Aging and Activity: A Biomechanical Assessment of Heterogeneous Bone Maintenance and Loss in Documented Individuals from a 19th Century Dutch Rural Community.

Bone loss is an inherent part of the aging process. However, sociocultural factors such as biological sex and differing habitual activity patterns can alter the manifestation of age-related cortical thinning across the skeleton, informing interpretations of skeletal health, aging, and the lives and experiences of past individuals. This thesis investigates heterogeneity in age-associated cortical bone loss in a 19th century documented rural Dutch population from Middenbeemster. Using a biomechanical framework, it evaluates how age, sex, and mechanical loading influenced cortical bone mass and distribution across different skeletal elements. Cross-sectional geometric (CSG) properties of the femoral midshaft and radial one-third site were obtained from CT scans of documented, non-pathological individuals (M = 19, F = 21; aged 23–84 and 21–78, respectively) and compared to previously published cortical index (CI) data for the second metacarpal (MC2) (Gilmour et al., 2021). Cross...Show moreBone loss is an inherent part of the aging process. However, sociocultural factors such as biological sex and differing habitual activity patterns can alter the manifestation of age-related cortical thinning across the skeleton, informing interpretations of skeletal health, aging, and the lives and experiences of past individuals. This thesis investigates heterogeneity in age-associated cortical bone loss in a 19th century documented rural Dutch population from Middenbeemster. Using a biomechanical framework, it evaluates how age, sex, and mechanical loading influenced cortical bone mass and distribution across different skeletal elements. Cross-sectional geometric (CSG) properties of the femoral midshaft and radial one-third site were obtained from CT scans of documented, non-pathological individuals (M = 19, F = 21; aged 23–84 and 21–78, respectively) and compared to previously published cortical index (CI) data for the second metacarpal (MC2) (Gilmour et al., 2021). Cross-sectional measures were standardized by body mass to account for sex-based variation in robusticity. Results indicated that age-related cortical bone loss was not uniformly expressed across the skeleton or between sexes. In men, no significant age-related decline was observed in the femur, radius, or MC2. Femoral properties were not significantly correlated with the radius or MC2, while radial cortical percentage was moderately associated with MC2 CI (r = 0.532, p = .021). This suggests that bone adaptation in men is unrelated to increasing age and is likely subject to limb-specific mechanical loading, which differs in the lower and the upper limb due to their functional divergence. In contrast, women exhibited significant age-associated endosteal resorption and cortical thinning of the radius and MC2, accelerating after age 50, likely linked to postmenopausal estrogen deficiency and insufficient compensatory subperiosteal apposition. However, no significant age-related bone loss was observed in the femur, likely connected to sustained mobility through participation in agricultural labor. CSG properties of the radius and femur were significantly correlated in women, indicating that mechanical loading did not differentially impact upper and lower limbs, attributed to less intense or directionally repetitive activity throughout life. Contrastingly, radial cortical percentage and MC2 cortical index were not significantly associated (r = 0.346, p = .124), despite the use of these skeletal elements in assessing osteoporosis. These results suggest that systemic factors influence cortical bone loss in women more than mechanical loading, but that the effects of age are more marked and variable on non-weight-bearing bones, which are more vulnerable to changes in hormonal status. Placed within the context of historical records and prior studies of postmedieval European populations, these findings align with the reports of a sex-based division of labor: men were responsible for more strenuous and demanding tasks involving field working, while women for household tasks and childcare. However, it was not uncommon for younger women to participate in outdoor farming activities when needed, which could account for the lack of age-associated bone loss in female femora and the lack of pronounced sex-related differences among male and female properties observed. Overall, these findings highlight the complex nature of age-associated bone loss, its dependence on biocultural identity, as well as the importance of examining multiple skeletal sites when reconstructing activity and aging in past populations.Show less

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Aging and Activity: A Biomechanical Assessment of Heterogeneous Bone Maintenance and Loss in Documented Individuals from a 19th Century Dutch Rural Community.