Properly applied resistance results in irradiation and reinforcement.
Definition
Irradiation. We define irradiation as the spread of the response to stimulation. This response can be seen as increased facilitation(contraction) or inhibition (relaxation) in the synergistic muscles and patterns of movement.
Th e response increases as the stimuli increase in intensity or duration wrote that it is resistance to motion that produces irradiation, and the spread of the muscular activity will occur in specific patterns.

Definition
Reinforcement. Reinforce, as defined in Webster’s Ninth New Collegiate Dictionary, is “to strengthen by fresh addition, make stronger.

Types of muscle contraction of the patient.
(a). Isotonic concentric: movement into a shortened range; the force or resistance provided by the patient is stronger.
(b). Isotonic eccentric: the force or resistance provided by the therapist is stronger; movement into the lengthened range.
(c). Stabilizing isotonic: the patient tries to move but is prevented by the therapist or another outside force; the forces exerted by both are the same.
(d). Isometric (static): the intent of both the patient and the therapist is that no motion occurs; the forces exerted by both are the same
The therapist directs the reinforcement of the weaker muscles by the amount of resistance given to the strong muscles. Increasing the amount of resistance will increase the amount and extent of the muscular response. Changing the movement that is resisted or the position of the patient will also change the results.
The therapist adjusts the amount of resistance and type of muscle contraction to suit the condition of the patient, for example, muscle strength, coordination, muscle tone, pain, different body sizes, and
the goal of the treatment.
Because each patient reacts diff erently, it is not possible to give general instructions on how much resistance to give or which movements to resist. By assessing the results of the treatment, the therapist can determine the best uses of resistance, irradiation, and reinforcement.

⇛Resist muscle contractions in a sound limb to produce contraction of the muscles in the immobilized contralateral limb.
Example Examples of the use of resistance in patient treatment: ⇛Resist muscle contractions in a sound limb to produce contraction of the muscles in the immobilized contralateral limb. ⇛Resist hip flexion to cause contraction of the trunk flexor muscles ⇛Resist supination of the forearm to facilitate contraction of the external rotators of that shoulder. ⇛Resist hip flexion with adduction and external rotation to facilitate the ipsilateral dorsifl exor muscles to contract with inversion . ⇛Resist neck flexion to stimulate trunk and hip flexion. Resist neck extension to stimulate trunk and hip extension. |

leg pattern flexion-adduction-external rotation;
b Irradiation for mid-stance support to the ipsilateral leg