Entheseal changes and demographic/health indicators in the upper extremity of modern Americans: Associations with age and physical activity

The purpose of this study is to further the understanding of the relationship between age and entheseal changes by using trends in living Americans compared to skeletal remains of modern Americans, and applying the knowledge to the bioarchaeological record. Documentation of age, activity level, body mass index, stature, and body mass was combined with entheseal change scores gathered from the upper extremity to statistically test the relationship between age and entheseal change with and without controls of documented demographic and health factors. An active subsample was constructed using self‐reported repetitive activities and discernment of position within stated career. Fibrocartilaginous entheses reported in the literature to be better suited to estimate occupation were separated from other entheses. A series of Cochran–Mantel–Hanzel and analysis of variance‐based tests were applied to the data. Interobserver reliability was also examined with a linear‐weighted Cohen's kappa. Statistical analysis shows only 1 enthesis has a significant positive relationship with age and 2 with activity. Body mass index and body mass were associated with 9 entheses that were spread across the occupation‐associated fibrocartilaginous entheses and all other entheses. Interobserver reliability ranged from low to substantial agreement. Interobserver error estimates suggest some entheses are more reliable than others. Results provide little support for a relationship between age and entheseal changes and activity and entheseal changes, which partially coincides with previous research. An increase in activity with age in our sample, around the age of retirement, mirrors trends in living Americans and supports our conclusions. For bioarchaeologists, these results suggest interpretations of entheses should be cautiously applied and revolve around body size rather than activity levels.