Refers to the tendons of four deep shoulder muscles (subscapularis, supraspinatus, infraspinatus, and teres minor) that form a complete circle (cuff) around the shoulder; they strengthen and stabilize the shoulder joint.

Correct Answer: A

Rationale: The rotator (musculotendinous) cuff is a group of four muscles subscapularis, supraspinatus, infraspinatus, and teres minor whose tendons encircle the shoulder joint, providing stability and enabling a wide range of motion. This cuff strengthens the glenohumeral joint, preventing dislocation during activities like throwing. Deep is a positional term, not a structure. Perineum is the pelvic floor region, unrelated to the shoulder. The diaphragm is the breathing muscle. The rotator cuff's specific role and composition match the question, making it the correct answer, as it's a critical anatomical feature in shoulder function and a common site of injury in sports or aging.

Correct Answer: A

Rationale: The trapezius inserts on the clavicle and acromion process of the scapula, stabilizing and moving the shoulder girdle, such as in shrugging. Pectoralis major inserts on the humerus, not the clavicle or acromion. Latissimus dorsi inserts on the humerus too, affecting the arm. Gracilis is a thigh muscle, unrelated. Trapezius is the correct answer, as its insertion matches the question's sites, playing a key role in pectoral girdle motion and posture, distinct from arm-focused muscles.

Correct Answer: A

Rationale: The origin is the tendon's attachment to a stationary bone, providing a fixed point for muscle contraction, like the scapula for the biceps brachii. The insertion attaches to the movable bone (e.g., radius), belly is the muscle's fleshy part, and aponeurosis is a broad tendon sheet. Origin is the correct answer, as it defines the stable anchor in muscle anatomy, essential for understanding how contraction produces motion by pulling the insertion toward it.

Correct Answer: A

Rationale: Voluntary muscles, synonymous with skeletal muscles, allow conscious control over actions like lifting an arm or turning the head. Linked to bones via tendons, they respond to brain signals via the somatic nervous system, enabling deliberate movement. No control describes involuntary muscles smooth and cardiac working automatically, like digestion or heartbeats. Automatic function fits those, not voluntary ones. Muscles fused together misrepresents anatomy muscles are distinct, not merged. Voluntary muscle's defining trait is this control, essential for daily tasks, contrasting with involuntary types' autonomic roles, highlighting its role in purposeful, cognitive-directed motion across limbs, neck, and torso.

Correct Answer: D

Rationale: In a hurdle race, a high-intensity, endurance-based activity lasting over a minute, leg muscles primarily rely on oxidative metabolism for energy. This process uses oxygen to break down glucose, fats, and proteins in mitochondria, producing ATP efficiently via the aerobic pathway, sustaining prolonged effort. Glycolysis provides quick ATP anaerobically but fatigues muscles due to lactate buildup, insufficient for a race's duration. Lactate and pyruvate are intermediates, not primary sources. Preformed ATP is limited, depleting in seconds. Oxidative metabolism dominates in events requiring sustained power, like hurdling, where oxygen delivery supports muscle contraction over time, distinguishing it from short-burst energy systems and aligning with the aerobic demands of such races.