Final answer:
A common substitution pattern seen in testing left shoulder abduction strength is the elevation of the shoulder girdle by the trapezius muscle, which occurs when the deltoid muscle is too weak to perform abduction on its own. This pattern assists in the movement and indicates a need for targeted physical therapy.
Step-by-step explanation:
During a test of left shoulder abduction strength, a possible substitution pattern might involve the patient using the trapezius muscle to elevate the shoulder girdle as a way to assist in the abduction movement. This compensatory action can occur when the deltoid muscle is weak or injured. Typically, the lateral deltoid is primarily responsible for shoulder abduction, and when it lacks the necessary strength, the body adapts by utilizing other muscles to perform the movement.
In assessing shoulder function, a physical therapist might observe this substitution during a strength test. If the test indicates that the patient has difficulty abducting the arm without raising the shoulder, this suggests that a muscular deficit or motor system issue is present. Identifying such patterns is critical for creating an effective physical therapy plan to address the specific weakness and rehabilitate the shoulder injury.