Dance Anatomy & Kinesiology

58 Dance Anatomy and Kinesiology

of its resting length, and this limit of shortening can

readily be reached when a muscle is shortening across

two or more joints simultaneously. In addition, muscle

has difficulty producing high contractile force when

in a very shortened position (length–tension relation-

ship), and so strength of that muscle will influence

how much range of movement can be achieved. Active

insufficiency can be demonstrated by simultaneous

performance of both actions of a two-joint muscle,

such as hip flexion and knee extension for the rectus

femoris as seen in figure 2.17A.

Lombard’s Paradox

Another special consideration with a two-joint

muscle comes into play when the required motion

at one joint is in the opposite direction to that

produced by that muscle. This condition is termed

Lombard’s paradox (Rasch, 1989). The classic

example used with Lombard’s paradox is co-con-

traction of the hamstrings and the quadriceps femo-

ris, such as during rising from a plié or standing up

from sitting in a chair. The hamstrings can produce

the desired action of hip extension but the unde-

sired action of knee flexion. On the other hand, the

rectus femoris produces the desired action of knee

extension but the undesired action of hip flexion.

So how can the desired action of hip extension and

knee extension occur from their co-contraction?

One would think that if they were used together

they would just neutralize each other’s action and

no resultant movement would occur. However, this

is not the case. The explanation for this apparent

paradox is that multijoint muscles often have a more

pronounced effect, due to having better leverage

and producing greater torque, at one of the joints

that they cross as shown in figure 2.18. In the case

of the hamstrings, this muscle has a longer moment

arm and so creates a greater torque at the hip than

the knee, with its action of hip extension predomi-

nating. Conversely, the rectus femoris has a longer

moment arm and so creates a greater torque at the

knee than the hip, with its action of knee extension

predominating. Hence, their co-contraction can

result in the desired motion rather than either no

motion or undesired motions. So, a two-joint muscle

can be utilized that has its primary action coincident

with the desired action at one joint, while another

muscle works synergistically to overcome the unde-

sired motion and create the desired action at the

second joint.

Learning Muscle Names and Actions

Now that some key principles of how muscles func-

tion have been covered, the next step in understand-

ing movement is to learn the names, locations, and

actions of specific muscles. There are approximately

434 muscles in the human body, with about 75 pairs

Passive Insufficiency

• Establishing passive insufficiency. Create passive insufficiency with the hamstring muscles by
  establishing a position opposite to the actions the hamstrings produce (e.g., hip flexion and knee
  extension) by lying on your back and using your arms to bring one leg up toward your shoulder while
  your knee is maintained in an extended position until a mild stretch is felt at the back of the leg (see
  figure 2.23B on p. 67). Note this endpoint.


• Adding knee flexion. Then bend your knee slightly and note that the leg can be brought
  higher.


• Why can you bring the leg higher with your knee bent?


• Application to other dance movements.


• Noting the degree of passive range that your body exhibits with your knee straight, how could
  this affect your ability to perform high kicks to the front or split leaps?


• If a dancer has less than 90° of hip flexion possible due to passive insufficiency, how would
  this influence the dancer’s ability to stretch the hamstrings while sitting with the legs straight
  to the front or in second position?

CONCEPT DEMONSTRATION 2.5