BIOL 1004 Lecture Notes - Elastic Energy, Superior Gluteal Artery, Erector Spinae Muscles

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28 Jan 2013

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Outline of Lecture 03
I. Phases of Gait
- Gait cycle = Stance phase (heel strike, flat foot, toe off) + swing phase
- 5/6 gait cycles is stance, rest is swing; ¼ of gait cycle has double support
- Transfer of weight during stance from heel along footprint to big toe
- Flexor hallucis longus tendon passes through sesamoid bone tunnel, allows
movement while weight is on big toe
II. Ballistic model of gait
- Lower limb forms inverted pendulum; most of gait is passive rocking over
stance leg
- Gait speed determined by height and gravity
- Walking is very efficient (~60-70% energy recovery; total energy relatively
- Must break into running at lower speeds when going uphill, and vice versa
III. Mechanisms to minimize displacement of body center of gravity
- With no mechanisms, path of body center is cycloid; with mechanisms nearly
- Pelvic rotation and plantarflexion raise lowest point
- Pelvic tilt and knee flexion lower highest point
IV. Muscles used during gait
- Provide accel. during toe-off, support swing leg side, smooth transitions, and
stabilize lower limb by deceleration
- Time profile of muscle usage
- Dorsiflexors, hamstrings, abductors, gluteus maximus fire right after heel
- Adductors, erector spinae fire right after heel strike and before toe-off
- Plantarflexors fire increasingly during stance phase
- During heel strike
- Extensors (hamstrings and gluteus maximus) decelerate limb
- Dorsiflexors prevent foot slap
- During flat foot, toe-off
- Abductors prevent excess pelvic tilt
- PLANTARFLEXORS provide forward acceleration, contract till toe-off
- During swing
- Dorsiflexors lift foot to clear ground
- Also, intrinsic foot muscles keep foot as rigid lever, upper limbs provide
- Pathologies
- High steppage gait and foot slap/drop (injury of common fibular n.)
- Pelvic slump (injury of superior gluteal n.)
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