Scaling with Size in Horses May Have Implications for Reconstructing Activity from Entheseal Changes

Changes in body size are reflected in all aspects of skeletal support system and muscle-tendon mechanics, therefore also in entheseal size and morphology. Interspecies comparisons reveal evidence of low positive allometric scaling of entheseal size with body size, but this scaling within species does not deviate from isometry. This mainly isometric scaling should reflect in entheseal morphology because large individuals exert their muscles more than small ones just to move their heavier bodies. In this study, we performed a simulation experiment of both isometric and interspecies scaling to examine effects of increasing body size to entheseal strain in the hock extension of the horse. Computations for hock extension were modelled for mid-stance phase in canter or gallop with all weight on one hindlimb. Results from our simulation models suggest that: (1) Large horses put more strain on their entheseal surface areas than small horses when carrying only their own weight; (2) Small horses may strain their entheseal surface areas more than large horses when carrying the same absolute amount of weight regardless of body size. These results indicate that body size should be considered when reconstructing the use of archaeological horses and other equids as beasts of burden.