Editing Bipedalism (section)

==Physiology==
Bipedal movement occurs in a number of ways and requires many mechanical and neurological adaptations. Some of these are described below.

===Biomechanics===
====Standing====
Energy-efficient means of standing bipedally involve constant adjustment of balance, and of course these must avoid [[feedback|overcorrection]]. The difficulties associated with simple standing in upright humans are highlighted by the greatly increased risk of falling present in the elderly, even with minimal reductions in control system effectiveness.

====Shoulder stability====
Shoulder stability would decrease with the evolution of bipedalism. Shoulder mobility would increase because the need for a stable shoulder is only present in arboreal habitats. Shoulder mobility would support suspensory locomotion behaviors which are present in human bipedalism. The forelimbs are freed from weight-bearing requirements, which makes the shoulder a place of evidence for the evolution of bipedalism.<ref>
{{Cite journal |last=Sylvester |first=Adam D. |year=2006 |title=Locomotor Coupling and the Origin of Hominin Bipedalism |journal=Journal of Theoretical Biology |volume=242 |issue=3 |pages=581–590 |doi=10.1016/j.jtbi.2006.04.016 |pmid=16782133|bibcode=2006JThBi.242..581S }}</ref>

====Walking====
[[File:Illu vertebral column.svg|thumb|128x128px|Profile view of the human spine]]
Unlike non-human apes that are able to practice bipedality such as ''[[Pan (genus)|Pan]]'' and ''[[Gorilla (genus)|Gorilla]]'', hominins have the ability to move bipedally without the utilization of a bent-hip-bent-knee (BHBK) [[Gait (human)|gait]], which requires the engagement of both the hip and the knee joints. This human ability to walk is made possible by the [[Vertebral column|spinal curvature]] humans have that non-human apes do not.<ref>{{Cite journal |last1=Lovejoy |first1=C. Owen |last2=McCollum |first2=Melanie A. |date=2010 |title=Spinopelvic pathways to bipedality: why no hominids ever relied on a bent-hip-bent-knee gait |journal=Philosophical Transactions: Biological Sciences |volume=365 |issue=1556 |pages=3289–3299 |doi=10.1098/rstb.2010.0112 |jstor=20778968 |pmid=20855303 |pmc=2981964 |issn=0962-8436}}</ref> Rather, walking is characterized by an "inverted pendulum" movement in which the [[center of gravity]] vaults over a stiff leg with each step.<ref name="books.google.com">{{Cite book |url=https://books.google.com/books?id=1sz5501URh0C&q=macmahon+muscles |title=Muscles, reflexes, and locomotion| isbn=978-0-691-02376-2 |last=McMahon |first=Thomas A. |year=1984|publisher=Princeton University Press }}</ref> [[Force plate]]s can be used to quantify the whole-body kinetic & potential energy, with walking displaying an out-of-phase relationship indicating exchange between the two.<ref name="books.google.com" /> This model applies to all walking organisms regardless of the number of legs, and thus bipedal locomotion does not differ in terms of whole-body kinetics.<ref name="ReferenceA">{{Cite book |url=https://books.google.com/books?id=yMaN9pk8QJAC |title=A moving topic: control and dynamics of animal locomotion |isbn=978-0-19-850022-3 |last1=Biewener |first1=Andrew A. |year=2003 |pmid=20410030 |last2=Daniel |first2=T. |volume=6 | issue=3 |pages=387–8 |doi=10.1098/rsbl.2010.0294 |pmc=2880073 |journal=Biology Letters}}</ref>

In humans, walking is composed of several separate processes:<ref name="books.google.com"/>
*Vaulting over a stiff stance leg
*Passive ballistic movement of the swing leg
*A short 'push' from the ankle prior to toe-off, propelling the swing leg
*Rotation of the hips about the axis of the spine, to increase stride length
*Rotation of the hips about the horizontal axis to improve balance during stance

====Running====
[[File:Running 3.jpg|thumb|192x192px|A group of children racing]]
Early hominins underwent post-cranial changes in order to better adapt to bipedality, especially running. One of these changes is having longer hindlimbs proportional to the forelimbs and their effects. As previously mentioned, longer hindlimbs assist in [[thermoregulation]] by reducing the total surface area exposed to direct sunlight while simultaneously allowing for more space for cooling winds. Additionally, having longer limbs is more energy-efficient, since longer limbs mean that overall muscle strain is lessened. Better energy efficiency, in turn, means higher [[endurance]], particularly when running long distances.<ref name=":13">{{Cite journal |last=Pontzer |first=Herman |date=2012 |title=Ecological Energetics in Early Homo |url=https://www.jstor.org/stable/10.1086/667402 |journal=Current Anthropology |volume=53 |issue=S6 |pages=S346–S358 |doi=10.1086/667402 |jstor=10.1086/667402 |s2cid=31461168 |issn=0011-3204}}</ref>

Running is characterized by a spring-mass movement.<ref name="books.google.com" /> Kinetic and potential energy are in phase, and the energy is stored & released from a spring-like limb during foot contact,<ref name="books.google.com" /> achieved by the [[plantar arch]] and the [[Achilles tendon]] in the foot and leg, respectively.<ref name=":13"/> Again, the whole-body kinetics are similar to animals with more limbs.<ref name="ReferenceA" />

===Musculature===
Bipedalism requires strong leg muscles, particularly in the thighs. Contrast in [[domestication|domesticated]] [[poultry]] the well muscled legs, against the small and bony wings. Likewise in humans, the [[quadriceps]] and [[hamstring]] muscles of the thigh are both so crucial to bipedal activities that each alone is much larger than the well-developed biceps of the arms. In addition to the leg muscles, the increased size of the [[gluteus maximus]] in humans is an important adaptation as it provides support and stability to the trunk and lessens the amount of stress on the joints when running.<ref name=":13"/>

===Respiration===
[[File:Human respiratory system pedagogical fr.svg|thumb|166x166px|The human respiratory system, encased by the rib cage]]
[[Quadrupedalism|Quadrupeds]], have more restrictive breathing [[Respiration (physiology)|respire]] while moving than do bipedal humans.<ref name=":02">{{Cite book |last=DeSilva |first=Jeremy |title=First Steps: How Upright Walking Made Us Human |publisher=Harper Collins |year=2021 |location=New York}}</ref> "Quadrupedal species normally synchronize the locomotor and respiratory cycles at a constant ratio of 1:1 (strides per breath) in both the trot and gallop. Human runners differ from quadrupeds in that while running they employ several phase-locked patterns (4:1, 3:1, 2:1, 1:1, 5:2, and 3:2), although a 2:1 coupling ratio appears to be favored. Even though the evolution of bipedal gait has reduced the mechanical constraints on respiration in man, thereby permitting greater flexibility in breathing pattern, it has seemingly not eliminated the need for the synchronization of respiration and body motion during sustained running."<ref>{{cite journal |last1=Bramble |first1=Dennis |title=Running and Breathing in Mammals |journal=Science |date=1983 |volume=219 |issue=4582 |pages=251–256 |doi=10.1126/science.6849136 |pmid=6849136 |bibcode=1983Sci...219..251B |url=https://www.science.org/doi/10.1126/science.6849136 |access-date=28 August 2022}}</ref>

Respiration through bipedality means that there is better breath control in bipeds, which can be associated with brain growth. The modern brain utilizes approximately 20% of energy input gained through breathing and eating, as opposed to species like chimpanzees who use up twice as much energy as humans for the same amount of movement. This excess energy, leading to brain growth, also leads to the development of [[Linguistics|verbal communication]]. This is because breath control means that the muscles associated with breathing can be manipulated into creating sounds. This means that the onset of bipedality, leading to more efficient breathing, may be related to the origin of verbal language.<ref name=":02"/>