In an isotonic contraction, the muscle:
rapidly resynthesizes creatine phosphate and ATP
maintains the same length while generating tension
changes length while maintaining constant tension
remains relaxed and passive during movement
The Correct Answer is C
Choice A reason: This choice confuses metabolic processes with mechanical muscle activity. While creatine phosphate and ATP are essential for muscle contraction, their resynthesis is not specific to isotonic contraction. These energy molecules are replenished during recovery phases and are not the defining feature of isotonic contractions.
Choice B reason: This describes isometric contraction, not isotonic. In isometric contractions, the muscle generates force without changing its length—such as holding a plank position. Isotonic contractions, by contrast, involve a change in muscle length.
Choice C reason: This is the correct answer. Isotonic contractions involve the muscle changing length while maintaining constant tension. There are two types: concentric (muscle shortens) and eccentric (muscle lengthens). These contractions are typical in dynamic movements like lifting or lowering weights.
Choice D reason: This is incorrect. Muscles do not remain relaxed during isotonic contractions. Instead, they actively contract and generate force to produce movement. Passive relaxation does not contribute to the mechanics of isotonic contraction.
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Related Questions
Correct Answer is A
Explanation
Choice A reason: Scoliosis is the correct answer. It is characterized by a lateral curvature of the spine, often diagnosed in adolescence. It can range from mild to severe and may require bracing or surgery depending on progression.
Choice B reason: Lordosis refers to an exaggerated inward curvature of the lumbar spine. It is a spinal deformity but not the most common.
Choice C reason: Kyphosis is an exaggerated outward curvature of the thoracic spine, leading to a hunched posture. It is less common than scoliosis.
Choice D reason: Osteosis is not a recognized spinal deformity. It may be a misused or fictional term.
Choice E reason: A slipped disc, or herniated disc, involves displacement of intervertebral disc material. It causes pain and nerve compression but is not classified as a spinal deformity.
Correct Answer is B
Explanation
Choice A reason: Microfilaments are components of the cytoskeleton found in many cell types, including muscle cells, but they are not the structural and functional unit of skeletal muscle.
Choice B reason: The sarcomere is the correct answer. It is the smallest contractile unit of skeletal muscle, composed of actin and myosin filaments arranged in a precise pattern. Sarcomeres are responsible for the striated appearance and contraction of skeletal muscle.
Choice C reason: The sarcoplasmic reticulum is an organelle that stores and releases calcium ions necessary for muscle contraction. While essential, it is not the structural and functional unit.
Choice D reason: Trabeculae are structural elements found in spongy bone, not muscle tissue. They do not play a role in muscle contraction.
Choice E reason: A fascicle is a bundle of muscle fibers, not the smallest functional unit. It is a larger structural grouping within the muscle
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