This may seem a question of semantics, but in the practice of Systema, I have noticed these terms used interchangeably, both by instructors and practitioners alike. I will share a little of my understanding of these three terms and their application to Systema, and Martial Arts in general.
Form is the dispersion of density throughout the body mass given any posture or position. It is a bit like your "shape", and can be compared to a bag of water, and its qualities. This is why it is possible to maintain good form even while changing heights, or while doing ground work. A fascinating aspect of "Form" is that it can be maintained in dynamic conditions.
Structure refers to the scaffold of the body and its designs. The relation between limbs, joints and core.
Posture refers to what position the structure has taken. It usually implies a static position.
"You can have good form but the structure of your arm (wrist, elbow, shoulder, body) might make for a weak strike." Sound mechanics and basic geometry are required every step of the way. The components of sound structure are simple in static modes; but it is when they get loaded, that the equations become more difficult. Concepts such as density, balance, weight transfer, force vs. power vs. strength, tension, resistance, all need to be considered. These are part of the bridge going from structure to form.
"Good form is when the body moves as one unit." The limbs might work independently, but the body is a single unit. There is no lower or upper parts. Using relaxation and/or resistance (not tension), weight placements and shifts, proper use of breath, the body as a whole functions as a unit. It remains master of its density and knows when to transfer, increase, decrease or neutralize.
It is possible to maintain good form within a compromised structure while moving, but when form goes, structure becomes very vulnerable.
This is a huge topic. Please take the time to ponder on these terms and use them appropriately!
Before being named as Founder and Chief Instructor of Roots Dojo, Vali Majd, since 1996 had been, and still is a student of traditional Ryabko – Vasiliev Systema. Vali Majd brings along an army of talent and could be considered honest and dependable; his lengthy exposure to the art, along with his abilities to practice, to teach, to demonstrate and to clearly articulate subtle concepts of Systema makes him and his dojo worth visiting.
2002-Formed Comox Valley Systema
1999-Founded Pacific Coast Systema (now Roots Dojo)
1995-Started at Russian Martial Art HQ, Toronto
Vali is a Medical First Responder and a Firefighter with the Denman Island Volunteer Fire Department.
For more information visit: http://www.pacificcoastsystema.com/
Systema Sydney Russian Martial Art