We define the types of muscle contraction as follows (International PNF Association, unpublished handout):
— Isotonic (dynamic): The intent of the patient is to produce motion.
- Concentric: Shortening of the agonist produces motion.
- Eccentric: An outside force, gravity or resistance, produces the motion. The motion is restrained by the controlled lengthening of the agonist.
1 Synergists are muscles which act with other muscles to produce coordinated motion.
- Stabilizing isotonic: The intent of the patient is motion; the motion is prevented by an outside force (usually resistance).
— Isometric (static): The intent of both the patient and the therapist is that no motion occurs.
The resistance to concentric or eccentric muscle contractions should be adjusted so that motion can occur in a smooth and coordinated manner. The antagonists of the facilitated muscles allow a coordinated activity and therefore they are sufficiently inhibited to allow that activity. Resistance to a stabilizing contraction must be controlled to maintain the stabilized position. When resisting an isometric contraction, the resistance should be increased and decreased gradually so that no motion occurs.
It is important that the resistance does not cause pain, unwanted fatigue, or unwanted irradiation. Both the therapist and the patient should avoid breath-holding. Timed and controlled inhalations and exhalations can increase the patient's strength and active range of motion.
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