1Biology, Institute of Systematic Zoology and Evolutionary Biology, Friedrich-Schiller-University Jena, Germany, 2Biology, School of Biosciences, University of Birmingham, UK, 3Veterinary Medicine, Small Animal Clinics, University of Veterinary Medicine Hannover, Foundation, Germany
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In accordance with the comparatively short lumbar region, long iliac blades, and small lateral epaxial tracts, locomotor studies have suggested that chimpanzees possess only limited trunk mobility. For instance, chimpanzees seem to lack the intensive sagittal bending occurring in monkeys during asymmetrical gaits. However, non-locomotor activities may reveal a greater range of motion because the maximal mobility of a joint is rarely used during locomotor activities. To test whether a greater range of trunk mobility is used during non-locomotor activities than during locomotion, we collected a comprehensive data set on trunk motions in chimpanzees in a zoo and a semi-natural environment. This information is integrated with morphological details such as the muscle fibre type composition of the perivertebral musculature, which we studied in 2,1 adults using immune-histochemistry. Our results confirm that chimpanzees show a far greater range of trunk motion during non-locomotor activities than during locomotion. For example, maximum lateral bending was observed during hanging positions. In contrast to the hypaxial muscles, which contained on average 66% fast fibres, only about half the fibres were fast in the epaxial muscles. The homogeneous fibre distribution indicates that all epaxial muscles are equally well suited to mobilize and stabilize the trunk. The relatively small lateral epaxial tracts combined with only 50% fast fibres may be associated with the reduced sagittal extension in galloping chimpanzees, while size and the fibre composition of the hypaxial muscles may facilitate spine flexions comparable to other galloping primates.
This study was supported by the Center of Interdisciplinary Prevention of Diseases related to Professional Activities funded by the Friedrich-Schiller-University Jena and the Berufsgenossenschaft Nahrungsmittel und Gastgewerbe Erfurt (Germany) and the Royal Society of London (UK).