The fourth finger is and has been the weakness of most violinists and it is generally said that it is because it is the weakest finger of all. While this is true, the cause of its difficulty in use is not due to its lack of strength. The fourth finger is strong enough to perform all the movements required to play the violin, as long as there is no pre-existing physiological problems.
The main problem with the fourth finger is the limited ability of the general population to control it. Both babies and toddlers are able to use the fourth finger in much the same way as the rest of the fingers. This capacity is reduced over time due to the lack of need to use it. For this reason, when beginning to study the violin at older ages, the dexterity of the fourth finger is reduced. This indicates that fine motor skills and proprioception are what should be trained and not the muscles themselves.
The reason many students feel that greater force must be exerted to control the fourth finger is to use other muscles in the hand to compensate for the lack of finger control.
In order to solve this problem, I have designed the following exercises where the balance of the force exerted by the different muscles of the fourth finger is mainly worked on. As can be seen from the computer analysis, the fourth finger must keep the flexion angles of its different joints stable. It is also possible to see the slight change in the amplitude of the angles of around two degrees, indicating that the balance and control is not perfect and there is still room for improvement.
The following exercises consist of two voices where the bass voice should not be played but the fourth finger should only be kept in that fixed position while the other voice is played with the bow. The high voice makes different alterations in order to make it difficult to control the balance in the fourth finger. The ultimate goal is to keep the joints angles of the fourth finger unchanged. Even if computer analysis is not available, it is recommended to record the execution to be able to observe if there are changes in the placement of the finger.