Final answer:
A depressed left shoulder suggests that the omohyoid muscle is likely to be hypertonic. Muscle tone and strength tests, which involve resistance exercises such as shrugging the shoulders, help to identify imbalances that indicate hypertonicity.
Step-by-step explanation:
When a practitioner observes that a client's left shoulder is depressed, we look at the muscles that may be causing this positional change. In the context of which muscle is most likely to be hypertonic, one must consider the muscles involved in shoulder movement. Specifically, the depression of the shoulder often involves the omohyoid muscle, which has a role in depressing the hyoid bone and, by extension, can affect shoulder position.
During a physical exam for muscle tone and strength, practitioners can distinguish a hypertonic muscle by looking for an imbalance in muscle strength. The strength of the omohyoid and related shoulder muscles can be tested by asking the patient to perform movements against resistance, such as shrugging the shoulders or flexing and extending the neck. If one shoulder appears weaker or has less ability to resist, it could indicate that its opposing muscle—the muscle that would normally elevate the shoulder—is hypertonic, meaning it is overly tense or stiff. In this case, a hypertonic omohyoid muscle could contribute to the left shoulder appearing depressed.