Dissertation Research: The effect of exercise on the morphology of muscle attachment scars

点击翻译按钮获取中文摘要

uscle insertion scars, or entheses, are easily observable but poorly understood features of bones and fossils. There is a long-standing assumption in the field of paleontology that large or obvious muscle scars are indicative of heavy muscle use. However, this assumption has never been thoroughly tested. This study will be the first to directly examine the relationship between known levels of muscle force and numerous aspects of enthesis morphology. The goal of this study is to examine if and how muscle use influences enthesis morphology so paleontologists may more confidently interpret these features on bones or fossils. This study will compare a variety of features of the entheses of sedentary and exercised adult sheep (Ovis aries). Preliminary work has indicated that moderate exercise induces no change in some aspects of enthesis morphology. Therefore the exercised sheep in this study will be run at a fast pace while carrying moderately heavy loads on their backs. This exercise regime is by design relatively intense, as one goal of the study is to determine whether intense muscle use is indeed related to large or obvious insertion marks. A variety of features will be measured on seven muscle insertion scars. Six of the scars are those of limb muscles that will be used in the running cycle. The seventh is that of the masseter muscle insertion on the mandible. This muscle should not be loaded differently in the two groups and thus its insertion will be studied as an internal control. The forces produced by each of the muscles will be quantified using force buckles and sonomicrometry. Thus this study will be the first to examine the morphology of entheses that had been subjected to known levels of muscle force in vivo. This study will develop the first objective, quantitative methods for describing the various features that are typically used to describe entheses. These methods will be used to test the hypotheses that increased muscle use significantly affects the size and rugosity of insertion scars. The first method is a previously tested latex molding method for measuring the three-dimensional surface area of insertion marks. The second method, to be heavily developed in this study, will measure enthesis rugosity, a feature that is often observed on bones and fossils but rarely quantified. The insertion scars will be scanned using a 3D-laser scanner and their topology will be analyzed using ArcView GIS 3.2, a Geographic Information System (GIS) software package. The rate of bone deposition under the insertions in both treatment groups will be measured using periodic administrations of fluorochrome labels. This information will provide insight into some of the physiological responses that occur in the bone beneath muscle insertions due to variations in muscle forces. It will also serve as a longitudinal measure of these responses and thus help control for pre-existing individual variation in enthesis morphology. In sum, the proposed study will provide much-needed insight into the relationship between muscle use and enthesis morphology. It is the first study to test the assumption that muscle use affects insertion scar morphology, and will demonstrate which aspects of this morphology are so affected. It will also provide the first method to objectively quantify the features of entheses. The results of this study should allow paleontologists to more confidently interpret the functional morphology of muscle insertion scars.