Chapter 8
Application of Biomechanics to Fitness Activities
 

Page 256: Questions # 2, 3, 4, 6, 7 [answers in bold]

2.    What is the feature of variable-resistance devices that makes them different from free-weight resistance?

The resistance is varied throughout the segment's range of motion so that greater resistance is encountered at joint angles at which the muscles are able to produce more torque.

3.    Explain the force and speed features if isokinetic devices.

Isokinetic devices provide for control of the speed of movement through the ROM regardless of the magnitude of the force applied.  This prevents the acceleration of the resistance with maximum force/torque application so the muscle group can contract with maximum tension throughout the ROM.

4.    Diagram on a stick figure the resistance force and force arm involved in holding a weight in your hand with the shoulder abducted (a) 90 degrees, (b) 45 degrees, (c) 180 degrees.  Which muscle group exerts tension to hold these positions?

Draw a weight force vector at the CG of the upper extremity and the weight force vector at the CG of the hand-held weight at each position.  Draw in the force arm for each vector from the shoulder joint axis.  The shoulder abductors exert tension to hold these positions.

6.    What does "isokinetic" mean and how is it used in osokinetic exercise devices?  List advantages and disadvantages of training with isokinetics.

Isokinetic is a term referring to exercises through a range of motion at constant speed; the force may vary, but the speed will remain constant except for the start (acceleration) and finish (deceleration) of the range of motion.  Advantages are in rehabilitation and strength-speed training, and monitoring progress in such programs.  Disadvantages are expense, and unrealistic (non-specific) movements speeds when training for specificity.

7.    What unique measurements and adjustments are available on computerized exercise machines that cannot be addressed with other devices.

Resistance levels, accelerations, declarations, speed, power, ROMs, directions of resistance.  Acceleration patterns of ballistic type movements can be matched for specific training.  Work output can be monitored.
 
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Chapter 8 continued (pp. 260-272)
Application of Biomechanics to Fitness Activities
 

Page 263: Questions # 2 plus # 8 to 12 inclusive  [answers in bold]

2.    Define muscular power.  How does power relate to work?

Muscular power is the ability of a muscle group to contract with force and speed.  Contraction that applies a large force slowly is force dominated power, whereas contraction that applies a smaller force very quickly is speed dominated power (P = Force x the speed of Force application).  Work divided by the time during which the work was performed is equal to power.

8.    Compare the difficulty of doing straight-leg sit-ups with (a) the hands beside the neck, (b) the arms crossed over the shoulders, and (c) the arms at the sides.  Explain the differences in difficulty in terms of motive and resistive torques and muscle groups being used (see Chapter 7.)

The hip joints will be the axis of rotation for the upper body in all three styles of sit-up.  The vertebral column flexors act to stabilize the trunk.  


A) with the hands behind the neck, more mass is positioned away from the hip axis, thereby increasing the resistive weight torque opposing the motive muscle torque applied by the hip flexors and making the sit-up more difficult to initiate.  Also, the rotational inertia of the upper body is increased, and the angular acceleration of the upper body will be smaller

B) with the arms positioned over the shoulders, their mass is brought closer to the hip axis, thereby permitting an easier and faster sit-up; c_ with the arms at the sides of the body, even closer to the hip axis, the sit-up will be the easiest and the fastest.

9.    Perform a muscular analysis of the straight-leg sit-up, the flexed-leg sit-up, and the straight-leg snap-up.  What are the differences in terms of motive and resistive torques, the muscular requirements, and the stabilization function of muscle groups?  (See Chapter 7.)

With a flexed-leg sit-up, the hip flexors are placed in a shortened position and the flexors of the vertebral column provide the motive torque for rotating the upper body toward the thighs.  The abdominals would concentrically and eccentrically contract.  In the straight-leg sit-up, the hip flexors are placed in a stretched position and can provide the motive torque to rotate the pelvis and lumbar vertebrae toward the thighs; in such a sit-up, the vertebral column flexors tend to remain in static contraction to stabilize the trunk, while the hip flexor muscles concentrically and eccentrically contract.  Trunk stabilization is necessary to prevent the lagging back of the upper vertebral column.  In a straight-leg snap-up, in which the lower body and upper body rotate upward to meet each other, the hip flexors and vertebral column flexors both concentrically and eccentrically contract (see Figure 7-6d).  The resistive torque is the greatest for each half of the body at the beginning of the snap-up when the mass of each half is distributed the farthest away from the hip and lumbar axes.  Therefore, the motive torques need to be the greatest at the beginning of the snap-up.  As the body halves approach one another, their resistive weight torques are minimized, thus requiring minimal motive torque.  In addition, the momentum of the two halves facilitates the "piking" motion.  The eccentric resistive muscle torques necessary on the way down are minimal at the top position and maximal at the bottom position.

10.    Identify three calisthenic-type exercies that can be done with less muscular effort by using stored elastic energy.

Quick forceful stretching of the muscle group to be used concentrically in an exercise will cause recoil of the elastic component to provide greater force on the segment to be moved: quick springy jumping jacks utilize the recoil in the ankle plantar flexors; standing trunk twisting done quickly causes stretch and recoil in the vertebral column rotators; standing forward-back leg swings done rapidly cause recoil in the hip flexors and extensors.

11.    Identify four specific skills that require strength-dominated power for success.

Strength-dominated power is used in activities in which a heavy load or resistance must be moved but not necessarily with great speed; usually such skills use larger muscle masses: weight lifting, press to a handstand, raising from an iron cross on the rings, wrestling.

12.    Identify four specific skills that require speed-dominated power for success.

Speed-dominated power is used when segments of the body must be accelerated quickly for speed of movement: sprinting, high jump, racquetball shots, kicking, karate punch, shot put, ball throw.
 
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Page 271: Questions # 1, 2 ,5  [answers in bold print]

1.    Differentiate between active and passive flexibility.

Active flexibility is the ROM available when a person uses his own muscles to move the segments through that ROM, as opposed to passive flexibility, where an outside force causes the ROM (another person, gravity), or the momentum of a body segment carrying a segment further than the ROM caused by muscle contraction.

2.    Explain the difference between the elastic and plastic elgonation of connective tissue.

Elastic elongation of connective tissue is the type of stretching that results in recoil to its original length (high force, short duration stretching).  Plastic elongation does not result in recoil; it affects the visco-elastic characteristics of connective tissue and is the more permanent type of elongation (low force, long duration stretching of warm tissue).

5.   Sit on the floor with your knees extenede, ankles plantar flexed.  Reach toward your toes, and hld the position of maximum reach.  While holding this reach position, dorsiflex the ankles and note the result.  Flex the knees slightly and note the result.  Discuss these results in terms of specificity of joint positions in an activity for which stretching exercises are given.
 
This exercise points out the importance of how the positions of other segments can influence the stretching effect attempted.  This should be considered in the performance of stretches designed to improve flexibility for simultaneous segmental movements involving more than single joint range of motion.