Force overlap in trotting dogs: a Fourier technique for reconstructing individual limb ground reaction force

Reliability of kinetic measurements of healthy dogs examined while walking on a treadmill

OBJECTIVE

To investigate whether an actual improvement in gait could be differentiated from physiologic differences or habituation effects during gait analysis of dogs.

ANIMALS

11 healthy dogs.

PROCEDURES

On 4 examination days, kinetic parameters were measured while dogs were walking on a treadmill. Differences in mean parameter values and habituation effects (ie, effect sizes) were quantified and compared among examination days. Coefficients of variation for repeated measurements were calculated to determine measurement reproducibility, and minimum differences were calculated to distinguish between physiologic fluctuation and an actual change in gait pattern.

RESULTS

Among the 4 examination days, mean absolute differences in peak vertical force and vertical impulse (VI) varied from 1.5% to 5.3% of body weight (BW) and 0.9% to 1.8% of BW·s, respectively. Mean absolute differences in the percentage of stance-phase duration (%SPD) and relative stride length (RSL) varied from 0.9% to 3.2% and 1.7% to 3.0%, respectively. Reproducibility of parameter measurements was good. Values for %SPD had the lowest amount of dispersion and largest effect size, suggesting a habituation effect for this parameter. Calculated minimum differences among the days for peak vertical force, VI, %SPD, and RSL did not exceed 9.9% of BW, 3.3% of BW·s, 5.8 percentage points, and 5.2 percentage points, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The %SPD of healthy dogs walking on a treadmill was the most sensitive and diagnostically reliable of the measured kinetic parameters, in contrast to VI and RSL. Findings suggested that actual changes can be distinguished from random physiologic fluctuations during gait analysis of dogs.

Influence of leash side and handlers on pressure mat analysis of gait characteristics in small-breed dogs

OBJECTIVE

To characterize the gait of small-breed dogs walked on a pressure walkway by handlers moving at a metronome-set tempo and to determine the influence of handler and leash side on gait characteristics.

DESIGN

Prospective study.

ANIMALS

5 healthy adult small-breed dogs weighing < 11.4 kg (25 lb).

PROCEDURES

Dogs were walked by each of 5 handlers moving at a metronome-set tempo (100 beats/min). Velocity, cadence, stance time, number of activated sensors, total pressure index (TPI), left or right hind reach, and symmetry indices were obtained with the leash on the left and right sides of each dog for each handler.

RESULTS

Coefficients of variation for TPI and stance time approximated 30%, whereas coefficients of variation for symmetry indices remained < 20%. Changing handlers and leash side did not influence hind limb variables. Changing handlers influenced the TPI of the forelimbs, inducing changes of up to 8%. Leash side accounted for 12% and 14% of the variation in symmetry indices of TPI and number of sensors activated between forelimbs, respectively (mean alterations for recorded variables, 9%).

CONCLUSIONS AND CLINICAL RELEVANCE

Symmetry indices appeared to vary less than variables obtained for individual dog limbs, and it may therefore be advantageous to determine those indices during large trials. Handlers or leash side may be changed in studies focusing on dogs' hind limbs without affecting results. Use of symmetry indices is recommended in forelimb studies requiring multiple handlers. Pressure walkway analyses of the forelimbs should include equal distribution of left- and right-sided leash-led trials, given that small-breed dogs tended to shift weight toward the forelimb opposite the leash.

Gait characteristics over the course of a race in recreational marathon competitors

We analyzed gait and function of the supporting limb in participants of a marathon race at three stages: prerace, midrace (18 km), and near the end of the race (36 km). We confirmed that the most successful runners were able to maintain running speed for the duration of the race with little change in speed or gait. Speed slowed progressively during the race for those with slower race times, but stride frequency-stride length relationships remained normal for the speed they ran. These findings differ from most lab-based studies of fatigue, in which runners are forced to match a constant preset treadmill speed. Small changes in maximum ground force were seen in both slow- and fast-running participants as race end approached.

Evaluation of a pressure walkway system for measurement of vertical limb forces in clinically normal dogs

OBJECTIVE

To compare ground reaction forces (GRFs) measured by use of a pressure-sensitive walk-way (PSW) and a force plate (FP) and evaluate weekly variation in the GRFs and static vertical forces in dogs.

ANIMALS

34 clinically normal dogs and 5 research dogs with lameness.

PROCEDURE

GRF data were collected from 5 lame and 14 clinically normal dogs by use of an FP and a PSW. Peak vertical force (PVF), vertical impulse (VI), and velocity measurements (determined by use of photocells and PSW data) were compared between groups. Peak vertical force, VI, stride length, ground phase time (ie, contact time), and static body weight distribution data were collected on 2 occasions, 1 week apart, in 20 different clinically normal dogs by use of a PSW; week-to-week variation in values was evaluated.

RESULTS

Measurements of velocity derived by use of the photocells were not different from those derived by use of the PSW. For any 1 limb, values derived by use of the PSW were significantly lower than values derived with the FP. For values obtained by use of either technique, there were no differences between left and right limbs except for values of PVF measured via PSW in forelimbs. Values of PVF, VI, contact time, stride length, and static weight distribution generated by the PSW did not vary from week to week.

CONCLUSIONS AND CLINICAL RELEVANCE

Values for GRFs varied between the FP and PSW. However, data derived by use of PSW were consistent and could be used to evaluate kinetic variables over time in the same dog.

Directionally compliant legs influence the intrinsic pitch behaviour of a trotting quadruped

Limb design is well conserved among quadrupeds, notably, the knees point forward (i.e. cranial inclination of femora) and the elbows point back (i.e. caudal inclination of humeri). This study was undertaken to examine the effects of joint orientation on individual leg forces and centre of mass dynamics. Steady-speed trotting was simulated in two quadrupedal models. Model I had the knee and elbow orientation of a quadruped and model II had a reversed leg configuration in which knees point back and elbows point forward. The model's legs showed directional compliance determined by the orientation of the knee/elbow. In both models, forward pointing knees/elbows produced a propulsive force bias, while rearward pointing knees/elbows produced a braking force bias. Hence, model I showed the same pattern of hind-leg propulsion and fore-leg braking observed in trotting animals. Simulations revealed minimal pitch oscillations during steady-speed trotting of model I, but substantially greater and more irregular pitch oscillations of model II. The reduced pitch oscillation of model I was a result of fore-leg and hind-leg forces that reduced pitching moments during early and late stance, respectively. This passive mechanism for reducing pitch oscillations was an emergent property of directionally compliant legs with the fore-hind configuration of model I. Such intrinsic stability resulting from mechanical design can simplify control tasks and lead to more robust running machines.