The way that the muscles move when writing are often controlled by the central nervous system.
This allows mobility and coordination in the shoulder, hand and arm area. The condition of the central nervous system is illustrated within the writing of the individual. If something has gone wrong within the body, the writing is often the first indicator which is often why doctors will have a person write out a few sentences when they have been suspected to have had a stroke or if they drink heavily or have Parkinson’s disease and other issues.
The emotional and mental state are also illustrated in the way one holds their writing implement to inscribe, which is often why, despite handwriting analysis being accused of being a pseudo-science, courts often bring experts into a case in order to verify the emotional state of a potential criminal. Graphologists take all of this information into account to research the pattern, movement, rhythm and consistency of the writing of any given individual and will then attempt to interpret that person’s mental state/physical health.