Stiftung Tierärztliche Hochschule Hannover Die ontogenetische ...

Studie II: Shift of the CoM in growing dogs
puppies’ force parameters were as symmetrical as those of adult dogs despite the
puppies’ seemingly more irregular gait.
----- Table 1 -----
During the course of the study, the dogs’ preferred trotting speeds increased and
therefore the Froude number differed slightly but significantly between the first and
the last recordings (PW11: U=0.5±0.1, PW51: U=0.9±0.1; Tab. 2). Consequently,
younger dogs trotted at treadmill speeds at which they still walked when older.
Because both vertical force and temporal gait parameters are dependent on speed
(see discussion), we will focus on fore- to hindlimb ratios of these parameters in the
following. Fore- and hindlimb values are detailed in the supplementary file (Tab. S1).
----- Table 2 -----
At all ages, peak vertical force and vertical impulse were significantly greater in the
forelimbs than the hindlimbs, indicating that the CoM was in a relatively cranial
position at all ages (Fig. 2, Tab. 3). The ANOVA revealed that both peak vertical
force and vertical impulse showed significant differences among the ages; with age,
they increased in the forelimb and consequently decreased in the hindlimb.
Accordingly, the fraction of the body weight supported by the forelimbs increased
from 59.2 1.7% to 62.9 1.9% (PFz) while that of the hindlimbs decreased from
40.8 1.7% to 37.1 1.9% during the course of the study. Similarly, vertical impulse
shifted by ca. 4% of the body weight from caudal to cranial. In contrast, mean
normalized vertical force was not significantly different among sessions (Tab. 3). The
ratio between fore- and hindlimb stance times increased significantly; thus, stance
time of the forelimb increased relative to the stance time of the hindlimb (Tab. 2).
While the time to peak vertical force did not change with age in the forelimbs, it
increased significantly in the hindlimb indicating that maximum force occurred earlier
during stance phase when the dogs were younger (Tab. 4).
The ratio of the thoracic vs. the abdominal diameter indicated that the trunk shape
of the puppies was nearly cylindrical (i.e., thorax-to-abdomen ratio 1.1 at PW11; Tab.
4). During the study period, the thorax-to-abdomen ratio increased significantly, so
that the trunk shape resembled a frustum at the end of the study (i.e., thorax-toabdomen
ratio 1.3 at PW51; Tab. 4).
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