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Comparison of the arm‐lowering performance between Gorilla and Homo through musculoskeletal modeling

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van Beesel,  Julia       
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Max Planck Society;
The Leipzig School of Human Origins (IMPRS), Max Planck Institute for Evolutionary Anthropology, Max Planck Society;

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Hublin,  Jean-Jacques       
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Max Planck Society;

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Melillo,  Stephanie Marie       
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Max Planck Society;

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Citation

van Beesel, J., Hutchinson, J. R., Hublin, J.-J., & Melillo, S. M. (2022). Comparison of the arm‐lowering performance between Gorilla and Homo through musculoskeletal modeling. American Journal of Biological Anthropology, 178(3), 399-416. doi:10.1002/ajpa.24511.


Cite as: https://hdl.handle.net/21.11116/0000-000A-188C-E
Abstract
Objectives:Contrary to earlier hypotheses, a previous biomechanical analysis indi-cated that long-documented morphological differences between the shoulders ofhumans and apes do not enhance the arm-raising mechanism. Here, we investigate adifferent interpretation: the oblique shoulder morphology that is shared by all homi-noids but humans enhances the arm-lowering mechanism.Materials and methods:Musculoskeletal models allow us to predict performancecapability to quantify the impact of muscle soft-tissue properties and musculoskeletalmorphology. In this study, we extend the previously published gorilla shoulder modelby adding glenohumeral arm-lowering muscles, then comparing the arm-loweringperformance to that of an existing human model. We further use the models to dis-entangle which morphological aspects of the shoulder affect arm-lowering capacityand result in interspecific functional differences.Results:Our results highlight that arm-lowering capacity is greater inGorillathan inHomo. The enhancement results from greater maximum isometric force capacitiesand moment arms of two important arm-lowering muscles, teres major, andpectoralis major. More distal muscle insertions along the humerus together with amore oblique shoulder configuration cause these greater moment arms.Discussion:The co-occurrence of improved arm-lowering capacity and high-muscleactivity at elevation angles used during vertical climbing highlight the importance of astrong arm-lowering mechanism for arboreal locomotor behavior in nonhuman apes.Therefore, our findings reveal certain skeletal shoulder features that are advanta-geous in an arboreal context. These results advance our understanding of adaptationin living apes and can improve functional interpretations of the hominin fossil record