ZUMWALT, A.C.; LIEBERMAN, D.E.; RUFF, C.B.; Johns Hopkins University, Baltimore, MD; Harvard University, Cambridge, MA; Johns Hopkins University, Baltimore, MD: Too good to be true? Testing the relationship between muscle function and attachment site morphology

Muscle attachment sites are bony features that may be indicative of in vivo muscular stresses. Many studies have used these features in reconstructing behavior from fossil material. The prevailing assumption is that larger, more rugose attachment sites indicate greater muscle activity. However, no experimental study to date has assessed the relationship between muscular activity and bony morphology at the attachment site. This study tests the hypothesis that increased muscular activity is correlated with increased bony attachment site surface area. Six sites were examined in juvenile (n=10) and adult (n=16) male sheep. For each age group, half of the animals ran for one hour/day for 90 days at a moderate trot (Fr ~0.5) while the other half remained sedentary. The surface area of each site was measured and adjusted for body size before further analysis. Attachment sites were considered individually as well as in terms of functional complexes (humeral flexors, humeral extensors, and gastrocnemius origin and insertion). There were no significant differences between runners and controls in the surface areas of the individual attachment sites or of the three functional complexes for either age group. Thus, at the moderate level of exercise tested in this study, muscle activity does not significantly influence attachment site area. These results do not support the common assumption that attachment site morphology directly reflects the activity of the attaching muscle. Further studies will test the influence of more intense exercise on this and other aspects of attachment site morphology. This study supported by NSF IBN 96-03883 to DEL.