Investigating the effect of manual physical activity on the form of human hand entheses

Reconstructing physical activity based on human skeletal remains comprises a fundamental objective of anthropological sciences. Entheses, the areas of muscle attachment on the bone surfaces, have been widely utilized as occupational stress markers. However, most previous methods for analyzing entheseal morphology (size and/or shape) are characterized by substantially low precision, lack of three-dimensional (3D) multivariate statistical analysis, and absence of individuals documented for their long-term physical activities. Furthermore, no previous study used histological methods for assessing the effect of physical activity on the interindividual variability of entheseal surfaces. My past research put forth a precise methodology for measuring the 3D size of hand entheseal areas, identifying two main multivariate patterns among entheses. On this basis, this PhD thesis performed a multi-disciplinary approach to the analysis of hand entheseal form (a term encompassing both size and shape) and its potential relationship with habitual physical activities. In Paper I, the hand entheses of a thoroughly documented sample were analyzed using a highly precise 3D method of quantification, followed by multivariate statistical analysis. The utilized material is part of an anthropological collection which is gradually becoming a unique universal reference for the most detailed documentation of the specimens’ lifelong physical activities. The results revealed a close statistical association between multivariate patterns of hand entheses and the nature of individuals’ long-term occupational profiles. In the framework of an ongoing multidisciplinary research project, the developed method of entheseal analysis was applied for reconstructing the occupational profile of an unidentified individual from Basel (Paper II). The results indicated that this specimen was involved in precise manual activities relying on thumb-index finger interactions. This outcome came in agreement with other research on the physical activities of this individual. Paper III introduced a new and precise geometric morphometric approach for investigating hand entheseal 3D shape, identifying a statistically significant interaction between 3D size and shape variation in three hand entheses. In this way, it set a novel basis for future research on both aspects of entheseal form (3D size and shape), bridging the gap between quantitative and qualitative methods of entheseal analysis. Furthermore, the results showed that larger phalangeal entheses present a proportionally more projecting surface, which is linked to greater moment arm and biomechanical efficiency for the attaching muscle. Finally, paper IV presented a microscopic histological analysis of hand entheses, which reported an interaction between entheseal morphology and the levels of applied biomechanical forces. Particularly, the elevated bone areas of hand entheses were associated with greater concentrations of calcified fibrocartilage, which is widely considered as a direct indicator of biomechanical stress. As a consequence, individual entheses with elevated marginal areas comprised evidence of greater biomechanical stress. Overall, this PhD thesis identified a clear interaction between physical activity and human hand entheses based on three methodological approaches and four separate analyses. The multivariate 3D analysis showed that the patterns among different hand entheses reflect the nature of an individual’s lifelong occupational activities. At the same time, the shape of larger entheseal areas is proportionally projecting, providing greater biomechanical efficiency for the attaching muscle. Finally, higher entheseal bone elevation seems to be related with greater biomechanical stress (i.e., higher concentrations of calcified fibrocartilage)

Sex determination using proximal hand phalanges

Sex determination is among the most important biological data to be obtained from human skeletal remains. In anthropological sciences, the applied methodology involves the analysis of the quantitative and qualitative characteristics of skeletal parts. Measurements of proximal hand phalanges have been shown to exhibit prominent sexual dimorphism, in different populations examined. The aim of this study is to assess the utility of proximal hand phalanges for the sex diagnosis and develop a discriminant formula to be applied to Modern Greek populations. The material utilized consists of 661 proximal hand phalanges (left and right) from the Athens Collection, corresponding to 160 adult individuals (86 males and 74 females). Classification accuracies ranged between 94.6% and 100% for left and between 87.7% and 100% for right proximal phalanges. The results of this study indicate that proximal hand phalanges can be used for accurate sex diagnosis

Experimental proof that multivariate patterns among muscle attachments (entheses) can reflect repetitive muscle use

Reconstructions of habitual activity in past populations and extinct human groups is a primary goal of paleoanthropological research. Muscle attachment scars (entheses) are widely considered as indicators of habitual activity and many attempts have been made to use them for this purpose. However, their interpretation remains equivocal due to methodological limitations and a paucity of empirical data supporting an interaction between systematic muscle forces and entheseal morphology. We have recently addressed the first issue with precise three-dimensional measuring protocols and rigorous multivariate analysis focusing on the patterns among different entheses rather than comparing each entheseal structure separately. In a previous study, the resulting entheseal correlations reflected synergistic muscle groups that separated individuals according to their lifelong occupational activities. Here we address the second issue by applying this methodology to existing micro-computed tomography data from rats that have undergone muscle stimulation under experimental conditions. In contrast to previous animal studies, we relied on blind analytical procedures across two research institutions and controlled for most factors of interindividual variability. Results demonstrated that the multivariate associations among different entheseal surfaces can directly reflect repetitive muscle recruitment and provide essential information on muscle use

Biocultural Evidence of Precise Manual Activities in an Early Holocene Individual of the High-Altitude Peruvian Andes

OBJECTIVES: Cuncaicha, a rockshelter site in the southern Peruvian Andes, has yielded archaeological evidence for human occupation at high elevation (4,480 masl) during the Terminal Pleistocene (12,500–11,200 cal BP), Early Holocene (9,500–9,000 cal BP), and later periods. One of the excavated human burials (Feature 15‐06), corresponding to a middle‐aged female dated to ~8,500 cal BP, exhibits skeletal osteoarthritic lesions previously proposed to reflect habitual loading and specialized crafting labor. Three small tools found in association with this burial are hypothesized to be associated with precise manual dexterity. MATERIALS AND METHODS: Here, we tested this functional hypothesis through the application of a novel multivariate methodology for the three‐dimensional analysis of muscle attachment surfaces (entheses). This original approach has been recently validated on both lifelong‐documented anthropological samples as well as experimental studies in nonhuman laboratory samples. Additionally, we analyzed the three‐dimensional entheseal shape and resulting moment arms for muscle opponens pollicis. RESULTS: Results show that Cuncaicha individual 15‐06 shows a distinctive entheseal pattern associated with habitual precision grasping via thumb‐index finger coordination, which is shared exclusively with documented long‐term precision workers from recent historical collections. The separate geometric morphometric analysis revealed that the individual\u27s opponens pollicis enthesis presents a highly projecting morphology, which was found to strongly correlate with long joint moment arms (a fundamental component of force‐producing capacity), closely resembling the form of Paleolithic hunter‐gatherers from diverse geo‐chronological contexts of Eurasia and North Africa. DISCUSSION: Overall, our findings provide the first biocultural evidence to confirm that the lifestyle of some of the earliest Andean inhabitants relied on habitual and forceful precision grasping tasks

New insights into the manual activities of individuals from the Phaleron cemetery (Archaic Athens, Greece)

Until the early 5th century BC, Phaleron Bay was the main port of ancient Athens (Greece). On its shore, archaeologists have discovered one of the largest known cemeteries in ancient Greece, including a range of burial forms, simple pits, cremations, larnaces (clay tubs), and series of burials of male individuals who appear to have died violent deaths, referred to here as “atypical burials”. Reconstructing the osteobiographies of these individuals will help create a deeper understanding of the socio-political conditions preceding the rise of Classical Athens. Here, we assess the habitual manual behavior of the people of Archaic Phaleron (ca. 7th – 6th cent. BC), relying on a new and precise three-dimensional method for reconstructing physical activity based on hand muscle attachment sites. This approach has been recently validated on laboratory animal samples as well as on recent human skeletons with a detailed level of long-term occupational documentation (i.e., the mid-19th century Basel Spitalfriedhof sample). Our Phaleron sample consists of 48 adequately preserved hand skeletons, of which 14 correspond to atypical burials. Our results identified consistent differences in habitual manual behaviors between atypical burials and the rest. The former present a distinctive power-grasping tendency in most skeletons, which was significantly less represented in the latter (p-values of <0.01 and 0.03). Based on a comparison with the uniquely documented Basel sample (45 individuals), this entheseal pattern of the atypical burials was exclusively found in long-term heavy manual laborers. These findings reveal an important activity difference between burials typical for the Phaleron cemetery and atypical burials, suggesting that the latter were likely involved in distinctive, strenuous manual activities. The results of this pilot study comprise an important first step towards reconstructing the identity of these human skeletal remains. Future research can further elucidate the occupational profiles of these individuals through the discovery of additional well-preserved hand skeletons and by extending our analyses to other anatomical regions

Technical note: Development of regression equations to reassociate upper limb bones from commingled contexts

The major upper limb skeletal elements (scapulae, humeri, ulnae and radii) are frequently utilized for sex determination and stature estimation. Consequently, in forensic cases that involve commingled remains, it is crucial to reassociate the aforementioned bones and attribute them to the right individual. The aim of the present study is to develop simple and multiple regression equations for sorting commingled human skeletal elements of the upper limb. In that context, ten common anthropological linear measurements of the articular surfaces of scapulae, humeri, ulnae, and radii were performed on 222 adult skeletons from the Athens Collection. The functions developed for sorting adjoining bones presented a strong positive linear relationship (r = 0.69–0.93, p < 0.05). The values of the determination coefficient statistics (r2 = 0.47–0.86) were found to be high and those of the standard errors of the estimate were found to be low (SEE = 0.88–1.61). Blind tests indicated that when metric and morphoscopic sorting techniques are combined, a reliable sorting of the skeletal elements of the upper limbs is possible