title: Analysis of the forearm rotational efficiency in extant hominoids: new insights into the functional implications of upper limb skeletal structure.
abstract: The greatly diversified locomotor behaviors in the Hominoidea impose different mechanical requirements in the upper limb of each species. As forearm rotation has a major role in locomotion, the skeletal structures involved in this movement may display differences among taxa that reflect functional adaptations. To test this, we use a biomechanical model that quantifies the rotatory capacity of pronator teres (rotational efficiency) from skeletal measurements. Using a large sample of hominoids, we aim to identify the morphological adaptations that confer differences in the mechanics of forearm motion and to assess the functional advantage of these adaptations. Forearm positions along the pronation-supination range where rotational efficiency is maximal depend on the orientation of the humeral medial epicondyle and differ among taxa. Our results indicate that these are related to locomotor mode. Knuckle-walkers exhibit a medial epicondyle more posteriorly directed, which, in elbow angles close to extension, causes rotational efficiency to be maximal in pronated positions of the forearm. Species with a significant amount of arboreal locomotion, such as vertical climbing, i.e., Pongo spp., Pan troglodytes and Gorilla gorilla, display more proximally oriented epicondyles, which, in elbow flexion, leads to maximum rotational efficiencies in supinated positions of the forearm. Hylobatidae, with the less posteriorly and proximally oriented epicondyle, show their maximum rotational efficiencies closer to the forearm neutral position throughout most of the flexion-extension range, which may be linked to brachiation in this taxon. In humans, the epicondylar orientation and thus the positions of the maximum rotational efficiencies fall between arboreal and terrestrial hominoids. This may be related to the enhanced manipulative skills of the upper limb. In conclusion, the current analysis indicates that the orientation of the humeral medial epicondyle is linked to the locomotor habits of extant hominoids and therefore can be used for locomotor inferences in fossil taxa.
authors.affiliation: Unitat d'Antropologia Biològica, Departament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain. Electronic address: pereibgi@gmail.com.
authors.forename: Pere
authors.initials: P
authors.lastname: Ibáñez-Gimeno
authors.affiliation: Servei de Patologia Forense, Unitat d'Antropologia Forense, Institut de Medicina Legal de Catalunya, Ciutat de la Justícia, Gran Via de les Corts Catalanes 111, Edifici G, 08075 Barcelona, Catalonia, Spain; Unitat de Medicina Legal i Forense, Departament de Psiquiatria i de Medicina Legal, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain. Electronic address: ignasigaltes@gmail.com.
authors.forename: Ignasi
authors.initials: I
authors.lastname: Galtés
authors.affiliation: Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain. Electronic address: joan.manyosa@uab.cat.
authors.forename: Joan
authors.initials: J
authors.lastname: Manyosa
authors.affiliation: Unitat d'Antropologia Biològica, Departament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain. Electronic address: assumpcio.malgosa@uab.cat.
authors.forename: Assumpció
authors.initials: A
authors.lastname: Malgosa
authors.affiliation: Institut Català de Paleontologia Miquel Crusafont (ICP), Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain. Electronic address: xavier.jordana@icp.cat.
authors.forename: Xavier
authors.initials: X
authors.lastname: Jordana
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005260:Female; D005542:Forearm / Q000033:anatomy & histology / Q000502:physiology*; D015186:Hominidae / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D008124:Locomotion; D008297:Male; D012399:Rotation
keywords: Biomechanics; Elbow flexion–extension; Humeral medial epicondyle; Locomotion; Pronation–supination; Pronator teres