Final answer:
Muscles contract and relax during exercise, increasing strength and efficiency. The sliding filament model describes muscle contraction.
Explanation:
Muscles work during exercise by contracting and relaxing. During weight lifting, skeletal muscles contract against resistance, leading to increased strength and size. The cardiac muscle in activities like running contracts faster to increase efficiency of the heart. The sliding filament model explains how muscles contract, with actin and myosin filaments sliding over each other to generate tension.
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