This article investigates the relationship between the cortical bone of the radius and the muscle area of the forearm. The aim of this study was to develop a method for muscle area estimation from cortical bone area at 65% of radius length where the muscle area at the forearm is largest. Muscle area and cortical area were measured directly in vivo by peripheral Quantitative Computed Tomography (pQCT). We found significant correlations between muscle area and cortical area (r 5 0.881) in the forearm that are in line with previous studies. We have set up a regression model by testing relevant parameters such as age, sex, forearm length, and stature that were all highly correlated to muscle area. The influence of age and sex on the proportion of muscle area to cortical area is strong and potentially related to the effects of testosterone and estrogen on the muscle-bone-unit. Muscle area estimation from cortical bone is possible with a Percent Standard Error of Estimate (%SEE) ranging from 12.03% to 14.83%, depending on the parameters available and the age and sex of the individual. Muscle area estimation from cortical bone can provide new information for the study of skeletal and/or fossil human remains. Anat Rec, 296:1695Rec, 296: -1707Rec, 296: , 2013. V C 2013 Wiley Periodicals, Inc.Key words: muscle-bone-unit; functional bone-tissue adaptation; pQCT; cortical bone; soft tissue reconstruction This article presents the results of a study that investigates the relationship between the cortical bone of the radius and the muscle area of the forearm. The underlying question of the study is whether it is possible to reasonably estimate muscular properties of the forearm from the cross sectional properties of the forearm bones, and if so, which parameters are required for such an estimation. We hypothesize that cortical bone crosssectional area can predict muscle cross-sectional area, and that such estimations of muscle area could provide valuable information for the study of human skeletal remains. Therefore, we aim to develop a prediction model for muscle area from cortical area.Paleoanthropologists, prehistoric human biologists, and forensic anthropologists almost always rely on skeletal material alone for the reconstruction of body shape and physical capabilities of fossil hominines, prehistoric humans, or unidentified recent skeletal human remains. The reconstruction of soft tissue properties from bone has therefore always been an aim in anthropology, from early attempts to assess the muscularity of Neanderthals from their postcranial dimensions (Klaatsch, 1901;Heim, 1976) to comparative studies on primates (e.g., Baumann, 1926;DeRousseau et al., 1983;Marzke et al., 1999) and modern in vivo studies on muscle activity using electromyography (Wall-Scheffler et al., 2010) or 3D neuromusculoskeletal models for fossil hominids (Nagano et al., 2005). It has also been recognized that data on postcranial muscle tissue might provide anthropologists with valuable information on physical strength, metabolic costs,...