Final answer:
The condition with lower crossed weak muscles in the upper extremities is Upper crossed syndrome. It is identified by an imbalance of muscles in the upper body, which can be tested for by assessing muscle strength and conducting a pronator drift test for UMN lesions.
Step-by-step explanation:
The condition called when lower crossed weak muscles are present in the upper extremities is known as Upper crossed syndrome. Upper crossed syndrome is characterized by an imbalance in the musculature of the neck, shoulders, and chest. This includes weak muscles in the posterior neck and shoulders (upper trapezius and levator scapula) and tight muscles in the anterior chest and neck (pectoralis major and minor). When it comes to assessing muscle tone and strength, practitioners typically have patients contract muscles against resistance to test the functioning of the corticospinal tract. A lateral difference in strength, such as being able to push against resistance with one arm but not the other, could indicate a unilateral deficit. Conversely, an overall loss of strength may suggest a more global issue. It's also important to conduct a pronator drift test, where a patient with closed eyes extends their arms out in front with palms up—if one arm drifts downward, it can be an indication of an upper motor neuron (UMN) lesion, often resulting from conditions like cerebral palsy, multiple sclerosis (MS), or stroke.