The Upper Extremity 431while the extensors arise proximally from around
the lateral epicondyle of the humerus. Depending
on their distal attachment and resultant line of pull,
they also can contribute to ulnar or radial deviation
of the wrist. For example, the flexor carpi radialis and
the extensor carpi radialis longus and brevis attach
distally to the second and third metacarpals and so
can produce radial deviation as well as their respec-
tive flexion or extension of the wrist. In contrast, the
flexor carpi ulnaris and extensor carpi ulnaris have
distal attachments that include the fifth metacarpal
and so can produce ulnar deviation as well as their
respective flexion or extension of the wrist.
Primary Muscles of the Fingers
There are five muscles that have proximal attach-
ments in the forearm (extrinsic muscles) that can
be used to flex and extend the fingers. Three of
these act on all four fingers at once, two to produce
flexion of the fingers (flexor digitorum superficialis,
flexor digitorum profundus) and one to produce
extension (extensor digitorum) of the fingers. The
remaining two muscles act selectively on the fingers,
one to extend the index finger (extensor indicis) and
the other to extend the little finger (extensor digiti
minimi). In addition, there are 14 smaller muscles
located within the hand (intrinsic muscles). Eleven
of these muscles work to flex, extend, abduct, and
adduct the four fingers. They are arranged in three
groups called the lumbricals (four muscles), dorsal
interossei (four muscles), and palmar interossei
(three muscles). Three additional intrinsic muscles
act selectively on the little finger (abductor digiti
minimi, flexor digiti minimi brevis, and opponens
digiti minimi) to flex, abduct, or aid in bringing the
little finger across the palm for important movement
of opposition with the thumb. Both the flexors and
extensors of the digits have complex splitting and
attachments of tendon slips onto various positions
on the phalanges to allow for isolated or combined
movements of the various digits of the fingers.
Primary Muscles of the Thumb
In addition, there are four muscles that originate
in the forearm (extrinsic muscles) that can be used
to flex, extend, abduct, or assist with opposition of
the thumb (flexor pollicis longus, extensor pollicis
longus, extensor pollicis brevis, abductor pollicis
longus). Four other intrinsic muscles can also pro-
duce movements of the thumb (flexor pollicis brevis,
opponens pollicis, abductor pollicis brevis, adductor
pollicis). These muscles form the rounded contour
that can be felt below and medial to the thumb
(thenar eminence).
Key Considerations for the Upper Extremity in Whole Body Movement.
In the upper extremities as a whole, a complex inter-
play of muscles is often utilized to allow for isolated
movement and stabilization of the relevant joints.
It is often necessary to utilize synergies to achieve
the desired movements and to avoid positions of
active insufficiency or passive insufficiency when
multijoint muscles are involved. Furthermore, in
functional movement, movements of the various
upper extremity joints are often linked, and a mean-
ingful movement analysis should take into account
the contributions of relevant joints.Actions of Multijoint
Upper Extremity MusclesMany of the muscles of the upper extremity, and
particularly the hand, cross two or more joints and
have actions or potential actions over each of these
joints. Because the tendency of a multijoint muscle is to
produce movement at all of the joints it crosses, other
muscles are often required to act as stabilizers and syn-
ergists so that the movement occurs at just the desired
joints and in the desired direction for a given task. For
example, when the desired action of the biceps brachii
is only supination, the elbow extensors (triceps brachii
and anconeus) can contract simultaneously (acting
as synergists) to prevent the undesired action of the
biceps (elbow flexion). Thus, when turning a door-
knob (supination), the elbow can be appropriately
positioned in extension to complete the task, rather
than having the elbow flex and the hand pull away
from the doorknob as supination is attempted.
In dance, synergies are often used to neutralize
or control the magnitude of secondary muscle
actions so that the desired aesthetics can be achieved.
For example, when the dancer raises the arms from
second to high fifth, the triceps brachii can again work
to limit elbow flexion while the biceps brachii is work-
ing to produce the desired supination of the forearm.
At the wrist, simultaneous contraction of the flexor
carpi radialis and flexor carpi ulnaris allows desired
slight flexion of the wrist while the respective radial
deviation and ulnar deviation are neutralized.
Also, remember that with multijoint muscles,
motion at one joint alters muscle length, which in
turn affects the muscle’s ability to produce force
or be stretched across the other joint(s) it crosses.
For example, components of the biceps brachii
and triceps brachii cross both the shoulder joint