Distribution patterns of fibre types in the triceps surae muscle group of chimpanzees and orangutans

Abstract

Different locomotor and postural demands are met partly due to the varying properties and proportions of the muscle fibre types within the skeletal muscles. Such data are therefore important in understanding the subtle relationships between morphology, function and behaviour. The triceps surae muscle group is of particular interest when studying our closest living relatives, the non-human great apes, as they lack a significant external Achilles tendon, crucial to running locomotion in humans and other cursorial species. The aim of this study, therefore, was to determine the proportions of type I (slow) and type II (fast) fibres throughout these muscles in chimpanzees and orangutans using immunohistochemistry. The orangutan had a higher proportion of type I fibres in all muscles compared with the chimpanzees, related to their slower, more controlled movements in their arboreal habitat. The higher proportion of type II fibres in the chimpanzees likely reflects a compromise between their need for controlled mobility when arboreal, and greater speed and power when terrestrial. Overall, the proportion of slow fibres was greater in the soleus muscle compared with the gastrocnemius muscles, and there was some evidence of proximal to distal and medial to lateral variations within some muscles. This study has shown that not only do orangutans and chimpanzees have very different muscle fibre populations that reflect their locomotor repertoires, but it also shows how the proportion of fibre types provides an additional mechanism by which the performance of a muscle can be modulated to suit the needs of a species.

Fibre type composition in the lumbar perivertebral muscles of primates: implications for the evolution of orthogrady in hominoids

“…This confirms previous observations from hindlimb muscles (Myatt et al. ) and agrees well with the orangutan's cautious and deliberate locomotor habits (MacKinnon, ; Thorpe & Crompton, , ). Similarly, a larger proportion of slow fibres have been observed in slow‐moving species such as the slow loris (Ariano et al.…”

“…; Myatt et al. ). A recurrent finding has been that muscles or muscle groups are regionalized; that is, they show regional accumulations of the type of fibre best suited for the function of that particular muscle or muscle region (Kernell, ).…”

Functional adaptations in the forelimb muscles of non‐human great apes

“…In addition to these variations in macro‐architecture, adaptations to more frequently used behaviours may well be reflected in muscle micro‐architecture (i.e. different fibre type proportions/distributions), and it may be this which fine‐tunes muscles to the output required by a given species, or different populations of the same species (see Myatt et al. 2011b).…”

The Effect of the Achilles Tendon on Trabecular Structure in the Primate Calcaneus

“…In chimpanzees, for example, the Achilles tendon constitutes a small percentage ( 7.5%) of the total muscle length (Table 1). This small tendon-to-muscle ratio permits a greater ankle joint excursion (Hanna and Schmidt, 2011;Myatt et al, 2011), which may permit the extreme dorsiflexion exhibited during vertical climbing in the apes (DeSilva, 2009). Interestingly, however, gibbons (Hylobates) have a relatively long Achilles tendon compared to the other nonhuman apes ( 35-45% of total muscle length) ( Table 1).…”