Dance Anatomy & Kinesiology

The Muscular System 69

Study Questions and Applications

1. List the four properties of skeletal muscle and explain their practical significance for
   dance.


2. Make a diagram of the contractile mechanism of a muscle cell and label and define the fol-
   lowing structures: A band, I band, H zone, Z line, actin, myosin, and sarcomere.


3. Describe the sliding-filament theory and how it relates to concentric, eccentric, and isometric
   muscle contractions.


4. Examine a pirouette, and describe when the calf muscles (gastrocnemius and soleus) would
   be working concentrically, isometrically, and eccentrically.


5. What difference in muscle fiber types would you expect to see in a world-class marathon
   runner versus a high jumper?


6. If the EA for a given muscle is 1.5 inches (3.8 centimeters) and the RA is 15 inches (38 centi-
   meters), what would the mechanical advantage be? What is the significance of this mechanical
   advantage in terms of the muscle force needed to effect movement against the resistance?


7. Describe how the relationship of the torque associated with muscle effort and the torque asso-
   ciated with the resistance changes with concentric, eccentric, and isometric contractions.


8. Distinguish between a synergist and stabilizer, and provide two examples from dance.


9. Using figures 2.19 and 2.20 for reference, identify a muscle that can serve as an antagonist
   to the following muscles: pectoralis major, gluteus maximus, erector spinae, biceps brachii,
   and quadriceps femoris.


10. Describe how the serratus anterior and trapezius work as a force couple.


11. Using figure 2.14 for reference, locate the proximal and distal attachments of the rectus
    femoris on the skeleton. Use these attachments to mentally construct the line of pull of the
    rectus femoris, and deduce the actions the rectus femoris could have at the hip joint and
    knee joint. Use figure 2.19 to check your deductions.


12. Apply the concept of active and passive insufficiency to the rectus femoris. Provide two examples
    of movements in dance in which these phenomena would be operative and what you could
    do to lessen the constraints.


13. Using the schema provided in table 2.5, perform a simplified movement analysis for raising
    the arms to the front from low fifth to high fifth.


14. A dancer wants to improve her form in a grand jeté. Her teacher notes that her back knee
    tends to bend and both legs do not reach adequate height to give the desired line in the
    jump.
    a. Describe what joint motions are occurring at the hip and knee of the front leg and the
    back leg.
    b. Describe how raising the front leg straight versus with a developing movement would affect
    the moment arm of the leg and potential height of the front leg.
    c. Taking into account the concept of active insufficiency, identify muscles that should be
    strengthened to help increase the height the front leg can be raised. Taking into account
    the desired hip joint motion of the back leg, identify muscles that should be strengthened
    to help increase the height to which the back leg can be raised. Which of these muscles
    would also tend to bend the knee of the back leg, and what muscle group could serve as
    a synergist to neutralize this undesired knee flexion? Looking at the desired position at
    the height of the leap, identify the muscles that would need very high levels of flexibility.
    Provide a cue to help the dancer achieve the desired line of the back leg.

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