Actually, may instrumentalists e.g. saxophonists, guitarist, (standing) bassoonists etc. use a strap for the same reason.
Instrument
Control
Holding the instrument
One of the most important subjects of playing an instrument is the correct playing position. Just like with other disciplines, the foundation on which playing skills are built decide the level of refinement obtainable. Professionally trained musicians spend many years training and fine tuning their playing position and muscle control through specialized therapies like Mensendieck, Alexander etc.. If you want to develop technical and musical skills which will enable you to play advanced music, you should begin with a solid knowledge of the correct playing position.
As with all musical instruments, there are two main objectives:
Standing up, or sitting
down
Most beginning concertina players prefer to sit down while playing. One
of the advantages is that you have more control over the instrument because it
rests on your knee. The stability also allows for more freedom of hand movement,
since you don't have to lift up the concertina. On the other hand, the arm and
hand position is not perfect in this position. The angle of the arms should be
close to 90 degrees.
Since (for most people) the torso is longer that the upper arm, the angle ends
up to be more than 90 degrees. Many players tend to correct this by slouching,
correcting the angle with their back. A better way is to use a guitar stool
under one foot, or to cross your legs. This way the instruments sits a little
higher, just enough to maintain a (almost) perfect arm angle.
With the exception of ensemble playing, especially on the heavier bass concertina, the concertina is best played standing up. This will improve the sound projection on a stage, especially in combination with, for instance, a (grand) piano, just as with violins, flutes, etc..
When playing in a standing position, it is advisable to use a
cord, just like they did in the 19th century (see the back ground picture). The
use of a cord is a logical consequence of the two objectives. It offers the same
advantages as resting the instrument on you knee in the sitting position. The
arm angle can be adjusted by the length of the cord.
Actually, may instrumentalists e.g. saxophonists, guitarist, (standing)
bassoonists etc. use a strap for the same reason.
Our variation of a cord attachment: Silver hook
and ring, attached to a leather strip
(complete set Euro 26.00, including a length of fancy cord and shipping).
order
Adjusting the thumb strap
The thumb straps are the only fixed contact with the instrument. In order to
have freedom of movement, the thumb should not be inserted all the way, since
this will obstruct most of the movement of the hand.
The thumb should work as a hinge, enabling the hand to reach the high notes and,
especially on tenor-trebles, also the lower notes. Therefore the thumb should be
inserted only up to the first joint. This way the hand is free to move.
If the strap is too tight, it will interfere with the blood circulation and will
become painful. If it is too loose, it will not give the necessary support. One
of the consequences of this is the 'pinching' with the thumb and little finger,
in order to obtain some control over the instrument. As a result of this, the
little finger, now necessary for holding the instrument, will not be available
for playing. A side effect of this pinching is an increased tension in the hand,
which will obstruct the movement of the other fingers. In other words, you'll
play a lot faster if you do not use your little finger for holding the
instrument.
Hand position
When the thumb is inserted in the thumb strap, lay your index, middle and
ring finger over the keys and your little finger on the finger rest. Now bend
you fingers, including the little finger. The basic fingering is; index finger
(finger 1) for row 1 and 2, middle finger (finger 2) for row 3, and ring finger
(finger 3) for row 4. Remember, this is only the basic hand position. In more
advanced music you will need to use all fingers, including the little finger
(finger 4) on all the rows.
Make sure not to stretch your thumb, this will obstruct the movement of the hand
muscles, and therefore the fingers. Bending your thumb slightly will relax the
hand muscles.
The little finger (4) is free to move over the finger rest and beyond,
especially when playing the highest or lowest notes it will often leave the
finger rest. Make sure to keep it bend. If you stretch your little finger, it
will force your thumb to (over) stretch which will pull your hand out of
alignment with the keys and obstruct the movement of the hand muscles, and
therefore the fingers.
In order to be able to us all your fingers, your arms should form one line with
the sides of the concertina. Avoid bending your wrists too much.
The correct hand position: Thumb slightly bend,
fingers rounded.
In this picture the little finger is being used for (chord) playing.
Pressure
points
You should always have two pressure points per hand on the instrument to
maintain control of dynamics and tone forming. Normally these pressure points
are your thumb and little finger. Because they are at opposite sides of the keys,
the concertina will be stable and not 'wobble'.
Later on, when you play polyphonic music (more melodies, up to 4, at the same
time) or chords, you will be needing your little finger for playing. In that
case the wrist will take over from the little finger. Your pressure points will
than be your thumb and wrist.
If you have problems controlling the ends and/or bellows, you can practice with
all three pressure points (thumb, little finger and wrist). It is also a good
pre-polyphonic exercise.