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.

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 subject's 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.

Vertical loading rates in clinically normal dogs at a trot.

Present data describe the rates of vertical loading and unloading generated by clinically normal dogs in a trotting gait. Forward velocity was found to influence maximal rates of limb loading and unloading in forelimbs and hind limbs. The rates increased as the velocity of the dog/handler increased. The position of maximal limb loading during the stance phase was independent of velocity in the forelimbs, but in the hind limbs, as velocity increased, the position of maximal unloading occurred earlier in the stance phase. Within velocity groups, the forelimbs had greater rates of vertical loading and unloading than did hind limbs. The position at which maximal loading occurred was earlier in the forelimbs than in the hind limbs. There was a difference in the position of maximal unloading between forelimbs and hind limbs, with the forelimbs unloading earlier in the stance phase. Difference between paired forelimbs or paired hind limbs was not found for any measurement within any group. Calculation of loading and unloading rates provides another method of examining functional limb loading in dogs. This method of analysis can be adapted to any animal gaited across a force platform in which single limb strides can be recorded. Calculations can also be done in any axis of measurement. Data indicated loading and unloading rates to be consistent and easily determined, Use of data generated from rates of limb loading can be classified into 2 areas: documentation of acceptance of load by the limb, and indirect measurement of functional stresses placed on bones of the appendicular skeleton.

A technique for locating the center of mass and principal axes of the lower limb.

The position of the human body in space is typically recorded using a fixed inertial coordinate system, often referred to as a laboratory coordinate system. Although these fixed reference axes simplify the collection and reduction of such position data, the results produced often have little or no anatomical significance. The purpose of this study was to develop the methods, both experimental and analytical, to construct a set of orthogonal principal axes for each the foot, shank, and thigh segments of the lower limb for use in motion analysis. The axes chosen were determined by targeting specific bony landmarks as suggested by the literature and forming the principal axes with respect to these landmarks. The location of the center of mass of each segment was also determined from these anatomical landmarks. It was found that the foot, due to its less rigid nature and more complex geometry, required a more extensive analysis using a single frame of standing data prior to the analysis of the motion data. The axes formed do not attempt to solve the problems of joint rotation axes, but provide an initial, anatomically significant set of reference axes that may be easily reproduced and utilized in further analyses.

A method for computing the three-dimensional angular velocity and acceleration of a body segment from three-dimensional position data.

A theoretical technique, based on the Method of Least Squares, was employed to solve for the three-dimensional components of the angular velocity and acceleration of a limb segment directly from experimentally recorded three-dimensional position data. Results showed that a minimum of four targets placed on the body segment, forming six relative position vector equations, were required to produce the most accurate results. It was also found that this method eliminates the errors due to soft tissue motion and system noise.

Force plate analyses before and after stabilization of canine stifles for cruciate injury.

Ground reaction forces were measured from the hind limbs of 9 dogs before and after stabilization of unilateral cranial cruciate ligament rupture. Before surgery, peak vertical force, associated impulses, and weight distribution were significantly less (multivariate analysis P less than 0.02) in the affected limb, compared with the clinically normal limb. Craniocaudal peak forces and impulses, divided into braking and propulsion, also were significantly less in the affected limb. At a minimum of 7 months after retinacular imbrication, all vertical and craniocaudal measurements in the affected limb were increased significantly. Significant changes were not found in the normal limb. Furthermore, at the postoperative evaluation, there was no significant difference in any measurement between the affected and normal hind limbs. The results indicated restoration of function in the cruciate-deficient limb when compared with the clinically normal hind limb at a walking gait during the study time period.

Force plate analysis of the walking gait in healthy dogs.

Ground reaction forces, impulses, and their relationships to morphometric measurements were evaluated for walking gait in 17 healthy dogs. A force plate was used to record forces at 1-ms intervals. Vertical, craniocaudal, and mediolateral forces were measured and normalized by body weight. Impulses, defined as the total force applied over time, were calculated in vertical and craniocaudal directions. Craniocaudal impulses were further divided into braking and propulsion phases. Braking impulses were significantly greater in the forelimbs (P less than or equal to 0.001), whereas propulsion impulses were generally greater in the hind limbs. Impulses and peak forces were then compared with morphometric measurements (body weight, humeral and femoral lengths, and paw length). All relationships were linear, with correlation coefficients significant (P less than or equal to 0.001). As the size of the dog increased, braking, propulsion and vertical impulses increased. Conversely, as morphometric measurements increased, peak vertical forces decreased. Thus, larger dogs had a lower peak force on each limb, but had a higher total impulse applied during stance phase. As stance phase time increased, peak vertical forces decreased. The results indicated that healthy dogs had significant correlations between ground reaction forces, impulses, and morphometric measurements.

Analysis of foot motion during running using a joint co-ordinate system.

The amount and rate of pronation and supination have been the subject of interest to runners for some time. Exact determination of the motions has been hampered by their complexities and use of a two-dimensional data collection protocol. "Rearfoot motion," measured by determining the projection of the angle between a line on the posterior of the shank and a line on the heel, has been a common approach. This projection measures a rotation about a laboratory axis and not a body segment axis and has a potential of error due to projection onto a plane. The angle measured in rearfoot motion is not the true angle between these lines in space and has projection distortion errors which are compounded during plantar and dorsiflexion and medial and lateral foot rotations. The rearfoot motion angle, however, does approximate foot inversion-eversion during much of stance phase. The proposed change in research protocol allows analysis of the three-dimensional position data of targets to construct a "joint coordinate system" which gives more accurate data on inversion-eversion and data on plantar-dorsiflexion and medial-lateral rotation of the foot. This analysis may allow the examination of measurable differences between individuals and running shoes of various design.