An article published in Archaeology, Ethnology and Anthropology of Eurasia describes Neanderthal men as having a level of hormones much higher than is found in modern humans. This would have given them more muscle mass, particularly in the upper extremities. The theory is based upon studies of a fossil humerous, the bone that runs from the shoulder to the elbow. It was found in Khvalynsk, Russia, and is thought to have belonged to a Neanderthal male who lived approximately 100,000 years ago.
     In work done by Maria Mednikova and her team, the bone was examined with computerized tomography, X-ray analysis and other tests. It was shown to have an extreme degree of mineralization, with unusually thickend walls and a narrow marrow cavity. This would have made the bone very strong.
     Neanderthals are believed to have had higher blood steroid levels leading to very muscular bodies. High steroid levels can also cause demineralization of bone. Mednikova postulates that the Neanderthal lifestyle contributed to the disproportionate arm strength. She argues that Neanderthal men hunted using spears and came into direct physical contact with their prey. This would have given an evolutionary advantage to those individuals with very strong dominant arms, usually on the right side. Diet and environment also may have contributed to this unique adaptation. Mednikova believes that Neanderthal women, while physically stronger than modern humans, had a more even distribution of muscle mass in their upper body.
     A diet consisting mostly of animal protein may have lead to this unusual hormone condition.      

Sources: Discovery News (6 July 2010), NYDaily News.com (7 July 2010)