3D volumetric muscle reconstruction of the Australopithecus afarensis pelvis and limb, with estimations of limb leverage
In this project, my main aim is to reconstruct the soft tissues of fossil hominins and then assess their locomotory capabilities… and I’m so pleased to announce that my preprint is finally available on BioRxiv! Before we can reconstruct movement, we first need to have a comprehensive overview of the musculature and its composition/space filling within the body. In this preprint, I recreated the musculature of the famous Australopithecus afarensis specimen AL 288-1’s (nicknamed Lucy) pelvis and lower limbs using the polygonal muscle modelling approach that my colleagues and I developed/published early in 2022 – see that paper here and the associated blog post here.
Don’t forget to check out the video of the muscles below!
For this part of my project, I first obtained scans of the AL 288-1 specimen and created a rigged skeleton – this means that joint centres and rotational axes were defined upon which movement can be animated. Polygonal muscles were then created in the software Maya Autodesk 2022 and a line of action was threaded through each 3D muscle to represent the muscles centroid. This permitted the creation of a musculoskeletal model for use in the biomechanical software OpenSim (for further details on the modelling approach, refer to the preprint or the blog post).
All pelvic, thigh, shank and most foot muscles were modelled (intrinsic muscles of the foot were omitted due to the scarsity of pedal remains in the fossil record). These polygonal muscles can be visualised in the below video:
The muscle origins (the proximal attachment) and insertions (the distal attachment) were identified using comparative dissection data of humans and chimpanzees, assisted by some muscle scarring on the bones and also via the creation of muscle map diagrams:
Sensitivity analyses confirmed the efficacy of the muscle paths and this data was compared to that of a human to assess the recruitment of muscle groups during joint rotations (at this stage, just the moment arms! Check back soon for the next steps…). The moment arm results suggest that muscle groups had comparable leverage to that of a human and, for now, no functional differences can be extracted, although this is not a limitation of the approach, but rather because only moment arms have been included which only tell a part of the story. Next up – we need to be looking at the dynamics of motion to extrapolate any functional differences!
I had a LOT of fun creating these 3D muscle reconstructions and I cannot wait to replicate the approach for other hominins!! I hope you enjoy reading the paper and exploring the muscles* as much as I had fun creating the models.
*all 3D data and scene will be made fully open access upon publication. Hopefully such tools will assist future biomechanical studies of hominins and perhaps even aid evolutionary anatomical teachings.
The Walking Hominins 