and series elastic properties of the dorsiflexors and individual plantarflexor muscles (gastrocnemius and soleus). As expected, the older adults performed more poorly on most balance tasks.

Neural representation of muscle dynamics in voluntary movement control.

Several theories of motor control posit that the nervous system has access to a neural representation of muscle dynamics. Yet, this has not been tested experimentally. Should such a representation exist, it was hypothesized that subjects who learned to control a virtual limb using virtual muscles would improve performance faster and show greater generalization than those who learned with a less dynamically complex virtual force generator.

Energy margins in dynamic object manipulation.

Many tasks require humans to manipulate dynamically complex objects and maintain appropriate safety margins, such as placing a cup of coffee on a coaster without spilling. This study examined how humans learn such safety margins and how they are shaped by task constraints and changing variability with improved skill. Eighteen subjects used a manipulandum to transport a shallow virtual cup containing a ball to a target without losing the ball.

Effects of age on mechanical properties of dorsiflexor and plantarflexor muscles.

Redundancy in the human muscular system makes it challenging to assess age-related changes in muscle mechanical properties in vivo, as ethical considerations prohibit direct muscle force measurement. We overcame this by using a hybrid approach that combined magnetic resonance and ultrasound imaging, dynamometer measurements, muscle modeling, and numerical optimization to obtain subject-specific estimates of the mechanical properties of tibialis anterior, gastrocnemius, and soleus muscles from young and older adults. We hypothesized that older subjects would have lower maximal isometric forces, slower contractile and stiffer elastic characteristics, and that subject-specific muscle properties would give more accurate joint torque predictions compared to generic properties.

Contractile and non-contractile tissue volume and distribution in ankle muscles of young and older adults.

Magnetic resonance imaging (MRI) enables accurate in vivo quantification of human muscle volumes, which can be used to estimate subject-specific muscle force capabilities. An important consideration is the amount of contractile and non-contractile tissue in the muscle compartment, which will influence force capability. We quantified age-related differences in the proportion and distribution of contractile and non-contractile tissue in the dorsiflexor and plantar flexor (soleus, and medial and lateral heads of gastrocnemius) muscles, and examined how well these volumes can be estimated from single MRI cross-sections.