Stiftung Tierärztliche Hochschule Hannover Die ontogenetische ...

Studie II: Shift of the CoM in growing dogs
et al., subm.). This together with the hindlimbs increasing in length and/or muscularity
more than the forelimbs leads to a net caudal translation of the CoM and thus a
decreasing relative forelimb loading in various growing mammals (rhesus macaque:
Grand, 1977; Turnquist and Wells, 1994; chimpanzee: Kimura, 1987; Japanese
macaque: Kimura, 2000; koala: Grand and Barboza, 2001; yellow baboon: Shapiro
and Raichlen, 2006; squirrel monkey: Young, 2012). On the other hand, mammalian
juveniles often appear plump and lack the athletic body shape that their adult
conspecifics show. Developing the adult appearance could therefore be associated
with a net cranial translation of the CoM in species like the dog that undergo a more
pronounced change in trunk shape. Furthermore, in contrast to the hindlimbdominated
species that have been studied previously, dogs provide a test for the
ontogenetic shifting of the CoM in a species that supports a greater proportion of the
body weight with the forelimbs.
In order to test whether mammals with a cranial location of the CoM also show a
net caudal translation of their CoM or whether they experience a net cranial shift
during growth, we studied the ontogenetic changes in the fore- vs. the hindlimb
loading in dogs. Because the distribution of body mass is reflected by the fore- to
hindlimb relationship of the vertical force (e.g., Rollinson and Martin, 1981; Budsberg
et al., 1987; Lee et al., 2004; Voss et al., 2011), we recorded the ground reaction
forces (GRF) in the dogs while trotting at steady speed on an instrumented treadmill.
Three parameters of the force distribution between the fore- and the hindlimbs were
tested: peak and mean vertical force as well as vertical impulse. Additionally to
evaluating the fore- to hindlimb vertical force ratio, we determined the stance
durations of the limbs, because a higher fraction of the vertical impulse of a limb is
associated with a relatively higher duty factor and the ratio between fore- and
hindlimb stance times has been suggested to reflect the antero-posterior mass
distribution of trotting quadrupeds (Lee et al., 2004; Witte et al., 2004). To evaluate
the change in trunk shape during postnatal development, we determined the ratio
between the diameters of the thorax and the abdomen in the growing dogs.
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