Not sure why you would need or want to train your pinky to be in that position?
You will never be able to do a 3 finger technique with that coin trick. The pinky needs to float with the ring finger.
I am missing the right index finger so essentially use a 3 finger technique -1.
There is no way that my ring finger would be useful at all with a coin held by my pinky.
Kirk
Your not training any one thing, you are through the use of holding the coin doing many things, one of which is allowing the fore and middle finger so work better and more efficient.
Our hands have two very distinct sides, each side has its own main blood and nerve supplies, so by giving the ulnar side a task to occupy it, that frees up the radial side.
The radial side is for dexterity, the Ulnar side is for strength and power.
This is not trying to restrict any finger, it is the opposite, it is given them a job to do so they do not react and interfere with other fingers....the floating up or twitching on the Ulnar side of the hand is a direct reaction to the radial side use.
The other benefit is that when decide you want use the ring finger it will be better prepared for use as you have been gently stretching the tendon and attachments it shares with the little finger.
It provides a balanced use of the hand rather than a dominated radial side use so it helps tone the whole hand, not just one side.
If we alter the relationship to between the little and ring finger, we also change the relationship between the ring and middle finger, that means the relationship between the middle and fore finger has been changed, that's why it is considered a balanced use.
Now the tendons of the ring finger are not so tight to the little finger, that's why you hold the coin gentle, and allows an easier independence of use.
When the hand gets tired, the muscle fibres will relax and the coin will fall out. This indicates time to take a rest, so it also gives you an indication to how the hand is developing its use and when to rest so you do not over do it.
Eventually the coin can be held indefinatly because the tendons are relaxed and gently stretched through use, then no more need for the coin, let playing develop the function. The coin can be used in warming up and then discarded when playing starts.
If I were a piano player this would not be an issue as the full hand gets used to play, again looking at this as a bass playing issue is a very narrow view of hand use.
Certainly it is hard to start with, but there is no physical reason why it would not benefit anyone that decided to develop it, there is every chance that you have already developed the use because of the lose of the index finger, so your hand uses the ulnar side of the hand more because of it.
For those that can hold the coin and play with no problems then you have already developed that side of the hand sufficient to use it....as I said it acts as an indicator to how good the function is or has been developed.
Our bodies have a great way of adapting when needed, the power properties of the Ulnar side can be adapted and trained to be dexterous like the Radial side.
