This study used an aggregate measure of robusticity (based on humeral areal and inertial cross-sectional components) to test the hypothesis that rowing on oceans led to more robust humeri than did rowing on rivers or not rowing at all. Results confirmed the hypothesis that male ocean-rowers had more robust humeri than did male river-rowers or nonrowers. However, although the females from the ocean-rowing populations did not row, they averaged more robust humeri than did females from the non-ocean-rowing populations. Males averaged greater robusticity than did females. The robusticity of ocean-rowing populations, therefore, does not seem to be due solely to bone remodeling resulting from strenuous rowing. Humeral robusticity is difficult to attribute to specific activities because, in humans, upper limbs are utilized for many activities. Some populations may have more robust humeri because certain environments require greater overall activity levels in order to survive. Am J Phys Anthropol 121:000–000, 2003. © 2003 Wiley-Liss, Inc.