Repeated loading influences bone mass, geometry and/or microstructure. Whether chronic loading in the frame of professional activity impacts bone, particularly cortical bone which markedly contributes to bone strength, is poorly documented. The influence of various occupation-dependent load intensities on geometry and mechanical properties of upper limbs bones was investigated in two models: ex-vivo in the SIMON anthropological skeleton collection, a homogeneous collection of the 20th century, using CT scans of bilateral humerus and radius from 219 men (age of death 20 to 93 years); in-vivo at distal radius in 180 65-years old men using high-resolution peripheral quantitative computed tomography and finite element analysis. In both models, heavy-loading professional activities were associated with higher bone strength. In ex vivo data, this benefit was associated with higher cross sectional areas (CSA) and cortical areas in young adult men skeletons compared with men with light-loading professional activity. These differences decreased in men who died at older ages. In older men, it was associated with smaller medullary area. This effect resulted in greater asymmetries of medullar area and of the cortical area/CSA ratio between the dominant and non-dominant humerus in men with unilateral versus bilateral heavy-loading professional activities. In vivo, heavy-loading professional activity was associated with higher trabecular density and lower trabecular spacing than in light-loading professional activities. Repeated loading during professional activity may positively influence cortical bone strength by two mechanisms: an increase of CSA in young adulthood followed by slowdown of the age-related endosteal bone loss.