What is the significance of the A band during muscle contraction?

Correct Answer: B

Rationale: The A band in a sarcomere represents the region containing thick myosin filaments, overlapping with thin actin filaments in striated muscle. During contraction, the sliding filament theory explains that actin slides over myosin, shortening the sarcomere as Z lines draw closer. However, the A band's length defined by the fixed length of myosin filaments remains constant. The I band (actin-only) and H zone (myosin-only) shrink as overlap increases, but the myosin span doesn't change, keeping the A band stable. Z lines anchor actin, not define the A band, and actin-only regions are the I band, not A. This unchanged A band length is a key feature in muscle mechanics, reflecting the structural integrity of myosin and the dynamic overlap driving contraction, a fundamental concept in understanding sarcomere function.

Correct Answer: B

Rationale: Tapering, reducing training volume pre-event, preserves energy and aids recovery but doesn't directly enhance fuel availability or use during prolonged endurance exercise, unlike nutritional strategies. Carbohydrate loading and the classic regime (depletion then high-carb intake) boost muscle glycogen stores, extending endurance. Exogenous carbohydrate ingestion during exercise (e.g., gels) maintains blood glucose, delaying fatigue. Tapering's rest focus, while beneficial for freshness, lacks the direct substrate impact of carb-based methods, distinguishing it as less performance-enhancing in fuel terms, key for endurance optimization.

Correct Answer: A

Rationale: A muscle's origin (fixed) and insertion (mobile) determine its action e.g., biceps originates on scapula, inserts on radius, flexing the elbow. Force depends on fiber type and size, not just attachments. Muscle names (e.g., flexor carpi) may reflect action or location, but origin-insertion directly dictates motion, not naming convention. Load capacity ties to training and physiology, not solely attachment points. Action derives from how bones move relative to these points, distinguishing it as the primary outcome, key for movement mechanics.

Correct Answer: C

Rationale: Rhomboid major and minor, retracting the scapula, lie deep to trapezius, a superficial back muscle covering them. Rectus abdominis is anterior, abdominal. Scalenes are in the neck, unrelated. Ligamentum nuchae, a neck ligament, aligns with deeper muscles but not rhomboids' position. Trapezius' superficiality over rhomboids distinguishes it, key for back layering.

Correct Answer: C

Rationale: Vitamin deficiencies cause specific symptoms based on their metabolic roles. Beriberi, characterized by muscle weakness, nerve damage, and heart issues, results from insufficient thiamine, a nutrient vital for carbohydrate metabolism and nerve function. Found in whole grains, legumes, and nuts, thiamine deficiency leads to energy deficits, manifesting as irritability and appetite loss. Vitamin K aids clotting, its deficiency causing bleeding, not beriberi. Vitamin B12 supports nerve health and blood formation, with deficiency linked to anemia and neuropathy, not beriberi. Vitamin B6 assists protein metabolism, its lack causing dermatitis or seizures. Thiamine's unique role in energy production and its association with beriberi's distinct symptoms pinpoint it as the correct vitamin.