Page 242: Questions # 4, 5, 8, 9 [answers in bold print]

4.    Discuss the back trauma impending on the weight lifter shown in Figure 7.9.  Discuss the compressive and shear forces on his lower back.

Trauma occurring between the third, fourth and fifth lumbar joints with extreme compression on the dorsal side and extreme tension on the ventral side requires strong anterior vertebral column muscles and ligaments in order to stabilize the intervertebral articulations from injury, particularly with the additional torque provided by the external weight.

5.    Figure 7.10 illustrates two people performing backward stunts.  Discuss the difference in the vertebral column positions.  Which tends to be more injurious?  Why?.

One tumbler uses the hyperextension of the vertebral column predominantly from the thoracic region, the other predominantly from the lumbar region.  The lumbar hyperextension may result in more injury because of the large range of motion provided by relatively few intervertebral joins rather than small range of motion provided by many intervertebral articulations.

8.    For the following activities, describe the contribution of the vertebral column (i.e., what movement is used): (a) a flop-style high jump, (b) a back handspring, (c) a tennis backhand stroke, and (d) a golf swing.

a.    hyperextension

b.    hyperextension

c.    rotation to the dominant side

d.    rotation to the non-dminant side.

9.    Discuss the differences among the long-leg sit-up, the hook-lying sit-up, the curl-up, and leg lifts in terms of the following:
            a.    The resistive torques.
            b.    The muscle forces and their lines of action for those crossing the hip and those crossing the vertebral column.
            c.    The stabilization function of the abdominal muscles.
            d.    The relative effectiveness and appropriateness of each exercise for (1) people with weak abdominals, (2)
                   people with strong abdominals.
            e.    The effect of introducing the time factor in sit-up tests, in relation to potential injury of the back.
 
a.    The greatest resistive torques will be provided by the long leg sit-up and leg lifts, with less in the curl-up.

b.    When performing leg lifts, the hip flexors are the motive torque, and the vertebral column flexors provide the stabilizing torque to the pelvis so that the pelvis will not be pulled into an anterior tilt position causing hyperextension at the intralumbar articulations.  When performing straight-leg sit-ups, the hip flexors provide some motive torque in addition to stabilizing the vertebral column.  When performing bent-leg curl-ups, the vertebral column flexors act as motive torques, and the hip flexors act minimally since the hip joins is already flexed.

c.    The abdominals act to stabilize the pelvis from tilting anteriorally with the pull of the hip flexor muscles during leg lefts and somewhat for straight-leg sit-ups.

d.    People with weak abdominals need an exercise that requires less resistive torque (curl-ups) and not one in which the abdominals are required to prevent potential back hyperextension injuries (leg lifts); therefore bent leg curl-ups would be the best.  People with strong abdominals need the greatest resistive torque (leg lifts, or straight leg sit-ups with the upper extremities headward as far as possible, thus increasing the resistance arm).  These people would be able to stabilize the pelvis and therefore would be able to prevent a potential back hyperextension problem.  Caution should be used when prescribing any exercise in which high resistance may cause the motive or stabilizing muscles or musculoskeletal junctions to be strained.

e.    A time factor ( as many sit-ups as possible in a given time limit) would be potentially dangerous for those whose abdominals would show fatigue prior to finish, for they would not have the strength to prevent lumbar hyperextension and would be prone to back injuries.  Those whose abdominals are strong enough to endure the limit would be able to perform a timed task without injury.