Evolution of bipedal walking

Define bipedal walking

Evident in earliest hominins 4.5-7mya

Marks divergence of human lineage from other apes

Why did bipedal walking evolve

Improved predator avoidance (looking over tall grass)

Hands free to carry objects

Thermoregulation - decreased SA exposed to sun

Reduced locomotor costs

Greater avail to be flexible across branches

How was chimpanzee and human walk compared through COL

Oxygen consumption was measured to identify energy used to do an activity during a treadmill exercise.

Why was the chimp experiment conducted

Measure energy and determine the forces generated, volumes of muscles activated and the foot-hand contact time of each step. mass specific COL factor of V of muscle activated per time during each step to generate required ground force.

How was the forces generated measured

Force plate and video was used to measure the contact time of foot to ground and how much area/volume of muscle mass being used

Why was respiratory masks used

To prevent oxygen exchange with the environment, measure proper oxygen consumption and the cost of locomotion ml of O2/kgm

What was the force plate used for

Used to measure force (ground reaction force) of each step How

How was video used in the experiment

Analyze limb movement and foot/hand contact time. Joint centers of forelimbs/hindlimbs marked with paint to measure flexion and extension of limbs during movement

What did the results of the tests state

Bipedall walking in chimps are ~10% more expensive than quadrupedal

High variability among the chimps (females bipedal costs similar/less than quadrupedal)

Human walking 75% less expensive than chimp locomotion

Result of experiment compared to other animals

Mass-specific COL higher than expected for chimps

Human walking is less expensive than expected

Effective walking is related to design of body and position of walk

What is the result of the muscle volume for humans

Human bipedal have smaller muscle volume activated per unit of ground force generated (using painted dot)

What is the result of the contact time of human bipedal

Longer tc at a given speed than a bipedal chimp due to longer legs, lower V/tc and lower locomotor costs

Chimps generate more force at faster rates

What joints are responsible for steps in chimps

Chimps walk with flexed hip and kneww

Bent knee/hip causes center of mass to be anterior to hip joint

Short limbs and posture req large movement/force to generate by hip extensors at knee

Large torque generated by hip flexion

Which joints responsible for human steps

Upright posture enables force vector to be near hip and knee joints, the ankle muscle has the largest torque to generate force

What are the differences between Vmusc/tc

Vmusc/tc bw gaits and species is very similar to differences in COL

Greater force required to be generated at a faster rate in chimps is responsible for greater COL

Why chimps have to walk with flexed hip and knee

Ischium (how far ur legs can extend) oriented in distal position which prevents hamstring from fully extending hip

How is the human ischium oriented

Dorsally which allows femur to fully extend by hamstring (standing up)