Re: Endurance running facts




Op 08-03-2008 00:43, in artikel
5df16648-0ddd-4b89-9165-240d21b70af1@xxxxxxxxxxxxxxxxxxxxxxxxxxx, Lee Olsen
<paleocity@xxxxxxxxxxx> schreef:

On Mar 7, 2:55 pm, Marc Verhaegen <m_verhae...@xxxxxxxxx> wrote:
The effect of pelvic dimorphism on locomotor cost:
are women less efficient than men?

http://tinyurl.com/2n8y2n

Carl Zimmer Science 2004

"It may come as a surprise to hear that humans excel in running.

Only in the eyes of prejudiced Savanna Fantasts.

An unbiased view:

Bramble and Lieberman (2004), in a much-discussed review article in Nature,
cite a number of derived Homo features they claim to be adaptations for more
efficient endurance running in arid, open habitats. However, while some of
these supposedly ?cursorial adaptations¹ appear first in the fossil record
in H. habilis, others appear first in H. erectus, and others still in H.
sapiens, suggesting a much more complex story than proposed by Bramble and
Lieberman. Their conclusions are reached without systematic comparisons with
other animals (including endurance runners) and with general comparisons
restricted to fossil hominids and Pan. Since convergent traits are strong
indicators of evolution in similar environments (Bender 1999), a systematic
comparison with a broad range of animals with a variety of locomotor
strategies would have been more informative.
In addition, discussion of possible locomotion styles is restricted to
walking and running, with no consideration at all given to activities such
as wading, swimming or underwater foraging, yet humans are regular waders
and more accomplished swimmers and divers than other primates. Most of the
list¹s ?adaptations¹ for walking could just as easily be explained by
wading. One of the frequent ?explanations¹ in the list is ³stress
reduction², a reference to the vertical posture of humans with the weight
resting on two legs. But this says nothing about endurance running, with
standing, wading, walking or short distance running all using a similar
posture, and therefore all requiring stress reduction. Other ?explanations¹
include ³counter rotation², ³thermoregulation² and ³stabilization², but no
comparative data to corroborate these interpretations are provided. In other
words, their ?explanations¹ are ad hoc suppositions, applied to one example
(human ancestors) without any consideration as to whether these supposed
adaptations are seen in other animals, which means their ?explanations¹ are
statistically invalid (n=1). Long legs, and possibly shortened forearms,
could be seen as running adaptations, but these are just as typical of
wading and swimming species compared with runners (Hildebrand 1974: 584,
Bender 1999).
In a waterside scenario, wading and swimming would be preadaptative to the
humanlike ?vertical¹ locomotion that Bramble and Lieberman believe to be a
direct adaptation to endurance running. In our view, frequent terrestrial
locomotion, whether for walking or for (relatively slow) running, was more
recent (H. sapiens) and could not be derived directly from an ancestral
locomotion in forests, whether on the ground or in the branches, because in
that case a more baboon-like locomotion would be expected (the ?baboon
paradox¹).
Most of Bramble and Lieberman¹s ?adaptations¹ are not what we would expect
in a cursorial (running) animal. For example, their list includes ³enlarged
posterior and anterior semicircular canals², but there are no comparisons
with, for instance, giraffes (heads high above the ground), gibbons (fast
and versatile locomotion), kangaroos (cursorial bipeds), or swimming or
diving species. It is conceivable in fact that the frequent change of
posture seen when diving for seafood (descending and ascending) required a
different labyrinth structure, and that the H. erectus labyrinth was adapted
to terrestrial walking and running as well as to wading, swimming and diving
locomotions.
There is no indication that an ³expanded venous circulation of neurocranium²
had anything to do with thermoregulation, but there is long-standing
evidence of expanded venous networks in diving species (Slijper 1936).
More balanced heads and short snouts are not seen in cursorial species,
whether bi- or quadruped, and low shoulders are compatible with wading and
diving.
What Bramble and Lieberman refer to as ³narrow body form², ³narrow thorax²
and ³narrow pelvis² is not clear to us: compared to most primates, humans
have a relatively very broad thorax and pelvis (laterolaterally), and this
was even more so in the case of australopithecines. In our opinion, the
combination of ?flared¹ iliac blades and very long and relatively horizontal
femoral necks as seen in H. erectus indicates well-developed ad- and
abduction, which is obviously not an adaptation for running, but would not
be unexpected and indeed would be advantageous for a species that had to
regularly wade, tread water, swim or climb. In H. sapiens the pelvis
(bi-iliac diameter) did become narrower and the femoral necks shorter and
more vertical, and we agree with Bramble and Lieberman that this could be
related to more frequent terrestrial locomotion.
Plantar arches, enlarged tubera calcanei, close-packed calcaneo-cuboid
joints and short toes are not seen in cursorials, whether bi- or quadruped,
to the contrary: running species are typically unguli- or digiti-, not
plantigrade and typically have elongated toes.
In conclusion, there is no evidence that any of the features described by
Bramble and Lieberman (2004) are typical either of savannah dwellers or
frequently running animals, whether slow or fast. Until the features are
considered in the context of swimming and wading as well as terrestrial
movement, their interpretations should be considered with extreme caution.
As it is, there is no obvious reason why any of the features cited could not
have been of advantage in a littoral environment. We do not deny that humans
today are adapted to terrestrial locomotion, but in our opinion the peculiar
human anatomy is not directly derivable from a typical primate ancestor who
moved from closed to more open, arid habitats.
At least two conspicuous anatomical features of H. erectus are notably not
included in the list of features cited by Bramble and Lieberman (2004).

1) H. erectus typically has a more robust, and therefore heavier, skeleton
than all other ­ fossil and extant ­ primates, including H. sapiens and the
other apes. One of its defining characteristics is the shape and size of the
femoral bone, which shows cortex thickening and densening (pachyostosis) and
a narrow medullar cavity (medullary stenosis). The cranial bones, especially
the posterior part (the occiput), are also notably thicker than in other
primates including H. sapiens. Unusually heavy bones would be a disadvantage
for a species relying on endurance running, and are not seen in running
mammals such as dogs or horses, whereas for a species collecting sessile
food from the water¹s edge, including underwater foraging, they could have
been a significant advantage. Human divers such as the Ama of Korea
frequently use weights to help them descend (Hong and Rahn 1967).
Slow-diving mammals for sessile foods typically have medullary stenosis and
pachyostosis to a much higher degree than in H. erectus (walruses, dugongs
and fossil littoral species such as Kolponomos, Odobenocetops and some
Thalassocnus species), while fast-diving mammals for mobile prey have
light-weight bones (dolphins and sealions).

2) H. erectus had less basicranial flexion than H. sapiens, meaning that
the eyes would have been more naturally oriented towards the sky if they
were standing with an upright posture (remembering that we do not know for
certain which posture H. erectus may have preferred when on dry land),
rather than directed more towards the horizon, as is the case when H.
sapiens stands with an upright posture. This would be a disadvantage for a
species relying on endurance running because, among other things, more
energy would be needed to look at where the feet were making contact with
the ground. In a diving position, as well as in a more procumbent body
position while wading for food, for example, the less flexed cranial base
would have resulted in the eyes being more naturally oriented in the
direction the individual was moving (i.e., in the case of swimming and
diving, head first through the water). We are not aware of any models which
suggest early Homo ran with a bent hip posture, but we do note that human
sprinters generally run with the body leaning forward.

Within many contemporary Homo sapiens populations there are individuals who
are capable of long distance running, but compared to typical savannah
species, humans are slow and inefficient (Figure 4). Moreover, recent
research suggests that endurance training in athletes sometimes causes
cardial arrhythmias and sudden death (Ector et al. 2007). Even Bramble and
Lieberman (2004) admit that ³humans are mediocre runners in several
respects² and ³running is more costly for humans than for most other
mammals². And since H. erectus generally had heavier bones than H sapiens,
longer femoral necks and shorter tibiae, it must have been even less
efficient in running than extant H. sapiens.

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