Elasticity and Contractility of the muscles used in Piano Technique

The difference between 1) elasticity and 2) contractility, lies in the fact that contractility depends upon the presence of a neural stimulus for its operation. Without this (or an artificially supplied stimulus) a muscle does not contract. The degree of contractility does not depend upon the spatial relationship between the points of origin and of insertion, it depends upon the intensity of the neural stimulus. A muscle may, therefore, have similar shapes yet be in opposite stages of contractility.
If the arm be sufficiently bent at the elbow by an outside force, the pressure of the forearm against upper arm will cause a swelling in the region of the biceps muscle.
A similar swelling occurs when the bicep is contracted voluntarily, but the physiological states of the muscle in the two cases are widely different. In one case

1. no muscular activity is going on,
2. no chemical changes are taking place

in the other work is actually being done with chemical changes in the production and elimination of heat and fatigue products .

The Contractility of the finger, hand, and forearm muscles "absolutely depends upon the presence of a neural stimulus for its operation". These muscles fall under the category of skeletal muscles, which are responsible for voluntary movements. Skeletal muscles rely on action potentials, which are electrical signals transmitted by motor neurons, to initiate contraction.
Here's a breakdown of the process:

1. Brain sends a signal: When you want to move your finger, hand, or forearm, your brain sends an electrical signal down a motor neuron.
2. Action potential reaches neuromuscular junction: The signal travels down the motor neuron until it reaches the neuromuscular junction, which is the connection between the nerve and the muscle fibers.
3. Neurotransmitter release: At the neuromuscular junction, the motor neuron releases a neurotransmitter, typically acetylcholine ^[1]
4. Muscle contraction: ACh binds to receptors on the muscle fiber, which triggers a series of biochemical reactions culminating in the contraction of the muscle fibers.

Without this neural stimulus, the skeletal muscles in your fingers, hands, and forearms would not be able to contract. However, some exceptions exist:

• Stretch reflexes: These are involuntary muscle contractions triggered by stretching a muscle. They occur through a spinal reflex arc, bypassing the brain.
• Rigor mortis: This is a post-mortem stiffening of muscles due to depletion of ATP, the energy molecule required for muscle relaxation. It occurs independently of any neural input.

In conclusion, the normal contractility of finger, hand, and forearm muscles depends heavily on the presence of a neural stimulus. This neural stimulus triggers the biochemical changes necessary for muscle contraction, allowing us to perform voluntary movements.

These facts are substantiated by records of the muscular contraction actually taking place in both types of movement. The method of direct observation, which does not involve the use of any apparatus, serves to illustrate certain features of the differences we are considering. The biceps contraction already mentioned is a case in point. With the back of the hand and the fore-arm resting upon a table, place the fingers firmly over the biceps muscle.
This is the muscle meant when the enthusiastic youngster asks his companions to "feel my muscle" and proceeds to flex the elbow and supinate the fore-arm. The muscle with the fore-arm resting upon the table will be found in a relaxed condition. Now proceed to lift the fore-arm slowly. The muscle will contract, and a part of this contraction can be felt before the hand or arm leaves the surface of the table.
In other words, before movement of the external parts has taken place. The points of origin and insertion of the muscle could not, therefore have been altered and thus is shown the independence of the degree of muscular contraction from the spatial position of the parts to be moved. A weight placed in the palm of the hand will intensify this reaction. A similar, more marked result , occurs when the hand is pushed against an immovable object, for example, pressed forcibly upward against a table or desk. The biceps will contract violently, yet the position of shoulder and fore-arm, the places of origin and insertion respectively, have not been altered. The contraction depends upon the force acting against the muscle, not upon the position of the parts.

[1]Acetylcholine: Acetylcholine (ACh) is a neurotransmitter, a chemical messenger that carries signals between neurons and other cells in the nervous system.