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Lecture 7

Kinesiology 2241A/B Lecture Notes - Lecture 7: Plantaris Muscle, Soleus Muscle, Flexor Digitorum Longus Muscle

Course Code
Kinesiology 2241A/B
Thomas Richard Jenkyn

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Kin 2241b Introductory Biomechanics Keenan Vanderkooi
Assignment #3 250866706
1. a) The movement that occurs is called upward rotation of the scapula, which ensures the
humerus rotates all the way over the head.
b) You begin to notice upward rotation of the scapula around 30 degrees.
c) This movement is necessary for the humerus to fully rotate over the head, and for humans
to reach outwards and upwards. Without the upwards rotation of the scapula, the humerus
would be limited in it’s range of motion to only what the glenoid fossa allows it to do.
Rotating the scapula upwards allows muscles of the rotator cuff to support and pull the
humerus upwards, while abducting the scapula ensures the motion occurs along the frontal
plane. This way, the humerus can maintain its range of motion in the glenoid fossa, while in
different anatomical positions.
d) Upward rotation of the scapula causes the glenoid fossa to also rotate upwards. This
ultimately enhances the joint’s ability to move, and allows the arm to fully rotate upward.
Without upward rotation of the scapula, the glenohumeral joint would not be properly
supported, and it would have a limited amount of freedom.
2. a) Hip extension, adduction and internal rotation, knee extension
b) Hip abduction and external rotation, knee flexion
c) Hip flexion and internal rotation, knee extension
d) Hip extension, knee extension
e) Hip external rotation, flexion, and adduction, knee extension
During these movements, there are multiple two-joint muscles involved. The anterior rectus
femoris crosses both the hip and knee joints, and allows for hip flexion, as well as knee
extension. The posterior semimembranosus and semitendinosus act in these movements to
extend the hip while flexing the knee. Another two joint muscle involved is the
gastrocnemius, which crosses the knee and ankle joints, and acts to flex the knee as well as
plantar flex the ankle. Two-joint muscles are commonly related to injury in athletes. Muscles
that cross two joints are more susceptible to injury because they are being used in a wide
range of functions. Passive insufficiency can cause too much passive tension in athletes, as
certain techniques require two-joint muscles to accomplish the specific movement. For
example, when doing hurtles, the subject is susceptible to tear of their rectus femoris. This is
because excessive force during simultaneous hip flexion and knee extension will cause strain
on those joints.
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