Try this: hold up
your hand with your fingers extended, and then turn it so you’re looking at it
side-on, with all your fingers lined up. Now bend your middle finger, trying to keep the others standing
straight up. What you probably see as
you move your middle finger is that your ring finger also moves out of place,
no matter how much your try to keep it still. Your index finger probably moves a little too. Don’t get too stressed if it’s hard to move
just your middle finger: our fingers are
designed to move together. The thumb moves
quite independently, but when we move each of the long fingers, other fingers
also try to move.
 |
| When flexing one finger, the other fingers move out of place too. |
There are two main reasons that this is true: first, each finger is connected to adjacent
fingers by skin webbing, tendons, and muscle fascia, so that when we move one
finger, it pulls on its neighbours. The
second and more relevant reason is that our muscle control of our fingers is
not completely separate.
You might think that motor control of our fingers works like
this: a certain area of our brain is
responsible for each finger. When that
part of the brain is active, a message gets sent to the muscle responsible for
that finger, which causes that finger to move. In this simple scenario, there is a straight line connection between 1
brain area, 1 muscle, and 1 finger. Unfortunately, this is not how finger control works.
The neurons that send motor commands to our finger muscles
are located in the hand area of the primary motor cortex. But there is not a separate area for each
finger. Studies looking at which neurons control which finger movements have found that the neurons that control the separate fingers are all kind of
jumbled together. Also, a lot of the
neurons that were studied were found participate in the control of more than
one finger.
This idea of mapping neurons onto finger movements gets even
more complicated when you look at the muscles that move our fingers. The muscles responsible for flexing (bending)
and extending (straightening) our fingers are located in our forearms, and
connect to the finger bones through tendons which go through our hands. But there are not separate sets of muscles
for each finger.
In fact, there are only two muscles that control flexing the four long
fingers: the flexor digitalis profundus and the flexor digitalis superficialis. Each
of these muscles has four tendons, one connecting to each of the long fingers
of the hand. The muscle has
different sections (known as muscle bellies) that each primarily activate one
finger, but they are not completely separate, and they also often contract
together, since the neurons that activate the muscles don't act independently either.
Similarly, to extend
the fingers, there is one main muscle:
the extensor digitorum communis, involved in extending all four long
fingers. There are also two smaller muscles:
the extensor digitali minimi (extends
the little finger) and the extensor
indicis (extends the index finger).
If we don’t have separate
muscles controlling each finger, how do we move them independently? The most
likely possibility is that we move our fingers individually due to the combined
action of more than one muscle, each of which has different amounts
of control over each finger. This
conclusion comes from the lab of Marc Schieber at the University of Rochester, who showed in 1995 that when monkeys move their fingers
individually, more than one muscle is active, and the amount of muscle activity
in each muscle is different for the movements of each finger.
In other words, when we try to move one
finger independently, we don’t just contract a muscle to move that finger, we
also have to contract other muscles to prevent the other fingers from
moving. For example, raising the ring
finger while keeping the middle finger still is difficult, because these fingers not only share a common extensor, but they are also joined
mechanically. In order to raise just the ring finger, you
need to activate the flexor going to the middle finger (in order to stabilize it), and
at the same time activate the common extensor. It’s also really handy to extend the little finger at the same time,
since this will pull on the ring finger and help it extend. See how complicated that is? No wonder moving our fingers individually is difficult.
Also, no wonder we can build up a lot of
tension in our hands while playing musical instruments. It’s very common for children to play with their hands very tense. By maintaining
activity in both the flexor and extensor muscles of the fingers, they can
stabilize their finger joints and prevent unwanted movement. This strategy of co-contraction does work, up
to a certain point. The problems very
quickly outweigh the advantages: with
too much tension in the hand, moving each finger is more work, and therefore
quick and fluent movements of the fingers are impossible.
Here is a video of a young boy whom I
teach who clearly has excess tension in his hand. Notice how his fifth finger is extended as he
plays.
This child’s problems with tension get
worse as he tries to increase the tempo of his pieces. He is absolutely unable to play fast
passages. This is typical of students
with tension issues. Worse, excess
tension leads to fatigue, pain, and eventually injury. Obviously, this
situation is something to be avoided.
What’s not obvious is the best way to
help students who have too much tension. When I do an on-line search, most of
the advice (as in this article) is to re-align
body and hand position, and then play simple exercises while focusing on mental
awareness of tension in the hand, wrist, and arm.
The good news is that our control
over individual fingers is not set in stone:
we can learn to use different muscle strategies to move our fingers
independently (as suggested in Winges & Furuya, 2015; Semmler et al., 2004). This is part of musical
training: all those Hanon exercises for
the piano (and Moyse studies for the flute, etc.) are designed to help us learn
to efficiently control our finger muscles so that we can move fluently between
different notes.
If you’ve had success in
minimizing hand tension (either for yourself or your students), I’d love to
hear about it in the comments.
References:
Schieber, M.H. (1995). Muscular production of individuated finger
movements: the roles of extrinsic finger muscles. J. Neurosci. 15,
284–297.
Schieber, M.H. (2002). Motor cortex and the distributed anatomy of
finger movements. Adv. Exp. Med. Biol. 508, 411–416.
Semmler, J.G., Sale, M.V., Meyer, F.G., and Nordstrom, M.A. (2004). Motor-unit coherence and its relation
with synchrony are influenced by training. J. Neurophysiol. 92,
3320–3331.
Winges, S.A., and Furuya, S. (2015). Distinct digit kinematics by
professional and amateur pianists. Neuroscience 284, 643–652.
