66 Dance Anatomy and Kinesiology
dumbbells, springs, elastic bands, or guided weight
apparatus. In the case of the first three forms of
resistance, an effective exercise also depends on
appropriate positioning of the body so that the action
of the muscle is opposed by gravity. For example,
when one is performing shoulder external rotation
with the elbows by the sides, an upright position of
the torso will allow effective opposition if a band is
being used for resistance, but not if a dumbbell is the
resistance. Instead, using a side-lying position of the
body would allow gravity to better resist the action of
shoulder external rotation. Similarly if one is trying
to strengthen the hip extensors, lowering the leg
from 90° would be hip extension but not effective
for strengthening the hip extensors. As seen in figure
2.22A, this movement is going in the same direc-
tion as gravity and would actually require eccentric
contraction of the opposite muscle group, the hip
flexors, to control the lowering of the legs. To make
the hip extensors the prime movers, the leg would
have to be lifted to the back in order to be working
against gravity as seen in figure 2.22B. However, in
the standing position the range of motion is quite
limited without necessitating a marked anterior tilt
of the pelvis and hyperextension of the lumbar spine,
which could be of concern if a heavy resistance was
being used. Furthermore, greater challenge to the
hip extensors will be provided when the leg lifts
higher such that the moment arm for the resistance
is longer. To allow more range of motion with a longmoment arm working against gravity, but less back
stress, hip extensor strengthening can be performed
with the torso leaning forward (such as with forearms
resting on a barre) or kneeling with the hands on
the floor as seen in figure 2.22C.In the design of strength exercises for two-joint
muscles, the exercise may incorporate movement at
just one of the joints or may combine the movements
at both joints. In the latter case, the positioning
used at one joint can influence which muscle of a
functional group is being emphasized. For example,
the hamstrings can be strengthened by an exercise
using only knee flexion such as knee curls, an exer-
cise using only hip extension such as back leg lifts,
or an exercise that combines both actions such as
seen in figure 2.22C. In this latter exercise, the knee
is just bent slightly to try to help the dancer “find”
the hamstring muscle. Then, the leg is lifted higher
(hip extension), focusing on using this same muscle
group to lift the leg. This approach can be used to
help the dancer emphasize use of the hamstrings
versus the gluteus maximus. In contrast, if the knee
is bent to an extreme range as seen in figure 2.22D,
the hamstring will be so shortened across the knee
joint that it will be difficult for it to be effective in
generating force for hip extension. This intentional
production of active insufficiency for the hamstrings
can be used to perform hip extension with a greater
use of the gluteus maximus.FIGURE 2.22 Influence of body position on hip extensor strengthening. (A) Ineffective relationship to gravity, (B) effec-
tive relationship to gravity but small range of motion, (C) effective positioning with hamstring emphasis, and (D) effec-
tive positioning with gluteus maximus emphasis.