Mary C. Verstraete

Determination of the step duration of gait initiation using a mechanical energy analysis

The analysis of gait initiation (the transient state between standing and walking) is an important diagnostic tool in the study of pathologic gait and the evaluation of prosthetic devices. Therefore it is important to know the step duration of gait initiation. However, there is little agreement in the literature regarding this step duration, since each author has based their conclusion on a different biomechanical parameter. In this study, gait initiation in seven normal subjects was studied using a mechanical energy analysis. The number of steps necessary to reach steady state was determined based on the fact that in steady-state gait, the net mechanical work of the body over one stride is zero (Winter et al. J. Biomechanics 9, 253-257, 1976). The variance of the work for a stride during steady-state walking was calculated for 100 steady-state trials from a separate database of normal subjects. The stride work was normalized to the subjects body weight (BW) and leg length (LL), and 95% confidence limits were defined from this data at -1.68%BW * LL < epsilon < 1.28%BW * LL. Total body energy during gait initiation was then computed for the seven test subjects. The energy analysis of gait initiation showed that steady state was attained by the end of three full steps. Therefore, a researcher studying gait initiation must allow his/her subject to take three full steps when recording data to ensure that the full event is included.

Modulation of head movement control in humans during treadmill walking

The purpose of this study was to investigate the coordination of the head relative to the trunk within a gait cycle during gaze fixation. Nine normal subjects walked on a motorized treadmill driven at 1.79 m/s (20 s trials) while fixing their gaze on a centrally located earth-fixed target positioned at a distance of 2 m from their eyes. The net and relative angular motions of the head about the three axes of rotations, as well as the corresponding values for the moments acting on it relative to the trunk during the gait cycle were quantified and used as measures of coordination. The average net moment, as well as the average moments about the different axes were significantly different (P<0.01) between the high impact and low/no impact phases of the gait cycle. However, the average net angular displacement as well as the average angular displacement about the axial rotation axis of the head relative to the trunk was maintained uniform (P>0.01) throughout the gait cycle. The average angular displacement about the lateral bending axis was significantly increased (P<0.01) during the high impact phase while that about the flexion-extension axis was significantly decreased (P<0.01) throughout the gait cycle. Thus, the coordination of the motion of the head relative to the trunk during walking is dynamically modulated depending on the behavioral events occurring in the gait cycle. This modulation may serve to aid stabilization of the head by counteracting the force variations acting on the upper body that may aid in the visual fixation of targets during walking.

A mechanical energy analysis of gait initiation

The analysis of gait initiation (the transient state between standing and walking) is an important diagnostic tool to study pathologic gait and to evaluate prosthetic devices. While past studies have quantified mechanical energy of the body during steady-state gait, to date no one has computed the mechanical energy of the body during gait initiation. In this study, gait initiation in seven normal male subjects was studied using a mechanical energy analysis to compute total body energy. The data showed three separate states: quiet standing, gait initiation, and steady-state gait. During gait initiation, the trends in the energy data for the individual segments were similar to those seen during steady-state gait (and in Winter DA, Quanbury AO, Reimer GD. Analysis of instantaneous energy of normal gait. J Biochem 1976;9:253-257), but diminished in amplitude. However, these amplitudes increased to those seen in steady-state during the gait initiation event (GIE), with the greatest increase occurring in the second step due to the push-off of the foundation leg. The baseline level of mechanical energy was due to the potential energy of the individual segments, while the cyclic nature of the data was indicative of the kinetic energy of the particular leg in swing phase during that step. The data presented showed differences in energy trends during gait initiation from those of steady state, thereby demonstrating the importance of this event in the study of locomotion.

Finite Element Analysis as a Tool for Parametric Prosthetic Foot Design and Evaluation. Technique Development in the Solid Ankle Cushioned Heel (SACH) Foot

In this study, we developed an approach for prosthetic foot design incorporating motion analysis, mechanical testing and computer analysis. Using computer modeling and finite element analysis, a three-dimensional (3D), numerical foot model of the solid ankle cushioned heel (SACH) foot was constructed and analyzed based upon loading conditions obtained from the gait analysis of an amputee and validated experimentally using mechanical testing. The model was then used to address effects of viscoelastic heel performance numerically. This is just one example of the type of parametric analysis and design enabled by this approach. More importantly, by incorporating the unique gait characteristics of the amputee, these parametric analyses may lead to prosthetic feet more appropriately representing a particular users needs, comfort and activity level.

Lower limb direct skeletal attachment. A Yucatan micropig pilot study.

ABSTRACT Regardless of the type of prosthetic lower limb, successful ambulation requires proper prosthetic attachment. To help alleviate many of the problems associated with prosthetic attachment, direct skeletal attachment (DSA) has been proposed as an alternative to conventional sockets. The purpose of the current study was to evaluate the feasibility of lower limb DSA in a micropig model and to develop a systematic approach to the development and analysis of DSA systems. The DSA device consisted of two stages. The load-carrying stage embedded in the bone canal was designed using bone remodeling theory in conjunction with finite element analysis to approximate implant-induced remodeling and stabilization out to 36 months postimplantation. The skin-interfacing stage was designed to maintain an immutable infection barrier where the prosthesis exited the body. Following successful design, fabrication, and benchtop evaluation, the device was surgically implanted in a Yucatan micropig. The animal trial was successful out to 10 weeks and revealed potential flaws in the surgical protocol related to thermal necrosis. However, no signs of infection were present at the time of implant retrieval. While results of this pilot study support the feasibility of a DSA approach to prosthetic limb attachment, additional animal trials are necessary to prove long-term viability.

Correlation between muscle activity and the center of pressure

The development of a method to assist in diagnosing balance disorders necessitates a study of the interactions between the parameter indicating the instability of the balance mechanism (COP) and the factors that assist in maintaining the balance. Thus, the objective of this study was to establish the existence of correlation between the COP excursions and the muscle activity during balance. A correlation was established between the COP excursions and the gastrocnemius (Ga) and tibialis anterior (Ta) muscle activity at the ankle joint. Further studies need to be performed to quantify this correlation in order to completely understand the balance mechanism of the human body and to determine a method for the diagnosis of balance disorders.<<ETX>>

A relationship between external work and internal energy during knee flexion/extension

The work/energy approach towards the analysis of human motion has wide ranging applications in both clinical and sports biomechanics. The present study aims at relating the external work done to the total energy in the EMG signal. The EMG activity from the major flexor and extensor muscles of the knee joint were measured. The external work done during extension/flexion movements at four speeds were computed. Preliminary results indicate that there exists a relationship between the external work done and the energy in the EMG signal.

Torque production vs. muscle activity during knee flexion/extension

The relationship between the torque production of a muscle and its EMG signal is, to date, not well defined. The development of such a relationship would allow researchers to determine the force produced by various muscles using only surface electrodes and to develop accurate models for the prediction of forces acting during locomotion and other activities. EMG data and joint torques were recorded for five subjects using surface electrodes and a BIODEX system, respectively. Data were normalized and averaged for 3 trials each for 4 speeds. The results indicated that the patterns for the torque and EMG were consistent for all speeds.<<ETX>>

Prediction of knee joint torque from muscle activity during knee flexion/extension

The relationship between the torque production of a muscle and its EMG signal is, to date, not well defined. The purpose of this study was to investigate the relationship between the knee joint torque and the EMG activity of five major muscles crossing the knee. Rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), semitendonosis (ST) and biceps femoris (BF) EMG activity and knee joint torque were recorded for five subjects using surface electrodes and a BIODEX system, respectively. Data were normalized and averaged for three trials, for each of four speeds. A relationship between torque and EMG was developed for both extension and flexion with r squared values ranging from 0.73 to 0.98.