Kenneth G Holt

Boston University | BU · Department of Physical Therapy and Athletic Training

Fast walking may require a non-uniform change of dynamic stiffness among lower limb joints to deal with this daily task’s demands. The change of dynamic joint stiffness may be distinct between females and males. This study aimed to test for differences in dynamic stiffness among lower limb joints in response to increased walking speed in males and...

The addition of a load during walking requires changes in the movement pattern. The investigation of the dynamic joint stiffness behavior may help to understand the lower limb joints’ contribution to these changes. This study aimed to investigate the dynamic stiffness of lower limb joints in response to the increased load carried while walking. Thi...

Background The alignment of the foot-ankle complex may influence the kinematics and kinetics of the entire lower limb during walking. Objectives This study investigated the effect of different magnitudes of varus alignment of the foot-ankle complex (small versus large) on the kinematics and kinetics of foot, ankle, knee, and hip in the frontal and...

Stroke-induced hemiparetic gait is characteristically asymmetric and metabolically expensive. Weakness and impaired control of the paretic ankle contribute to reduced forward propulsion and ground clearance—walking subtasks critical for safe and efficient locomotion. Targeted gait interventions that improve paretic ankle function after stroke are t...

Objective: The aim of the study was to evaluate the effects on common poststroke gait compensations of a soft wearable robot (exosuit) designed to assist the paretic limb during hemiparetic walking. Design: A single-session study of eight individuals in the chronic phase of stroke recovery was conducted. Two testing conditions were compared: wal...

Stroke-induced hemiparetic gait is characteristically slow and metabolically expensive. Passive assistive devices such as ankle-foot orthoses are often prescribed to increase function and independence after stroke; however, walking remains highly impaired despite—and perhaps because of—their use. We sought to determine whether a soft wearable robot...

Background: Only very recently, studies have shown that it is possible to reduce the metabolic rate of unloaded and loaded walking using robotic ankle exoskeletons. Some studies obtained this result by means of high positive work assistance while others combined negative and positive work assistance. There is no consensus about the isolated contri...

Introduction: Task-specific focal dystonia (TSFD) is a disorder marked by degraded coordination in complex and exacting psychomotor tasks, such as musical performance. Its development is associated with prolonged and intensive practice of these tasks, but the etiology of TSFD is still unknown. The prevailing hypothesis was informed by findings in...

Background: Recent advances in wearable robotic devices have demonstrated the ability to reduce the metabolic cost of walking by assisting the ankle joint. To achieve greater gains in the future it will be important to determine optimal actuation parameters and explore the effect of assisting other joints. The aim of the present work is to investi...

Gait can be powered from the hip and/or from the trailing ankle [1] and a trade-off exists between the two [2]. The verbal cue to “push more with your foot when you walk” increased ankle pushoff, reduced internal net hip muscle moments [3] and decreased the anterior hip joint force [4] in shod walking. Large forces at the hip have been associated w...

Background Carrying load alters normal walking, imposes additional stress to the musculoskeletal system, and results in an increase in energy consumption and a consequent earlier onset of fatigue. This phenomenon is largely due to increased work requirements in lower extremity joints, in turn requiring higher muscle activation. The aim of this work...

To understand the effects of soft exosuits on human loaded walking, we developed a reconfigurable multi-joint actuation platform that can provide synchronized forces to the ankle and hip joints. Two different assistive strategies were evaluated on eight subjects walking on a treadmill at a speed of 1.25 m/s with a 23.8 kg backpack: 1) hip extension...

Conference paper AMAM, Cambridge MA, June 2015

In this paper, we present the first application of a soft exosuit to assist walking after stroke. The exosuit combines textile garments with cable driven actuators and is lighter and more compliant as compared to traditional rigid exoskeletons. By avoiding the use of rigid elements, exosuits offer greater comfort, facilitate donning/doffing, and do...

Patellofemoral pain syndrome (PFPS) is characterized by anterior knee pain, which may limit the performance of functional activities. The influence of hip joint motion on the development of this syndrome has already been documented in the literature. In this regard, studies have investigated the effectiveness of hip muscle strengthening in patients...

We present the design and evaluation of a multi-articular soft exosuit that is portable, fully autonomous, and provides assistive torques to the wearer at the ankle and hip during walking. Traditional rigid exoskeletons can be challenging to perfectly align with a wearer’s biological joints and can have large inertias, which can lead to the wearer...

Development of biologically inspired exoskeletons to assist soldiers in carrying load is a rapidly expanding field. Understanding how the body modulates stiffness in response to changing loads may inform the development of these exoskeletons and is the purpose of the present study. Seventeen subjects walked on a treadmill at a constant preferred wa...

The focus of this paper is on characterizing the physical movement forms (e.g., walk, crawl, roll, etc.) that can be used to actualize abstract, functionally-specified behavioral goals (e.g., locomotion). Emphasis is placed on how such forms are distinguished from one another, in part, by the set of topological patterns of physical contact between...

In this paper we present a soft lower-extremity robotic exosuit intended to augment normal muscle function in healthy individuals. Compared to previous exoskeletons, the device is ultra-lightweight, resulting in low mechanical impedance and inertia. The exosuit has custom McKibben style pneumatic actuators that can assist the hip, knee and ankle. T...

The discovery of a relatively complete Australopithecus sediba adult female skeleton permits a detailed locomotor analysis in which joint systems can be integrated to form a comprehensive picture of gait kinematics in this late australopith. Here we describe the lower limb anatomy of Au. sediba and hypothesize that this species walked with a fully...

Wearable assistive robotic devices are characterized by an interface, a meeting place of living tissue and mechanical forces, at which potential and kinetic energy are converted to one or the other form. Ecological scientists may make important contributions to the design of device interfaces because of a functional perspective on energy and inform...

The biomechanical mechanisms that link foot structure to injuries of the musculoskeletal system during gait are not well understood. This study had two parts. The purpose of part one was to determine the relation between clinical rearfoot and forefoot angles and foot angles as they make contact with the ground. The purpose of part two was to determ...

Previous research has considered infant spontaneous kicking as a form of exploration. According to this view, spontaneous kicking provides information about motor degrees of freedom and may shape multijoint coordinations for more complex movement patterns such as gait. Recent work has demonstrated that multifractal, multiplicative fluctuations in e...

Background: Classification systems (Nagi, International Classification for Function [ICF]) have become popular for categorizing the level of ability (ICF) or disability (Nagi) associated with movement disorders. Nevertheless, these classifications do not explore the ways in which one level may influence other levels. For example, how might the wea...

To conduct a systematic review and meta-analysis using the International Classification of Functioning to determine the summary effect of electrical stimulation on impairment and activity limitations relevant to gait problems of children with cerebral palsy. We identified 40 cerebral palsy and electrical stimulation studies, and 17 gait studies qua...

After years of walking practice 8-10-year-old children with typical development (TD) and those with Down syndrome (DS) show uniquely different but efficient use of dynamic resources to walk overground and on a treadmill [Ulrich, B.D., Haehl, V., Buzzi, U., Kubo, M., & Holt, K.G. (2004). Modeling dynamic resource utilization in populations with uniq...

This study examined the transverse plane kinematics of the pelvis, thorax and head while participants walked at a range of speeds on a treadmill under three load conditions: no load, with a loaded backpack with no hip belt and with a loaded backpack with a hip belt. Research has suggested that one mechanism for adapting to heavy loads carried with...

Although the description of mature walking is fairly well established, less is known about what is being learned in the process. Such knowledge is critical to the physical therapist who wants to teach children with developmental delays. The purpose of this experiment was to test the notion that learning to walk efficiently involves fine-tuning the...

Mechanical strain on the hip can result from varus malalignment of the foot. This study was undertaken to explore the cross-sectional relationship between varus foot alignment and hip conditions in a population of older adults. The Framingham Osteoarthritis Study cohort consists of a population-based sample of older adults. Within this sample, we m...

The authors propose that preadolescents with Down syndrome (DS) initially adapt to contexts that challenge their stability by increasing stiffness and impulse but, with practice, they will continue to adapt, but in the opposite direction, by decreasing stiffness and impulse. The purpose of this study was to explore changes in stiffness and impulse...

This study investigated changes in the kinematics of elderly people who experienced at least one fall 6 months prior to data collection. The authors hypothesized that, in order to decrease variability of walking, people with a history of falls would show different kinematic adaptations of their walking patterns compared with elderly people with no...

Children with cerebral palsy (CP) often are faced with difficulty in walking. The purpose of this experiment was to determine the effects of functional electrical stimulation (FES) applied to the gastrocnemius-soleus muscle complex on the ability to produce appropriately timed force and reduce stiffness (elastic property of the body) and on stride...

The authors investigated the self-selected, overground walking patterns of 7 children (aged 11 months to 1 year, 5 months) at the initiation of walking (brand-new walkers [BNWs]) and for the next 6 months at 1-month intervals. Walking speed, stride length, and stride frequency increased significantly between the first 2 visits without significant c...

Research suggests that abnormal coordination patterns between the thorax and pelvis in the transverse plane observed in patients with Parkinson's disease and the elderly might be due to alteration in axial trunk stiffness. The purpose of this study was to develop a tool to estimate axial trunk stiffness during walking and to investigate its functio...

The role of biomechanics can be critical in understanding the development of control and coordination only when theory recognizes the role that physical constraints of the environment and tasks in helping shape movement patterns and their development. A systems-theoretic approach and biomechanical model are briefly outlined that capture the interpl...

Five healthy male subjects walked on a control surface (level concrete), and two sloped rock surfaces (walking ballast-rock about 1.9 cm across; main line ballast-rock about 3.8 cm across) while their rearfoot motion (defined throughout as ankle inversion/eversion as seen from the frontal plane) was measured to determine if the different walking su...

This study was designed to investigate the capability of the joints and segments to reduce transmission of forces during load carriage. Eleven subjects were required to carry a backpack loaded with 40% of their body weight and to walk at 6 speeds increasing from 0.6 to 1.6 ms(-1) in increments of 0.2 ms(-1), and then decreasing in the same manner....

In this study we used a damped inverted pendulum and spring with an escapement function model to compare the global levels of stiffness and forcing used by 12 preadolescents with Down syndrome (DS) and 12 with typical development (TD). Participants walked overground at their self-selected speed and on a treadmill at speeds slower and faster than ov...

As humans increase walking speed, there are concurrent transitions in the frequency ratio between arm and leg movements from 2:1 to 1:1 and in the phase relationship between the movements of the two arms from in-phase to out-of-phase. Superharmonic resonance of a pendulum with monofrequency excitation had been proposed as a potential model for this...

The atypical walking pattern in children with spastic cerebral palsy is assumed to involve kinematic and morphological adaptations that allow them to move. The purpose of this study was to explore how the requirements of the task and the energy-generating and energy-conserving capabilities of children with cerebral palsy relate to kinematic and mec...

The primary objective of this research was to determine changes in body and joint stiffness parameters and kinematics of the knee and body center of mass (COM), that result from wearing a backpack (BP) with a 40% body weight load at increasing speeds of walking. It was hypothesized that there would be speed and load-related increases in stiffness t...

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, 12 subjects walked on a treadmill at a range of walking speeds (0.6-1.6 m s(-1)) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking, load carriage decreases trans...

We examined the effects of mobile reinforcement on intralimb coordination of kicking of 4-month-olds with and without ankle weight. Subjects in each of two experiments were 10 healthy, 4-month full-term infants. The experimental protocol was 2-min of baseline (spontaneous kicking), 8-min of acquisition (mobile reinforcement without weight (Experime...

The purpose of this experiment was to investigate the effects of systematically manipulating the transverse plane moment of inertia (MOI) of the upper body on upper body torque, lower body torque, the phase relationship between the upper and lower body, and oxygen consumption. It was hypothesized that increasing the MOI of the upper body would resu...

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, twelve subjects walked on a level treadmill at a range of walking speeds (0.6 m/s - 1.6 m/s) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking load carriage decr...

The purpose of this experiment was to determine the effects of wearing a backpack on transverse plane upper and lower body torque. During unloaded walking the upper and lower body counter-rotate to reduce the net angular momentum of the body. There is less counter-rotation while carrying a load, suggesting a more rigid link between the upper and lo...

The objective of this study was to assess the capability of an escapement-driven inverted pendulum with springs and damping model to estimate the effects of impairments (e.g. spasticity, muscle weakness) on the dynamics and patterns of locomotion of children with spastic cerebral palsy. Kinematic data of six children with spastic hemiplegic cerebra...

The purpose of this experiment was to determine the effects of walking speed and wearing a backpack on trunk coordination and upper and lower body angular momentum, Twelve subjects (5 male, 7 female, mean age, yr: mean +/- SD = 26 +/- 7.1) walked on a treadmill at increasing speeds from 0.6 m(exp s-1) to 1.6 m(exp s-1) in 0.2 m(exp s-1) increments....

: The purpose of this paper is to discuss how concepts from the Dynamical Systems Theory and the Nagi Disablement model provide useful frameworks to guide physical therapy students in the examination and management of patients with neurological dysfunction. A process of systematic testing is presented using a hypothesis driven approach to assist st...

The Dynamical Systems Theory (DST) and Nagi Disablement Model are used as the conceptual and theoretical approaches and tools to assist students in developing skills that will allow them to form hypotheses and problem-solve as they learn to become physical therapists. One of the examples we use relates to the problems of spasticity and weakness in...

Previously, we suggested that neurological insults will change the dynamic resources available to an individual, and a pattern will emerge that is specified by, and facilitates the use of the available resources [K.G. Holt, J. Obusek, S.T. Fonseca, Human Movement Science, 15 (1996) 177]. Dynamic resources refer to the sources of energy (e.g., muscu...

The location of several sensory systems in the head implies that maintenance of head stability may be a potentially important part of locomotor activity. A limited amount of research, however, has been conducted to measure stability or to compare head stability among different groups. The purpose of this study was to determine whether a method for...

Clinical assessment of the effects of spasticity in active and functional movements in children with cerebral palsy is problematic for therapists. A dynamic model was proposed and tested that can potentially capture changes in stiffness, and muscle forcing capability during active and functional movements. In this study, the task of actively swingi...

An experiment was conducted in which volume of used oxygen per stride time and the total segmental changes in kinetic energy generated per stride time, &grD;E(k)>s(-1), of 11 participants were determined on Day 1 for 7 treadmill running speeds. Gait transition speeds were determined on Day 2. Running metabolism and transition speed were predicted f...

An experiment was conducted in which volume of used oxygen per stride time and the total segmental changes in kinetic energy generated per stride time, DeltaEk s-1, of 11 participants were determined on Day 1 for 7 treadmill running speeds. Gait transition speeds were determined on Day 2. Running metabolism and transition speed were predicted from...

This study was designed to investigate the capability of the joints to absorb shock while walking at a constant speed on a treadmill under various frequency conditions. Eight subjects were required to walk at their preferred frequency, at a frequency predicted as the resonance of a hybrid pendulum-spring model of the legs and at metronome-driven fr...

Children voluntarily adopt a frequency and movement pattern for walking. The force-driven harmonic oscillator (FDHO) model was used in this study for accurate prediction of the preferred walking frequency of nondisabled children and children with spastic hemiplegic cerebral palsy. Four potential optimality criteria with which the preferred walking...

Upper motor neuron disorders (UMN) result in abnormal movement patterns that are due to spasticity, weakness, cocontraction of muscles, inappropriate timing of muscle activations in relation to maximal mechanical advantage, and changes in the mechanical properties of muscles and connective tissues. Since many of the patterns observed in gait are re...

Movement patterns in impaired gait are not selected by a smart central nervous system (CNS), but arise by virtue of mutual constraints of task, limitations in personal dynamics available for the task, and optimality criteria. An oscillatory model of gait cycle is presented that exemplifies this control and coordination scheme. Preferred gait patter...

It is hypothesized that metabolic and mechanical changes in human locomotion associated with changes in speed v are constrained by two attractive strategies: Qmetab = 1 and delta Qmetab/delta v = a positive definite constant. Qmetab = delta Eks-1/ml O2s-1 where delta Eks-1 is the summed increments and decrements per unit time in the translational a...

Human leg swinging is modeled as the harmonic motion of a hybrid mass-spring pendulum. The cycle period is determined by a gravitational component and an elastic component, which is provided by the attachment of a soft-tissue/muscular spring of variable stiffness. To confirm that the stiffness of the spring changes with alterations in the inertial...

The possibility that preferred modes of locomotion emerge from dynamical and optimality constraints and the energetic and dynamical constraints on preferred and predicted walking frequency are explored in this article. Participants were required to walk on a treadmill at their preferred frequency, at a frequency predicted as the resonance of a hybr...

Human locomotion has been modeled as a force-driven harmonic oscillator (FDHO). The minimum forcing function in locomotion has been shown to occur at the resonant frequency of the FDHO and results in the suggestion that oxygen cost may be considered an optimality criterion for locomotion. The purposes of this study were twofold: first, to determine...

It has been suggested that a disruption in timing between the subtalar and knee joints may be a possible mechanism for knee injury. It has also been documented that shoe construction can alter rearfoot motion. The purpose of the study was to describe the relationship between the subtalar and knee joint actions during the support phase of treadmill...

This paper presents some of the ways we are attempting to understand why physically challenged children adopt the movement patterns they do. It focuses on the skill of walking and compares non-neurologically disabled persons with children with cerebral palsy. A multidisciplinary approach is advocated in which the tools of biomechanics, physiology,...

Preferred stride frequency (PSF) of human walking has been shown to be predictable as the resonant frequency of a force-drive harmonic oscillator (FDHO). The purpose of this study was to determine whether walking at the PSF and FDHO leads to minimal metabolic and mechanical costs. Subjects walked on a level treadmill at the PSF, FDHO, and frequenci...

Preferred stride frequency (PSF) of adult human walking has been shown to be predictable as the resonant frequency of a force driven harmonic oscillator (FDHO). The purpose of this study was to determine whether the PSF of 9-year-old children was predictable using the same resonance formula as that of adults. Subjects walked around a gymnasium at a...

The study was conducted to determine whether the preferred frequency of locomotion was predictable as the least amount of energy required to drive a harmonic oscillator. Subjects were instructed to walk at a preferred rate under conditions where their ankles were unloaded and bilaterally loaded. These results were compared to the frequency which wa...

Research in adult human walking and running gait, children's walking gait, and crutch walking performed in our laboratory is summarized. A theoretical model in which it is claimed that experienced ambulators are sensitive to the resonance properties of their limbs has been tested in these conditions. Results indicate that experienced subjects ambul...