We must now undertake the further clarification of the forearm rotation element, which is perhaps the most important of all pianistically and physiologically. Hence this module is devoted to forearm rotation, which enables the player to achieve a sense of continuous motion. The forearm rotation implemented by the left and right hand enable the player to be balanced on the surface of the keys at all times.
Success or Failure in piano playing: Success or failure technically depends of an understanding and mastery of these forearm rotatory-adjustments. Just here, however, we find perhaps more vagueness and misunderstanding than anywhere else. Rotatory movements which had already been recognized and approved "for occasional use" in tremolos through out the history of piano playing can be applied to various aspect of keyboard technique. What I am directly referring to is 1) rotatory actions or stresses, 2) inactions and reactions, mostly unaccompanied by any movements whatsoever. During slow practice, the rotatory adjustments are visible. During performance they are not visible and the motions are minimized.
Pronation and Supination
Pronation and supination are rotational motions that exist exclusively in the forearm.
The mechanical bases for these movements are the existence of two forearm bones and the presence of two coupled trochoid joints.
(PRUJ) proximal radioulnar joints: The proximal radioulnar joint is a pivot type of synovial joint, which consists of the head of the radius articulating with the radial notch of the ulna. The radial head is tightly bound into the radial notch of the ulna by the anular ligament that secures it in place.
(DRUJ) distal radioulnar joints. The distal radioulnar joint (DRUJ) is a pivotal joint located in the wrist, connecting the radius and ulna bones of the forearm. This joint plays a crucial role in allowing the rotational movements of the forearm, known as pronation (palm down) and supination (palm up), which are essential for various hand functions.
The ulna and radius, two parallel bones in the forearm, are inherited traits from a remote ancestor. This anatomical structure is found in all tetrapods[1], a group that includes amphibians, reptiles, birds, and mammals, and has been a feature of this lineage for hundreds of millions of years.
The ulna and radius bones first appear in the fossil record in the late Silurian and early Devonian periods (around 420 to 360 million years ago), corresponding to the evolutionary emergence of the first tetrapods. These ancestral organisms, such as Acanthostega and Ichthyostega, exhibited primitive forms of these bones as part of their transition from aquatic to terrestrial life.
The function of these bones has evolved in the context of the diverse adaptive needs of different species. In certain tetrapods, like birds, the radius and ulna have adapted for flight, while in primates, they have developed for flexible movement and tool manipulation. In humans, the two bones articulate with the humerus in the upper arm to allow for a range of motion, including rotation. These homologous structures, or structures with a similar anatomical position and evolutionary origin but potentially different functions across species, serve as robust evidence for common descent from a remote ancestor. They illustrate the principles of evolutionary biology, demonstrating how structures can adapt and evolve over time to fit diverse environmental niches while maintaining a fundamental blueprint inherited from common ancestors.
Despite the vast differences in size, lifespan, habitat, and lifestyle among tetrapods, the presence of the radius and ulna in all members of this group reflects their shared evolutionary heritage. This unique ability to transfer rotational force to the grasping hand must have played a decisive role in the human evolution.
Advantages of having 2 bones in the Forearm
Two bones in comparison to one bone with one joint brings the following advantages:
There is no tendon, nerve, and vessel twisting at the wrist with decreased function.
Furthermore, only two bones at the forearm provide a wide range of motion but stable and light construction.
The DRUJ and PRUJ together work as a single forearm joint, resulting in pronation/supination.
The proximal ulnar and distal radial segments create a unit similar to the tibia[2].
The proximal radial and distal ulnar segments create a unit reminiscent of the fibula with the ulnar styloid resembling the lateral malleolus.
[1]tetrapods: Tetrapods are four-limbed vertebrates, encompassing a vast group of animals that evolved from lobe-finned fish ancestors. This diverse group includes amphibians, reptiles, birds, and mammals, all sharing the fundamental characteristic of having four limbs, or modified versions thereof, for locomotion and other functions.
[2]tibia: The inner and larger of the two bones of the lower human leg, extending from the knee to the ankle.
