Within primates, the nuchal region is considered particularly important for understanding variation in postural and locomotor behaviors. Nonetheless, there has not yet been a quantitative study of comparative nuchal muscle function. We investigated the influence of 1) trunk posture, 2) head turning behaviors, and 3) forelimb-dominated below-branch suspensory behaviors on the nuchal musculature in five primate species with a diversity of positional behavioral specializations. We used DiceCT, 3D muscle fascicle-tracking, and 3D muscle visualization to compare the attachment sites, 3D orientations, and force generating capacity of 19 muscles. Results demonstrate that all muscle force estimates scale with isometry. Suspensory taxa have a more dorsoventrally oriented cranial belly of the trapezius muscle when compared to non-suspensory species. Orthograde primates have relatively less powerful longissimus capitis muscles than do pronograde primates. Primates that employ dramatic head-turning during locomotion have more transversely oriented (Carlito) and more powerful sternocleidomastoid as well as more powerful obliquus capitis superior muscles (Carlito and Propithecus). These results support the hypothesis that positional behaviors influence the moment-generating capacities of certain key nuchal muscles. Osteological correlates of nuchal muscles may be useful in reconstructing fossil primate behaviors, but more investigation is necessary especially into the effects of phylogeny.