Locomotion Flashcards
what is the swing stance pattern
- alternating pattern of swing stance
- flexors active during swing (e.g. TA, hamstrings, hip flexors)
- extensors active during stance (e.g. triceps, surae, quadriceps, gluteus)
what is the ground reaction force during walking
- large vertical force upon heel strike
- accompanied by a decelerating (backward) shear force (dotted line)
- push off includes an accelerating shear force, accompanied by a secondary vertical force
why are there numerous muscles controlling walking
- alternating pattern of eccentric and concentric muscle contraction
- at beginning of stance - eccentric contraction of extensors provides a ‘braking’ action
- at end of stance - concentric action of extensors provides ‘push-off’ power
- during swing, hip, knee and ankle flexors carry leg through the air
what is the strut and pendulum action
- bones of the leg / hip act similar to a rigid strut that pivots about the ankle joint
- causes characteristic vertical motion of the centre of mass
- during running, the leg ‘compresses’ during stance
- hence, vertical centre of mass motion is the opposite to that during walking
what is passive dynamic walking
- gravity used to supply energy to walker
- human-like gait is achieved with entirely passive mechanisms
- legs work like pendulums - just like human walking
- nervous system exploits the passive dynamic properties of the limbs to produce walking action
what are the animal preparations for studying locomotion when decebrate
- midbrain transection
- brainstem and cerebellum left intact
- locomotion initiated either spontaneously or by stimulation of brainstem region called: mesencephalic locomotor region (MLR)
- walking speed matched to treadmill speed
- aka ‘shik preparation’ after russian physiologist
what is the mesencephalic locomotor region (MLR)
- electrical stimulation of MLR induces locomotion
- gait speed not related to stimulus frequency
- increasing intensity causes increase in gait speed
- MLR does not produce locomotor pattern
- MLR triggers locomotion and determines speed
what are the animal preparations when studying for locomotion in the spine
- spinal cord transected at lower thoracic level
- isolates spinal segments controlling hind limbs
- adrenergic drugs administered to trigger locomotion
- sensory feedback intact
what are the animal preparations when studying locomotion (deafferented)
- rhythmic activity for stepping is generated by networks of neurons in the spinal cord. the existence of such networks was first demonstrated by Thomas Graham Brown in 1911. he developed a preparation in which the dorsal roots were cue, so that no sensory information from the limbs could not reach the spinal cord
- proof that the spinal cord can independently generate oscillatory activity, independently of sensory feedback: central pattern generation
what is central pattern generation (basic generator of the locomotor pattern)
- locomotor GPC: a relatively complex (spinal) neural network capable of producing functional locomotor muscle activation patterns without any contribution from afferent feedback (although in normal circumstances, feedback does not contribute to the locomotor pattern)
what are CPG half centers
- Graham-Brown proposed the concept of the ‘half-centre’ for generating CPG pattern
- two populations of excitatory motor neurons - flexors and extensors
- inhibitory interneurons cause mutually inhibition
- i.e. when flexors are active, extensors are inhibited (and vice versa)
- stimulation of sensory neurons can induce an alternating pattern of flexion-extension
- these neurons are flexor reflex afferents
how can CPG be modulated by sensory feedback
proprioceptive information from hip flexors initiated swing phase
what are the descending influences on CPG
- motor cortex: alters locomotor output based on visual signals e.g. obstacle avoidance
- MLR: initiates locomotion
- cerebellum / brainstem: adjusts pattern based upon ongoing sensory feedback
what is the difference between bipeds and quadrapeds
sprinting around a bend increases effective body weight, as body mass experiences both gravity and centripetal acceleration. Human athletes respond to this by increasing the proportion of time per stride that each foot spends on the ground (the ‘duty factor’). As swing time of the foot and its angle during contact (stance angle) are constrained, this results in a deduction in speed. Athletes running on inside lanes, where bends are tighter, are at a disadvantage - see, for instance, the results from the 2004 world indoor championships 200m race; the bias is so extreme that the indoor event has now been abandoned by the IAAF
what is the effect of humans running around curves
tighter curve leads to slower speed
