People sometimes speak of muscular weakness, when muscles are actually being inhibited by reciprocal inhibition, the process by which when flexors (e.g., biceps) flex, extensors (e.g., triceps) are inhibited by the brain to permit the flexion, and vice-versa. This pattern of reciprocal inhibition applies to all opposing/complementary muscle groups.
When agonist muscles are habitually contracted in SMA ("Sensory-Motor Amnesia" | See the book, Somatics: ReAwakening the Mind's Control of Movement, Flexibility and Health, by Thomas Hanna), the antagonists are inhibited. When this situation is described as muscular weakness, what is being disclosed is failure to understand reciprocal inhibition.
In that case, the typical thinking and approach is in terms of "strengthening" the inhibited antagonist muscle(s), when what should be done is to restore the capacity to relax the opposing agonist(s), and thereby turn off habituated reciprocal inhibition.
In the case of Trauma Reflex (See Somatics), the untraumatized side is inhibited; the traumatized side is in SMA contraction toward the somatic center. That shows up as reluctance to put weight on, or otherwise to use, the traumatized side, experienced as weakness.
In stereotypical Trauma Reflex, that withdrawal from function shows up as a twist pattern in which the thigh of the traumatized side is adducted (pulled in) and the shoulder of that side is pulled back; pulling the shoulder back narrows that side, and thereby shifts the center of gravity (weight) toward the other side, where better function is available. That act of narrowing can't be accomplished by bringing the shoulder forward because the clavicle prevents narrowing that way; the only ways narrowing can be accomplished are either by bringing the shoulder back or by bringing it up -- and the contraction of Trauma Reflex toward the somatic center opposes bringing the shoulder up, so back it goes. (Note: When the neck is traumatized a shoulder or shoulders go up; when the side of the ribs is traumatized, the arm clamps over the traumatized zone and doesn't respond to the typical Trauma Reflex protocol.)
The general feeling of the traumatized side is of weakness, of non-support, visible as a walking limp, for example, even though that is the contracted side. (Weakness also results from muscle fatigue, and again, therapists apply the "strengthening" approach, when what is needed is relaxation and refreshment, upon which strength returns in a minute or so.)
Strengthening is almost never needed because muscular function rises to the level of habitual demand. (Muscular atrophy is an exception.) What is needed is typically normalization (or right-left equivalence) of control, so that reciprocal inhibition occurs only with the momentary demands of free movement.
See, Completing Recovery from an Injury.