4. Select three discrete close motor skills. For each, identify the following phases: preparation, execution, and recovery.
The following are examples of three discrete skills, the primary mechanical purpose, and the preparation, execution, and recovery phase of each.
Place kick for a field goal - to project an object for maximum accuracy
Preparation - step forward on the non-dominant foot
Execution - transfer weight; swing lower extremity forward to contact
Recovery - continuation of execution movements (follow through)
and stepping forward to regain balance
Pushup to manipulate a resistance
Preparation - assume a starting position in the "down" position
Execution - raise the body from the floor
Recovery - lower the body to the starting position
Racing start in swimming - to project the body for maximum horizontal
distance
Preparation - assume a starting position on the block
Execution - push of of the block until entry
Recovery - underwater glide
5. Identify three movements, skills, or tasks used frequently in daily living and three movements, skills, or tasks used in work-related situations. Determine whether each is discrete or continuous or repeated discrete, open or closed, and list the constraints associated with each.
Activities of daily living (ADL):
brushing teeth - continuous with constraint of limited mouth space
stepping stairs - continuous with constraint of step height, perhaps
extensor strength, endurance
sitting down - discrete with constraint of chair height.
Work tasks:
stuffing envelopes - repeated discrete with constraints of time
and space available
washing windows - repeated discrete with constraints of balance
and boundaries of glass
climbing ladder - continuous with constraints of step length, balance,
perhaps extensor strength.
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Page 311: Questions # 1, 2, 3, 9 [answers in bold print]
1. For the following list of activities, state the
overall performance objective from Table 9.1.
a. Pole vault
b. Baseball batting
c. Fielding a line drive
d. 50-m sprint
e. Bobsledding
f. Mountaint climbing
g. Body building
h. Shot put
i. Long jump
j. Basketball jump ball
k. Free throw
l. Softball pitch (fast pitch)
a. to project the body for maximum vertical distance
b. to project an object for maximum horizontal
distance
c. to project an object for maximum accuracy when
the speed of the projectile enhances its effectiveness
d. to move the body over a prescribed distance
as fast as possible
e. to move the body over a prescribed distance
as fast as possible
f. to move the body with the intent of interacting
with natural environment
g. to manipulate resistance
h. to project an object for maximum horizontal
distance
i. to project the body for maximum horizontal
distance
j. to project the body for maximum vertical distance
k. to project an object for maximum accuracy
l. to project an object for maximum accuracy when
the speed of the projectile enhances its effectiveness
2. For the following discrete skills, divide the performance
into discrete parts or phases: pole vault, long jump, shot put.
Pole Vault
Part 1: from the first contact of the pole with the box to the maximum
pole bend
Part 2: from maximum pole bend to maximum pole straightening
Part 3: from maximum pole straightening to pole release
Part 4: from pole release to bar clearance
Part 5: from bar clearance to landing
Long Jump
Part 1: from initial movement into the approach to the penultimate
stride
Part 2: from the penultimate stride to maximum knee flexion on the
toe board
Part 3: from the maximum knee flexion on the toe board to the last
instant of toe board contact
Part 4: from the last instant of toe board contact to the first
heel contact with the pit
Part 5: from first heel contact with the pit to the end of the jump
Shot Put
Part 1: from the initial movement of the put to the maximum downward
crouch
Part 2: from the maximum downward crouch to the time at which the
rear foot leaves the ground
Part 3: from the time rear foot leaves the ground until the maximum
downward movement following the slide
Part 4: from the maximum downward movement following the slide until
the front foot contacts the ground
Part 5: from the initial contact of the front foot to the point
that the shot leaves the hand
Part 6: from the time the shot leaves the hand until the end of
the follow through
3. For the skills listed in question 2, write the
Overall Performance Objective (OPO) and the mechanical purpose (MP) of
each of the discrete parts.
Pole Vault
OPO of the pole vault is to project the body vertically as high
as possible
MP of the discrete parts are listed below:
Part 1: to store as much potential energy as possible in the pole
Part 2: to position the body for receiving the elastic energy of the pole
Part 3: to add velocity to the body before leaving the pole
Part 4: to position the body over the bar so that it does not touch the bar
Part 5: to position the body for a safe landing
Long Jump
OPO of the long jump is to project the body horizontally as far
as possible.
MP of the discrete parts are listed below:
Part 1: to gain as much horizontal velocity as possible
Part 2: to adjust the body for accurate placement of the lead foot on the toe board and to position the body for use of the stretch reflex and series elastic component of the muscles of the lead leg
Part 3: to generate high take off velocity and to optimize the take off angle
Part 4: to delay forward rotation and to position the heels as far forward of the center of gravity as possible at heel contact
Part 5: to enhance the forward rotation of the body over the heels
Shot Put
OPO of the shot put is to project the shot horizontally as far as
possible.
MP of the discrete parts are listed below:
Part 1: to position the body for the use of the stretch reflex and series elastic component of the muscles of the trunk and rear leg
Part 2: to generate high horizontal velocity and to place the power leg accurately under the body
Part 3: to position the body for the use of the stretch reflex and the series elastic component of the muscles of the power leg
Part 4: to place the front leg in a position to provide a stable base upon which the other segments can rotate and to generate high rotational velocity of the base segments by increasing muscle torques through the use of the series elastic component in the rear leg.
Part 5: to generate high end point velocity through sequential rotations of the body segments and to produce the optimum projection angle
Part 6: to safely decrease the segmental rotations
9. Select an occupational task that is discrete. State the OPO, MP of the phases of the movement, the BFs, the BPs, and the CFs of each of the phases. Discuss how this movement may result in injury to the performer.
Example: moving a heavy box from a countertop to a conveyor belt
1 meter behind the lifter (discrete)
OPO: to manipulate resistance
PREPARATION PHASE
MP: to maintain body balance while grasping the box to prepare for a safe lift
BFs: CG and base of support (BS), torque, friction vs. normal F
BPs: - the body will be balance if the C of G is positioned over
the BOS
- the close the
distance of a load to the axes of rotation (joints), the less the resistance
torque to be overcome by muscle torques
- friction force
depends on adequate normal force applied to prevent slipping.
CFs: - keep the feet spread in the direction the load will
be brought toward the body
- grasp the
load as close to the body as possible to reduce resistance torque
- place hands
under box to prepare for lift, rather than pressing on vertical sides of
box which
necessitates large pressing forces to prevent slipping
- for back
safety, keep back vertical when preparing to lift.
EXECUTION PHASE
MP: to maintain body balance while applying optimal upward and sideward force on the box to safely translate it across a horizontal distance.
BFs: see preparation phase
BPs: see preparation phase
CFs: Keep the feet spread in the direction the body will move after placement. Keep back vertical
A review of Chapter 7 (page 239) on the vertical column will provide
information on the mechanics of safe lifting.