Simplify the following text for a Grade 11 native English-speaking person.
Original: Stretching is a form of physical exercise in which a specific skeletal muscle ( or muscle group ) is deliberately elongated , often by abduction from the torso , in order to improve the muscle 's felt elasticity and reaffirm comfortable muscle tone .
Simplified: Stretching is a kind of physical fitness exercise in which a muscle ( or muscle group ) is stretched on purpose to its fullest length in order to help the muscle 's elasticity and its tone .