Final answer:
The brachialis muscle performs an eccentric contraction, a form of isotonic contraction, when setting down a glass, where it maintains tension while lengthening to lower the object in a controlled motion.The correct answer is (A).
Step-by-step explanation:
When setting down a glass, the brachialis muscle is involved in an eccentric contraction. This type of contraction is a subtype of isotonic contraction, where the muscle maintains constant tension while the muscle lengthens. In this scenario, as the muscle elongates, the tension is gradually reduced to lower the glass in a controlled manner.
The sliding filament mechanism describes how the sarcomeres in muscle fibers operate during contraction and relaxation. Myosin heads bind to actin to form cross-bridges, pulling the actin filaments over the myosin, which either shortens or lengthens the muscle depending on contraction type.
In an eccentric contraction, the muscle tension diminishes and the muscle lengthens. When setting down a glass, the brachialis muscle is elongating as it controls the descent of the glass, which is an example of eccentric contraction. During eccentric contractions, the sarcomeres in the muscle fibers lengthen as cross-bridges are released and the angle of the joint increases.