https://www.eurekalert.org/news-releases/992054

A Cambridge University researcher has digitally
reconstructed the missing soft tissue of an early
human ancestor – or hominin – for the first time,
revealing a capability to stand as erect as we do
today.

Dr Ashleigh Wiseman has 3D-modelled the leg and
pelvis muscles of the hominin Australopithecus
afarensis using scans of ‘Lucy’: the famous fossil
specimen discovered in Ethiopia in the mid-1970s.
....
Wiseman was able to use recently published open
source data on the Lucy fossil to create a digital
model of the 3.2 million-year-old hominin’s lower
body muscle structure. The study is published in
the journal Royal Society Open Science.

The research recreated 36 muscles in each leg, most
of which were much larger in Lucy and occupied
greater space in the legs compared to modern humans.

For example, major muscles in Lucy’s calves and
thighs were over twice the size of those in modern
humans, as we have a much higher fat to muscle ratio.
Muscles made up 74% of the total mass in Lucy’s thigh,
compared to just 50% in humans.

Paleoanthropologists agree that Lucy was bipedal, but
disagree on how she walked. Some have argued that she
moved in a crouching waddle, similar to chimpanzees –
our common ancestor – when they walk on two legs.
Others believe that her movement was closer to our own
upright bipedalism.

Research in the last 20 years have seen a consensus
begin to emerge for fully erect walking, and Wiseman’s
work adds further weight to this. Lucy’s knee extensor
muscles, and the leverage they would allow, confirm an
ability to straighten the knee joints as much as a
healthy person can today.
....

The Royal Society Open Science paper links for this
don't work but the pre print is open access

https://www.biorxiv.org/content/10.1101/2022.11.24.517817v1.full.pdf
3D volumetric muscle reconstruction of the
Australopithecus afarensis pelvis and limb,
with estimations of limb leverage

Abstract
To understand how an extinct species may have moved,
we first need to reconstruct the missing soft tissues
of the skeleton which rarely preserve, with an
understanding of segmental volume and the muscular
composition within the body. The Australopithecus
afarensis specimen AL 288-1 is one of the most complete
hominin skeletons. Whilst it is generally accepted that
this species walked with an erect limb, the frequency
and efficiency of such movement is still debated. Here,
36 muscles of the pelvis and lower limb were
reconstructed in the specimen AL 288-1 using 3D
polygonal modelling which was guided by imaging scan
data and muscle scarring. Reconstructed muscle masses
and configurations guided biomechanical modelling of the
lower limb in comparison to a modern human. Muscle moment
arms were calculated and summed per muscle group.
Simulated error margins were computed using Monte Carlo
analyses. Results show that the moment arms of both
species were comparable, hinting towards similar limb
functionality. Moving forward, the polygonal muscle
modelling approach has demonstrated promise for
reconstructing the soft tissues of hominins and providing
information on muscle configuration and space filling.
This approach is recommended for future studies aiming
to model musculature in extinct taxa.

> https://www.eurekalert.org/news-releases/992054

Thanks a lot!
I sent this to the author:

:-) Thanks a lot for this very interesting & innovating article.
IMO it beautifully confirms our view that early hominids (Gorilla-Homo-Pan) were vertical aquarboreals in swamp forests:
they frequently waded bipedally & climbed arms overhead in the branches above the swamp, google "aquarboreal".
I my recent book p.299-300, I hypothesized this happened late-Miocene in the swamp forests of the then incipient Red Sea:
"De evolutie van de mens - waarom wij rechtop lopen en kunnen spreken" Acad..Uitg. Eburon 2022 Utrecht NL,
google "gondwanatalks verhaegen bonne".

_____

Three-dimensional volumetric muscle reconstruction of the Australopithecus afarensis pelvis and limb, with estimations of limb leverage
Ashleigh LA Wiseman 2023 doi org/10.1098/rsos.230356
To understand how an extinct species may have moved, we first need to reconstruct the missing soft tissues of the skeleton (which rarely preserve) with an understanding of segmental volume a muscular composition within the body. The Au.afarensis spm AL 288-1 is one of the most complete hominin skeletons.(hominid: Lucy was a fossil relative of Gorilla --mv)
Despite 40+ years of research, the frequency & efficiency of BP movement in this spm is still debated.
Here, 36 muscles of the pelvis & lower limb were reconstructed, using 3D polygonal modelling, guided by imaging scan data & muscle scarring.
Reconstructed muscle masses & configurations guided musculo-skeletal modelling of the lower limb vs a modern human.
Results:
the moment arms of both spp were comparable, hinting towards similar limb functionality.
Moving forward, the polygonal muscle modelling approach has demonstrated promise for
- reconstructing the soft tissues of hominins &
- providing information on muscle configuration & space filling.
This method demonstrates that volumetric reconstructions are required to know where
- space must be occupied by muscles &
- lines of action might not be feasible due to interference with another muscle.
This approach is effective for reconstructing muscle volumes in extinct hominins for which musculature is unknown.

_____

A Cambridge Univ.researcher has digitally reconstructed the missing soft tissue of an early human ancestor – or hominin – for the first time,
it reveals a capability to stand as erect as we do today.
(no human ancestor, of course: all hominids & probably eaven all Hominoidea had fully erect=vertical Miocene ancestors:
they spent a lot of time in swamp forests, wading bipedally + climbing arms overhead in the branches above the water (+- cf. Nasalis & Rhinopithecus in mangroves?).
Dr Ashleigh Wiseman has 3D-modelled the leg & pelvis muscles of the hominin Au.afarensis (better: Praeanthropus --mv) using scans of ‘Lucy’ (the famous fossil spm discovered in Ethiopia in the mid-1970s).
.... Wiseman (in Royal Society Open Science) was able to use recently published open source data on the Lucy fossil, to create a digital model of the 3..2-Ma hominin’s lower body muscle structure.
The research recreated 36 muscles in each leg: most were much larger in Lucy, and occupied greater space in the legs vs Hs, e.g.
major muscles in Lucy’s calves & thighs were over twice the size of Hs (we have a much higher fat/muscle ratio):
muscles made up 74 % of the total mass in Lucy’s thigh, vs 50 % in Hs.
PAs agree that Lucy was BP, but disagree on how she walked.
-Some have argued that she moved in a crouching waddle cf chimps (our common ancestor) when they walk on 2 legs.
-Others believe that her movement was closer to our own upright BPism.
Research in the last 20 years have seen a consensus begin to emerge for fully erect walking - Wiseman’s work adds further weight to this.
Lucy’s knee extensor muscles (+ the leverage they would allow) confirm an ability to straighten the knees as much as a healthy person can today. ...