Humeral Asymmetry Research Articles

Asymmetry in linear measurements and cross-sectional geometry in the humerus during ontogeny.

Adult upper limb asymmetry is used to reconstruct behavior. However, the developmental trajectory of asymmetry in bone length, cross-sectional geometry (CSG), and joint dimensions is poorly understood. This study examines the development trajectory of humeral asymmetry and if asymmetry in bone length, joint size, and CSG develop in concert. Linear measurements of bone length and metaphyseal/epiphyseal breadth, bending rigidity (Imax and Imin), and cross-sectional shape (Imax/Imin) at 30%, 50%, and 70% of bone length were acquired from 3D models of humeri from four skeletal samples of prehistoric hunter-gatherer populations (n = 82). Dental age cohorts were used to assess ontogenetic trends. Percent absolute (%AA) and directional (%DA) asymmetry were calculated for paired measures. Percentage of matching direction of asymmetry across variables and correlation analysis tested relationships between variables. Within the total pooled sample, Imax shows the highest %AA and %DA, followed by shape and linear dimensions. Asymmetry is lowest in neonates and increases with age, particularly %DA of Imax in mid-proximal sections. Correlations among variables are low to moderate and strongest between Imax measures. Matching direction of asymmetry between variables is low and generally increases with age. Higher correlations with age in CSG likely indicate greater responsiveness to mechanical loading. Low correlations in magnitude of asymmetry and side dominance suggest independence in the development of asymmetry between maximum rigidity, shape, and linear measures. Differences in how asymmetric loading affects the ontogeny of linear and CSG variables may account for the heterogeneous development of asymmetry.

Adapting in the Arctic II: Upper limb diaphyseal robusticity and habitual activity in Late Holocene hunter-gatherers from Alaska.

This study compares humeral diaphyseal robusticity and asymmetry between Late Holocene hunter-gatherers from Alaska with the goal of reconstructing habitual activity in relation to culture and environment. Ancestral remains from four geographic regions of Alaska were divided into five site groups defined by subsistence strategies and technology: Aleutian Islands, Coastal Bay, Far North Coastal, Inland/Riverine, and Tikeraq. Mid-distal humeral diaphyseal robusticity was quantified using cross-sectional geometric properties standardized by estimated body mass and bone length. Humeral strength and bilateral asymmetry were greatest in Aleutian Island males, moderate in Far North Coastal and Tikeraq males, and reduced in Inland/Riverine males. Left-biased directional asymmetry and reduced humeral strength were found in Coastal Bay males. Aleutian Island males had relatively mediolaterally strengthened humeri compared with other groups. Aleutian Island females had elevated humeral strength, while humeral asymmetry among females was moderate and did not vary between groups. Humeri were relatively round among Aleutian Island and Tikeraq females and anteroposteriorly (A-P) strengthened among Coastal Bay, Far North Coastal, and Inland/Riverine females. These results suggest elevated humeral strength and asymmetry in males that engaged in rowing and unimanual projectile hunting, while reduced humeral strength and asymmetry may reflect bow-and-arrow or ensnarement technologies. Left-biased humeral asymmetry may be associated with net-fishing. Humeral strength and asymmetry are consistent with select instances of unimanual projectile hunting in females, while differences in humeral A-P/mediolateral strength may reflect variation in butchery and processing of prey versus rowing and throwing behaviors.

Bow and muscles: Observed muscle activity in archers and potential implications for habitual activity reconstruction

Previous research has suggested that reduced humeral asymmetry in robusticity in European Late Pleistocene and Early Holocene populations may be a result of increased left humeral robusticity due to muscle loading from increased use of bow hunting. This paper provides a basis for considering the causes of such changes by assessing the overall intensity and level of asymmetry in the distribution of muscle activation and muscle force among living male archers. In this experiment, 20 right-handed archers drew a replica of the self bows characteristic for the Upper Paleolithic and Neolithic. We measured activation of eight muscles (biceps, triceps [long head], triceps [lateral head], deltoid [anterior part], deltoid [middle part], deltoid [posterior part], infraspinatus, and latissimus) using surface electromyography. We observed about a 15%–28% left bias in total maximum muscle force. The main muscles employed were triceps (lateral head), deltoid (middle part), and deltoid (posterior part) on both sides and triceps (long head) on the left arm. The most asymmetrical toward the right arm was the activation of biceps (123% right bias in mean muscle activation) and toward the left was triceps (long head) and triceps (lateral head) (70%–110% left bias in mean muscle activation). We conclude that left biased asymmetry in maximum muscle force produced during bow shooting may be responsible for the increase in robusticity of the left humerus and that the pattern of activation of specific individual muscles suggests that archery may be identifiable in the prehistoric record using skeletal features associated with muscle activity.

Structural properties of humeral diaphyses of East Asian modern humans from the Late Pleistocene to Early Holocene

AbstractObjectivesThis study aims to explore the structural properties along entire humeral diaphyses of Late Pleistocene and Early Holocene East Asian modern humans relative to the contemporaneous Neandertal specimen Regourdou 1 to provide insight into adaptive behaviors within temporal and regional hominin contexts.Materials and methodsThe humeri of three individuals from East Asia securely dated from the Late Pleistocene to Early Holocene were selected: Tianyuan 1, Zhaoguo M1, and Qihe M2. These specimens were scanned using microcomputed tomography to evaluate structural properties: cortical bone thickness (CBT), second moment of area (SMA), external radius (ER), and polar moment of area (J).ResultsThe distribution patterns of CBT, ER, and J were similar across all specimens. However, the magnitude of these variables was notably large in Regourdou 1 right humerus. The SMA, ER, and J of left humerus of Tianyuan 1 were less than that of other East Asian specimens, whereas those from the right humerus of the Qihe M2 individual were slightly larger than two other East Asian individuals. Additionally, the humeral asymmetry of Tianyuan 1 was greater than that of Zhaoguo M1 and Qihe M2.DiscussionCompared to Regourdou 1, East Asian specimens had reduced humeral robusticity. Within East Asia, the Late Pleistocene modern humans exhibit greater humeral asymmetry than the Early Holocene humans, indicating a universal reduction of humeral asymmetry related to technological changes across Eurasia during this time. The current study contributes to developing a more thorough understanding of intergroup humeral structural variation across Eurasia during the Late Pleistocene and Early Holocene.

Biomechanical Evaluation on the Bilateral Asymmetry of Complete Humeral Diaphysis in Chinese Archaeological Populations

Diaphyseal cross-sectional geometry (CSG) is an effective indicator of humeral bilateral asymmetry. However, previous studies primarily focused on CSG properties from limited locations to represent the overall bilateral biomechanical performance of humeral diaphysis. In this study, the complete humeral diaphyses of 40 pairs of humeri from three Chinese archaeological populations were scanned using high-resolution micro-CT, and their biomechanical asymmetries were quantified by morphometric mapping. Patterns of humeral asymmetry were compared between sub-groups defined by sex and population, and the representativeness of torsional rigidity asymmetry at the 35% and 50% cross-sections (J35 and J50 asymmetry) was testified. Inter-group differences were observed on the mean morphometric maps, but were not statistically significant. Analogous distribution patterns of highly asymmetrical regions, which correspond to major muscle attachments, were observed across nearly all the sexes and populations. The diaphyseal regions with high variability of bilateral asymmetry tended to present a low asymmetrical level. The J35 and J50 asymmetry were related to the overall humeral asymmetry, but the correlation was moderate and they could not reflect localized asymmetrical features across the diaphysis. This study suggests that the overall asymmetry pattern of humeral diaphysis is more complicated than previously revealed by individual sections.

Internal structural properties of the humeral diaphyses in an early modern human from Tianyuan Cave, China

Since the cross-sectional geometries of long bone diaphyses preserve evidence of a bone's mechanical loading history, examination of a bones' cross-sectional properties can be used to inform its loading history. Here, we use a novel colormap method to quantitatively visualize the topography of cortical bone, second moment of areas, and polar moment of areas along the humeral diaphyses to shed light on the potential manipulative behaviors of the Tianyuan 1 fossil human (Homo sapiens). We compare both humeri of Tianyuan 1 to two Holocene Chinese populations. Our results show that the standardized cortical bone thickness, standardized second moment of areas, and standardized polar moment of areas of Tianyuan 1's right humeral diaphysis are greater than those of the left diaphysis. This evidence supports the hypothesis that the individual was right-handed. The greater medial and lateral cortical reinforcement in the right midshaft humerus, relative to that of the left humerus, may be related to increased unilateral physical activity of the right arm. Unlike the lower humeral asymmetry of recent human agriculturalists, the relatively higher bilateral asymmetry, combined with the relatively larger femoral robusticity, indicate that Tianyuan 1 lived an activity lifestyle compared to the agriculturalists investigated in this study. The bilateral asymmetry of the right and left humeri may be more informative for discriminating between fossil and recent modern human samples than cortical thickness or rigidity values in only one side. This study also indicates that upper limb internal structures can provide important information for inferring the behavior of ancient hominins.

Evaluation of Bilateral Asymmetry in the Humerus of Human Skeletal Specimen.

Several studies have established a relationship between morphological and behavioral asymmetry making investigations of bilateral bone asymmetry an attractive and important research area. The purpose of this study was to investigate bilateral asymmetry patterns of skeletal specimen from five geographical locations (Rwanda, Burundi, Congo, Kenya, and Uganda) at Galloway Osteological Collection, Department of Anatomy, School of Biomedical Sciences, Makerere University College of Health Sciences. The angle of torsion and retroversion, mid-shaft circumference, length, and weight of 232 pairs of humeri were determined. A Torsiometer was used to measure the angle of torsion in degrees according to Krahl and Evans 1945, a tape was used to measure the mid-shaft circumference at the level of the apex of the deltoid V, and the length in cm was determined. An osteometric board was used to measure the length of the humerus in centimeters. A weighing balance was used to measure the weight of the humerus in grams. The analysis of humeral asymmetry with respect to parameters of the human skeletal specimen at the Galloway Osteological Collection Mulago revealed bilateral asymmetrical status observed in the angle of torsion, length, weight, and mid-shaft circumference. Our result mostly showed lateralization to the right in all the parameters investigated except the torsion angle which is to the left. Our investigation revealed that humeral torsion is inversely proportional to weight, length, and mid-shaft circumference of the humerus. This study established the existence of bilateral asymmetries in the humeri of all the geographical regions investigated with more asymmetry observed in the male compared with the female.

The palaeopathology of the Ohalo 2 Upper Paleolithic human remains: A reassessment of its appendicular robusticity, humeral asymmetry, shoulder degenerations, and costal lesion

AbstractThe 23,000 BP Ohalo 2 human remains, from the Upper Paleolithic of south‐west Asia, have been described by Hershkovitz and colleagues as very robust but especially as pathological with respect to its level of humeral asymmetry and its large anteroinferior costal bony growth. Reassessment of its appendicular robusticity, in the context of western Eurasian and North African Upper Paleolithic human remains, indicates that the Ohalo 2 limb remains are unexceptional in terms of muscular enthesis development, diaphyseal cross‐sectional shape, and major long bone diaphyseal hypertrophy. If anything, the muscular insertions and the humeral diaphyseal robusticity are modest for an Upper Paleolithic human. Similarly, the level of humeral asymmetry, as well as humeral versus radial diaphyseal asymmetry, is well within Upper Paleolithic ranges of variation. None of these aspects require palaeopathological explanations. The minor osteoarthritic changes of the right clavicle and scapula are common and of little importance. However, the massive lower thoracic ossification of the caudal sternum, ribs 6 and 7 and the intervening costal cartilages, has implications beyond the differential diagnosis of Hershkovitz and colleagues. It indicates constraints on thoracic expansion and hence on elevated respiration; as such, it would have placed limitations on the activity levels of this Upper Paleolithic forager. Ohalo 2 therefore joins a growing sample of Upper Paleolithic humans with serious developmental or degenerative abnormalities.

Patterns of humeral asymmetry among Late Pleistocene humans

Human humeral diaphyseal asymmetry in midshaft and mid-distal rigidity is assessed through the Late Pleistocene in samples of late archaic (Neandertal) and early modern humans. It is considered with respect to directionality (handedness), levels of asymmetry, body size and sexual differences. The overall Late Pleistocene sample indicates a right-handed preference in frequencies (right: 74.8%, left: 15.0%, ambiguous: 10.3%), which are similar to those of recent human samples. Average levels of humeral asymmetry are elevated relative to Holocene samples through all but the small Middle Paleolithic modern human and eastern Eurasian late Upper Paleolithic samples. Humeral asymmetry is especially high among the males relative to the females, and the possibility of a division of labor between uni-manual tasks (mostly male) and bi-manual tasks (mostly female) is considered. At the same time, there is a general pattern of increased asymmetry with larger body size, but it remains unclear to what extent it reflects body size versus sexual effects on bilateral humeral loading. There do not appear to have been substantial changes in humeral asymmetry through time, indicating a continuity of similar manual behavioral patterns through the Late Pleistocene, despite considerable changes in technology through the Late Pleistocene.

A bioarchaeological approach to the reconstruction of changes in military organization among Iron Age Samnites (Vestini) From Abruzzo, Central Italy.

The Samnites were an Iron Age population that shifted from warlike mountain dwellers to the largest sociopolitical unit of central Italy, able to dispute with Rome the domination over the peninsula. Archaeological and historical evidence suggests that this major shift in the scale of conflict may have involved a reorganization of the military system, which changed from an elite militia to a conscript or standing army from the Orientalizing-Archaic (800-500 BC) to Hellenistic times (400-27 BC). We propose a bioarchaeological framework jointly analyzing skeletal properties and funerary treatment in male Samnites to investigate on this shift in military organization. We anticipated that, when Samnites had an elite militia, the warring force was constituted by the wealthier segments of the society. Conversely, we expected the warring force of the standing/conscript army to be mainly drawn from the lower social strata. We considered high asymmetry in J, a measure of humeral torsional rigidity (calculated via cross-sectional geometry, CSG) as a proxy for pre- and peri-adolescent-onset weapon training. The social standing of the individual was approximated via funerary treatment analysis (Status Index). Results show that in the Orientalizing-Archaic period, humeral asymmetry and Status Index are positively correlated, and the high-status subsample shows significantly higher asymmetry than the low-status subsample. Among Hellenistic Samnites, no correlation between Status Index and humeral asymmetry is present, and the low-status subsample is the most lateralized. Results support the use of CSG in a strong theoretical framework to investigate past changes in military organization and their correlates in terms of sociopolitical development, alterations of power relationships, and warfare.

Changes in skeletal robusticity in an iron age agropastoral group: The samnites from the Alfedena necropolis (Abruzzo, Central Italy)

Cross-sectional geometrical (CSG) properties of an Iron Age Samnite group from the Alfedena necropolis (Abruzzo, Italy, 2600-2400 B.P.) are compared with a Ligurian Neolithic sample (6000-5500 B.P.). In the period under examination, Samnites were organized in a tribal confederation led by patrilinear aristocracies, indicating incipient social stratification. In comparison, Neolithic society lacked clear signs of social hierarchy. The subsistence of both groups was mainly based on pastoralism and agriculture, but changes in habitual behavior are expected due to the socio-economic transformations that characterized the Iron Age. The Samnites' warlike ideology suggests that unimanual weapon-use and training would have become frequent for males. The intensification of agriculture and the adoption of transhumant pastoralism, performed by a smaller subset of the population, likely led to a lower average level of logistic mobility. The strongly genderized ideology of the period suggests a strict sexual division of labor, with women primarily performing sedentary tasks. CSG properties based on periosteal contours were calculated for humeri, femora, and tibiae (N = 61). Results corroborated the expectations: Alfedena males show substantial humeral bilateral asymmetry, indicating prevalent use of one arm, likely due to weapon training. In both sexes lower limb results indicate reduced mobility with respect to the Neolithic group. Sexual dimorphism is significant in both humeral asymmetry and lower limb indicators of mobility. Although both groups could be broadly defined as agropastoral based on archeological and historical evidence, CSG analysis confirmed important differences in habitual behavior.

Sex differences in humeral bilateral asymmetry in two hunter‐gatherer populations: California Amerinds and British Columbian Amerinds

This study uses two prehistoric Amerindian populations of hunter-gatherer subsistence patterns to determine whether levels of sexual dimorphism in humeral bilateral cross-sectional asymmetry are related to sex-specific differences in activities among these populations. Results confirmed that males of the California Amerind population who engaged in the more unimanual activities of spear hunting and warfare were more asymmetrical than were their female counterparts who engaged in the more bimanual activities of grinding acorns. California Amerind males were also more asymmetrical than British Columbian Amerind males who rowed (using both arms) extensively. Sex differences within British Columbian Amerinds were not statistically significant, nor were female differences between populations. In general, levels of humeral asymmetry appear to be more dependent on sex and population-specific behaviors rather than broad subsistence patterns.

Mobility and subsistence economy: A diachronic comparison between two groups settled in the same geographical area (Liguria, Italy)

The purpose of this article is to investigate temporal shifts in skeletal robusticity to infer behavioral changes in two populations (Neolithic, NEOL and Medieval, MED) settled in the same geographic area but involved in different subsistence economies (pastoralism and coastal resources exploitation). This comparison allows us to test the hypothesis that occupational stress and mobility in the same environment produce predictable changes in the robusticity of both upper and lower limbs. Results show a lower degree of humeral robusticity and a similar degree of humeral asymmetry in the two sexes in the MED population. These results are consistent with the relatively less stressful subsistence economy documented in the MED population relative to that of the NEOL. Lower limb results suggest that femoral robusticity does not correlate directly with the level of logistical mobility, but is instead due to the summation of several diverse factors that place biomechanical loads on the hindlimb, particularly unevenness of the terrain. However, female femoral gracility seems to indicate that below a certain "threshold" of mobility, i.e., movement over the natural terrain, terrain conformation is no longer the main contributing factor to femoral robusticity. The femoral shape index I(x)/I(y) declines through time, particularly in males. This agrees with the expected mobility of the samples based on archaeological and historical data, providing further evidence on the reliability of this index in inferring terrestrial mobility.

Postcranial robusticity in Homo. II: Humeral bilateral asymmetry and bone plasticity

The analysis of humeral asymmetry in Recent human skeletal samples and an extant tennis-player sample documents minimal asymmetry in bone length, little asymmetry in distal humeral articular breadth, but pronounced and variable asymmetry in mid- and distal diaphyseal cross-sectional geometric parameters. More specifically, skeletal samples of normal modern Euroamericans, prehistoric and early historic Amerindians, and prehistoric Japanese show moderate (ca. 5-14%) median asymmetry in diaphyseal cross-sectional areas and polar second moments of area, whereas the tennis-player sample, with pronounced unilateral physical activity, exhibits median asymmetries of 28-57% in the same parameters. A sample of Neandertals with nonpathological upper limbs exhibits similarly low articular asymmetry but pronounced diaphyseal asymmetries, averaging 24-57%. In addition, three Neandertals with actual or possible post-traumatic upper limb alterations have the same low articular asymmetry but extremely high diaphyseal asymmetries, averaging 112-215%. These data support those from experimental work on animals, exercise programs of humans, and human clinical contexts in establishing the high degree of diaphyseal plasticity possible for humans, past and present, under changing biomechanical loading conditions. This lends support to activity-related functional interpretations of changing human diaphyseal morphology and robusticity during the Pleistocene.

Asymmetry and activity‐related change in the male humerus

AbstractSome previous studies of activity‐related change in the human skeleton have been of doubtful validity because specific changes have been related to particular tasks. Claims to establish such relationships have often concentrated on the development of entheses. Such work is marred by the incorrect assumption that muscles work in isolation in the performance of a single activity. In addition, normal skeletal asymmetry is often ignored, as is age and sex.In the present work, paired humeri of males from two medieval British sites, Norwich and Henry VIII's flagship, the Mary Rose, were compared using a series of measurements. Comparison of left and right sides demonstrated that humeral asymmetry decreases with age. Comparison of the sites showed that the Norwich males were more asymmetric than those from the Mary Rose. All asymmetries exhibited a right‐sided dominance. The majority of the species is right‐handed: the Norwich males followed this trend. The general lack of asymmetry in the Mary Rose males suggests that they were using their arms more equally. When left and right sides were compared directly, a new measurement of the greater tubercle (where three muscles insert) and measurement of the diameter of the head demonstrated that the Mary Rose males had significantly larger dimensions of the left shoulder than the Norwich males. These results extend earlier work, which had suggested a correlation between the use of heavy medieval longbows and os acromiale. Statistical comparison of the sites demonstrated that such work can indicate patterns of activity but not individual occupations.