Musculoskeletal stress marker (MSM) differences in the modern American upper limb and pectoral girdle in relation to activity level and body mass index (BMI)

Obesity is a widespread condition affecting modern Americans. The prevalence of obesity has led to questions of how it can affect the skeleton, and if so can it be identified in unknown skeletal material. This study attempts to decipher the effects of activity level and body mass in modern Americans by employing musculoskeletal stress markers (MSM) to estimate osseous responses to workload and body weight. A total sample of 108 skeletons of known activity level and body mass index (BMI) was observed for MSM in the upper extremity (excluding hands). The entheses selected included arm muscles used during the sit-to-stand transition, which is common in most persons, regardless of activity level and BMI. Using the three categories: normal, active, and obese, logistic regression was calculated on MSM to ascertain which markers were the best indicators of these three categories. Numerous muscles of the upper limb were significant predictors of activity level and body mass, although they did not perform much better than chance. MSM may be used as predictors of activity level and/or BMI in forensic contexts; however, they should be used in conjunction with other indications of workload and/or BMI.