Effects of erect bipedal standing on the morphology of rat vertebral bodies

Abstract

An osteometric approach was used to demonstrate the relationship between vertebral body morphology and bipedal standing using 17 rats, which had been divided into control and exercise groups. Only the latter group (n = 9) performed a series of bipedal standing exercises using operant conditioning. Statistical analysis was conducted to allow for inter-group comparisons with respect to six linear dimensions and five indices for each of the 24 vertebral bodies, from the third cervical through the last lumbar vertebrae. Detected effects of bipedal standing exercises on the vertebral body were as follows: (1) dorsal height decreased from the caudal thoracic to the lumbar vertebrae; (2) the dorsoventral diameter of the cranial surface increased at the thoracolumbar level; (3) the dorsal-to-ventral height ratio decreased in the lumbar vertebrae; (4) the dorsoventral-to-transverse diameter ratio of the cranial surface increased in the middle thoracic and lumbar vertebrae; and (5) the height-to-dorsoventral diameter ratio decreased in the fifth thoracic vertebra, and from the tenth thoracic to the fourth lumbar vertebrae. In vertebral bodies at the thoracic and lumbar levels, experimentally induced osteological changes such as wedging, dorsoventral elongation, and craniocaudal robusticity were discussed in terms of their comparative morphology in humans and quadrupedal mammals, and then compared with those of a bipedally trained Japanese macaque.