Chapter 3
identify the phase of a squat exercise in which quadriceps femoris is acting (a) concentrically and (b) eccentrically.
Concentrically: to stand up from a semi squat position, the body must extend at the hip joints and knee joints, but gravity resists that extension. The muscles must develop sufficient Force to overcome the force of gravity as the muscle shortens in a concentric action, pulling on the bones to cause extension. eccentrically: going down into the squat position.
explain how the trunk has such a large ROM even though each intervertebral joint within it only has a few degrees of motion.
although movement between adjacent vertebrae it's just a few degrees, when combined over the whole vertebral column, the ROM of the trunk is substantial. movements of the trunk occur in all three planes: flexion and extension, lateral flexion to the left and right, and rotation to the left and right.
explain in terms of torque how in abdominal crunch is more difficult when the arms are extended overhead compared with folded across the chest.
during an abdominal crunch, the position of the arms determines the length of the resistance arm and, therefore, the amount of resistance torque against which the abdominal muscles have to work to flex the trunk in with the shoulders off the floor. The arms may be held at the sides of the body to bring the upper body mass closer to the axis of rotation and reduce the required muscle Force. To increase the challenge of this exercise, the arms can be raised with the hands on the back of the head. The resistance arm can be increased by holding the arm straight out overhead, which increases the resistance torque and therefore increases the muscle Force required to perform the exercise.
using rotational inertia in your answer, explain why Runners naturally Flex the knee of the leg that is swinging forward.
during jogging, the knee of the recovery limb is partially Flex to reduce the limbs rotational inertia around the hip joint. Less muscular force is needed to swing the recovery leg forward compared with a more extended knee, which reduces local fatigue of the hip flexors. In sprinting, on the other hand, the quicker the recovery limb is brought forward, the faster the running speed.
what type of muscle contractions are involved in exercises performed in water?
movements performed in water demand concentric muscle contractions. Since water is a dense medium, it provides some support for the weight bearing joints against the force of gravity.
explain from an anatomical Viewpoint why the knee is vulnerable to injury.
the knee does not have good bony stability in flexion due to the flattened surface of the tibial Plateau; therefore, it relies on ligaments to provide stability, making it vulnerable to injury.
name the three Cardinal planes and their Associated axes.
the mediolateral axis is perpendicular to the sagittal plane, and joint rotations about this axis are flexion and extension. the end anteroposterior axis is perpendicular to the frontal plane, and Joint rotations about this axis are abduction and adduction. the longitudinal or vertical axis is perpendicular to the transverse plane, and rotations about this access are internal and external rotation.
why is walking up an incline more challenging for the gluteal muscles than walking on level ground?
walking or running up an incline elicits greater action from the gluteus maximus muscle at the hip and from the knee extensors to raise the body against Gravity. The ankle dorsiflexors are more active immediately before landing in order to match the position of the ankle joint to the angle of the incline. Because the ankle is in a more dorsiflexed position, the plantar flexors begin acting during push off from a more stretched position. For these reasons, hill climbing requires greater flexibility in the plantar flexors, especially the soleus muscle, and greater strength in the dorsiflexors.