Chapter 10
Performance Analysis of Pushlike Movements
 
Pages 366-367: Questions # 1 to 8 inclusive [answers in bold print]

1.    Perform a vertical jump with the nonreaching arm held at the side throughout the jump and the reaching arm held above the head.  Measure the jump.  Repeat the jump, swinging both arms upward just before takeoff.
       a.    Explain any difference between the two techniques in regard to the height of the projection.
       b.    What is the acceleration-deceleartion pattern during the ROM of the arms relative to the extension of the hips?
       c.    Does a sequence of segmental rotations occur during the jump, or are the rotations simultaneous?

a.    The height of projection of the body using an arm swing should be greater than the height attained when not upward causes a downward reaction of the body.  The greater force upward by the ground, in reaction to this greater downward force, adds to the projection velocity of the body, and hence, to the greater hegith attained.  According to the transfer of momentum concept:  the arms acquire momentum as they accelerate upward; when the arm movement decelerates or stops, this momentum is transferred to the total body; and the total body wil take on the momentum of the arms.  Of course, isnce the body has a much greater mass than the arms, it will not assume as great a velocity as the arms had.

b.    The acceleration pattern of the arms may be difficult for the student to observe, compared to the acceleration of hip extension.  The arms should begin their upward acceleration of hip extension.  The arms should begin their upward accleration before the hips begin to extend, and the hips should continue to acclerate as the arms begin to decelerate (approximately 90 degrees flexion).

c.    A distinct sequencing of the jumping pattern may be observed through the use of electrogoniometry and a force plate.  The jump is initated bye arm swing, followed by the extension of the trunk about the hip joints, followed by the simultaneous extensions of the hip and knee joints, and, finally, by plantar flexion of the ankles.

2.    Stand on a scale in anatomical position.  From this position, perform the following actions while watching the weight indicator: (a) flex the elbows quickly, (b) flex the shoulder joints slowly, (c) flex the shoulder joints rapidly, (d) quickly flex the hips, knees, and ankles, (e) from a half-squat position, extend the hip, knee, and ankle joints rapidly.  Explain the reactions of the scale in this experiment in terms of acceleration and deceleration of the segments.  Relate this to the weighting and unweighting of the lower segments and the upward reaction force created at the feet.

The magnitude of the reaction force at the feet will depend on the amount of mass being accelerated upward and the magnitude of the acceleration of that mass.  The greater the mass being accelerated upward, the greater will be the reaction force at the feet, and the greater will be the increase in the scale reading.  The greater upward accelration of the segments, the greater will be the reaction force at the feet, and the greater will be the scale reading.  During the middle of the range of motion of the segments, the scale reading should decrease and possibly reach zero.  This is indicative of the deceleration of the segments, the transfer of momentum to the total body, and the resulting "unweighting" of the body.

Note:  If a simple bath scale is used, the dial of numbers will rotate rapidly with fast movemnts and slowly with very slow movements, and the numbers will never be discernible  Therefore, the student should be instructed to watch for the immediate directional change of the dial as being indicative of greater or smaller ground reaction force.

3.    Complete this sentence:  Whenever the free end of a kinetic link system is more massive than the fixed end, the system is called a ______ kinetic chain.

Closed Kinetic Chain

4.    Compare the force and veleocity components and the power requirements of a bench press and a snatch lift.

                                    Bench Press            vs.            Snatch Lift
Force component             higher                                    lower
Velocity compoment:        lower                                    higher
Power component:            lower                                    higher

5.    What three mechanical purposes do pushlike activities fall into?

Achieve maximum force (e.g.  to manipulate lots of resistance), achieve maximum power (e.g. to project for maximum horizontal distances), to achieve accuracy.

6.    Explain the power transfer of uniarticulate and biarticulate muscles in jumping.

According to a study by F.E.Z. ajar (1993), the uniarticulate muscles of the lower extremity produce most of the power in jumping while the biarticulate muscles provide the coordination of the sequencing of the segmental rotations.

7.    Describe the similarities and differences between jumping patterns of mature jumpers and young children.

Both mature jumpers and young jumpers follow a similar pattern of force application.  However, the young jumpers have less strength, balance, perception, and motivation.

8.    Discuss the mechanical factors important in successfully producing an accuracy-type activity.

- consistency of movements
-straight line motion just prior to during and just after release/impact
-solely a rectilinear path when projecting for a short distance
-changing from a curvilinear path to a rectilinear path just prior to and during release/upright when projecting for accuracy -when speed enhances the performance of the task.