Modeling skeletal traits and functions of the upper body: Comparing archaeological and anthropological material

Abstract

The aim of this study is to look at upper body functional modifications caused by mechanical loading. We look at 4th lumbar vertebra as well as fibrous humeral musculoskeletal stress markers (MSMs). This study uses information provided by magnetic resonance images of living individuals from the University of Oulu Hospital data banks (N=91), archaeological skeletons from Sweden (N=54) and England (N=61), and autopsied skeletal collection of early 20th century Finns in Natural History Museum, University of Helsinki (N=48). The lumbar vertebrae and MSM are subjected to mechanical loading caused by the upper body weight and loads lifted and/or carried. We hypothesized that the vertebral size reflect body size, habitual mechanical loading and the overall skeletal robusticity as mechanical competence to withstand mechanical loading standardized to body size, which has decreased over millennia. For Helsinki material occupation, age and sex is known and the material was used in Niinimäki (2011). In the study by Niinimäki (2011) MSM were found to be affected by the intensity of muscular action as well as body size and age. This study is reviewed here in light of re-analysis of the data to follow the current anatomical understanding of the entheses as well as viewing MSMs as a part of upper body functional complex. Only fibrous entheses were included in the re-analysis. Furthermore, due to small number of females where activity intensity could be assessed, females were dropped from the re-analysis.Our findings reveal that the size and shape of the 4th lumbar vertebra has changed significantly from medieval times through post-medieval to modern day affecting the biomechanical characteristics of the lumbar vertebrae, possibly making spine fractures increasingly common. MSM are affected by the skeletal robusticity and activity level, although age bias is significant after biological maturity, where results remained the same after the re-analysis. The close relationship between biomechanics and therefore skeletal modeling is clearly revealed by the extent to which the level of habitual mechanical loading reflects in our skeletal anatomy.