Adaptations to humeral torsion in medieval Britain

Abstract

Adaptations to the humeral torsion angle have been identified in the professional throwing athlete. This movement pattern increases the humeral torsion angle, and also increases the extent of external rotation movements in the dominant, throwing limb when compared with the nondominant limb. The purpose of this paper is to test the hypothesis that the humeral torsion angle is an adaptation to upper limb use. This project examines the humeral torsion angle in a number of medieval British populations, as well as a modern cadaver-based sample. The results identify significant differences in the humeral torsion angle both between and within male (P < 0.001, ANOVA) and female (P < 0.014, ANOVA) populations, although the results are not consistent with expected behavior patterns. Statistically significant differences between males and females within the same site were identified in 2 of the 5 samples examined. The mean level of bilateral asymmetry does not approach that reported for the professional throwing athlete. However, a number of individuals have high levels of asymmetry in excess of that identified in the professional throwing athlete. This analysis demonstrates the need for individual rather than population-based analyses, as the heterogeneity within population samples obscures individual variation in activity patterns. The diversity within British medieval society and a lack of specific known behaviors prevent further identification of the functional significance of the humeral torsion angle within the archaeological record examined here.

Evolutionary transformation of the hominin shoulder

“…However, while it is tempting to attribute the reduced torsion in Neanderthals to enhanced throwing ability, attempts to use this relationship to account directly for variation in the degree of humeral torsion in ancient modern populations has met with only limited success. 77 In addition, it should be pointed out that the amount of reduction in torsion that has been observed in association with an increase in range of external rotation at the shoulder in humans is relatively small, on the order of 10-158, and is therefore unlikely to explain the very low torsion values observed in KNM-WT 15000F or LB1 (Fig. 7).…”

“…I suggest that the lower degree of humeral torsion often observed in non-Western or prehistoric human samples is related to the influence of muscular forces and/or the demands for a particular range of motion associated with typically higher activity levels. While associating differences in torsion with activity levels is not new (for example, Rhodes 77 ), instead of trying to relate lower humeral torsion to particular behaviors such as overhand throwing, I believe that it is the high degree of torsion in Western samples that needs to be explained. In other words, the more moderate degree of humeral torsion in non-Western and prehistoric populations is what should be viewed as characterizing modern humans in comparisons to other hominin taxa, while the high levels of torsion in groups such as Europeans or Americans constitute a very recent phenomenon related to reduced physical demands on the upper limb associated with industrialized culture.…”

Modos De Vida De Los Cazadores-Recolectores De La Costa Arreica Del Norte Grande De Chile: Una Aproximación Bioarqueológica a Las Poblaciones Prehistóricas De Taltal

“…La retroversión humeral corresponde a una curvatura de la diáfisis respecto de la cabeza, causado por un estrés muscular en la zona (Kennedy 1989) y por el giro de la articulación (Rhodes 2006). En el caso de la muestra estudiada se puede decir que se pudieron observar 24 tercios proximales de diáfisis de húmeros de ambos lados, observándose en 13 de ellos la torsión de la diáfisis, correspondiente a los sitios Punta Loreto, San Lorenzo 3, Alero Bandurrias 2, Portezuelo Choluto 4, Punta Salitre J4 y La Puntilla 1 (Figura 4).…”

Bilateral Asymmetry of Humeral Torsion and Length in African Apes and Humans

“…This angle is measured using the intersection, viewed from the cranial perspective, of a line drawn through the centre of the humeral head dividing it into anterior and posterior halves, and a line passing through the centre of the capitulum and trochlea (as defined by Evans and Krahl [1945], Rhodes [2006] and Cowgill [2007]; see figure legend for details).…”