Stiftung Tierärztliche Hochschule Hannover Die ontogenetische ...

Studie II: Shift of the CoM in growing dogs
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3.6. Discussion
Influence of speed on force and stance parameters
In the current study, Froude number significantly increased between 11 and 51
weeks of age. Because many gait parameters depend on locomotor speed, the
observed changes in the vertical force and the stance time ratios may potentially
result from differences in speed rather than age. In adult dogs, for example, peak
vertical force increases and vertical impulse decreases with increasing trotting
velocity (Riggs et al., 1993; McLaughlin and Roush, 1994, Voss et al., 2010).
Because maximum vertical force increases more in the forelimbs than the hindlimbs
when dogs trot faster, the increase in the fore- to hindlimb peak vertical force ratio
observed in the current study may partially be explained by the increase in relative
velocity with age. However, compared with the change in the peak vertical force ratio
observed in this study (ca. 4%), the speed related changes reported for adult dogs
across a similar change of relative velocity were small (ca. 2%; Riggs et al., 1993;
McLaughlin and Roush, 1994). Furthermore, in adult trotting dogs, the vertical
impulse of fore- and hindlimbs decreases at similar rates with increasing speed and
therefore impulse ratio is independent of speed (Riggs et al., 1993; McLaughlin and
Roush, 1994; see also Witte et al., 2004). In contrast, the fore- to hindlimb impulse
ratio increased significantly with age in the current study; that is, the forelimbs’
vertical impulse was relatively larger in older dogs than puppies. This observation
resembles results from adult dogs, in which experimental loading of the pectoral
girdle resulted in an increase of the vertical impulse ratio (Lee et al., 2004). In
summary, our data suggest that the position of the whole-body CoM undergoes a
net-cranial translation in growing dogs and accordingly the forelimbs support a
relatively smaller proportion of the body weight in puppies than adult dogs.
Similar to other mammals, when dogs increase locomotor speed, stance time
decreases (Arshavskii et al., 1965; McLaughlin and Roush, 1994; Maes et al., 2008).
Because stance duration decreases more in the forelimbs than the hindlimbs, stance
time ratio decreases when adult dogs trot faster (McLaughlin and Roush, 1994). In
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