Postexercise and positional variation in mechanical properties of the radius in young horses

The metacarpal of the horse is severely loaded during vigorous exercise. Me tacarpal specimens have a greater impact strength in young horses that have been exercised than in those that have only been walked. We did not find a corresponding difference in the radius of the same horses. We show that cranial (anterior) cortical bone from the radius, which is loa ded in tension during locomotion, has a greater Young's modulus, and tensil e and bending strength, than bone from the caudal (posterior) cortex, which is loaded in compression, Caudal bone is, however, stronger in compression . The differences can be explained by differences in the histological struc ture developed by the 2 cortices and are presumably adaptive. This work con firms the work of others. Furthermore, we demonstrate that the impact energy absorption of cranial bo ne is nearly twice as great as that of caudal bone. The caudal cortex has a pparently paid a heavy price in its reduction in resistance to accidental i mpact loading for being stronger than the cranial cortex in compressive loa ding.