When lifting a weight, muscles become shorter and thicker but the tone or tension remains the same and is referred to as isometric contraction.?

The right answer is ISOTONIC contraction (not isometric)

During an isotonic contraction, the length of the muscle varies but not the tension. For example, an athlete achieves (approximately) isotonic contraction when he lowers an extremely heavy weight, at a slow and constant speed, against maximum resistance.

When the body is lifting weight, the muscles of the body become shorter and thicker but the tension or tone of the body remains the same.This condition is known as isotonic contraction.

The isometric contraction can be defined as the condition when a person pushes a wall or attempt to lift a huge boulder, the muscles involved in this exercise remains at a constant length while the tension against the muscles increases.

So, the given exercise is isotonic contraction.