Chimpanzee strength vs human strength
Cris Waller
A friend and I have been trying to find material on the anatomical
reasons that chimpanzees are so much stronger than humans of
comparable weight. The only references I have found mention the great
strength of chimps but not why they are so strong. Is the relative
weakness of humans due to differences in muscle leverage caused by
adaptations to bipedalism, or is there a qualitative difference in
chimpanzee muscular fibers? Also, the only comparative references I
have found are to upper-body strength. Is the great upper-body
strength of chimps an adaptation to brachiation? Is the lower-body
strength of chimps also greater, or do we bipedal humans have the
advantage?
Cris Waller
Cr...@ix.netcom.com
E-mail may be posted as I see fit!
Ian A. York
In article <5arfea$r...@nntp1.u.washington.edu>,
Cris Waller <Cr...@ix.netcom.com> wrote:
>A friend and I have been trying to find material on the anatomical
>reasons that chimpanzees are so much stronger than humans of
I'm always happy to leap into subjects about which I have little
knowledge, especially when I can do so by reusing old posts as opposed to
actually thinking.
Subject: Re: Humans vs Horses (was Re: Niven)
From: iay...@panix.com (Ian A. York)
Date: 1996/01/31
Message-Id: <4ep50o$m...@panix.com>
Newsgroups: rec.arts.sf.science,rec.arts.sf.written
Given that, here's my educated guess: I don't think there's any need to
postulate 'more efficient' chimpanzee muscles. Instead, it's much more
likely that chimpanzees gain their greater strength through leverage
effects and sheer muscle bulk. Chimpanzees have large muscle attachment
surfaces on their long bones than do humans (I'm basing this on a column
by Cecil Adams some time ago) allowing relatively larger muscle mass than
in humans. Moreover, the attachment is positioned somewhat differently,
providing more leverage during contraction. I base this not only on
half-remembered ape anatomy, but on this article:
Hunt KD.
Mechanical implications of chimpanzee positional behavior.
American Journal of Physical Anthropology. 86(4):521-36, 1991
"...Some elements of the chimpanzee anatomy, including an abductible
humerus, a broad thorax, a cone-shaped torso, and a long, narrow scapula,
are hypothesized to be a coadapted functional complex that reduces muscle
action and structural fatigue during arm-hanging. Large muscles that
retract the humerus (latissimus dorsi and probably sternocostal pectoralis
major and posterior deltoid) and flex the elbow (biceps brachii, probably
brachialis and brachioradialis) are argued to be adaptations to vertical
climbing alone. A large ulnar excursion of the manus and long, curved
metacarpals and phalanges are interpreted as adaptations to gripping
vertical weight-bearing structures during vertical climbing and
arm-hanging. A short torso, an iliac origin of the latissimus dorsi, and
large muscles for arm-raising (caudal serratus, teres minor, cranial
trapezius, and probably anterior deltoid and clavicular pectoralis major)
are interpreted as adaptations to both climbing and unimanual suspension."
I interpret this as saying essentially that the chimpanzee depnds more on
climbing than do humans, meaning that it needs to be able to support its
body weight from its arms more often and more easily, and that bone
structure is adapted to make this more efficient through bone shape and
muscle attachment sites.
This brings up another point, which has already been raised by others,
with regard to gene therapy. Let's assume that chimpanzees do have
stronger muscles and that this could be spliced into a human. What would
happen? I'd expect that she'd promptly rip out the muscle attachments,
rupturing tendons and possible fracturing bone.
In other words, you often can't make a single change. If you want a human
to be as proportionately strong as a spider, no, wait, sorry, a
chimpanzee, you need to alter the rest of the anatomy to match; you'd need
to alter the leverage, increase the size of the muscle attachment
protuberances, and in general you'd end up with someone who looked pretty
Neanderthal (note that it's widely suggested that Neanderthals were
stronger than modern humans, based on the size and (I believe) positioning
of the muscle attachment sites. Along with this, though, you probably
alter speed of movement and flexibility (or at the very least, alter the
flexibility). Not impossible, given the basic premise, but you'd wonder
if it's worth the trouble; give me a tractor with a front-end loader,
after all, and I'm stronger than any chimpanzee.
Subject: Re: Humans vs Horses (was Re: Niven)
From: throopw%sheol...@dg-rtp.dg.com (Wayne Throop)
Date: 1996/02/01
Message-Id: <4eraav$2...@aurns1.aur.alcatel.com>
Newsgroups: rec.arts.sf.science,rec.arts.sf.written
:: Graydon <saun...@qlink.queensu.ca>
:: A bit of better leverage (proportionally wider muscle attachement
:: shelves on the large joints) but it's mostly stronger muscle fibers.
: From: iay...@panix.com (Ian A. York)
: Have you a reference for this? I'm willing to accept that chimps have
: lots of muscle, proportionately, but actin/myosin is actin/myosin,
: right? So far as I know (and so far as I can find in Medline) there's
: no evidence that chimps' muscle fibers are stronger than humans.
: I think it's all leverage and muscle mass.
The strength of muscle fiber varies only 20 to 30 percent among
vertibrates[1]. A given muscle can vary much more than that in strength
per gross cross section[2], but muscles that are penniform in chimps
are also penniform in humans.
Therefore, I agree with Ian: it's all in leverage and muscle...
well, not "mass" (though it is correlated somewhat); gross cross section.
: Incidentally, wider muscle attachment shelves mainly means that
: there's more muscle to attach; as far as the leverage goes, it may or
: may not be better, depending on where (relative to the joint) that
: muscle attachment site is located.
The muscle attachment "size" (area of the tendon/bone joint) is
essentially related to how much force the muscle applies, which in turn
(other things being equal) is proportional to the amount of muscle
attached there. But in the general case, remember the
penniform/fusiform *can* make other things not be equal,
(though IMHO it isn't a factor in the chimp/human case).
Note that the extra strength per gross muscle cross section is
gotten at the expense of range of motion. Looking closely at
why the packing is effective, we see that it's also a matter
of "leverage", and you can see why the tradeoff between force
and range of motion occurs, just like it does in a lever or
pully system or whatnot; in the muscle fiber packing deal, though,
this is all hidden in networks of connective tissues that give
the structure to the muscle fibers, and from superficial appearance,
no "levers" or "pulleys" are visible.
--
Wayne Throop throopw%sheol...@dg-rtp.dg.com
thr...@aur.alcatel.com
--
[1] Knut Nielson, Scaling, Why is Animal size So Important,
Cambridge Univ Press, 1984, page 163
It appears that the maximum force or stress that can be exerted by
any muscle is inherent in the structure of the muscle filaments.
The maximum force is roughly 3 to 4 kgf/cm2 cross section of muscle
(300 - 400 kN/m2). This force is body-size independent and is the
same for mouse and elephant muscle. The reason for this uniformity
is that the dimensions of the thick and thin muscle filaments, and
also the number of cross-bridges between them are the same. In fact
the structure of mouse muscle and elephant muscle is so similar that
a microscopist would have difficulty identifying them except for a
larger number of mitrochondria in the smaller animal. This
uniformity in maximum force holds not only for higher vertebrates,
but for many other organisms, including at least some, but not all
invertebrates.
[2] Adrian & Cooper, "Biomechanics of Human Movement"
Benchmark press, 1989, page 78
There are two main types of arrangement of muscle fibers: fusiform
and penniform. In the fusiform arrangement the muscle fibers are
distributed in longitudinal fashion in the muscle, allowing for
maximal range of contraction. [...] The large range of contraction
is acheived at the sacrifice of strength. [...]
The penniform arrangement of muscle fibers is similar to that of the
barbs of a feather. A tendon is in the position of the quill of
the feature. Variations in the penniform arrangement include
demipennate, unipennate, bipennate, multipennate, and circumpennate.
[...]
The diagonal pulling position of the penniform muscles allows a
greater number of fibers to act in a given mass, but there is a loss
in the range of motion because these fibers are shorter. [...] The
great numbers of fibers available for action in the penniform
muscles allows only a limited shortening of the muscle, but
provides great strength.
--
Ian York (iay...@panix.com) <http://www.panix.com/~iayork/>
"-but as he was a York, I am rather inclined to suppose him a
very respectable Man." -Jane Austen, The History of England