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. 2022 Oct 30;12(21):2987.
doi: 10.3390/ani12212987.

Elbow Extensor Muscles in Humans and Chimpanzees: Adaptations to Different Uses of the Upper Extremity in Hominoid Primates

Marina de Diego  1 , Aroa Casado  1   2 , Mónica Gómez  1 , Neus Ciurana  1 , Patrícia Rodríguez  1 , Yasmina Avià  2   3 , Elisabeth Cuesta-Torralvo  2   3 , Natividad García  4 , Isabel San José  4 , Mercedes Barbosa  4 , Félix de Paz  4 , Juan Francisco Pastor  4 , Josep Maria Potau  1   2
Affiliations

Elbow Extensor Muscles in Humans and Chimpanzees: Adaptations to Different Uses of the Upper Extremity in Hominoid Primates

Marina de Diego et al. Animals (Basel). .

Abstract

The anatomical and functional characteristics of the elbow extensor muscles (triceps brachii and anconeus) have not been widely studied in non-human hominoid primates, despite their great functional importance. In the present study, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms in the elbow extensors in humans and chimpanzees. Our main objective was to identify differences in these muscles that could be related to the different uses of the upper extremity in the two species. In five humans and five chimpanzees, we have analyzed muscle mass (MM), muscle fascicle length (MFL), and the physiological cross-sectional area (PCSA). In addition, we have assessed the expression of the MHC isoforms by RT-PCR. We have found high MM and PCSA values and higher expression of the MHC-IIx isoform in the triceps brachii of chimpanzees, while in humans, the triceps brachii has high MFL values and a higher expression of the MHC-I and MHC-IIa isoforms. In contrast, there were no significant differences between humans and chimpanzees in any of the values for the anconeus. These findings could be related to the participation of the triceps brachii in the locomotion of chimpanzees and to the use of the upper extremity in manipulative functions in humans. The results obtained in the anconeus support its primary function as a stabilizer of the elbow joint in the two species.

Keywords: anconeus; chimpanzee; elbow joint; triceps brachii.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Medial view of a triceps brachii muscle dissection in (a) Homo sapiens and (b) Pan troglodytes and lateral view of an anconeus muscle dissection in (c) Homo sapiens and (d) Pan troglodytes. Tclo = Triceps brachii caput longum; Tcla = Triceps brachii caput laterale; Tcm = Triceps brachii caput mediale; A = Anconeus; ED = Extensor digitorum; ECU = Extensor carpi ulnaris.
Figure 2
Figure 2
View of the (a) triceps brachii and (b) anconeus of Pan troglodytes displaying the architectural arrangement of their muscle fascicles. MFL = muscle fascicle length; θ = pennation angle.
Figure 3
Figure 3
Boxplots of the differences between Homo sapiens (HS) and Pan troglodytes (PT) in NMFL and NPCSA values in the (a,c) triceps brachii (TB) and (b,d) anconeus (A).
Figure 4
Figure 4
Expression of MHC isoforms in the triceps brachii and anconeus in Homo sapiens and Pan troglodytes. MHC = myosin heavy chain; HS = Homo sapiens; PT = Pan troglodytes. The data bars represent mean values, and the error bars represent the standard error. * indicates statistical significance.
See this image and copyright information in PMC

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