Variance associated with the use of relative velocity for force platform gait analysis in a heterogeneous population of clinically normal dogs

Abstract

Factors that contribute to variance in ground reaction forces (GRF) include dog morphology, velocity, and trial repetition. Narrow velocity ranges are recommended to minimize variance. In a heterogeneous population, it may be preferable to minimize data variance and efficiently perform force platform gait analysis by evaluation of each individual dog at its preferred velocity, such that dogs are studied at a similar relative velocity (V*). Data from 27 normal dogs were obtained including withers and shoulder height. Each dog was trotted across a force platform at its preferred velocity, with controlled acceleration (±0.5 m/s2). V* ranges were created for withers and shoulder height. Variance effects from 12 trotting velocity ranges and associated V* ranges were examined using repeated-measures analysis-of-covariance. Mean bodyweight was 24.4 ± 7.4 kg. Individual dog, velocity, and V* significantly influenced GRF (P < 0.001). Trial number significantly influenced thoracic limb peak vertical force (PVF) (P < 0.001). Limb effects were not significant. The magnitude of variance effects was greatest for the dog effect. Withers height V* was associated with small GRF variance. Narrow velocity ranges typically captured a smaller percentage of trials and were not consistently associated with lower variance. The withers height V* range of 0.6-1.05 captured the largest proportion of trials (95.9 ± 5.9%) with no significant effects on PVF and vertical impulse. Use of individual velocity ranges derived from a withers height V* range of 0.6-1.05 will account for population heterogeneity while minimizing exacerbation of lameness in clinical trials studying lame dogs by efficient capture of valid trials.

Variance associated with walking velocity during force platform gait analysis of a heterogeneous sample of clinically normal dogs

“…15 Our data were normalized to body weight to help account for that heterogeneity. Morphometric GRF normalization by use of WHV* specifically can further reduce variance, 16,24 and we therefore examined WHV* in our analysis.…”

“…New clinical exams and gait analysis were obtained from all dogs that had participated in previous gait analysis research. 15,16 …”

“…Seven distinct walking velocity ranges were identified for trial validation, 7,18–23 and variance effects associated with these ranges were determined using a previously described method. 15,16 After data acquisition, trials were reviewed and data from valid trials were coded with one or more of the seven velocity ranges of interest. During statistical analysis, a novel velocity range was created on the basis of the initial results and analyzed in the subsequently developed statistical model.…”

“…Repeated-measures ANCOVA was performed, in which dog, trial number, limb (left vs right), and absolute velocity or WHV* were analyzed for effects on GRFs. Subsequently, variance effects of walking absolute velocity and associated WHV* ranges were examined in the statistical model, as described previously, 15,16 to determine velocity range performance. Factor effect sizes were calculated.…”

“…14 In heterogeneous populations, it is advantageous to evaluate individual dogs at their preferred absolute velocity, such that dogs are assessed at a more consistent velocity or V*; a high proportion of total trials yield valid data when velocity or V* ranges span the preferred velocity of the dog. 15,16 …”