Performance And Motor Control Characteristics Of Functional Skills Flashcards
Centre of mass (COM)
Weighted average of all segments in body, the body’s balance point
Centre of pressure (COP)
Point location of the vertical ground reaction force
Base of support (BOS)
The area defined by contact with a support surface
Area beneath an object or person that includes every point of contact that makes with supporting surface
Margin of stability (MOS)
Distance between the COM position and the edge of the BOS
Equation for COM
Com= mi x ri / mi
MiRi = sum of segment masses x distance from reference
Mi= total mass
COP equation
COPx = Momentx / FORCEvertical
- average of pressures over the surface in contact with ground
What are examples of base of support
Body parts, feet or hands, or crutches, or chair person sitting on
To remain standing balance what must happen
COM must remain within the BOS
During standing what happens
COP acts to control the COM and keep it within the BOS
What happens if the COM moves outside the BOS
BOS must be changes quickly to “catch” the COM or a fall will occur
How to maintain dynamic balance (walking balance)
BOS must change to control COM movement
Summary of balance control
To prevent fall, COM stays within BOS or projected into a forthcoming BOS
COP helps control the COM
How can stability be assessed
Measuring the margin of stability (MOS)
What is involved in control of locomotion (gait)
Central pattern generators (CPG) in spinal cord
What is CPG in spinal cord provide
Basis for stereotypic rhythmicity of walking and running gait patterns (include arm swing)
What else influences gait
Proprioceptive feedback from muscle spindles and GTOS
- timing of locomotive cycle
- size of muscle response
How do CPGs work
- Motor signal from higher brain structures to CPG in spinal cord to extensors and flexors
- Proprioception from flexors and extensors to CPG in spinal cord to higher brain structures
What is the rhythmic structure of locomotion
- components of a step cycle
- rhythmic relationship between arms and legs
- pelvis and thorax relationship during walking
What is the relationship between pelvis and thorax during walking
In at slow speeds
Out at higher speeds
What is the practical benefit of analyzing rhythmic structure of gait patterns
Allows for assessment of coordination problems of trunk and legs (ex Parkinson’s disease)
What is another important motor control characteristic of locomotion
- head stability
Vestibular canals and vision both based in head
What happens at critical speed
People spontaneously change from walking to running gait and vice versa
Why do spontaneous gait transitions occur
Most popular hypothesis: minimize metabolic energy use
When walking or running what is vision important for
Enabling us to contact objects and avoiding contact with objects
What vision control system is responsible for contacting objects
Tau (time to contact)
How does vision help with avoiding contact with objects
- provides advanced info to determine how to avoid contact - step over, dodge
- provides body scaled info to determine how to walk through door, to step on a step
What is the speed-accuracy trade off
When both speed and accuracy are essential to perform a skill
When speed is emphasized
Accuracy is reduced
When accuracy is emphasized
Speed is reduced
Fitt’s law
Most significant laws associated with human movement
Mathematically predict movement time for speed accuracy skills
What do we need to know for Fitt’s law
Spatial dimensions of 2 variables
Movement distance
Target size
What else can be calculated base on Fitts law
Index of difficulty
What is index of difficulty
Quantitative measure of the difficulty of performing a skill involving both speed and accuracy requirements
Speed-accuracy skills: Fitts law
As target size becomes smaller or as distance gets longer, the movement speed will decrease in order for accurate movement
Open loop
- does not use feedback
- initial speed, direction, accuracy under CNS control
- at movement initiation, initial movement instructions are sufficient to move limb to vicinity of target
- efferent info only (eg. Basketball freethrow)
Closed loop
- does use feedback
- control center send only enough info to effectors to initiate movement
- relies on feedback to continue and adjust if needed (eg. Dribbling a basketball)
What 2 motor control processes underlie performance of speed-accuracy skills
Open loop control
Closed loop control
Where is accuracy for closed loop control
At termination of movement
What does Closed loop feedback need to hit target accurately
From vision and proprioception needed at end of movement to ensure hitting target accurately
What is important in closed loop control
Whether person has time to make necessary corrections as limb nears the target
What is the third phase proposed
Movement preparation phase
Movement prep phase
Person uses vision to determine the regulatory conditions that characterize the environmental context in which action will occur
Prehension
Reaching for and grasping an object
3 distinct components of prehension
- Transport
- Grasp
- Object manipulation
Transport
Movement of hand to object
Grasp
Hand taking hold of object
Object manipulation
Functional goal of prehension
- makes pretensions different from reaching and pointing
- influences characteristics of transport and grasp
What does prehension demonstrate
Speed accuracy trade-off
- during transport phase, arm will accelerate and then decelerate
- as object size decreases, length of deceleration phase increases (longer to reach target)
Biannual coordination skills
Motor skills that require simultaneous use of two arms
What may biannual coordination skills require
Arms to move with same or different spatial and/or temporal characteristics
Two types of biannual coordination skills
Symmetrical biannual coordination (clapping, lifting, rowing a boat)
Asymmetrical biannual coordination (playing musical instrument, patting head and rubbing stomach)
What are motor control characteristics related to biannual coordination
The two arms prefer to perform symmetrically
Three phases of catching a moving object
- Initial positioning of arm and hand
- Shaping of hand and fingers
- Grasping the object
Two critical time periods in visual contact time needed to catch a moving object
Initial flight
Just prior to hand contact
What visual contact is needed between the two critical periods
Brief, intermittent visual snapshots sufficient to make contact
Ball speed effect
Skilled strikers demonstrate similar bat movement time for all ball speeds
What visual contact with moving ball do skilled strikers do
Do not maintain throughout ball flight but visually “jump” from early flight to predicted location in area to strike ball
- head stability important
