The Bernstein Perspective:
II. The Concept of Muscle Linkage or Coordinative Structure
Betty Tuller, M. T. Turvey, Hollis L. Fitch University of Connecticut and Haskins Laboratories
The puzzle of the control and coordination of movement as seen by Nicolai Bernstein can be expressed succinctly: How can the many degrees of freedom of the body be regulated systematically in varying contexts by a minimally intelligent executive intervening minimally? A reasonable hypothesis is that nature solves this puzzle by keeping the degrees of freedom individually controlled at a minimum, and by using "units" defined over the motor apparatus that automatically adjust to each other and to the changing field of external forces ( Gel'fand, Gurfinkel, Tsetlin, & Shik, 1971). In accordance with this hypothesis we introduce and explore the concept of muscle linkage or coordinative structure, defined as a group of muscles often spanning several joints that is constrained to act as a single functional unit.
Consider the contrast between a person who is a novice at shooting a gun and a person who is highly skilled. What makes these two people different? Imagine that you aim a gun and try to zero in on a target. And imagine that a light is attached to the end of your gun so that, when you aim, the beam focuses in the region of the target. The beam of light will not remain motionless at one spot, but rather it will wander around the target area. This is because, when you aim, your body in general and your arm in particular are not perfectly motionless. Now, in the case of the skilled marksperson, the light will wander around, but generally it will remain very close to the target; that is, the "scatter" is within a limited area around the target. In the case of an unskilled marksperson, however, the light will wander over a wide range around the target. So a skilled marksperson--not surprisingly--keeps the gun on target much better than the unskilled. What we want to know is how the skilled marksperson is able to do this. The question is, how has the person organized the body with reference to the specific problem of