David A. Winter's research while affiliated with University of Waterloo and other places

Publications (124)

Article
The biomechanical (kinetic) analysis of human gait reveals the integrated and detailed motor patterns that are essential in pinpointing the abnormal patterns in pathological gait. In a similar manner, these motor patterns (moments, powers, and EMGs) can be used to identify synergies and to validate theories of CNS control. Based on kinetic and EMG...
Article
Figure A.1 Walking Trial—Marker Locations and Mass and Frame Rate Information Table A.1 Raw Coordinate Data (cm) Table A.2(a) Filtered Marker Kinematics—Rib Cage and Greater Trochanter (Hip) Table A.2(b) Filtered Marker Kinematics—Femoral Lateral Epicondyle (Knee) and Head of Fibula Table A.2(c) Filtered Marker Kinematics—Lateral Malleolus (Ankle)...
Article
Technical note. To provide background theory and information and to describe relevant applications of autocorrelation and cross-correlation methodology as they apply to the field of motor control in human movement and rehabilitation research. Commonly used methodologies for pattern and event recognition, determination of muscle activation timing fo...
Article
Low back pain is a primary source of disability and economic costs. Altered trunk muscle activation in people with low back pain, specifically agonist/antagonist co-activation, has been previously demonstrated. Prevailing theory considers this muscle activation pattern to be adaptive to low back pain. Muscle activation patterns prior to, and during...
Article
Full-text available
The aims of the present study are twofold: (1) to compare the postural control mechanisms of young and elderly people as well as in Parkinson's disease (PD) patients during quiet standing and (2) to assess the impact of a stooped posture on these mechanisms. All subjects were required to maintain both a side-by-side and a 45 degrees foot position....
Article
Movements of the whole-body center of mass during quiet standing have been estimated from measurements of body segment movements. These whole-body center of mass movements have been compared with movements of the center of mass as predicted from a simple inverted-pendulum model of standing. However, the total body center of mass is a weighted avera...
Article
Peripheral nerve researchers frequently use the rat sciatic nerve crush model in order to test different therapeutic approaches. The purpose of this study was to determine the sequence of changes after an axonotmetic injury by means of a biomechanical model of the foot and ankle, and compare them with walking track analysis, over a fixed period of...
Article
The purpose of this paper is to highlight the motor mechanisms involved in balance as the human, as a biped, continuously defends against gravitational and internal forces to maintain a safe posture. The search for these mechanisms needs precise and valid 3D measurements including both limbs plus valid biomechanical models. The literature shows the...
Article
Computerized analysis of rat gait is becoming an invaluable technique used by some peripheral nerve investigators for the evaluation of function. In this article we describe the use of a biomechanical model of the foot and ankle that allows a quantitative assessment and description of the ankle angle, reflecting plantarflexion and dorsiflexion duri...
Article
Anticipatory control of upright posture is the focus of this study that combines experimental and modeling work. Individuals were asked to raise or lower their arms from two initial postures such that the final posture of the arm was at 90 degrees with respect to the body. Holding different weights in the hand varied the magnitude of perturbation t...
Article
This research presents new data and reanalyzed information to refute the criticisms of our model of stiffness control during quiet standing. A re-review of their references to biomechanical research on muscle ankle stiffness confirmed muscle stiffness estimates of the ankle series elastic elements that agreed closely with our estimates. A new techn...
Article
The purpose of the present study was to examine the effect of sample duration on the magnitude and reliability of centre of pressure (COP) summary measures commonly used to characterize the control of upright stance. COP was recorded from 49 participants who stood quietly during three consecutive 120 s trials. Each record was subdivided into 15, 30...
Article
Postural control strategies have in the past been predominantly characterized by kinematics, surface forces, and EMG responses (e.g. Horak and Nashner, 1986, Journal of Neurophysiology 55(6), 1369-1381). The goal of this study was to provide unique and novel insights into the underlying motor mechanisms used in postural control by determining the j...
Article
Postural control strategies have in the past been predominantly characterized by kinematics, surface forces and EMG responses (e.g. Horak and Nashner 1986 Journal of Neurophysiology 55(6), 1369–1381). The goal of this study was to provide unique and novel insights into the underlying motor mechanisms used in postural control by determining the join...
Article
Full-text available
Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved ha...
Article
Full-text available
Gait initiation is a transient movement between upright posture and steady-state gait. Kinematic, kinetic and electromyographic data have been documented in healthy young subjects. However, there is little published data on the elderly and on Parkinson's disease (PD) subjects who are known to 'freeze' when initiating gait. It was the purpose of thi...
Article
Full-text available
As more and more prosthetic feet become commercially available, the selection of the appropriate device is a more difficult task for clinical team members. To date, ranking prosthetic feet based on biomechanical parameters has been done using the spring efficiency. The current analytical technique for calculating spring efficiency has two flaws: fi...
Article
Laser-induced fluorescence profiles of chlorophyll and phycoerythrin pigments and chromophoric dissolved organic matter (CDOM) fluorescence acquired over an iron-enriched phytoplankton patch are compared to profiles made over adjacent, naturally occurring phytoplankton patches. A total of four airborne missions were flown during an 8 day period fol...
Article
The utilization of passive dynamics to control the swing trajectory is one mechanism which serves to minimize energy costs during locomotion, in addition to reducing the complexity of the neural control. In a reactive situation (e.g. trip or slip during walking), the energy cost may not be a major determinant of the locomotor activity as there is a...
Article
Full-text available
Walking is one of the most common of all human movements. It exists to transport the body safely and efficiently across ground level, uphill or downhill. Walking is learned during the first year of life and reaches maturity around 7 until 60 years. Elderly walking performance then starts to decline and the elderly slow down gradually. Falls are a m...
Article
A three-dimensional, two-part model of the foot, for use in a simulation of human gait, is presented. Previous simulations of gait have not included the foot segment (e.g. Siegler et al., 1982, J. Biomechanics 15, 415-425) or have fastened it to the ground (e.g. Onyshko and Winter, 1980, J. Biomechanics 13, 361-368). A foot model based on viscoelas...
Article
Full-text available
1. Control of posture in quiet stance has been quantified by center of pressure (COP) changes in the anterior-posterior (A/P) and medial-lateral (M/L) directions from a single force platform. Recording from a single force platform, researchers are unable to recognize two separate mechanisms that become evident when two force platforms are used. Dep...
Article
Full-text available
Biomechanical tools were used to assess stability for 11 patients who, following the surgical amputation of one lower limb, required the assistance of a walking frame to ambulate. The Walker Tipping Index (WTI), as derived from the forces applied to the walking frame, was developed specifically for this study to examine the relationship between sta...
Article
Kinetic analyses (joint moments, powers and work) of the lower limbs were performed during normal walking to determine what further information can be gained from a three-dimensional model over planar models. It was to be determined whether characteristic moment and power profiles exist in the frontal and transverse planes across subjects and how m...
Article
The goal of this chapter is to demonstrate the role of integrated biomechanical analyses in complex movements such as gait in alerting researchers of the goals and synergies of the CNS. Because of the large number of segments involved and the potential for the CNS to take advantage of inter-limb coupling it is only through appropriate biomechanical...
Article
Full-text available
Previous research reported calculation of mechanical power of ankle-foot devices using the dot product of the ankle moment times the ankle angular velocity. Unfortunately, there are two errors in this analysis technique. The biomechanical model used assumed a rigid foot articulating around the ankle and there was no accounting for energy storage or...
Article
The purpose of this paper is to address four aspects of surface electromyography associated with crosstalk between adjacent recording sites. The first issue that is addressed in the potential crosstalk between electrodes located on muscles with different functions: antagonist pairs, or muscles with one common and one different function (i.e. soleus...
Article
Full-text available
Research to date has shown that the large inertial load of the head-arms-trunk (HAT) is controlled within a few degrees in both the frontal and sagittal planes over the gait cycle. Also, there are limited reports of major attenuation of the head anteroposterior () acceleration in spite of large inertial perturbations at the hips during weight beari...
Article
Anticipatory adjustments of our locomotor patterns are necessary in order to negotiate our uneven daily environments. Recent work (McFadyen and Winter 1991) has shown the re-organization of lower limb mechanics for obstacle avoidance during level walking. The present work describes a model which sets the ground work for predicting how such re-organ...
Article
The movement strategies and the underlying organization of the muscular responses for recovery from a tripping perturbation applied in early and late swing during walking were studied in humans. The latencies of the reflex response (60-140 ms) suggested that polysynaptic pathways are involved. The most common movement outcome was an elevating strat...
Article
Full-text available
1. Isometric muscle force and the surface electromyogram (EMG) were simulated from a model that predicted recruitment and firing times in a pool of 120 motor units under different levels of excitatory drive. The EMG-force relationships that emerged from simulations using various schedules of recruitment and rate coding were compared with those obse...
Article
A method for quantifying the stability of a patient using a walking frame is presented. Data collected from a walker-dependent patient recovering from surgical amputation of his right leg were used to demonstrate the derivation and interpretation of a proposed walker user risk index (WURI). WURI curves express risk to the walker user in terms of ho...
Article
A model of the human foot is proposed in which the foot is represented as eight rigid segments and eight monocentric, single-degree-of-freedom joints. The soft tissue under the foot is divided into seven independent sites of contact, or loading, and each of these is modelled as a nonlinear spring and a nonlinear damper in-parallel. The model was us...
Article
A number of conflicting measurement techniques and somewhat erroneous interpretations have become evident in the research on body balance and posture while standing. The dialogue has become even more confusing because terms like centre of mass (COM), centre of pressure (COP), and sway have been used almost interchangeably by some researchers. The p...
Article
A whole-body inverted pendulum model was used to investigate the control of balance and posture in the frontal plane during human walking. The model assessed the effects of net joint moments, joint accelerations and gravitational forces acting about the supporting foot and hip. Three video cameras and two force platforms were used to collect kinema...
Article
The balance control system of a group of healthy and fit, young and elderly subjects was studied during the initiation of stepping in one of three directions: forward, sideways, and backwards in response to a light cue. The performance of these movements requires shifting support from two to one foot, moving the centre of mass outside the initial b...
Article
Strain gauges were built into the legs of a standard aluminium walking frame to simultaneously record forces in three dimensions from all four legs. Preliminary data from six walker-dependent lower-limb amputee subjects suggests that the primary function of a walking frame during ambulation is to enlist the upper extremities to supplement the lower...
Article
Five initiation and five termination plus three steady-state walking trials were collected for each of four subjects using three videos cameras and three force platforms. Data were analysed using a 13-segment three-dimensional biomechanical model. During initiation 90% of steady-state velo-city was achieved during the first step and 100% by the sec...
Article
Full scale biomechanical and EMG analyses of the balance during human gait are required to understand the neural control of locomotion. The purpose of this paper was to develop an inverted pendulum model of upper body balance in both the plane of progression and the frontal plane, and a medical/lateral balance model of the total body. EMG evidence...
Article
Clinical gait laboratories have proliferated over the past two decades and an increasing number of research papers are reporting 'assessments' of pathological gait. Some criticisms have been levied at the value of most of these assessments, and some of their arguments are justified. Unfortunately, their review of the pathological gait literature wa...
Article
The purpose of this study was to develop a biomechanical technique to analyse the kinetics of cane-assisted gait. Biomechanical measures such as ground reaction forces (force platforms), cane reaction forces, and kinematics have been routinely measured. However, a full kinetic analysis of both the lower limb and the cane-assisted limb has not been...
Article
Full-text available
In quiet standing with feet side by side the motor control sites were investigated in the anterior/posterior (A/P) and medial/lateral (M/L) directions. In the A/P direction the left and right limb center of pressure (COP) changes were quite synchronized while in the M/L direction they were antiphase. In the A/P direction the total body net COP chan...
Article
An EMG-driven muscle model for determining muscle force-time histories during gait is presented. The model, based on Hill's equation (1938), incorporates morphological data and accounts for changes in musculotendon length, velocity, and the level of muscle excitation for both concentric and eccentric contractions. Musculotendon kinematics were calc...
Article
The purpose of this study was to develop a major temporary perturbation to the peripheral neuromuscular system and to quantify the motor adaptations on the first gait strides taken after the perturbation becomes effective. A unilateral ischaemic block to the leg was induced by a cuff inflated to 200 mmHg; sensory block was evident after 15-20 min a...
Article
Deterioration of balance control system with age results in a higher incidence of falls. To assess the performance of the balance control system we need to select appropriate body posture and/or motion, decide on the type and level of perturbation and study the response using selected measures. The guidelines we should use to determine the task, pe...
Article
Full-text available
A model of the motor unit action potential was developed to investigate the amplitude and frequency spectrum contributions of motor units, located at various depths within muscle, to the surface detected electromyographic (EMG) signal. A dipole representation of the transmembrane current in a three-dimensional muscle volume was used to estimate det...
Article
The trajectory of the heel and toe during the swing phase of human gait were analyzed on young adults. The magnitude and variability of minimum toe clearance and heel-contact velocity were documented on 10 repeat walking trials on 11 subjects. The energetics that controlled step length resulted from a separate study of 55 walking trials conducted o...
Article
The task of walking is an extremely complex motor control problem. Firstly, the task requires the integration of the central system with many peripheral sensory systems to control scores of muscles acting on a skeletal system with many degrees of freedom. Secondly, the human mechanical system operates in a gravitational environment on two small bas...
Article
We present a technique to combine muscle shortening and lengthening velocity information with electromyographic (EMG) profiles during gait. A biomechanical model was developed so that each muscle's length could be readily calculated over time as a function of angles of the joints it crossed. The velocity of shortening and lengthening of the muscle...
Article
Pseudorandom binary sequence (PRBS) exercise tests involve repeated switching between two work rates (WR) according to a computer-generated pattern. This paper presents an approach to analysis of O2 uptake (VO2) in the time domain. First, the autocorrelation function (ACF) of the input WR was recognized to be a triangular-shaped pulse that can be t...
Article
Three different pennation angle assumptions are compared to experimental data from Huijing and Woittiez (Neth. J. Zool. 34, 21-32, 1984) that relate fibre length to angle of pennation changes. The assumptions tested are: (1) neglecting pennation; (2) assuming a fixed pennation; and (3) assuming a constant muscle volume and thickness resulting in pe...
Article
The purpose of this investigation was to study the kinematics and kinetics of the joints between the leg and calcaneus during the stance phase of walking. The talocrural and talocalcaneal joints were each assumed to act as monocentric single degree of freedom hinge joints. Motion at one joint was defined by the relative rotation of a point on the o...
Article
Full-text available
A descriptive study of the biomechanical variables of the walking patterns of the fit and healthy elderly compared with those of young adults revealed several significant differences. The walking patterns of 15 elderly subjects, selected for their active life style and screened for any gait- or balance-related pathological conditions, were analyzed...
Article
A model of the lower extremity was created and analyzed to estimate the magnitude of the loads at common injury sites during running and the proportions due to muscle and ground reaction forces. The range of peak loads, normalized to subject body weight (BW), estimated from five running trials were: (1) Achilles tendon force: 6.1-8.2 BW; (2) ankle...
Article
A descriptive study of the biomechanical variables of the walking patterns of the fit and healthy elderly compared with those of young adults revealed several significant differences. The walking patterns of 15 elderly subjects, selected for their active life style and screened for any gait- or balance-related pathological conditions, were analyzed...
Article
Full-text available
Balance and posture of the body is essential to most human locomotion. Because humans are bipeds with about 2/3 of their mass located 2/3 of body height from the ground the control system is critical. In the elderly balance control degenerates. Falls represent a major health problem and the fear of falls is the major deterrent to daily mobility. Ma...
Article
The dynamic response of oxygen uptake (VO2) was investigated with two different cycle ergometer tests in which the work rate changed as a pseudorandom binary sequence (PRBS). One sequence had 15 units, each of 30-s duration for a total of 450 s (PRBS1). The second had 63 units, each of 5-s duration for a total of 315 s (PRBS2). The useful range of...
Chapter
Human walking represents an extremely complex motor control task and the control of balance during that task is especially challenging. First, humans are bipeds who spend 80% of their time on one limb during natural walking. Thus only two 10% double support periods are available for restabilization and this time decreases as cadence increases until...
Article
The biomechanical (kinetic) analysis of human gait reveals the integrated and detailed motor patterns that are essential in pinpointing the abnormal patterns in pathological gait. In a similar manner, these motor patterns (moments, powers, and EMGs) can be used to identify synergies and to validate theories of CNS control. Based on kinetic and EMG...
Article
The classic book on human movement in biomechanics, newly updated. Widely used and referenced, David Winter's Biomechanics and Motor Control of Human Movement is a classic examination of techniques used to measure and analyze all body movements as mechanical systems, including such everyday movements as walking. It fills the gap in human movement s...
Article
Full-text available
Human walking is a complex motor control task requiring the integration of central and peripheral control of scores of muscles acting on a skeletal system with many degrees of freedom. Associated with the goal of forward progression is the overriding need for a safe transit: balance con­ trol to prevent falling over, a support control to prevent co...
Article
Center of pressure characteristics were examined for 3 stance postures and 3 sensory conditions. The centre of pressure signal was calculated from force plate data collected over 30 sec for each condition. The standard deviation, frequency band width and mean power frequency of centre of pressure fluctuations were computed for analysis. Normative v...
Chapter
The detailed kinematic and kinetic patterns in human gait and their variability within and between subjects provide considerable insight into the control structure of the central nervous system. Kinematic variables such as joint angles and trajectories of the center of mass of the trunk and of the heel and toe are consistent during both stance and...
Article
Centre of gravity (C of G) and centre of pressure (C of P) were simultaneously analyzed, in both sagittal and frontal planes, during quiet stance and exaggerated sway about the ankle. Under these conditions, the C of P is dependent directly on the moments generated at the ankle. Thus Cc of P measurements reflect the neuromuscular system's regulatio...
Article
No analysis of the relative contribution of the ankle extensors (primarily soleus and gastrocnemius) and the m-p flexors (flexor digitorum longus, flexor