Summary - lecture, tutorial work - topic 2 locomotion PDF

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Topic 2 Locomotion ...

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Locomotion The Reasons for Our Locomotion 4 Elements of Being a Good Biped Habitual: We are anatomically committed to bipedalism, we have sacrificed other options of locomotion for bipedalism Upright: There are different was of being a biped, and our way is to be upright Bipedal: We only use two limbs, the hindlimbs - Hindlimbs are the same length as the forelimbs in quadrupeds, shorter in knuckle walkers, and longer in bipeds, which enables us to stride efficiently Striding: The longer the stride, the more efficient it is Advantages of Being a Biped  Bipedalism required major structural adaptations, so there must have been different selective pressures during the evolution of bipedal walking and endurance running - WRONG: Big brains developed due to took use and making and lead to bipedalism – but bipedalism predates the increase in the size of the brain. (Eg. Bipedal Lucy) - LESS WRONG BUT NOT LIKELY: Adaption to a wading life, however swimming doesn’t come naturally which endurance running does, also other not-bipedal animals wade - LESS WRONG BUT NOT LIKELY: To threaten and kill, however 4 legged animals can be more powerful and scary - LESS WRONG BUT NOT LIKELY: Sexual display, however bonobos are more sexually aware than us but aren’t bipedal - LESS WRONG BUT NOT LIKELY: Peering over grass, however meerkat does this but isn’t bipedal - LESS WRONG BUT NOT LIKELY: Carrying things, MAYBE GOOD as chimps walk bipedal when they carry stuff - GOOD: Thermoregulation is strong selective pressure for endurance running, less so for walking. Bipedal locomotion helps animals living in warm climates (which is where most of our evolution happened) by; o Reducing the amount of sunlight that falls on the body o Increasing the animals exposure to air movements o Immersing it in lower temperature air - VERYGOOD:Ene r gyEffic i e nc y–Bi pe da ll o c o mo t i o ni s e ffic i e n ti nhe a tr e g ul a t i ona n dwa t e rc o ns e r v a t i on o Ea c hmo l e c u l eofg l uc o s eme t a bol i z e dt oyi e l de n e r gy f ora c t i v i t ya l s og e ne r a t e swa s t ehe a ta n dus e swa t e r( a s d oe st h ea c t i v i t yi nt hi n g sl i k es we a t ) (Calories/hr) (KJ) o Sogr e a t e re ne r gye ffic i e nc yr e qu i r e smi n i ma l i s a t i o nof Sleeping 65 (272) wa s t ehe a ta n dc o ns e r v a t i onofwa t e r o En e r gye xpe n di t u r ef orhu ma ns t a ndi n ga ndwa l ki n gi sn o t Lying still 90 (377) t h a tmu c hgr e a t e rt h a nf orl y i n gs t i l l Standing relaxed 100 (418) o Huma nwa l ki n gi s7 5% l e s sc os t l yt ha nbo t hqu a dr upe d a l At attention 115 (481) a n dbi p e da lwa l ki n gi nc hi mps

Level walking 5 km/hr 350 1100

Habitat Change and Facultative Bipedalism Climbing stairs - Late Miocene climates started drying (c. 7.2 – 5.3 mya) - Fruiting trees, which they had been relying on before, become separated by open country - Some hominids were no longer able to make a living in continuous forest, as hominids were quite small so the larger would get more of the of the food - Once you spend more than 60-70% of your time on the ground it is energetically more efficient to be a biped than maintain arboreal features – A longer stride and balance on 2 limbs benefits efficient walking over flat ground (chimps with longer hindlimbs walking bipedally show increased energy efficiency over those with shorter hind - As the predictability of food decreased, and becomes more patchy, it began to select for larger brains, as you could remember where the food is. As brains are very energy costly, this selected for energy efficient bipedal walking

(1464) (4602)

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ALTERNATIVE: Scrambling Man – Tectonic activity created rough topography in East and South Africa. An upright stance with long hindlimbs, short forelimbs and a rigid foot structure, longer stride and balance on 2 limbs benefits scrambling over rough terrain. Also rough terrain helps avoid predation a little bit.

Running  What are advantages of walking and standing, cause a serious cost to running. Humans are relatively unstable and slow at SPRINTING - When walking we use our legs like inverted pendulums which is relatively stable and keeps a rhythm - When running we use our legs like springs – the mass spring gait - Running is less stable than walking, so mechanism have evolved to help stabilise us when we are running  Anatomical Adaptions for Endurance Running 1. Nuchal ligament and higher connection between pectoral girdle with back and head: a. Stabilises the head which is decoupled from the shoulders b. Leaves a small ridge – seen in Homo but not seen in Austrilopithecines and Pan (seen from homo ergaster onwards) c. High connection in pectoral girdle is unnecessary in walking alone 2. Greater limb length of hindlimbs relative to body mass in Homo compared to Australopithecines – so more stability between lower limbs and feet 3. Greater joint surfaces in Homo a. Impact force on body much greater (3-4 times more) in endurance running relative to walking 4. Appearance of full plantar arch and greater Achilles tendon stretch in Homo 5. Shorter toes in Homo 6. Greater gluteal (bum) muscles and attachment areas on iliac spine in Homo 7. Larger semicircular canal in ear and better reflexes between eye and ear for stabilising images when running on Homo  Importance of endurance running - For endurance running speeds the metabolic cost of transport is essentially flat (until you get to a sprint) compared to the U-shaped COT curves for walking. The only animal similar to us in this respect is the kangaroo. - Humans are unusual in being able to sustain long distance even in heat and into advanced age - Human endurance speeds lie above the trot/gallop transition of many cursorial animals (dogs, ponies, even horses ect) - Homo ergaster – possible the first true runner, as they have poor quality hair covering and were sweaty.

The Mechanics of Bipedality 1. Bringing the supports under the body o Bringing the feet under the centre of mass. This is done by; o Narrowing of the pelvis, seen through the smaller distance between the femoral heads in the acetabula  Causes the Obstetric Dilemma though – which was a problem once brains started to increase in size  Females: No extra cost to walking BUT for running

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 Slower at running (9.1% difference maximum velocity)  11.6% shorter stride length when running  Greater energy cost of running Femoral Inclination: Enables greater efficiency of the hip abductors and balance on one limb

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The angle of inclination (proximal end of femur) The angle of femoral anteversion (proximal end of femur)

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Bicondylar angle (distal femur)  The medial condyle on the distal femur is deeper than the lateral and when placed on a flat surface the femur creates an angle of 8 to 14 degrees to the perpendicular (this is the bicondylar angle).  The size of the femoral condyles are unequal due to the femur sloping inwards at the knee. So the medial condyle is larger as the force acts through it more than the outer

2. Arranging the mass of the body so that the line of gravity passes through the support base o As the body mass is balances, less muscle action required to maintain posture and balance. The less muscle action needed, the more energy efficient. o The chimp must squat to keep its feet in the line of gravity, as the line of gravity falls well infront of the hip joints. o Humans however, have developed a longer and more flexible spine which bends backwards over the hipjoint, and the compensatory thoracic and cervival curvatures that follow o The vertebrae are slightly curved with allows the spine to curve o Consequence of having the whole line of weight over the body’s supports o A larger flatter articulation between the tibia and the tarsal bones o Ad duc t e dHa l l ux : Bi gt o emo v e da r o undt h ef r ont–i ti s l e s se ffic i e n tbu ti t a c t sa sab e t t e rs up por tb a s e o Sp r un ga r c h e soft hef oo t ; o Thea r c he sa r ema i nt a i n e db yt hes ha peoft hebo ne s ,t hemu s c l e t e n do nsa n dt hel i g a me n t s . o Whe ny ouwa l k,ha l foft hee ne r gyi sr e c o v e r e df r omt hel i g a me n t s a n dt e nd onswh e nt he yr e c oi l , a l s of r omt h emu s c l es ho r t e n i n g . Thi sme a nsi t ma k e si tmo r ee ffic i e n t .Oft h et o t a le ne r gys pe nt , h a l fi sr e c o v e r e d.  Australopithecus afarensis had adapted big toe 3. Reducing protrusions away from the line of gravity

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From our ancestors the climbers or vertical clingers and leapers we developed; Antero-posteriorly flattened thorax, very mobile laterally facing shoulders, and shoulders on the back Thorax and arms; o Chest is shallow and long, which is different to others which are deep and long. o Dorsal scapula (join to neck) as opposed to a lateral scapula in chimps.  Human neonate has a much deeper chest Head; o Orthognathic as possible, to limit the weight infront of the support base o Central foramen magnum, to keep articulated with the vertical spine, to keep balance – this means less muscles are needed to keep the head balanced.

o 4. Lowering the centre of gravity o A larger proportion of the weight is held lower, than in gorillas o There is a relative increase in the lower limb length from birth to adult which; o Improves stability in adults and means its less muscle work to balance

Chimps head & trunk = 66.5% arms = 15.5% lower limbs = 18.0% Humans head & trunk = 58.6% arms = 9.4% lower limbs = 32.0% o  Doing each of the above in a way that minimises muscle action because muscle action uses energy

Walking The Cycle - Stance phase: 60% o From heal strike, to full foot, to heal lift and finally toe lift - Swing phase: 40% Achieving Stride 1. Extending limb behind axis of the hip joint  This is effected by the shape of the pelvis o The attachment of gluteus maximus is extended onto the sacrum o The posterior portion of the gluteus maximus can extend limb behind plane of the hip joint  Hyperextension (this is very original) o HOWEVER, this means the origin of the hamstring lies nearer to the line of the hip joint with rotation of the pelvis 2. Minimising vertical and lateral displacements of the centre of gravity o The abductors (away from the body): The abductor action of the lesser gluteal muscles (medius and minimus) on the support limb is the key to efficient human striding. They bring the trunk into a position of balance over the single support limb. The lesser gluteals are no longer extensors. o The abductor muscles tilt the pelvis over the single support foot  If someone has a problem with their abductors: Weight substituting by tilting the thorax over the support foot. o The mechanical efficiency of the abductors is improved whilst keeping the pelvis (and support base) narrow by the outward flaring and curving of the iliac blades  Puts abductors over the single support base. This is present in Lucy’s pelvis too, 1. Footfalls on a single track

This is achieved by; o Decreasing the distance between the hips o Femoral Inclination o Rotation of the pelvis through passive action of the foot bones at heel strike (restores energy)  Adductors/stabalises - Depending on the stage of the cycle; o Extension and deceleration of the hip extension o Flexion and decelerating hip flexion o Decelerating hip abduction o

Movement - Flexion: Movement in the sagittal plane towards the ventral surface of the body – usually decreases the joint angle - Extension: Movement in the sagittal plane towards the dorsal surface – usually increases the joint angle - Hyperextension: Movement in the sagittal plane towards the dorsal surface – usually increases the joint angle to an extended angle - Abduction: Movement in the frontal plane lateral to the body (away from the midline) - Adduction: Movement in the frontal plane medially to the body (towards the midline) - Rotation: Movement around the long axis of the bone - Pronation: Open palm to palm down - Supination: Down palm to up palm - Dorsiflexion: Movement of the foot in the sagittal plane towards the shin  these muscles act at heel strike - Plantarflexion: Movement of the foot in the sagittal plane away from the shin (pointing toes) Muscle

Attachment 1

Attachment 2

Main Action

Iliacus and Psoas (Ilio-Psoas)

Pelvis surface ilium (iliacus) and the lumbar vertebrae (psoas)

Lesser trochanter (both)

Rectus Femoris

Anterior inferior iliac spine

Tibial tuberosity

Other Quadriceps – Femoris muscles

Shaft of femur – linea aspera

Tibial tuberosity

Flexes hip and balances trunk when sitting – stop forward momentum of the body at the end of the stance phase and brings the limb up and provides forward momentum at the beginning of the swing phase Extension at the knee + flexes thigh at the hip  Bring the limb up and provide forward momentum at the beginning of swing phase Extension at the knee

Gluteus maximus

Gluteal surface of ilium (posteriorly)

Gluteal tuberosity of the femur

Abductors (Gluteal medius and

Gluteal surface of the ilium (laterally)

Greater trochanter of the femur

Extension at the hip (walking up stair) + abducts thigh + prevents trunk from pitching forward during walking + helps stabilise femur on tibia  Stops abrupt flexion of trunk at the hip when heel strikes the group Abduct and medially rotate thigh – stops the

minimus  minimus UNDER medial) Hamstrings

Ischial tuberosity

Proximal end of tibia and fibula

Adductor group

Pubis, ischiopubis ramus and ischium

Medial femur down to the knee

pelvis slumping towards the unsupported side as the swing limb is lifted off the ground Flexes knee – slow down the forward movement of the limb at the end of swing phase Adducts at the thigh

Action of the Main Groups During Walking - The Flexor group; Contracting at the end of the stance phase, and continues to contract through the initial stages of swing phase to bring the thigh forward. Also at the start of the stance phase to aid with the forward motion of the body. They also support the knee to keep it straight. o If the flexors were faulty a person would go onto their toes and try to use momentum the swing the body forward - The Abductor group; Contracting on the stance limb when the opposite limb is off the floor to help keep the pelvis level when one foot is off the ground. o Trendelenburg gait: If the abductors aren’t working properly the hips will tilt and the person will have to slump to the side to keep the weight of the trunk over the stance leg. - The Extensor group; Contracts at the end of swing phase through to the beginning of the stance phase for propulsion and stabilisation of the thigh and trunk. It also controls putting the foot down at heel strike. They also act on the swing limb to slow down the forward movement near the end of the swing phase so the foot can be put down on the group in a controlled manner.  Gluteus medius: Acts as an abductor for modern humans, Homo ergaster, Australopithecus afarensis EXCEPT acts as an extensor in chimpanzees....