Exercise prescription and specificity
Course objectives, Control of Human Movement 2
Tissue adaptations appear to be fairly specific. Exercise prescriptions produce changes that are specific to:
- muscle group
- joint angle or range of motion
- type of muscle action
- speed of muscle action
- muscle fiber type
- metabolic energy system
We can understand the anatomical basis of exercise specificity in several ways.
- One approach is physiological; different demands and stresses cause different gene expression in living cells. Wolf's law and Davies' law exemplify this understanding.
- Another approach relates to motor control. Because different tasks entail different control problems for the motor system, it solves them in different ways.
"...Practice, when properly undertaken, does not consist in repeating the means of solution of a motor problem time after time, but is the process of solving this problem again and again by techniques which we changed and perfected from repetition to repetition. ...Practice is a particular type of repetition without repetition" (Bernstein, 1967).
Different tasks entail different control problems, which people solve by activating muscles in different synergies:
- Knee extension against resistance in open and closed chain tasks
elicits different muscle synergies. During closed chain knee extension, muscle activity is paradoxical."
- Trunk flexion in open chain ("sit-up") and closed chain ("reverse trunk curl") tasks
also elicit different abdominal muscle synergies.
- Training a lateral weight shift in standing
may not carry over to a similar weight shift in walking ( Winstein, Gardner, McNeal, Barto, & Nicholson, 1989).
- Upper extremity reaching tasks may involve muscle synergies
among the rotator cuff, deltoid, and scapulothoracic muscles that some therapeutic tasks do not duplicate.
Motor learning research illuminates the selection of therapeutic tasks
So does the definition of a 1RM:
Repetition maximum (RM): "maximal number of times a load can be lifted before fatigue using good form and technique (ACSM, 1998)."
"Good form and technique" includes control, the ability to solve a motor problem by activating muscles in appropriate synergies, with appropriate timing.
References:
Bernstein, N. (1967). The coordination and regulation of movements. New York: Pergamon.
Winstein, C.J., Gardner, E.R., McNeal, D.R., Barto, P.S., & Nicholson, D.E. (1989). Standing balance training: Effect on balance and locomotion in hemiparetic adults. Archives of Physical Medicine & Rehabilitation, 70, 755-62.