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Overloaded low back and lower extremity joints during bipedal locomotion cause knee and back pain later in life. In females, to walk upright may be difficult and painful to carry as well as deliver a baby with a large brain.

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Dinesh ^club

. . . Ellen Davis Kelley, a physical education professor at the University of Oklahoma, neatly summarized the physiological challenge of human posture in teaching handbook:

Posture is a distinct problem to humans because the skeleton is fundamentally unstable in the upright position. A four or even three legged chair or stool can be quite stable. But who ever heard of a two legged piece of furniture? The two legged human body presents a continuous problem in maintaining balance, a problem augmented because the feet are very small base of support for a towering superstructure. And as though this were not a problem enough, the trunk, head, and arms are supported from the hips upward by a one-legged arrangement of the spine.

The purpose of the chair is to provide respite from this precarious balancing act. But the instability that Kelly described is, if anything, compounded when one sits down. The weight of the body is concentrated on the ischial tuberosities, or sitting bones, at the base of the pelvis. These bones, which resemble the rockets of a of a rocking chair, provide support only laterally and allow the body to rock back and forth in the other direction. A chair back provides the support that allows the muscles to relax, but a too-vertical backrest causes the sitter to slump, while simply angling the seatback creates an unnatural backward leaning posture. . . Page 54

4 weeks ago. Edited 4 weeks ago.

Dinesh ^club

askananthropologist.asu.edu/ups-and-downs-two-legged-walking

The ups and downs of two-legged walking
Bipedal locomotion, or walking on two legs, has many benefits:

1) It frees the hands for carrying tools and infants
2) It improves our ability to cool-off
3) It allowed our ancestors to see over the tall grasses
4) It allows us to travel long distances

However, these benefits of walking on two legs may make other activities more difficult.
One benefit of bipedal locomotion is that it frees the hands for carrying tools. Long before we used our hands to text on phones while walking, our hominin ancestors used their free hands to carry tools and even infants (as human babies cannot cling to their mothers).
However, the physical changes required for bipedal walking have negative effects on our bodies. For example, the curvature of the lower spine, or lordosis, makes it easier to balance on two legs. However, pain is frequently experienced when the back curves too much due to weakened muscles or illness. Lower back pain is very common. Perhaps your mom or grandpa suffers from back pain.

We have very long legs with muscles ideally oriented for bipedal locomotion. Our big toe, or hallux, is positioned next to our other toes. This position is ideal for toeing off (pushing off with the toe) from the ground during walking. However, it also makes our ability to climb in trees clumsy and less efficient. Our big toe cannot grasp the branches as well as other primates. Being able to climb trees is important for both feeding on fruit and escaping predators.
It may seem odd that adaptations that make us better able to walk would make other activities, like climbing trees, more difficult. But it is important to understand that evolution is often a compromise between enhancing some traits while diminishing others.

4 weeks ago. Edited 4 weeks ago.

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